Supercharger v. High compression; re. Fuel octane

You will want as much octane as you can afford. The blower will add heat as well as compression. If you have a Knock sensor on the engine, It will be retarding as spark knock is detected. But the factory system has it's limits, and retarding will defeat the power of the supercharger. Start with the mid grade and check for knock. advance or retard as needed. Contact someone that is more familiar with the supercharger installations on tour 5.0. Those pistons will only accept so much boost before they shatter.

Thanks bob c.

This engine will spend most of its life on LPG anyway which I am told has an RON of about 105 so for the rare times I am running on petrol I will make sure it is 98 or 100 and I guess, make sure it doesn't spend too long in the tank.

I have talked to a few people about the acceptable limit of boost on a stock 5.0 and the concensus seems to be 9psi.

Thanks again

Thanks bob c.

This engine will spend most of its life on LPG anyway which I am told has an RON of about 105 so for the rare times I am running on petrol I will make sure it is 98 or 100 and I guess, make sure it doesn't spend too long in the tank.

I have talked to a few people about the acceptable limit of boost on a stock 5.0 and the concensus seems to be 9psi.

Thanks again

Yes you would have use a higher octane rating for the stock EFI system. If i may add some pointers.

I'm running a 9:1 on my Alfa 2.0 gtv an increase of 4psi boost will theoretically increase my static C/R to 11:1 about its std limit, giving me +-30 HP. EFI's work on a closed loop system the Lambda sens for O2 in the exhaust and knock sens are used to tell the CPU all about mixture. At higher densities of air intake (boost) you would be wise to make the mixture more rich. You might be on the max limitations of the stock EFI. You may also want to increase the size(displacement volume) of the injectors. You could also increase the fuel pump pressure(although not very effective) A leaned out motor on full taps can burn holes in pistons!!!! Detonation also really hammers conrods, pistons and cranks. For safety i would add another knock sensor to a control circuit to shut down the ignition in the event of a lean out. The mixture control is really all about the stoichiometric ratio of air fuel. Feel free to search up on it it's quite interesting.

Hope these pointers help.

Yes, very helpful. The limitations of the stock ECU is something I have been wondering about. Fortunately for us we will be able to replace our stock ECU with a locally developed unit that will replace both the factory petrol and "piggyback" LPG ECUs that are currently in the car. It will be released in the new year and we have on on order already. The petrol fuel system we have we will probably keep as most (99%) of our driving is on LPG and the gas injectors we have are good for 500HP (so they say) which will more than fuel our ambitions

glad to see you're progressing with this plan!

for what it is worth... I helped a friend turbocharge his 94 mustang a few years back... stock 5.0... with the turbo from the 7.3 superduty diesel trucks on it.. non-intercooled. he ran it initially w/no wastegate, put 23psi into the engine, which was fine for a short time... till he blew up a radiator & overheated the engine... eventually he put on a wastegate, ran non-intercooled still, 10psi on 93 octane (highest pump gas we can get out here... and that's being phased out.... ggrrr)... can ran fine with no indications of knock for several months before he blew it up doing stupid stuff with nitrous @ the track :)

but anyway, by putting boost (psi) to it, you are effectively increasing the compression ratio of your engine... which obviously leads directly to a need for increased octane levels (or DARN good tuning) to prevent knock. i believe the comment above was made "get the highest octane you can... just to be safe" i would agree... go high, do what you can to tune in for that, then try & do a tune for a slightly lower level of octane for those times that you just can't find the good stuff

I still recommend getting an IC in there, if @ ALL possible... not only will it let you run a lower octane (less heat being introduced), it will give you cooler, denser air... which = more power potential :) AND more "whoops" room in case something isn't quite right in the tuning

-Nate

I like the idea of the inter-cooler also. Free power. If you use a pressure switch to monitor engine boost, you can spray a water/ alcohol mixture at the inter-cooler for more power yet.

The LP, or CNG he is planning on using raises some questions that I don't have answers for.

Cheers Nate. I am now realising that at both levels of boost that I wish to have the option of, I will need to cater for the differences in octane of the fuels I will need to use. On low boost 91RON petrol and 105RON LPG and high boost 98-100RON petrol and 105RON LPG. I have just sent an email to the ECU developer (www.profire.com.au) to see if I can have four distinct fuel ignition maps (I get a little wiser every time I visit here)

An intercooler I am pretty much sold on now. I talked to young bloke today who drag races blown old school Aussie six cylinder cars and he knows of an IC that sits flat between the blower and manifold. It is water/air with the external heat exchanger in front of the radiator, is said to be very efficient and is not that pricey. I'll put up the link when I find it.

Hey bobc, is water/alcohol injection what is known as "aftercooling"? I have heard it is very effective and not that hard to set up.

The only reference I know of for aftercooling is on Detroit Diesel Engines. In that configuration, it lies in the hollow V between the cylinder heads.It cools the air going into the engine after it passes through both the turbocharger and the blower. The aftercooler is cooled by relatively cold engine coolant.

I was referring to spraying the water-alcohol mixture on the outside of the air to air intercooler. The evaporation should drop the temperature dramatically. Size the reservoir depending on driving style.I was planning on a 55 gal drum.

Go here......

www.blowerdriveservice.com

Thank you for the link. I have been Googling every combo of supercharging I can think of and haven't come across this one. Even after a perfunctory read of this site I have decided to ask them specifically if my choice of 9psi for our high boost option is wise on a stock windsor. They seem to mention 7psi quite a bit in a generic sense.

One site I found in the States that did did put in my favourites was PSE engineering. They specialise in the remanufacture of all kinds of superchargers.

