best exhaust pipe size to run.

[Nick1234]

3.1 turbo with no mufflers or cat. What would be the best size pipe to run?

[Prospeeder]

2.5 inch is optiumal on all 2.8/3.1/3.1T, bigger because of the turbo might be a good idea

[mfewtrail]

2.5'' is adequate, but you can go with 3'' if you want. A guy here used to have a full 3'' exhaust on his car. Using three inch piping *might* make your car a tad slower when not in boost(normal driving basically) though.

[RareGMFan]

I'm looking at exhaust work soon, too. Will be Mandrel bent. I was contemplating custom 3" including the downpipe all the way back. I'll have to have a cat and mufflers in IL, though, on account of emissions. Is that really too big for the TGPs?

[Guest TurboSedan]

sometimes going with too big of an exhaust will cause boost creep. but only if the wastegate puck is too small to handle the boost level. what happens (if the wastegate puck is too small..and i don't know if it is on a stock TGP turbo) is the wastegate cannot flow enough exhaust gas to regulate boost pressure at a desired level - the exhaust gas instead flows through the turbine (and your now free'er flowing exhaust system) causing boost to creep up, even to the point of hitting fuel cut.

 

i don't see any reason at all to go larger than 2.5". the turbine itself should be addressed before going 3". i think you'd need a substantially larger turbo to justify a 3" exhaust. which isn't saying much, considering the stock turbocharger is so small. i think 2.5" mandrel bent exhaust would be fine (GREAT!) on the TGP. and maybe 3" would too...i really don't know. i just think that not only would 3" be harder to fit into the car, but also more expensive, and it is probably overkill considering the size of the stock turbine.

[mfewtrail]

For what it's worth, Jason(eclipse5302) was the one with the 3'' mandrel bent exhaust on his TGP engine swapped Cutlass. I remember him saying it did make a noticeable difference in performance, he also had a getrag 282 in his car.

 

Here's a quote from him.

 

"TG160 chip

K&N filters

Magnecor plug wires

NGK V-grove plugs

3 inch exhaust

other stuff I can't think of now... "

 

^From other posts, I gathered that he made 202whp and 275 ft-lbs to the wheels with the above modifications on a motor with 180,000 miles on it.

 

EDIT: Oops, his run WAS made with the Getrag in the car....I guess he self-modified the Topgun chip since he mentioned modding the chip in some other posts.

[RareGMFan]

Well, I'm thinking ahead is why I'm considering 3". I'd definitely like to go bigger turbo eventualy (whenever Jeff M has his bigger turbo/injectors package ready). In the meantime, I'd like a new exhaust system, and want to do it right the first time. I think I may have found a place to do it dirt cheap. The guy telling me about it said he's getting a 3.5" (don't ask) custom Mandrel Bent exhaust, with stainless steel mufflers (no cat) for $400. :shock:

[kuntzie]

I was contemplating custom 3" including the downpipe all the way back.

 

iasked abot this a while back and the downpipe cant get any bigger, there is not enough room in there

[Garrett Powered]

Mandrel bends don't have that wrinky stuff in the bends like the stock exhaust right?

[Garrett Powered]

I gotta have it 8). Can the turbo be welded so you don't have that wastegate leak problem or boost creep? I mean like a bead or small plate, I have heard of this on Subaru turbos.

[dbtk2]

I think I'd worry about a bigger turbo before opening up the exhaust more. Actually, I'd throw magnaflows on it (cause it is really raspy with light throttle with no mufflers as you know) and leave the exhaust how it is and put on a bigger turbo. I don't think there is much performance to be gained in a 14.4 second w-body car with a T25...you just can't go much quicker without swapping turbos. Also, the injectors in that car are maxed out with its current setup, the pulse width is 27, so without getting bigger injectors you're not gonna go much faster unless you can get traction or reduce load on the engine (which is why I did the UD pulley). Although if you got some injectors that problem would be solved.

 

Shawn

[Nick1234]

yea someone told me the turbo will spool up quicker if the exhaust pipe is a larger diameter. I just want to get it running good. Im not going to get a bigger turbo cause i don't think the tranny will handle that too well. Shawn did you get your tranny beefed up and are you still running with a t25? I also want to get all my gauges working right. The speedometer is off 10% and the tach pegs itself all the time. Do you think i need a new cluster or is it something else. Plus isd it hard to fined a cluster for a euro that has the oil pressure reading on it?

[dbtk2]

yea someone told me the turbo will spool up quicker if the exhaust pipe is a larger diameter. I just want to get it running good. Im not going to get a bigger turbo cause i don't think the tranny will handle that too well. Shawn did you get your tranny beefed up and are you still running with a t25? I also want to get all my gauges working right. The speedometer is off 10% and the tach pegs itself all the time. Do you think i need a new cluster or is it something else. Plus isd it hard to fined a cluster for a euro that has the oil pressure reading on it?

 

That is a stock '90 Euro cluster, its never been changed so all you have to do is find a '90 Euro cluster and it should work. The only thing I'm not sure about is if the speedo would be off with a new cluster because IIRC skalor told me that he adjusted the speedo with the chip to make it closer, but I could be wrong there.

 

The turbo will spool a little quicker with larger exhaust, however, don't you think it spools quick enough already!?!? You can't even come close to finding traction from a dead stop or really any speed under ~10mph, so I don't think getting the turbo to spool quicker is an issue, it spools almost instantly already. If you get a manual boost controller for it, then it basically does spool instantly. I had one on it for about 2 weeks but cringed in fear everytime I went WOT under 25mph for the trans, the damn thing would just smoke the tires off. I'd turn onto a street, get straightened out and go WOT and the tires would take forever to catch traction. You can get manual boost controllers pretty cheap ($30 or less, talk to "TurboSedan" he can tell you what to get), but I don't know if I'd put one on.

 

I am still running the T25 and a stock tranny in my STE, but keep in mind I've gone through two trannies with it already. The T25 is way past being at its limits in that car. Its fully spooled at WELL under 2k rpms, and it doesn't hold full boost all the way to the shifts. (and when I say full boost we're talking 8psi not 11-12 like I ran before the topend) I also have stock injectors in it which are maxed out. (which is one of the reasons I only run 8psi) Basically my setup is about as far as I can go without changing a LOT of stuff. If I changed the turbo, intercooler, injectors, got a tranny that could hold the power, and put in 1.6 rockers my STE could run 12's easily on slicks, I'd bet some good money on that, but right now its about a whole second slower than that because so much stuff is at its limits. And the Lumina isn't much slower than my STE. With the same cam I put in the STE in the Lumina, assuming you can find some traction and pull a 2.0 or 2.1 60', it could be in the 13's no problem. With it setup exactly as it was when you picked it up, with good conditions and a sticky track I have no doubt it could go 14.2's.

 

Shawn

[Nick1234]

Yea i do like the way it runs now. I guess basically im just trying to understand more of how it runs and how it all works together. I just want all the gauges to work. Thanks for the info shawn.

 

Nick