78 GMC Pickup Engine Conversion for Better Mileage

Regarding the possibility of propane conversion;

would you have to pay road tax on fuel?

Would the propane conversion produce enough power for your needs?

I remember Ak miller experimenting with turbo-charged/ propane fueled Ford six-cylinders in the early '70's, seemed promising, the expanding gas helped cool the fuel/air charge, somewhat off-setting the introduced heat from the turbo.

don't know if a similar set-up would give you a desirable ROE

Major -- Thanks for your comments and questions. I'm glad someone is interested. CR-4 has been kind of quiet the last few days.

What I know about propane is that you give away about 10% of your peak power; but I have margin for that with the original "rat motor".

In California you are supposed to pay a road tax on propane one way or another. I'm inclined to do that even if it means remiting a calculated amount with my annual CA income tax. What concerns me some is the availability of propane fuel for a reasonable price in some of the US western outback areas. There is room in my pickup bed for a fairly large propane tank.

I vaguely remember that work that Ak Miller did. I'm a little reluctant to mess with turbos unlesss they are OEM on a replacement engine. I don't know enough about them to be able to cobble up my own setup. And by the time I'd buy all new pieces in the aftermarket I think I'd lose any worthwhile cost savings.

Actually what attracts me to the propane idea is that if I don't have to deal with the electronic bureaucrats in the smog inspection system I'll have some leeway to experiment with other mileage increasing mods to the engine.

Ed Weldon

I guess I wouldn't consider 235 Hp on a 454 to be all that powerful but then thats just me.

If it was me I would lean towards the propane conversion myself along with some added engine modifications to pick up the efficiency. Here is my write up on a my Mazda B2600 I did a full propane only conversion to last summer.

http://cr4.globalspec.com/thread/59332

I have also done a number of propane conversions now including a worked over 1977 Ford 460 out of a Lincoln that I put in my 1985 F150 extended cab with a beefed up E4OD overdrive transmission with a PCS controller behind it that was pushing 400 Hp on propane and got in the low teens fuel mileage when driven conservatively.

A few things to consider with propane is it likes high compression, around 12:1 is where its power and efficiency come out at. Also being its a smoother faster burning fuel you can step up into the more aggressive end of the towing camshafts, intakes and exhaust headers and still have good idle and drivability with it. Lastly with a big block engine putting an overdrive on it that brings the RPM's down is a big help.

tcmtech -- That's very interesting info on propane. Especially the part about it liking compression. That tends to change the picture for me. I'm thinking a straight propane conversion would satisfy the DMV referree; but it wouldn't get the efficiency improvement with the low stock compression ratio of the 454 motor. And the efficiency is what this is all about.

Your topic on the B2600 is fascinating and very informative. I'm going to save your comments from there for future reference. At this point I've got a lot to learn about propane for vehicles. I'm not sure whether it'll be the best answer for my 78 GMC. I have a good bit of research to do on refueling sources. The 454 V-8 doesn't really need a rebuild which is what would happen with new high compression pistons to raise the compression ratio.

But your experience may help with a future project. I have this fantasy about building a Cyclops. But that's another topic.

Thank you for your valuable help...... Ed Weldon

Tobugrynbak - Many thanks for all the good info, both on propane and your experience with a diesel. Gotta go study the Impco site.

I'm not sure CA will let me pass smog with a dual fuel motor in the 78 GMC. That will take some checking. But that would solve any concerns about refueling in out of the way places here in the USA. Our West is somewhat like your Outback in that trips need a bit of planning around fuel stops once you get off the interstate highways.

But after tcmtech's comments about the importance of compression ratio to get best efficiency with propane I have to consider whether I want to go that deep into the rat motor. At 60K miles the motor is still strong, but as soon as I start thinking about new pistons for more compression the cost of doing the motor begins to be a big factor in the decision.

Ed Weldon

Hi Ed,

I have the same engine and tranny in my 86 GMC. I don't know all the fancy stuff about power curves and all of that, but here's what I did. The truck loves it, and it got my mileage up to about 14mpg.

Switch out distributer to HEI, I used an Accel high performance, along with high performance plugs and wires.

Then,I got one of these with the optional in dash timing adjustment.

Based on my experience, your not going to get any huge increase in mileage with the existing 454. My truck really likes this changeover, and I like the ability to adjust the timing from inside the cab for different driving conditions and different gas, which varies greatly.

I'm also reading about fuel injection crossover systems that claim to improve fuel economy. I just use my truck to haul my boat and ladders and equipment from time to time, so I'm probably not going to dump more money into it than I have.

I'm feeling pretty good with this setup. The brand new trucks with big blocks that are coming out get about the same mileage as mine. I'm up to about 200K miles on my last rebuild.

kramarat -- very interesting about the ignition. That I'm going to dig into. Overdrive sounds interesting. They are not cheap; but do offer an interesting possibility. Nice thing about an aftermarket OD unit is that it can be taken back out of the truck fairly easily if for some reason I can no longer use the truck as planned. Or maybe a switch to a late version 700R4 tranny in place of the turbo 400 if that should develop issues. A 700R4 or later version 4L6xx series is a decent investment with good value holding potential. Still have a lot to learn here.

Thank you for your help. ............Ed Weldon

A 350 will bolt right up to your tranny.They are available with many options that will take you up to 400hp+.Check out the Holley Carburetor page, and you can build one to your own specific needs.They will calculate the gear ratios for you, as well as other factors.Good place to start.When properly matched,16 highway is easy,not pulling a load,just the truck.

A one-step up in rear end ratio will also help without hurting the power too much.

