Remote mount turbocharger

[adjuster]

I've seen a few Squires Turbo setups, and they are well made, and work fine.

I've thought about doing this very same thing to my last 3 Audi's, as I've owned a Turbo Supra since 1995, and would like the same type of "boost" on my daily driver sedan. (Nearly bought an RS6 for this reason.)

I'd be interested to find out how well the 4.2 with the higher static CR works out on a force fed diet. (I built a 9:1 static CR 3.24L stroked 7MGTE that was awesome on the street, as it had great power off idle, while still handling 18psi on pump fuel, but I coated everything that could be coated, and had forged internals to handle the stress.)

Even just a 5psi setup that replaces the rear muffler, would be worth the extra tourqe in the mid range, and of course, it should fill in the power too on top at high rpm.

My thought on intercooling is to use extruded aluminum formed with heat sinks on one side, similar to what they use on snowmachines. (They are 1"x4" wide, with 1/2" fins on "top" of the boxed section. Use two of these side by side to bring the boost back up under the floor, and merge them into a single 3" inlet to then blow through the stock hot wire sensor prior to the throttle body.) Should be light, and effective, but you'd have to merge the two at the turbo as well. (No big deal if you can weld aluminum to merge the boxed sections into one, and then into a single 2.5" inlet side that you can hook up to the turbo compressor housing outlet.)

The oil less Comp Turbo would be awesome too, as running cooling lines back to the turbo would be easy compared to oil and a scavange pump return system. (Heck, you might be able to just mount a seperate rear pump for coolent, an expansion tank and stacked plate cooler tucked up at the rear bumper in air flow there would be enough to cool the CHRA, especially as it's on it's own, so no engine heat added to the coolent, and the turbo would be back away from the engine, so quite a bit of heat is lost in the exhaust system distance anyway too.)

Just thinking outloud, give us an update if you have any news.

Thanks.

[71camaro]

Quick update, this isn't dead, but I may be going smaller turbos at the manifold (think GT2560r) and a head spacer setup.

[71camaro]

Still playing with options, might go large frame turbo around where the stock airbox was, thinking about plumbing issues is all.

[RallyQuattro]

There is no room for a 3" downpipe to get down on the side of the engine if you mount a turbo on the airbox place.

Best is 1-2 turbos behind the engine like RS6 (I have an RS6 engine in my S8-97)

A friend to me have a rear mounted turbo on his Audi A8-95 but with the high comp ratio in the stock A8 engine he can only have about 0.4bar/6psi of boost with gasoline.

[adjuster]

I would think that 6psi of boost on the S8 engine would add plenty of power to an already powerful engine.

Any ideas on the tourqe your friend with the single rear turbo has on his 97?

That's where I've seen the most gains that are effective on the street, take a nice engine, and pressure feed it, and you get serious tourqe at lower engine speeds, and it really wakes up the motor/car.

Sure, top end power is fun, but peak HP is not the problem on this car. (And the reason the RS6 is so much fun, is the tourqe peak at 1800rpm of over 400lbs.... with AWD, it just hooks up and goes.)

I have kicked around this idea for years as I've gone through 3 A8's now. (And have an S8 currently.)

My take is you want to plan on no more than 7psi. Get a LARGE waste gate, 50mm would be good, with a light spring so you can't over boost the engine, and break stuff. (If you are limited to 6psi, have the spring set to open at 5psi, and then add a simple bleeder valve, to fine tune the last PSI of pressure.)

With 4.2L of displacement, and a good stock exhaust design on the S8 already, remove the CAT blocks, weld in pipes there to keep the flow smooth, and where the rear muffler is located, you put your turbo, waste gate, and intake filter.

Since it's at the rear of the car, you don't have as much heat, but you will be dealing with pressure still, and some heat, so it will work, but not be as responsive as having a turbo closer to the exhaust ports, where much of the heat will be captured as energy to spool the turbo faster.

