reatta turbo. I know this has been discussed before but..

[Guest Recian]

I know this has been a big topic of discussions before on this site but a new performance shop opened up across the street from my house and it's also a consignment shop/performance-powder coating shop. I stop in to check on his stock and learn some things from time to time. We were discussing the idea of a reatta FWD turbo. It didnt seem much like a possibility in fwd due to room. There's room to put turbos but the components they'll be against cant handle the heat. If you used the crossover pipe you wouldnt get true 6 cyl turbo and it'd just be a lag. We came up with a design from when imports first got big and it's kind of a not too popular idea but we thought a rear mount would work. There's enough room where the muffler would be to mount a turbo and necessary components. You could put a 3-6" outlet pipe looking like an OEM tail pipe so nobody looking outside could tell it's a turbo and as for the intercooler it wouldnt be necessary as the piping running from the turbo to the t-body would be under the car in the exhaust tunnel (wrapped to eliminate heating) and over the tranny to the t-body. The filter would also be in the rear with the turbo (with a bag of corse for water). It's a rather simple design and seems to require the least modification. An alternate boost controller/gauge with 2 settings for street/track would help keep low boost on streets to eliminate excessive wear and Im aware of the trans being the weak link but running 5 lbs of boost daily and high boost when you wana play wouldnt be too bad. Any ideas on what downsides i would have here?

[padgett]

Turbo on a P-47 was about 20 feet away but lag might be significant.

Edited August 15, 2011 by padgett (see edit history)

[2seater]

The factory did both low and high boost prototypes in the late '80's, since destroyed, but it can be done in the engine bay. I did my own installation , essentially scratch built piping, and it does fit under the hood, but there isn't a lot of room. The Squire's type installation of rear mount turbo has pros and cons. The obvious pro is the space available for the turbo itself but the cons are several: the lubrication system must be either self contained and recirculating, plus cooling, or a scavenge pump must return drain oil to the engine oil pan. The drain side of the turbo center section cannot have any residual pressure or the seal(s) will leak. The environment under the rear of the car does not lend itself to cool, clean inlet air to the compressor plus you must run what is essentially another complete exhaust pipe from the turbo back to the throttle body. I am sure it can be done, STS makes kits for various automotive applications, but it isn't as simple as it might seem.

[padgett]

Well you could mount in the trunk and use pressured oil for a lube though I'f add a small sump for start-up. The next issue is to keep the exhaust gas hot because as the temperature drops it contracts.

Then there is the lag issue - if you size the pipe from the turbo to the throttle body for max rpm flow, there is going to be a noticable lag as pressure builds, it won't work well on sudden transients since the exhaust pressure must build before the turbo can spool up and build pressure in the inlet.

The best answer would be to put the throttle plate and MAF on the tubo inlet so it can stay up to speed but then you have linkage problems (see "blow through" issues).

[Guest Recian]

2seater did you do a twin turbo with one on each manifold or a turbo bolted to the outlet of the rear manifold? mounting under the tunnel

[2seater]

My installation was a single turbo, an amalgam of a few turbos from the Garret T3 family. The photo with the black ceramic coated piping is my installation. The rear manifold was scratch built with a crossover around the front of the engine and connecting to the stock front manifold between #1 & #3 exhaust. (That's why my my coil pack is rotated 90deg.) The downpipe was actually a two piece afair constructed so the turbo assembly could be removed and the stock crossover pipe would drop back on so the engine could be operated in N/A form (no confidence for a first attempt)?

The other photo is one of the original factory Reatta turbo installations. I have more photos but cannot find them at the moment, but, there have been previous posts on this forum with the original magazine articles about those cars. The actually made a RWD high boost (read GN) engine as well.

My next installation will be a single turbo powered from the front manifold only. I actually have it all ready to go, ceramic coated piping is done, but have lacked the time to complete the installation. I believe this will work well for a low boost, 8-10psi, installation and will make it vastly easier to install a bit of boost without reinventing every thing else.