129CBRider -- Thanks for the good data point. I've heard of high mpg Chevies like this. I suspect that has a lot to do with higher compression ratios in the earlier small blocks in addition to the low axle ratio. I'm considering a small block in place or the rat motor as one possibility. But I think the best route for the 78GMC in that direction would be a late 90's modern fuel injected motor complete with all the smog related stuff out of a wreck.

One thing I need to be careful with is having too low a ratio when pulling a heavy load out here in the West beyond the plains country. When you get on secondary roads the hills can get steep and real problems pulling a load "out of the hole" can happen. You can churn a torque converter at low speeds only so long before it starts complaining.

Ed Weldon

If you use it for pulling most of the time then you need to think 'Motorhome' and Torque.

A different cam, tranny cooler, headers tuned for torque, triple core radiator, HD ignition, silicone plug wired, titanium plugs.

You shouldn't worry at all about horsepower. It is what sets land speed records.

Torque is what pulls and that should be your objective. The 454 kinda comes 'standard' with a lot of torque but a LOT of motorhomes come with the Dodge 360 with RV cams in them that will pull an RV up a mountain towing a car behind them.

Here's one for the 454:

http://cgi.ebay.com/ebaymotors/Chevrolet-427-454-RV-Torque-Camshaft-Cam-kit-lifters-_W0QQcmdZViewItemQQhashZitem2c506d6d70QQitemZ190327909744QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

Easiest thing to do would be to change the RV cam, tranny to an L80E, 2.76 diff gears and install a vacuum guage and keep it in the green!

I have a 2000 Chevy Z71 4x4, single cab Flareside with the 5.3 V8 with shorty headers, performance chip, OEM style K&N filter, Air Raid intake tube, modified air intake sensor (knocked the BBQ grill out of it) dual cat-back Gibson mufflers but the original 3.73 gears and I get 19 on the highway but only 15 towing a 6x12 box trailer with 5 motorcycles in it (total weight of trailer would be only about 3800#).

Your best bet for total change out would be to just find a 1978 Motorhome with 15,000 miles on it and swap the whole drivetrain!

I've done a few conversions on mid and late 50's Chevy trucks with late 90's to early 2000's injected small blocks good mpg and plenty of tasty horsepower= Just an idea, Good luck Tim

Tim - I've got questions that I think you can answer. A complete small block would work if it has enough horsepower and can hold the power output for most of an hour pulling the I80 grades to Donner Pass.

What is a typical price to pay for a complete running engine/tranny/harnesses etc. of the type you have worked with?

What area of the country do your numbers come from?

Are there any particular years or models to avoid?

Thanks for your comment, Ed Weldon

I hate to break it to you but you live in the peoples republic of CA. Any major visible modifications, EVEN if they render 100 mpg will not pass visual smog inspection. Any vehicle 76 or newer must have a smog check. The reason for the 76 cutoff year is due to the widespread use of catalytic converters adopted by many automotive manufactures for that year. That being said, you can try rejetting the carburetor, but if you do, watch your engine temperature. You may also want to check your differential ratio by checking the codes on the drivers side front fender or in the glovebox. If it starts with a 4 you might want to try something that begins with a 3. You will lose speed in your starts but will drop rpms at cruising speeds, gaining fuel mileage.

tundrawolf - Thanks for your comments. But the CA engine swap approval isn't a simple "no". There's a formal protocol involving the DMV referree. The following link is a good description.

http://www.jagsthatrun.com/Pages/Chevrolet_S-10_V-8_Smog.html

I'm pretty well tuned into that system and expect my conversion will go through OK before I start buying stuff.

Ed Weldon

G'day Ed,

How similar to LG is Propane. I believe Propane is constituent of LPG but I ain't familiar with the proportions.

In Australia, nearly all cabs run on LPG, so the economics must be okay. If you run dual fuel, you run into efficiency problems due to the crude mixer often used and the need for the timing to be set for petrol. There are ignition modules that will advance the timing to suit the LPG (Propane). You will lose mileage either way but power and economy improves dramatically with the timing advanced.

If you want to run straight LG or Propane, a company called Gas Research www.gasresearch.com.au has a gas carby that with camshaft, head and ignition mods, equals or betters a similar engine on 98 RON petrol. There are even LPG injection systems now that are OEM (Ford).

Straight gas will not only be cheaper to buy but your motor will last longer. We have cabs that regulary get 300 to 500 miles between engine work.

Royce

Royce -- I have to get closer to what you folks in Oz have been doing with propane motor fuel. Sounds like you have a bunch of experience building up. www.gasresearch.com.au sounds well worth a visit. I've bought things from Australia before, the transactions were quite easy and the shipping costs reasonable.

Thanks for the info. ........... Ed Weldon

Hi Ed,

I just read about you considering the 700R4 or 4L60 overdrives. I would stay away unless you spend big $ beefing up. In stock form they fail early just in regular driving. You can add the Gear Vendors .78 overdrive to your great Turbo 400 or bolt in an electronic overdrive 4L80 or 4L85 which are quite good. They are sort of based on the Turbo 400 and can last almost as long. The turbo 400 and it's overdrive derivatives were even used in Hummer H1 m(military version) and by Rolls-Royce and Ferrari.

Hi Ed,

If your going to keep your 454, you might consider adding TBI fuel injection plus the timing control mentioned previously. With all that plus overdrive you might get 17 mpg with synthetics in everything not towing as your big engine won't be working too hard.

Maybe run a leakdown test on your engine to see how tight it is.

