Rear-Mounted Turbocharger

After the link - what to say?

Back to the technical issues - might work. I was always under the impression that turbos worked more on the thermal side than on the pressure side, so if true you might want to trap that heat on the run back to the turbo.

In addition the run back from the turbo to the intake may contribute to problems with surge, so consider a blow-off valve, but with one eye toward your fuel setup.

More at wiki

It would be unusual.

Is this the same engine the C-4 is being fed to?

Actually, on this engine I was going to use another explosive - gasoline. I'm confused about the first post; certainly the turbocharger is powered by pressure and not heat. The purpose of mounting it in the back is to reduce heat; turbos mounted on the exhaust manifold blow cherry red at night, which is brutal on the turbo bearings and also heat up the engine compartment a lot. I'm guessing that the turbo will be at least 300 degrees cooler in back. Furthermore, I'm going to run the turbo intake into the trunk where the jack sits with a K&N filter; much cooler air. You could even throw a couple of bags of ice in there if you wanted to get a real cold air setup. Cold air is much denser and it does provide a significant free boost in power and mpg. This would be a much better cold intake system than one mounted in a hot engine compartment. Another thing with this setup is that I'm also going to run a set of headers, which isn't possible with the traditional turbo setup.

I agree with everything you say, many good ideas - except one.

certainly the turbocharger is powered by pressure and not heat.

Follow the link I gave you and rethink - I'll grant it is counter-intuitive.

And the cherry red and the heat is well within the design profile of a turbo. Mine glows red all the way across the desert for hours and hours - they are quite robust.

Ya mean water isn't taken from the upper area of the dam so heat can increase power generation?

Na, they actually take it from the top (at least when its released into the stream below), because the water from the bottom is so cold that it kills organisms etc in the downstream environment & the river has environmental imbalances (I only just learnt that from a workmate who is involved with the local native fishing club!).

Hi Route89,

I think you answered your own question when you said colder air is much denser. As the exhaust cools it also contracts resulting in pressure reduction so there will be less pressure to operate a remote mounted turbo. In a closed system temperature and pressure are not independent.

Remote-mounted turbos have been successfully implemented and marketed. They have several advantages, many of which you have identified, and a few disadvantages (mostly a second pipe from the turbo back to the engine compartment). Check these guys out. I say go for it! Have fun.

Just to make it easier, I have taken the liberty to copy and paste the key points of the Wiki article referenced:

Turbochargers are sometimes mounted well away from the engine, in the tailpipe of the exhaust system. Such remote turbochargers require a smaller aspect ratio due to the slower, lower-volume, denser exhaust gas passing through them. For low-boost applications, an intercooler is not required; often the air charge will cool to near-ambient temperature in route to the engine. A remote turbo can run 300 to 600 degrees cooler than a close-coupled turbocharger, so oil cooking in the bearings is of much less concern. Remote turbo systems can incorporate multiple turbochargers in series or parallel

A turbocharger is a small radial fan pump driven by the energy of the exhaust gases of an engine. A turbocharger consists of a turbine and a compressor on a shared shaft. The turbine section of a turbocharger is a heat engine in itself. It converts the heat energy from the exhaust to power, which then drives the compressor, compressing ambient air and delivering it to the air intake manifold of the engine at higher pressure, resulting in a greater mass of air entering each cylinder. In some instances, compressed air is routed through an intercooler before introduction to the intake manifold. Because a turbocharger is a heat engine, and is converting otherwise wasted exhaust heat to power, it compresses the inlet air to the engine more efficiently than a supercharger.

Looks to me like a heat operated engine/compressor, which can work just fine in a remote mount situation.