Edited August 16, 2011 by 2seater (see edit history)

[padgett]

Suspect you could power a turbo from the crossover and just block off the collector on the rear pipe. Flow would probably be improved and boost would overcome the small intake and ded cam.

My major concern would be the exhaust from the turbo crossing the fuel lines but they could be re-routed up and over.

Where is the throttle plate and MAF ("C" MAF is flow limited anyway)? I see a block off plate where the MAF should be and have always preferred putting the throttle plate upstream of the turbo - goes far to eliminate lag.

[2seater]

Others have done exactly that, using the stock system and crossover as the feed to the turbine. It looks like a no brainer, but getting the exhaust back out and down the rear of the engine is a challenge. It is best to re-orient the #6 exhaust to the new exhaust flow pattern but is not critical. I admit I gave up trying to figure out how to route a second pipe through the area at the rear corner of the engine and avoided the issue altogether. The O2 sensor must also be relocated to the outlet from the turbine (somewhere in the downpipe). I am told the high backpressure ahead of the turbine affects the O2 accuracy.

The throttle body is in the stock location and my first installation did not use an intercooler so the compressor blows directly at the MAF/throttle body. Lag was not a problem. It would reach full boost during the time the transaxle took to downshift. Too fast really, given the relatively weak transaxle. I tried the MAF in two locations, stock, and also in a fabricated adapter ahead of the compressor. No real difference in performance except the small MAF on the inlet had the effect of slowing the boost buildup. Easier to blow through a small opening than to suck through it. My main concern was to get a better handle on the actual air temperature entering the MAF, since there is a chart in the ECM program that uses it to modify timing and the MAF response. My latest attempt uses a vin L throttle body, adapted to the stock intake, and a modified intake air sensor located inside the throttle body so it sees actual air temperature at the throttle. There will also be an intercooler which could be added to the original installation with some additional work. I "think" the dead cam will make the single manifold feed to the turbine feasible since there is NO overlap above .020" tappet lift, even with the slightly more aggressive '88 cam. It has been done before and Saab actually had a V6 with that style of turbo from '96 - 03'.

[Guest Recian]

When you did have it working right was the power gain worth the hastle? Making new rear manifold and crossover pipe to run to the turbo then custom piping from the turbo to the exhaust pipe. There's enough room on the driver side to fit a turbo and the rest would be easy just the custom piping would be tough seeing I dont have access to those things

[2seater]

Is it worth the hassle? I guess that depends on wether you enjoy the challenge and fiddling with things, or not. The fitup of parts was done using photographs, careful measuring and a spare engine hanging on the stand. I'm no ace welder, and everything was put together with a 110v Lincoln wire feed welder (MIG). Most of the piping was made from a couple of sets of stock manifolds, cut apart and various bits of regular exhaust tubing added. All piping and turbine housing is ceramic coated, so the type of pipe used is not terribly important and some fancy header style of hookup is not needed. A plain old log style manifoild works just fine. The power increase is infectious and with a turbo, the faster it goes, the faster it wants to go. Tuning was the biggest issue, and was never really solved since the MAF sensor goes over the high limit very quickly. I looked at my old test run records and the MAF reaches maximum flow of 170 gm/sec in as little as two seconds and under 30 mph from a dead stop. A turbo is not directly linked to the engine and primarily responds to load so the tuning process will take a bit of doing. The chip changes from Ryan @ Sinister Performance did make the car very driveable and I put over 20k miles on it in turbo form. Now that the boost gauge stops @ zero, I do miss the easy surge it used to have. I am hoping the new single manifold setup will provide what I desire and will greatly simplify the addition of a turbo without a bunch of plumbing changes, plus I can address some of the issues from my first attempt. The easiest route for increased power, and the way a GS version should have been built, would be to drop in a SC engine as has been done plus most of the tuning issues are known since this was a factory option on other models.