There is a diy fuel injection computer in kit form or built which can run any engine from 1 -12 cyl. called Megasquirt. About $250 and up. The injectors and sensors cost extra $. It's quite popular and has been mentioned in Hot Rod Mag. I think you could get the throttle body injector and sensors for low $ at a junkyard as demand would be low. Maybe a used factory computer could be had for low $ too and used with aftermarket software for tuning. The name HP Tuner's comes to mind. You would also gain knock sensing capability for sure which would automatically keep the timing at the best for MPG.

What are you using for tires and wheels as they can affect MPG?

As mentioned by someone else you may not be able to add fuel injection etc to your 454 if it doesn't pass the visual. Maybe they wouldn't pull the air cleaner to see a throttle body fuel injection system you added? Check the rules.

I did read somewhere if you change the engine in CA it can be newer as long as you add all the emissions equipment for that new year and it passes visual and tailpipe checks for the newer year. GM sells a complete 6.2 LS engine with everything needed for older vehicles for $7.5K. It will pass the latest smog regs.

I think the diesels I mentioned are exempt from any annual testing , but you would have to ask. I think you mentioned it too. I think any excess visual smoke might get you in trouble though from what I read.

rmyauck -- The CA DMV referrees are pretty good at what they do. It'll be hard to fool them if I choose to go after a sticker. But I have options that play it the other way involving changes undetectable by a "test only" smog station and plan on an annual "deconvert; reconvert" sequence.

Useful info on the $7.5K cost of an LS engine. That's a lot of money but as I mentioned in another reply here it represents an investment that is not necessarily tied to the one truck. If I no longer need a tow truck for a car trailer I could always put the LS engine into a nice everyday driver street rod. Nothing new to me about such a project.

Thanks for your posting. .....Ed Weldon

Gotta check out that TBI fuel injection and the Megasquirt you mentioned here. Be interesting to see if the TBI setup is practical and if it's CA emmission compliant. And if not is it practical for an annual deconvert/reconvert sequence.

"Nother good tip. Thanks again, rmyauck. ......... Ed Weldon

rmyauk -- You sure did me a good favor with all this good info on the diesels. I have to chew on it for a while.

That 5.9 Cummins sounds like a great piece of hardware. I mentioned in a previous post that I fear the weight may be too much for my truck which because it is a "Trailering Special" and not a "Camper Special" it's fitted out as a long bed half ton. Am I wrong? I don't think the little 3.9b series 4 cyl. has the horsepower at 150 to pull the pulling 5000 pounds of trailer up those western mountain passes at any reasonable speed. You just end up behind the slowest truck in the right lane with everybody mad at you.

But maybe I'm jumping to conclusions. Got a lot of studying to do. And rereading of all the great info I've gotten.

Thank you for all your help. .......Ed Weldon

I'd go with a 350 small block and an "RV" cam (not so much of a lift increase but added duration) and a dual plane manifold. The Vortec head (you'll find them on Chevy trucks all day) in stock condition would be perfect for you. No modifications, just bolt them on. They breathe nicely in the mid range without having a soggy bottom. You don't need HP as much as torque. I don't know how much of a hot rodder you are but I'm sure you've heard of stroking to get more torque. A 383 stroker might be a nice choice to consider. If you do it right you can get almost as much torque as your 454. Your compression ratio is tricky. The higher you go (to a point) will increase your torque. But it also hurts your emissions and mileage. The cam you select would weigh heavy on the best "final compression ratio" you use. Your 400 will hook right up. You never mentioned your rear gear ratio, I assume it's low. If most of the miles your truck see's are on the hwy you can change the ratio to reduce RPM. There's nothing wrong with pulling it down in to 2nd and driving in the slow lane to climb those hills at a slightly reduced speed. It sounds like a fun project. If you go ahead with it it would be nice to keep updated.

Fredski -- You're not off topic in my book. Looks like we have an OT sprinkler hanging out here.

Building a small block that is fitted out as a carbureated engine of the same period or newer is a posibility. The problem is that there are not a lot of them still on the road that have all the right little pieces of smog hardware that the DMV referree is going to look for. Probably better to find a complete car. A rusty or dented Camaro with that was below the collector car quality level could be perfect engine donor.

I've been a hot rodder for a long time so I know what you're talking about. It's just that I never got into Chevies. I think I'd build it as a 372 since this is an SCTA "C" motor size and that venue would be my best bet for getting my money out of it if my need for the truck went away for any reason. I think I'd also take a look at one of those pricey overdrive boxes. It's the kind of thing that can be easily removed and resold.

Interesting thing about upping the compression ratio to the point where high octane pump gas is needed. As the price of gasoline goes up the percentage difference in between regular and "extra" goes down since this is a refinery cost not directly related to the crude cost. Meantime the efficiency and thus mileage gain from higher compression stays the same since the laws of physics don't include a factor for fuel cost. Luxury car manufacturers have figured that out; but they won't up the compression ratios on traditional lower priced brands because the average consumer with his biases can't be easily made to understand what I just said. The exception seems to be the BMW Mini.

Thanks again for your interest and comments. Talking about this approach this has given me an opportunity to think this alternative through.

Ed Weldon

Economically speaking: Considering you drive 5000 miles a year, it will take 10 years of driving before you could recover a minimum of $6000 you may put into the conversion with a 30% fuel economy boost. At 60000 miles, the drive train is practically just broken in. Is it worth converting it or just staying with it 'as is' and using it for those special towing and other occasions. May be you will drive less than 5000 miles. Why fix something which is not broken. Just a thought, because that is what I will do and keep the truck original. Pretty soon these trucks will not be available any more.