I'd like to reiterate that the pressure and temperature of the exhaust gases both contribute to the total energy present in the exhaust and that may be used by the turbocharger to compress the inlet air. So, there's no magic: as you mentioned, there are a lot of advantages in installing the turbo remotelly, but keep in mind that this distance will provoque a pressure loss in the piping both in the exhaust and the inlet, and the exhaust temperature loss will contribute to less energy available to the turbo. Actually, the ideal would be that the turbine side was installed directly in the exhaust, while the compressor remotely mounted. Hum, just gave me an idea... how about an electric generator and an electric fan? Or a custom turbocompressor unit with lenghened shaft? Oh ok, ... It will surelly work, but the turbo will spend more energy to compress the same amount of air than a coupled to the engine one would. Maybe the advantages compensate the losses. Only a measurement between two identical systems would tell. Very interesting, I think it's a good idea to try, if you're concerned about longevity. Please, keep us informed about your progress. I'd try if I had such hardware in my garage...

What you describe is an electrically driven supercharger, with an exhaust gas driven turbine auxiliary alternator.

I understand your point about exhaust temp and the resultant loss in compressive pressure when the turbo is remotely located, but I'm not really that concerned with maximum horsepower. In fact, I'm thinking of putting a bypass pipe ahead of the turbo so I can route the exhaust straight through the muffler if I don't want to run the turbo all the time. Thanks for all the input, I'll let everyone know about my progress. Just another goofy thought - what if someone made a turbocharger that was small enough to mount it to a single exhaust port? Would there be any advantage to having six small turbochargers, one per cylinder, instead of one big one?

What about using a remote adjustable wastegate that you could dial in the boost pressure.

With six individual turbo's, with a four stroke motor, the exhaust valves is open when the inlet valve is closed, so the benefit of the 'puff' of the exhaust gas is reduced i would think. Otherwise to make this somewhat viable I would think you would need the exhaust of one cylinder to pressurise a different cylinder, the exhaust and inlet manifold could be a real piece of art. The sound could be interesting though.

Routing the exhaust to bypass the turbo is more work than necessary. It is a lot easier to utilize a simplified means of, if you wish, to manually control the already existing internal waste gate of that Garrett. Which could also be done from the inside of the car in order to turn up or down your boost pressure. Or they make one for the pressure side off the compressor which is the high pitched sound they make that all the young-uns find cool.

You loose a lot of available boost pressure with the loss of heat. The efficiency design of the turbo is to utilize waste heat from expansion of the exhausting gasses.

More importantly you will have to use an oil pump from the return side of the CHRA (center housing and rotating assembly) to get oil back to the oil pan to recirculate as in a higher positioned turbo that has a natural drain back into the pan. Often referred to as a sump.

Rear mounted turbos require a much smaller turbine size referred to as an A/R ratio (area/radius) in order to get enough expanded heat and pressure to spin the compressor fast enough to get even 3 to 5 pounds out of it. However I've seen some reporting 10psig (at the gauge as apposed to psia) Also the V-trim will need to be larger on the turbine side and the compressor side to get more air pressure out to do a decent amount of work. However if you have a high mileage car often the pressure can aggravate already existing blow by.

Also it is better for you to have a low pressure system as you will have to make little or no change to your ignition, injectors and timing system. Often the requirements of a low pressure output system can be compensated by your current ECU capabilities and settings. You will find in turbo applications utilizing more than 6 pounds require timing retardation and fuel enrichment. The ECU may also need a re-mapping. Again there is more to the over all operating system than placing a compressor on the induction side of an ICE regardless of it's motivation.

There are many, many places on line you can find great information about what you are trying to accomplish. Understanding exactly how turbos work and the options available will help you make more efficient use of your time and energy to get the maximum results for your efforts. There are some fun things you can do with what you are trying to accomplish with a little study.

http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech102.html This is a great place to start for a quick read. Also you can find out by the serial number on your turbo what exactly you have in terms of it's operating efficiencies and see what the exact specs are related.

Good luck, learn what you can and have some fun!

In reference to the oil getting to hot or cooking, the term "they" utilize is "coking".