Keeping that in mind, one of the new sell contained turbo designs, where you don't have a source of pressureized oil, and the drain, scavange pump, return line, supply line etc. (But just have the turbo, and a life time fill of synthetic oil in the CHRA does the job.) You can also locate the turbo any way you want too, so placement options are improved.

Now, add the 50mm waste gate, light spring, and bleeder valve.
Most of your exhaust gas at high RPM is going to be dumped prior to the turbo, but while you are just using the vehicle in a moderate way, it will not be open, and all exhaust gas will go out via the turbo, so noise is moderate automatically, being quiet when you are not pushing, and louder when you are boosting, and the waste gate dumps excess exhaust gas. (I had this setup on my last Supra, and loved it, quiet around town, and a nice roar when it was boosting and the gate opened up!)

I like a bypass valve, not a blow off valve, so that part is quiet too, and it keeps pressure up by not wasting the energy you create to the atmosphere, but diverts it back to the turbo intake, and helps to spool the turbo between shifts, or when you lift off for a moment. This can help defeat lag, especially if you have to backpedal due to loss of traction, or sliding in a corner.

The diverter valve can be near the turbo at the back, and you just plumb it into the intake. (My last Supra build used two Bosch Porsche spec ones, and it had the added benefit of "leaking" air past them off boost, to enhance throttle response, since air can bypass the turbo before boost is built up, but then they seal up under pressure, and only bypass when you lift off and manifold pressure drops to a negative number again.)

My idea to use flat, extruded alloy boxed sections with cooling fins will work great with the ASF. You can run two boxed, low profile sections forward from the turbo to the engine, and it will cool any intake charge on the way. No need for an intercooler up front.

I figure the stock exhaust canister can be cut off at the end, and the waste gate plumbed to one tip, while the turbo exhaust uses the other. This hides the turbo, and keeps it looking sanitary. If done right, it might also protect the turbo from road debris/water/snow/ice etc.

The air intake can be a simple cone filter with a "pre-filter" sock on it to limit water intake. (And heat/splash shields added as needed depending on where it ends up. It could be located, and plumbed to the turbo from the other side of the rear subframe/suspension actually if the space is needed. The divertor valve(s) could be located there too.

All the normal stuff would work fine, and the system would be blow through, so the computer should work, but I'm not sure the fuel pressure regulator is up to the job, but it appears to be a 1:1 setup, with it increasing pressure as the intake pressure increases based on vac line signal. If not, an aftermarket one from Areomotive would not be too difficult to replace it with, as well as a pressure gauge to help with fine tune, and to be sure that fuel pressure is enough to feed the beast.

Any photos of the rear turbo install on the net? I've looked, but never found them.

Thanks in advance for any photos, details or anything your buddy with the turbo on his A8 wants to share. (As in how did he add more fuel?)

[adjuster]

One of these for example.

http://aerocharger.com/66series.php

No oil supply or return needed.
No waste gate needed.

Very fast spool, and since the bearings are "forward" of the compressor wheel, v/s being in the middle/CHRA like most turbo's, this design runs cooler, and uses thinner oil, so along with the variable vanes, the thin oil allows for very fast spool up.

Full boost of say 6lbs at 1800rpm would be a nice addition to the S8 in every day use, and while it's not going to make monster power, it will make amazing tourqe, and plenty of top end power for this street car.

With the lack of a waste gate, just replace the stock muffler with this, the other pipes to get the boosted air to the engine, and it's done in theory. (Now just need to figure out the additional fuel...)

And come up with about 4k to make it happen.

[71camaro]

Comp turbo is also building with self-contained centers. I'd drop compression to 10:1, run 10-12 PSI, call it a day. 550+ hp and early spool, particularly if using a twin-scroll turbo or a spool valve of some sort.

[RallyQuattro]

My friends car:
He has an air scoop on the bottom that pushes air up through the intercooler, but because it is so warm air under the car (from the engine, cat and exhaust systems)
the intake temperature is above 70°C=158°F, so he has now also mounted an intercooler in the front.