You're right but that isnt fun! He wants a project.

In that case, it will be interesting to know what he does. I hope he keeps us posted.

Fredski - I'm not really looking for a project. Just looking for the easiest practical solution. The race car is my project. The tow truck is just part of it. I'd much rather spend my operation budget on race fuel than fuel for the truck.

If anything in my life gets too complicated it has a tendency to not get done. Besides the layout of my shop work area really does not lend itself to working on that big truck. It's a grind all the way that I'll want to be over sooner than later. So this calls for a lot of creative thinking. The fun part will come if I can figure out how to get the most mileage improvement for the least cost within all the constraints of my particular situation.

Ed Weldon

kajbaba -- You make a very valid point. Doing nothing and just eating the cost of fuel whatever it is in the future has been my position the last couple of years. But there are a lot of factors in my particular calculation and a lot of uncertain constants. One as you point out is the long term resale value of my particular truck. Certain types of conversions I'm considering are better than others with respect to resale value. The truck the way it sits now probably wouldn't bring more than $1000 because it is in that age range where it has to pass CA smog tests and costs about 50 cents/mile to run.

If it had a decent quality diesel conversion I could probably run it for some years and turn around and get my entire investment out of it. Not sure yet whether a propane setup of one type or another would measure up that far.

And if I opted for a modern LS series fuel injected small block I probably would not get as much in a resale as the same truck with nice diesel. But, and this is an important but, I could pull the engine and tranny and "off" the rest of the truck for a minimal amount. I would have at least two other good uses for the smallblock.

Thanks for your interest in my project. ........... Ed Weldon

One possibility with your 1978 454 is to simply get a good used set of heads and have them milled way down to bring the compression up. A.075 head cut was all it took with may Mazda to go from around 8.8:1 to 12:1 compression.

With the 454s that big of cut would require shorter push rods and some mill work on the intake to match it up but for the most part its a off the shelf parts bolt on type of conversion.

Do some port cleanup work and toss a bigger camshaft in it and I don't see any reason you couldn't pass the 450+ foot pounds of torque point at under 2000 RPM's with a 350+ HP top end all on propane!

As far as a propane mixers goes I would recommend an Impco 425 size for a 454 engine. the 300 series might come in as being too small when you get on the pedal and will limit your torque and power.

Unlike gasoline propane is not fussy about having an over sized carb system air flow wise. My 460 I built ran a 800 CMF 4bbl Edelbrock carb with a 1000+ CFM rated propane mixer on top of it and it was wonderfully snappy to drive.

Also with a full propane conversion the gasoline carb is basically nothing more than a throttle body at that point so even if its completely gutted and all the fuel passages plugged off all it still works. Finding big worn out carbs is fairly easy and cheap too. All they need is good throttle blades and shafts and the rest is not necessary.

If you are curious I have quite a few new old stock large capacity vaporizers and mixer units that where specifically for the big block engines in RV's from back in the mid to late 80's. they are the style that sits right on top of the original carb and look like a fancy performance air cleaner. I will happily sell you a pair of those and three vaporizers, so that you have spare parts, plus fuel hose and related parts you need for $750 and I would include the shipping to. You just need to supply the carb and a fuel tank at that point. They are dual fuel style so an on the go switch between gas and propane is basically pull a knob and flip a switch or they can be permanetly set up as a propane only system as well.

Just something to think about.

tcmtech -- You've given me lots more good ideas to follow. At this point propane is looking better than a diesel primarily based on the cost. You've given me some good leads to follow.

One thing I want to check on, since I'm not real knowledgable on chevies, is whether anyone makes an aftermarket cast iron racing big block head like the Dart heads for the small blocks. I'd like to aviod pulling the engine if I'm going to stick with the rat motor. I don't want to put too much money into this motor as with time their value in most any form is decreasing because I really have no other use for it. A small block is a different story. But that means a deeper up front investment.

I have another question you or someone else close to propane use on small vehicles. It's about the tanks. I've seen nice looking setups in open pickup beds crosswise against the cab end. I like to run a shell because I carry a lot of expensive gear in there because my trailer is open and trucks in parking lots are pretty vulnerable. I'm wondering how to deal with a propane tank and a shell.

Does a propane tank have to be "outside" such an enclosure since it is no longer a legal passenger compartment? Do those large tanks for horizontal mounting come with end connections for filling? The cab high shell I have is an old steel one and could be easily modified to have a specially vented compartment isolated from the shell interior.

Or am I better off just removing the left side auxiliary 18 gallon gas tank on the left side and replace it with a propane tank?

Thanks again, friend. I really appreciate the help from you and the others in our CR-4 community. ......................Ed Weldon

I can't say what your local rules are regarding LPG installations.

Here in Oz, the general regulations regarding tank installations are that the tank must be sealed from the closed/passenger area and vented (down, LPG is heavier than air) outside. So yes you could put a tank across the front of the bed (build a shelf across the top so you can load stuff on top, but you must leave access in front of the tank to get to the shut off valve on the tank) and have your canopy.

Not sure if they are available in the U.S., but we have Toroidal shaped LPgas tanks which will fit in the spare wheel well or can be mounted under the rear chassis where you spare wheel sits. Just add a bash plate.

http://www.bluelpg.com.au/

http://www.rta.nsw.gov.au/registration/downloads/vsi/vsi14.pdf

Don't panic too much about over heating on LPG, I can understand euro cars with single row radiators having a problem. Your case not so much, one of the secrets is to mount the convertor/vapouriser such that it is lower than the engine heads. This ensures that there is always coolant without bubbles in the vapouriser so it doesn't freeze. Dropping in a thermostat one range lower so it opens sooner is another trick but you must run a thermostat.