Read #7 very carefully. If you look close you can find the name of one of the most reputable companies dealing with forced induction systems.

There a book I checked out from the library its something like Design of superchargers and turbchargers.

Here is a tidbit of info for you. RON is always 7 to 10 points higher than MON So compared to the US standards you serve up 88, 91, and 94 Octane versus US 86, 89, and 91.

94 octane will get you a 12 to 1 compression ratio naturally asperated engine.

At a 8.2 to 1 compression ratio you should be able to get 22 psig boost with aftercooling. Go to 9 to 1, and 13 psig is maximum with after cooler. with no after cooler you are at the limit of 9 psig running 100MON octane.

"At a 8.2 to 1 compression ratio you should be able to get 22 psig boost with aftercooling. Go to 9 to 1, and 13 psig is maximum with after cooler. with no after cooler you are at the limit of 9 psig running 100MON octane."

This is very broad basic information. Each engine has it's good points, and bad points. Do Windsors tolerate more or less timing than Cleavland heads? Are the heads aluminum or cast iron? How free is the exhaust? Back pressure can have a detrimental effect on timing also. Blower Drive Services has more experience in blower installations than anyone I can think of. The risk of catastrophic engine failure is too much to risk to a book. Unless this book is covering a specific engine build up, and the OP's engine matches the components of the "book" motor, I would stick to those that have learned the hard lessons of over timing.

Notice I said get the book first. From experience on some cars I've seen I gave approximate "wide values".

I talked to an old racing guy that rescued a Paxton super charger from an Avainti back in the earlt 70's. He said it had a :variable speed pully system on it. We agreed it looked likr the old style variable speed system on a "shop smith" multi-tool wood shop system. He said they put it on a small block Chevy and had variable boost.

Ahhh! I've often wondered why American fuel octane numbers seemed so much lower than ours. Their obviously not. So our 100 is your 94, give or take. I know of a very nice N/A car over here that runs 12.5:1 C/R on pump 100 and it works well. If he cant get 100 he has to use a very expensive additive to a tank of very expensive 98RON to stop pinging. LPG is just around the corner for him.

Cheers again bobc, I have high hopes that advice from BDS will be setting definitive parameters regarding boost and tuning. Probably some parts too.

If I am not mistaken, the 351W do not have 4-bolt mains, an advantage that the old 4-barrel Cleveland has. Be careful of your boast regardless because you may experience premature bearing failure due to stretching of the bottom end caps. Also, one can change compression by switching heads. I believe the 4BL heads had a bigger combustion chamber than the 2BL heads. So in a quick pinch, change your heads if need be to lower your original compression ratio, giving you some pressure boost flexibility and timing retarding. MSD ignition is a must with remote variable timing which can reduce your octane requirements. Max boost will require you to use some jet fuel, but you'll have some tire smoking fun!

The cost of good quality heads has fallen through the floor. For what used factory heads cost, it would be more practical to purchase used aftermarket performance heads. World, Dart, Twisted Flow, Edelbrock, maybe even Wall Mart sell better heads than Ford sold.

The Ford design that had the big differences, was the Cleavland design. 2bbl to 4bbl was dramatic, including intake ports that demanded different manifolds. The rare Boss 302 Cleavland heads were bigger ports than almost all of the 351 4bbl heads. You could hide a tennis ball in the intake ports.

The MSD is the most sophisticated ignition system on the market today. With any power adder, it is a must.

Jet fuel is close to kerosene. It has no place in a gasoline engine, never mind a boosted gasoline engine. I must disagree with you on this point.

I am glad you brought these points up, as I had, um, pre-mature posting. After I posted I made references to 351W... Old school here. I agree on all your points, and as of my reference to "Jet Fuel", my bad again, as I referred to the 119 octane racing fuel I have used in the past as "Jet Fuel" amongst my friends. Thank you for checking me. You may have saved an engine.

I also suffered from the premature thing. Better now though. Cheers.

My lovely wife liked your post. She doesn't know what 351W or 4bbl is but she reckons I should have 'em In fact if it was up to her I would have a wooden box in my shed with "Bugatti performance accessories dept-contents: 1 engine" stencilled on it

Your wife sounds like a truly loving and concerned person. But if she really loves you, she will let you put a big piece of glass on top of the air cleaner of your spare Ford engine and use it as a coffee table.

If she will allow a matching pair to be used as end tables, I want to marry her.

Lol, Yes she would, and no you cant. It took waaay to long to find her. We were childhood sweethearts...(add 25 years)...and then we met again. She is indeed a catch and this project of mine is all the sweeter thanks to her enthusiasm.

Lynny asked the other day what an 8/71 blower was. I explained that it related to the original way of rating superchargers and that it refered to 8 cylinders of 71 cubic inches each. She understood that, thought about it, and then asked if they came any bigger

I love my wife.

Andrew

The largest GMC unit i have seen is the 8-92 units. 12, and 16 cylinder motors use 2 of the 6 or 8 cylinder blowers. I personally have never seen any of the 149 series engines. They are used in power generating, and really large marine installations.

The down side to these huffers is the parasitic drag. The design of these engines-blowers dates back to early forties. The newer designs from Eaton and Magnacharger are much more efficient. These designs have gone from 2 lobes, to three and have twisted them for better efficiency. ( I am not sure who has which features)

Well, that just made my day! Lol…sounds like you got yourself quite a catch there. Might as well put on the "must have" list the High Polished Double-Chrome Super Shifter Knob (shift pattern optional).

These are available for flush handles on toilets . Honest.

Speaking of gearboxes...

I hadn't considered the ignition system hardware needing upgrading. I will definitely be looking at that now. MSD is quite popular over here.