rear mounted turbos on a front engined car

[masraum]

I don't remember ever seeing the thread with the whole build up being posted before.

99 GT DIY Remote TT Install - MPH Forums



There's a lot more to this than the above picture indicates. I'm not sure it's a good idea, but it's actually fairly well carried out.

It's better than that Supra turbo build up that was out on the net where they put the weird grind marks into the head. I think that build was in Spain.

[Tim Walsh]

ya, I can't say it's fail yet, he hasn't finished the project yet! Definitely interesting. Wonder how bad the lag is going to be.

[kaisen]

STS makes rear-mounted turbos and they work VERY well, esp for late-model GM V8s like Camaro, GTO, CTS-V, and full size truck/SUV

Squires Turbo Systems - Turbocharged Innovation!

[kaisen]

[beepbeep]

Err...nice workmanship but inherently flawed design. The whole point of turbocharger is to reuse heat in exhaust gases to do something useful (like pump air). With those long pipes, EGT will plummet and it will be very laggy and boost will come high up.

It would work better for a steady-state application (airplane or locomotive).

[widebody911]

[porsche4life]

Search for it on here.... Some idiot tried it on a 944.... Using PVC sprinkler pipe to plumb it all up....

[masraum]

Originally Posted by porsche4life

Search for it on here.... Some idiot tried it on a 944.... Using PVC sprinkler pipe to plumb it all up....

That should have worked really well!!

[onewhippedpuppy]

Err...nice workmanship but inherently flawed design. The whole point of turbocharger is to reuse heat in exhaust gases to do something useful (like pump air). With those long pipes, EGT will plummet and it will be very laggy and boost will come high up.



It would work better for a steady-state application (airplane or locomotive).

I've always wondered the same thing. Very cool concept, nice execution, but how well does it work?

[The Gaijin]

Turbo lag is the #1 problem for auto applications..

[javadog]

Originally Posted by onewhippedpuppy

nice execution?

Ahh, no. Pretty bad, actually. Consider the very restricive piping. The part under the side sills is especially bad. Visualize what the internal muffler piping looks like. From the picture shown on his thread, you can guess what the layout looks like and it ain't good. Consider his allowances for thermal expansion, or lack thereof.

It's a bad idea to begin with and his execution makes it much worse.

JR

[sammyg2]

The world is full of turbo experts who haven't designed or built a turbo system. Maybe the read a book?

in high school they told me I couldn't turbo my vw bug. I did, it worked.
Many years later I was told you can't turbo a 914. I did and it worked well.
I turbo'd a 911SC but that had been done before.
I supercharged a chrysler hemi, but that had been done to death.

Some folks say that if a turbo system doesn't put out at least a bar and double the hp it isn't a good system. bunk.
Yes there are many compromises on that design and many opportunities for improved efficiency. That doesn't mean it work work well, it only means it won't work as well as it could potentially work. I don't believe he's going to get the performance he expects but it should still work.

Forced induction systems offer diminishing returns. the first pound of boost provides more improvement in performance than the second, the second offers more than the third, and so on.

Maybe someone can explain to the group why torque curves tend to fall off between 4200 and 5200 rpm on most street engines, and what effect just 2 or 3 pounds of boost has on those curves?


That low of boost may not increase peak torque much at all but it will flatten and extend the curve and maintain closer to peak torque much higher into the rpm range. We all know what that means, right?

All engineering projects have compromises and trade-offs. Ask any engineer.
Sometimes you can't build what you want to build so you build what you are allowed to build.

The point is this:
if a cheap, simple, easy to do turbo system works and puts out a few pounds of boost without other trade-offs, it should be considered a success. Probably more is than a system that is extremely complex and costs $12k to install.

[javadog]

Originally Posted by sammyg2

The world is full of turbo experts who haven't designed or built a turbo system. Maybe the read a book?

You're right, I've never even seen a turbocharged car. I once found a JC Whitney catalog in a used bookstore and it had a picture of a turbo kit in it. Way cool.

Originally Posted by sammyg2

I don't believe he's going to get the performance he expects but it should still work.

Maybe. For a little while.

Originally Posted by sammyg2

Maybe someone can explain to the group why torque curves tend to fall off between 4200 and 5200 rpm on most street engines, and what effect just 2 or 3 pounds of boost has on those curves?

It generally raises the whole curve. It might change the slope, depending upon the turbo used and a couple other things. There probably will be be a slight decrease in the curve, at rpm levels below where the turbo generates any significant boost.

Originally Posted by sammyg2

That low of boost may not increase peak torque much at all but it will flatten and extend the curve and maintain closer to peak torque much higher into the rpm range.

Maybe. It depends on a bunch of things.

Originally Posted by sammyg2

All engineering projects have compromises and trade-offs. Ask any engineer. Sometimes you can't build what you want to build so you build what you are allowed to build.

I think he built this system the way he did to hide it from view. I suspect he'll do a little drag racing with it and doesn't want his competition to know that he has a turbocharged engine. Good luck with that, I say.

Frankly, I don't see why you'd have anything good to say about this, from a technical point of view, or an ethical one... Your systems shown in the photos had nothing in common with this one, for good reason.

JR

[herr_oberst]

I don't know much about turbos but what I do know is they can quiet the exhaust down to the point that no mufflers are necessary, so the first picture is kind of funny in that regard. IIRC, the STS system described above for GM cars eliminates the rear mufflers, (but the air filter change requires taillight removal.)

[porsche4life]

Originally Posted by masraum

That should have worked really well!!

http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/507675-n-tailpipe-turbo.html



For your viewing pleasure..... Be sure to get in all the pictures..... I may have provoked the poor guy..... He blew up.... He called out my car wanting to know what made it so great.... thats when the pictures got posted.... Anyways... He eventually got kicked off the board... Not sure if he ever went to that other Porsche site or not....

[beepbeep]

I'm sure it'll work (if he can keep everything leak-free etc.). It's just that it will offer poor response and very high boost treshold.

Gases coming out of engine have temps up to 950 C. This allows them to expand (PV=nRT, where T is temperature). This is good as there will be more gas to keep the turbine spinning. Typically, you will see 200 deg. temperature drop over the turbine.

But in his case, gases will propagate trough (lengthy) exhaust, cool down and contract. There won't be much gas lest to keep the wheels spinning. He might try to wrap the pipes going to turbo but I still believe he's looking at full boost arriving in 4000-4500 RPM range (if not higher). Then there are those long boxy air ducts that must be filled.

It would make pretty good hi-speed hauler or something...

[onewhippedpuppy]

If I recall correctly, aren't the under/rear mounted turbos for applications where space prohibits an under-hood install? While compromised, it may represent the only option for that application.

[javadog]

That's true of the one in Kaisen's photo. My opinion is that this guy was trying to hide them. There's no other good explanation for mounting them on top of the mufflers.

JR

[GG Allin]

E60 m5.

[herr_oberst]

All that work, but the solution is so simple . . .

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