I never had a problem in my F350 on gas, it was a ex Ambulance 351 4 speed manual Tare weight was 3.5 tonnes not including my lunch. Clevelands are reknown for overheating if things aren't right but I never had a problem, and I was living in Queensland at the time. You should not have a problem with your 454 if you've already sorted your truck for towing.

If it were me, I would get a good diesel, but as the torque from a similar BHP diesel is generally much higher than the petrol engine, the original transmission may not like that.....check first or change the transmission.

I also like the fact that diesel does not catch fire anywhere near as badly/quickly as petrol does.

If you are really clever, you will find a 4WD diesel and drive train......maybe from a junkyard....

I can recommend against a gas conversion as if you are towing anything, or running up mountains, most gas conversions may not be run under such circumstances as the engines run significantly warmer than with petrol, it has turned out to be a real problem here.....even increasing the size of the radiator may not help enough as a petrol engine on LPG or similar may still overheat......

There is also a bad history of reliability as some of the parts are being forged and you cannot tell the difference between an original part or the far east forgery.....

I have a friend in the car business and he says that it can work on large engines with relatively low power outputs and a good conversion kit. But do not be surprised if it still brings problems.

Sadly I have no statistics to back me (and him) up......

An engine designed and built to run on such gas would be best of all and then no problem.....

I personally would love a modified diesel engine for my car with LPG as such an engine still uses diesel to start the burning process, but gas supplies the main power.....its used in many cities as a cleaner alternative (almost) to diesel for buses....but as far as I am aware, not generally for cars and trucks at this time.

Andy -- thanks for your comments from the EU side. There is always a lot to learn form you folks.

Your expressed concerns about propane/LPG running hotter is a very useful red flag that I'll have to check out carefully. I expect to see myself more than once on a hot summer afternoon pulling a 2300 kg load up the 100 km grade to Donner pass. It starts just east of Sacramento, CA at 300m elevation and 110F air temp to Donner pass at 2700m in heavy truck and car traffic. This is a real test of a any cooling system.

By the way you've given me a very useful answer. Contrary to what someone else in this forum seems to think you are definitely not off topic.

Ed Weldon

So where would this extra heat come from?

propane is higher octane & lower in BTU's

you will be able to find propane between your house & Bonneville or Black Rock, there are plenty of RV's that run on propane, campers also use it for cooking. next time you do a run take note along the way

the payback is going to depend on how much it costs for the motor [head] work

EFI off a newer model would be promising too, since you have a good handle on the referee process. People have no idea the stuff you can get on the road here, by being willing to go through the process

Dear Garth, I have no personal experience of the LPG problems, but there have been several TV programs about such problems with LPG conversions here. I also have a friend in the car business and he will not touch a converted car with a barge pole.

You may not understand why, and I cannot answer your question myself, but I can operate "Google"!!

I decided to have a look around on the web for links regarding the LPG problem using a search with "overheating lpg engines", it gave me around 2,480,000 hits!! Which in itself should be warning enough! But not all are to do with the problem we are discussing, but quite a few are.....

Some of these links make horrific reading....if you still need more convincing, google yourself!!

Please read some of them for yourself, just taken from the first two pages only, not "selected" just for the problem:-

http://www.landyzone.co.uk/lz/f10/range-rover-p38-4-6-overheating-lpg-43616.html

http://www.ciao.co.uk/LPG_Conversions__Review_5411033

http://www.lpgforum.co.uk/viewtopic.php?f=30&t=8458

http://www.lpgforum.co.uk/viewtopic.php?f=30&t=8458

http://www.fixya.com/cars/t1438131-occasional_overheating_when_running_lpg

http://phorums.com.au/archive/index.php/t-183533.html

http://www.myautomotiveforum.com.au/forums/index.php?showtopic=3606

http://www.fordmods.com/ford-4l-and-6-cylinder-f1/xf-on-lpg-overheating-t44501.html

http://www.bmwland.co.uk/forums/viewtopic.php?f=6&t=40425

All I did was ponder the possible causes of overheating & you flame me, of course none of those links are relevant to Ed's situation.

you might as well have posted this

as the search gets more specific, no relevant hits

there's a few references to small block propane conversion problems, but the context [or lack] would lead you to believe the conversions were badly done

run a propane conversion too rich, the motor gets too hot

a full conversion including raising the compression, will take advantage of the higher octane.

anyone wanna bet against Ed having a properly maintained cooling system?

another possible problem would come from an undersized exhaust system

Thats not "Flaming"......

I just did what you could/should have done before posting.

I am sure that some of the conversions work fine, if you are a betting man then take a chance!!

My personal take was calculated a few years ago and my take was:-

Cost of car + cost of conversion + cost of fuel for 50,000 Kms was more than the diesel car + diesel fuel for 50,000 Kms.

The diesel version won hands down!! Full car manufacturer guarantee (3 years) and lower costs....

Even without the possibility of landing between the conversion firm and the car manufacturer when it don't work as required.

Some manufacturer's (most) take the guarantee off the engine after an LPG conversion, unless they did it (seldom)......and the guarantee from some conversion companies is not worth the paper its printed on!!!

Obviously you did not have time to search through them, but all the links I posted were talking about LPG and overheating!!!! Many different vehicles, mostly in the USA!!

It was meant as a "Heads up".......so don't get touchy for no logical reason!!