But one problem is to fit pressure pipe past the rear axle under the car, he found no place so he pulled the tube on the inside of the car coupe!
But since he still took out all the interior and only use the car on track days, it does not matter that there is a thick pipe inside the car ..

He has bigger injectors and use Megasquirt standalone ecu = don't need the LM.

[adjuster]

Figured the stock ECU would not work with a pressurized system.

What does the 2003 RS6 have for an ECU? (Same basic engine, so I'd think if we can put that into the S8, it work with less time invested to completely write a new fuel/spark map for this engine.)

That is one way to get a turbo back there.. I'd rather not lose my spare tire/trunk however.

If you buddy put a large puller type fan on that intercooler, it would have worked better, pulling air and dumping it into the trunk, with that large hole cut in it for the turbo would be fine. (However, at speed, I'm not sure what would be the case, if it's low, or high pressure, and that might make cooling interesting if the air flow is cut down by the flow of air over/under/around the body of the car.)

I know the stock car is setup to have areas of LOW pressure just behind the rear wheels, and that's why Audi, and many others have vents there, to pull air out of the car's interior at that point.

Of course, with the large hole cut in the rear trunk pan/floor, that's all out the window pressure wise.

The Comp turbo's are an option, but the design of the one I linked is better I think, and with the VATN v/s Waste Gate, there is better flow, and less lag, so perfect for this setup, since you want massive flow, as you only need 5 to 6 psi on the stock CR. (And if I have to pull the heads to put a thicker gasket to lower static CR, then it's defeating my idea of not making this a seriously complex upgrade to the S8. )

Also, the simple nature of this turbo I linked allows for the plumbing to be less complex, no Waste Gate needed etc. Bring the dual exhaust together into one T3 flange, mount the turbo, and you have one outlet, that you can then split into the stock dual tip setup. Simple and easy. Given some time, I might even be able to fit it all into what's left of the stock muffler, turning it's case into a heat shield of sorts, and a "panel" to hide the turbo from interested eyes... I like a stock looking car, and this mod might keep it somewhat stock looking, but the turbo sound will be there no doubt, but not too loud.

Another option would be two smaller turbo's, but at 2500.00 each, you are 5k in just those two before you figure out the fuel system.

My thought is one of the larger units, run it at 5psi, add a piggy back fuel computer that only adds fuel under boost, and have them just prior to the throttle body, say 4 large, 780cc units, seperate fuel pressure regulator. Adding the fuel there would further cool intake charge temps, and even as complex as the S8 intake manifold is, fuel moving under pressure at that intake speed while the engine is boosting, should stay in suspension pretty well, and as noted, cool the air very well at the same time.

I think there are piggy back fuel systems that use a wideband for fuel trim feedback, and give you a goal to set, and maintain. (Say 12.5 at 5psi, and 14.5 at 1psi with the system keeping it rich enough to avoid melting down pistons in the area between 1psi and 5psi.)

Anyone have any experience with how much air pressure the stock S8 can "read."

I know it's got to handle sea level pressure, and normal variations in barometric pressure, so those of us that live at higher altitudes, can in theory, run some boost, and not exeed what the stock fuel system is designed for anyway.

Another option is going stand alone, like the Megasquirt.... but with a throttle by wire, that's not my first choice. (Also the fuel computer and other stuff is tied into this.. like your cruise control? It's part of the ECU I'd guess.)

I wonder what the guys selling superchargers for this 4.2 are doing? (They clearly have fuel figured out to 6psi.)

[awolfinsheepsclothes]

Hi
Thanks rallyquattro for the picture of your friends rear mounted turbo system. any more??. I've been interested in these for a while, I like the simplicity in a cramped engine bay, there should be no need for aftermarket Ecu's though as almost all standard Ecu's can be remapped and adapted to see boost pressure.
Maybe bigger injectors & different fuel regulator and Map sensor. You just need the right engine management specialist. Has the car been on the dyno yet? It would be nice to get a bit more power out of the S8 as many modern performance cars are now over 500bhp!
Cheers Dave