A patented remote turbo charger system

GA from me as you said it all perfectly......

But he appears to have the money to try it out, should be fun to see if the Turbo lag etc is acceptable or not!!!

He can always put it in the right place later.....

I don't know if this will help you at all, but Practical Performance Car magazine over in the UK recently had a rear turbo setup article. I think they had one fitted to a small Peugeot. Might be worth having a search for it.

From what I remember, it was quite successful, but they did comment on the lag being rather noticeable.

I agree that a turbo is just a boost in pressure forcing air into the engine and has nothing to do with heat.

There is an inherent delay in accelerator pressure and actual boost on a normal manifold mounted turbo. I believe you will increase this delay substantially by moving the turbo to the rear of the car. The turbo will need to build up pressure in the entire pipe heading back to the engine before you realize any boost.

I agree with you jab. It's all related.

GA from me, you got my money 100%, well done and welcome.

jab2 makes and interesting point and possibly a method to eliminate turbo drag if moderated by using a compressed gas or air which may provide further cooling and stabilize boost.

UGGh! as Charlie Brown often said. I've been implementing turbo technology and that related for over 20 years now on all sorts of racing vehicles and non racing.

First off, if you have clicked on the link to Leno's garage from Bwire and watched the video with the rear mounted turbos on the Vetts, you'll see they operated just fine. There are some over all efficiency losses obviously. However from an operational standpoint it's back to utilizing the right Turbine/Compressor combinations with the right A/R ratios to fine tune to the application.

Those big V-8's with a little enrichment, and the proper turbo combinations obviously have little lag. We've mated different turbo housing selections from different manufactures ie: Holsets with Schwitzer etc., to get combinations that were not available due to the specifics of our engine requirement. Machining a new backing plate and even machining our own seals were often required.

And yes, understand thermodynamics related pressures of expanding exhaust gasses, volume, travel velocities, cooling of the gasses, etc. Understanding the sciences related that make use of the turbos for a specific use.

I remind the readers that ideally, closer to the exhausting gasses is always the most efficient use of the those gasses and combustion heat and surrounding waste heat. Before they cool including using thermo coated headers or to wrap them.

There is so much information on the Web not to mention some great books, if people would actually READ the damn things. Ie: Turbochargers by Hugh Maclnnes by HP Books is one of my dog eared reference books I still use today when I get a brain fart. Street Turbocharging by Mark Warner, P.E. is another good one more related to the electronics by todays standards, another HP Book. Also of course "Maximum Boost" by Corky Bell. Another GREAT book for all interested in related subject matter is "The Romance of Engines" by Takashi Suzuki, Ph.D. Which gets into all the adiabatic discussions and thermodynamic principles related and of course turbo charging related.

So read damn it!

touche

One other point I would make is that if you are concerned about cooking your oil due to high temps, I might suggest you really should be using synthetic oils anyway. Their maximum operating temps are much higher than conventional mineral oils. They also are much better at keeping the combustion products in solution than mineral oils because mineral oils have all the modifiers and additives that they have to keep in solution too, witch leaves less solubility capacity for combustion products. Synthetics, being more or less homogeneous don't have to be modified with a lot of different additives like mineral oils, so they have a higher solubility capacity.

Large pipeline compressor engines don't have their oil changed every 30 days, their change interval is much longer. The maintenence crews just change the filters and top off the oil sump most of the time, and they use synthetics almost universally.

If you are running a turbo and not running synthetics, you are shooting yourself in the foot if you ask me.

Here is a great vid of the "2 Guys Garage" installing an STS Turbo to a Camaro.

www.youtube.com/watch?v=hAS5yUcg7iw

From what I gather this would be totally possible.

Try this link

A rear mounted turbo system is very possible and is actually being done by a company called STS here is the link. I have put 3 of the systems on Corvettes and they have performed flawlessly with very little turbo lag and the power developed is absolutely amazing. Hope this helps and good luck.