& not one chevy big block in the bunch

all very generalized stuff

& most of the links were from UK or down under

the diesel advice is fine if Ed were replacing his truck or had a good donor lined up...

Dear Ed,

I am pleased to be of service, remember though that I passed the information on from a Guy in the car business here, I have (luckily) no direct personal experiences with LPG.

With regards to the Off Topic point, it means little to me, as does On Topic or GAs, I don't post for Brownie points, I try and post for the Original Poster......something useful.

I am retired and online a lot, you make good friends like yourself, and some of the others too.....the last ones are like water off the proverbial Duck's back.......

As the USA often has much larger engines in its vehicles, the over heating problem may not be as pronounced as here, or even nonexistent.....a good look/check around on the web will help usually I feel.....

Please keep us informed of what you finally do, it sounds very interesting, and may stir some similar ideas in others....

THere is the cheap and easy way. Swap in a 6.2 diesel. It bolts right up to the TH400. And can be had easily for under $1,000.

With 4.10 gears on a 3/4 ton $X$ it will get 14 mpg with or without a load. In a 2WD with gears in the low 3.XX range it should get 20+ mpg. But its a gutless wonder.

You can swap in a Cummins 4BT with an OD trans and get in the 20's easy and a LOT of life. Its a more expensive swap however.

Smoothy -- Thanks for the suggestions. May work for some but I need more horsepower than either the 6.2 or the 4bt can produce.

Torque is nice for start and stop and around town but you need horsepower to pull 10,000 pounds up long western hills or you get stuck behind loaded 18 wheelers for hours doing 20 mph. A 6bt would be a nice choice but my truck is a rare half ton rated "trailering special" and the 6 cylinder weighs almost twice as much as the rat motor.

I suppose the 4bt can take a pretty decent horsepower boost but I need to get a better handle on the associated costs and other possible issues before I'd make that part of a plan.

Ed Weldon

I missed any comments you may have had about towing that much weight before my post. You CAN tow that much with the 6.2 Detroit diesel...but it won't be fun and it won't be fast...and like you said...going to be a lot of upset people behind you on hills. I've done it all of twice...and never on a mountain. And yeah...a long steep grade would be a problem.

I just saw the typo in my post....as I have an 87 heavy duty 3/4 Ton 4X4 with that engine ( J-code) If I used it more I'd do a Cummins swap. And with a 1/2 ton 2WD I also think the 6BT would be too heavy for your application. Not sure what is different about yours but I'm venturing a guess its got a 14 bolt semi-floater with 5 lug axels and smaller brakes than I have on mine.

Hi Ed,

Thought you had the 3/4 ton as I really didn't see any reference to a 1/2 ton because you had the 454. I've got the camper special 8,200 GVW with the optional woodgrain sides. The 79 must of been the last year for the 454! I think you need the HD 3/4 with the Full Floater rear end for the 5.9 Cummins. It weighs 1,100 lbs and the 1/2 tons have a lighter frame and front end too. Your right it's too heavy for your truck.

What is your rear end gearing (mark a wheel and the driveshaft with chalk marks and rotate the wheel one turn counting the number of turns of the driveshaft). I like the 454 as it is a much more durable engine than the small block. According to the engine Chevy engine guru's the block can take 1,400 HP which is double the small block. It was designed to win races! It was the only American engine to stand up to Porsche in endurance racing years ago. It's even been put in airplanes which is an extreme test of durability too. Your truck may be a nice hot rod the way it is! I think there is mileage much potential to be gained as long as it passes a leakdown test.

That 6.2L LS3 is called the E-Rod Package and Popular Hot Rodding April issue has an article about it. Price is actually as low as $7.6K according to them. You get 430 HP & 424 Ft lbs, wiring harness, computer with emissions cal, cat converters, exh. manifolds, oxygen sensors and sensor bosses, all other sensors, fuel tank evap canister, air filter, mass airflow sensor complete, electronic gas pedal, & instructions.

The 3.9 4BT has much potential according to the Diesel mags. The B series were designed for industrial use ( came out in 84 and was co-developed with Case) and can take huge power increases by tuning up the boost with bigger turbo's more fuel etc. The only mod needed to the basic engine unless it is really boosted to the max is head studs. They add block girdles too. The drag racer's and tractor pullers etc boost the power on the 3.9's to 600 HP and the 5.9's to 1000 without blowing them up so I think bringing the 3.9 up to 200-250 HP wouldn't be a problem. Just close to 1 HP to cu in like Cummins did with the 5.9 around 2003. There are other Industrial Diesels such as the Perkins and Izusu mentioned that are probably just as good, but they may be harder to find, but may be inexpensive to pick up due to lack of popularity. They made 4 cyl versions too just like Cummins did. All these Industrial diesels use SAE bellhousings so adapting trans shouldn't be a problem. Cummins and others sells bellousings to adapt any popular trans.

Swapping engines and doing all this adapting could take a lot of money so you may want to do as I did and consider buying an old Dodge 3/4 with the 5.9 (years 89-97). The newer style 94 and up ride much better with the longer leafs in the rear and the coil spring front end, but aren't as simple, but drag coefficient and looks may be better to you. I think the heavy trucks are better too for 5000 lb plus towing in the mountains in that you get HD parts, brakes etc. You also get the crash safety of a newer vehicle (diesel fuel is much better in that regard too). Plus that towing weight won't bring down the MPG much. These diesel trucks are very addictive! You won't regret buying one. I recently bought a 95 too! If you want more info I'll be glad to help.

