New TGP Exhaust System

[TGPvsTIII]

lets do some basic high school math. 2.5 inch piping has an area of 4.90625 square inches. dropping to 2.25 piping at the Y is 3.9740625 square inches for each pipe or a total of 7.948125 square inches for both tail pipes. The stock tips at 1 5/8 inches equals 2.072890625 square inches each or 4.14578125 square inches total for the 2 tips. So your flowing just under 5 square inches back to the Y where it gets bigger at a total of just under 8 square inches then come the OEM tips at just over 4 square inches total. The bottle neck would be the tips.  Dropping to the 2.25 at the Y flows just fine even dropping to 2 inch at the Y would still give a total of 6.28 square inches for the Y section of the system. I would get bigger tips of at least 2 inch to stop the bottle neck at the tips.
Tim

[TGP Nick]

I will DEFINITELY post pics when I get this done.  Sounds like running a 2.25" Y will work the best.  Undecided on the tips... I am considering cutting the tips and welding a larger piece of pipe onto where they attatch to the mufflers.  What would be the best size to run for the tips?  You said I should run AT LEAST 2" on the tips, but ideally, what would be the best size?  You seem to know what you are talking about with exhaust.

[intern8tion9l]

i left my stock exhaust size on from the subframe back, which is 2". its WAAAAY too small and it restricts the hell out of the engine. can't boost past 9psi without the whole car sputtering and puffng out black smoke

[TGP Nick]

On the W-body forum, someone is suggesting that I run a 3" exhaust.... should I??  Why or why not??

[TGP Nick]

http://www.w-body.com/forum/index.php/topic,54852.0.html
This is what is going on over there... I have suggestions from running 3" exhaust to all kinds of crazy sh**.  Any suggestions for exhaust size? 

[mfewtrail]

As I posted on the other board, 2.5'' is adequate. 3'' would not hurt anything though, I'm not sure how much(if at all) it would help with a relatively stock engine & the T-25 still in place though. As far as I know, only one person has done a 3'' exhaust, and that was Jason(eclipse5302). He had a LG5/getrag 282 swapped Cutlass with custom tuning, alcohol injection(not sure if he used it though?) etc. so there's no good comparison of his car vs. a similarly modded one to compare it to(his car dyno'd 202hp and 275 ft lbs) as we don't know what tuning he had done, what type of dynomometer that was on, etc.

Again, look at what Josh's Cutlass made on the dyno with a stock TSTE exhaust(minus the cat I believe, he can answer that for us). The stock exhaust piping is what, like 2.25'' and then necks down near 2'' at rear from what I remember(I never measured it, but it seemed smaller than the other piping by a bit, it's been 3yrs+ since I've seen the stock TGP piping though...)

[twinturbosedan]

Again, look at what Josh's Cutlass made on the dyno with a stock TSTE exhaust (minus the cat I believe, he can answer that for us). The stock exhaust piping is what, like 2.25'' and then necks down near 2'' at rear from what I remember(I never measured it, but it seemed smaller than the other piping by a bit, it's been 3yrs+ since I've seen the stock TGP piping though...)

yeah, stock '91 Cutlass exhaust with the exception of the obvious TGP downpipe and a test pipe in place of the cat all the way back to below the rear seats.  that's where i welded on the exhaust from my old Turbo STE (which is the same size pipe).  not only that, but this was all going into two VERY rusty stock 160,000 mile mufflers that i'm sure flow like dogshit and i really think i lost out on a few whp there.

while i do think larger exhaust would help (sounds like you're on the right track), the bottleneck is really the turbine.  like Matt said, 3" won't hurt anything and might be a good idea if you plan on upgrading the turbo later on, but for a stock TGP i think 2.5" mandrel bent exhaust going into 2.25" mandrel bent pipe at the Y would be great.  just make sure you use straight through mufflers and mandrel bent pipe not crush bent.

[TGP Nick]

Okay yeah I'm still undecided on the exhaust size... I know with our turbos, the less backpressure the better, but would 3" have TOO LITTLE backpressure?  Possibility?  Also, do you guys think I could/should make a bigger downpipe as well? At this point, I'm leaning toward having 2.5" exhaust from the DP to the Y, with a 2.25" Y. 
I know TGPvsTIII, you were comparing the 2.25" Y versus the 2.5" Y... I'm a little confused with what you wrote.... would the 2.5" Y flow much better than a 2.25" Y? 
Thanks for all your help guys!
Nick

[TGPvsTIII]

lets do some basic high school math. 2.5 inch piping has an area of 4.90625 square inches. dropping to 2.25 piping at the Y is 3.9740625 square inches for each pipe or a total of 7.948125 square inches for both tail pipes. The stock tips at 1 5/8 inches equals 2.072890625 square inches each or 4.14578125 square inches total for the 2 tips. So your flowing just under 5 square inches back to the Y where it gets bigger at a total of just under 8 square inches then come the OEM tips at just over 4 square inches total. The bottle neck would be the tips.  Dropping to the 2.25 at the Y flows just fine even dropping to 2 inch at the Y would still give a total of 6.28 square inches for the Y section of the system. I would get bigger tips of at least 2 inch to stop the bottle neck at the tips.
Tim

Just doing the math and making the numbers easier to read the 2.5 pipe is about 5 square inches to flow. The Y section with 2.25 pipes is a total of about 8 square inches. So as the exhaust hits the Y the Y is actually bigger and should have no issues flowing. I also said if you did the Y in 2 inch pipe the 2 would flow a little more then 6 square inches 1 whole inch more then the pipe feeding it. The restriction would be using the factory tips. With them at 1 5/8 inch the 2 only flow a little over 4 square inches thats less then any other part of the system.

Personally I don't think a 3 inch system would be a bad idea if you can get it done. A 3 inch pipe is 7 square inches. My only thoughts would be is if the turbo is to small for 3 inch. I don't think the engine is too small. I would have to go look and see what the dodge guys issue was with too big of a pipe on the cars running the small mitsu turbos. Turbosedan might know. I run a 3 inch mandrel bent system with 3 inch cat and no muffler on my T3 turboed TIII 2.2.
Tim

[TGP Nick]

Ok thanks for clearing that up.

[TGP Nick]

How big is the stock downpipe? 

[TGP Nick]

How big is the stock downpipe? 

Bump?

[mfewtrail]

How big is the stock downpipe? 

Bump?

2.25'' according to an old post by Jason...

[TGP Nick]

Well I found a thread: http://www.tgpforums.com/index.php?topic=852.0  That told me that the stock DP is only 2.25"! :icon_eek:  That NEEDS to be made bigger... does anyone with experience here know if I can cut the stock DP, use teh stock flange/mounts/coupler, and as you go further down the DP, I was thinking of cutting it there, and welding a 3" pipe onto there.  Could I do this?
Also, in that thread, they talk about certain resonators giving too much backpressure, due to their design.  Does anyone know of a resonator they recommend running that doesn't have the backpressure problem?
Thanks

[mfewtrail]

 :laugh: Beat ya' to that post by a minute. ;)

As for a resonator, check with your local exhaust shops...several of them in my area carry straight through resonators(not shitty glasspacks!, they do look similar though).