Hot rod your classic 454 for better performance and mileage as I think it will be more desirable with the 454 and use it for running around or as a spare truck. Maybe you don't have room for another truck either, but just a thought. Good luck! Randy

This is interesting. Here's the new truck MPG. Bear in mind, you've got a 7.4L V8, you're using it to tow a fairly large load, up and down hills, the posted MPG is always more than real life................and if you click on the larger trucks/fuel economy, they won't even give you fuel economy numbers. Click on vehicle line up/2500/fuel economy.

I don't think anything you do is going to save much money. You might be able to squeek another 3-5 MPG out of it, but I wouldn't spend a lot to get there.

http://www.gmc.com/sierra/1500/specsFuel.jsp

Here's what the, "professional", automotive engineers have been able to do in the 33 years since your truck was built, including the new, "flex fuel", models.

XFE Truck: V8, 5.3-liter, 6-speed automatic (Flex Fuel)

• Gas: 15 city | 22 highway
• E85: 11 city | 16 highway

V8, 5.3-liter, 6-speed automatic (Flex Fuel

• Gas: 15 city | 21 highway
• E85: 11 city | 16 highway

V8, 6.2-liter, 6-speed automatic (Flex Fuel

• Gas: 13 city | 18 highway
• E85: 9 city | 13 highway

2011 GMC Sierra 4WD Pickup Trucks

6-cyl, 4.3-liter, 4-speed automatic

• 14 city | 18 highway

Your best bet may be a two speed auxiliary transmission. Either a rear differential two HI-LO or an in-line addition. Either one takes a lot of doing. The differential dequires an axle tear-down. The in-line requires frame mounting additions and custom drive shafts. Either one should give you an extra 2:1 ratio increase, lowering fuel consumption but sacrificing torque and increasing stress on components. start out in "low" for city driving. When you're nicely on the highway and in the groove shift it to "high" and enjoy the better milage.

Gazu - Thanks for your comments. Either 2 speed approach looks like more work and cost than it's worth. This particular 78 GMC 1/2 ton has a 12 bolt rear. Easy to change out. On the other hand the whole exhaust system would have to be changed to make room for a gearbox in the middle of the drive shaft. That adds to the frame and drive shaft work. I'm set up to do that and even do my own driveshafts. But you're right, its a bunch of work. The rear end switch would be a lot easier and I'd just keep the old 12 bolt intact out in the bushes somewhere.

I do have a third alternative and that is to swap out the rear for a champ quickchange. This approach is not for everyone. But to me the whine of the spur gears in a quick change is music to my ears almost a sweet as Crosby, CCR and the Nitty Gritty Dirt band. And if they wear out they are cheap to replace. I'm used to doing gear changes in those things and have a smaller Halibrand roadster quickie in my race car. Takes about 15 minutes and I'd be carrying the tool setup for job anyway. A plus is I'd only have to do the change once on most trips to Bonneville or El Mirage and that would be after the initial pull up my driveway. Used Halibrand, Winters and Frankland quick changes are pretty readily available and so are disk brake setups for them. I suspect the whole deal might be cheaper than the 2 speed plus I get exactly the ratios I want. Unlike the race car that has to be jacked up to change gears there is plenty of room under the back of the 8 foot long bed to do a gear change without jacking or taking down the spare. Just throw down a ground cloth put on some nitrile gloves and go to work.

Funny thing here, looks like as Randy (rmyauck) suggested, I'm turning my old truck into a hot rod, as if I need another one...... Ed Weldon

Now that sounds like an idea... a two speed rear end (assuming it exists for the truck). I dealt with that on a fuel truck back in my younger days. It would be alot cheaper than engine transfers, technology transfers... diesel... gasses etc.

I normally don't respond to CR4s this late, but this time Ed deserves this.

Bill

I have a few thoughts to toss out.

If diesels interest you, what about the Isuzu NPR or NQR cab over engine. They make more torque than the FI Chevy V8 used in the same truck. 4 cylinder turbo, and plenty of them around. They have an Asian 4 speed OD transmission with them.

That 454 can make better mileage if you want. The adjustable timing. I had a MSD system with the timing adjuster, and loved it. On long stretches, just adjust the timing control for most speed without moving the gas pedal. How about low restriction air filters? If you have the room, just stack 2 filters on top of each other. Toss one in the cab for inspections. There must be a ton of CARB approved manifolds for the BBC. Edelbrock and Holly make aftermarket FI setups. I think they have CARB approval. Talk to users to see how they affect mileage. Exhaust back pressure. Headers, collecter extentions, ballence tubes, low restriction mufflers and big fat pipes. All should be available with approvals needed. Are carb spacers legal? They should help torque at low speeds.

What is your axle ratio? You can try moving it around some by varying tire sizes. Try using Light Duty truck tires, with higher load and pressure ratings. Lower rolling resistance. on them.

Have you thought about replacing your water pump fan with high efficiency electric(s)? (That wouked well for me on a S10)

Good luck.

bobc -- More interesting ideas. The Isuzu diesels have always been a point of interest to me for a possible smaller vehicle project. But I've viewed them through the horsepower lens as I've mentioned above in reference to the Cummins 4bt engines. Much of this has to do with my conservatism over power increases in diesels born of a lack of famiiarity with common garden varieties practical for conversions. If I make the plunge I'd probably get over that restraint. But I suspect there would be a dollar cost associated with my learning curve especially when it comes to turbos. Messing around with carburation and ignition on the rat motor seems to hold some promise of gains with minimal investment.

Interesting idea on air filters. That's a easy experiment. I'm not crazy about messing with the exhaust system alone. What's on the truck is in beautiful shape right now. Changing out mufflers is a possibility; but I think the only way to see a significant improvement will be to do the entire system including the headers. I'm not high on the idea of adding noise with no measurable economy gain.

I mentioned some thoughts on rear ends in reply#55 to gazu. Also the cooling fan idea is real interesting and would be easy to experiment with. Again those parts can easily find other uses if they don't work out on my first application to the truck. One would make a great exahust fan for the inside of the shell on hot days.

Thanks for tuning in here. I value you thoughts on these subjects.

Ed Weldon

Other than the exhaust, most of the components can have an afterlife if the ends do not justify the means.

Ed & I had some exchanges a while back on NPR drive trains

I used a 15000 Gvw flatbed cab over 4 speed auto, turbo diesel, which we regularly loaded to 18000+ mileage was as high as 14 running 65-70

A cabover will turn inside pickups & most SUV's problem is the price of admission is in the 1000's, not the 100's, even a wrecked one commands a substantial price

Ideally you would do a hauler with out a trailer, so you could cruise above 55, but there's that pesky price tag.

I'm sure Ed could come up with a nifty integration of the 2, but that's a big ol project, which would cut into the rest of his life & budget

It sounds like the rearend, ignition & some other minor mods will be the chosen path

Like you said, the big question in my mind, is the price of a NPR drive-train. If a rollover chassis was found, It might be cheap enough. But would it be worth the up front investment for the limited mileage he does? Some of the Items I mentioned could pick up 2 to 3 MPG for the cost of my phone bill. I do think that an RV cam would pick up a good percentage if so motivated.

And he could always do a hydrogen conversion, and get 50, 75 perhaps even 100 MPG.

An aftermarket throttle body fuel ionjection system would help as would an ignition upgrade and headers. I had a 94 GMC with a 350 and installed a Jacobs ignition in it. That single change netted a 2 MPG increase in fuel mileage. The bottom line becomes how much money do you want to spend? A 4L60 or 700R4 overdrive transmission would help also.

I would NEVER consider a 700R4 towing anything bigger than a utility trailer nuch less a 10,000lb payload. Even upgraded I don't think they are up for that sort of abuse.

Thanks smoothy. Seems to be a general consensus about 700R4's. Leave them to the streetrodders and stick with something stronger like the low mileage turbo 400 I already have. Or go over to a big old granny gear 4 speed or whatever might come with some diesel like the Isuzu. I know from past experience one of those would work.

A good friend had for many years a 57 chevy 3/4 ton with a 283 and a truck 4 speed. From time to time I would borrow it during my years with the ill fated 318 Dodge van. That old truck of his could pull a house up my driveway. It just laughed at 2 yards of granite gravel. ............Ed Weldon

I had a friend that inherited an old Dodge Power Wagon. 53 I think it was. Flat out I don't think it could hit 60. But that old flathead could was geared so low that low range was useless for anything except playing.

Sorry, I didn't see this thread until now, and I didn't read through all the other comments. Here's my question:

How do you expect to get an ROI? Are you looking for fuel cost savings? If so, let me look at it this way?

You currently drive 5000 miles a year, get 9 MPG (let me use 10 for ease of calculation), and you spend say $3.50 a gallon on gas. (I'm sure you pay more that that in California).

So, you're spending something like $1750 a year on gas. And, if you doubled your MPG to say 20 MPG, you'd save about half that, or around $875. So, if you want a 4 year payback (a 25% ROI), you have about $3500 to spend.

So, what can you do with that? I'm guessing you could get a new engine, but I'm not sure you could find any engine to get you 20 MPG with that (longbed) pickup pulling a trailer. If you could get 15 MPG, maybe (without doing the math), you're 4 year payback might give you a budget of say, $2500 to spend.

After crunching the numbers I have your answer. You need to install a 2 foot tall wheel in the bed of the truck, being a longbed you should have plenty of room. Put 3 hamsters on the wheel for city driving, 4 for hwy and 5 for mountain climbing. Attach the shaft of the wheel to a generator that's charging a lithium/sulfur battery. The battery will be attached to a 100 HP DC drive with a chain located on the driveline (still haven't worked out the size of the gear on the driveline, need your driveline diameter). Depending on table scraps and the unpredictable price of hamster feed you should be able to drive your fuel costs down to about $2.00 a gallon without modifying the 454.

What kind of lame idea is that? With an 8 ft bed, it would be much better used by converting it to a sail. Fit the drive-line with regenerative braking, and a load of batteries to drive the 100 hp motor for the return trip. Hell, he can sell that rat, and pay for the 100 hp motor. Plenty of battery storage room up front then.

I had considered a sail and a 50 foot mast. He was a bit short of info. He didn't provide wind direction or lane width for tacking. Nor did he mention height of any bridges or power lines. So I went with the most compact design.

Good for light humor in an otherwise serious subject. Remember the ROI always includes a "scrap value" factor that tends to be trivial in most commercial situations. It is definitely not trivial in my situation. A lot of the alternatives I'm considering have a substantial resale value at the end of life (in my use) of this truck.

Not being critical here, guys. All forms of humor are welcome even when I'm the butt of the joke. Life has taught me that laughing at myself produces wonderful dividends. The sail idea and the hamsters would make a great cartoon. I think I'll ask my wife to see what she can build with her Corel Graphics around a side view photo of the truck.

Ed (thanks for the ideas......)

Maybe "painted or airbrushed" on both cab doors?

Good call on the distributer mods. I have used the adjustable advance before. Good at adjusting for mileage. The centrifugal advance can also be tailored to help, but it is harder to adjust on the fly.