Okay so I am now looking to swap out my rear portion of my exhaust system. I currenlty have Borlas connected to the exhaust on the car. We have already removed all the cats and I have a turbo setup on the 400.

I prefer low rumble and louder rather than quiter, In fact I really like the borlas and probably wouldnt be looking to change them out but they are a 2" pipe and the rest of the exhaust is 2.5 inches, so I want to remove the restriction in hopes of better performance


I am almost done

 

Hey Morris. You've been doing some serious work. Can't wait to here more when your done.

I'm paying close attention to exhaust mods related to removing all restrictive catalytic converters plus adding headers jbrady is working on. Whats your take on removing the cats...any available pipes off-the-shelf to do this?

 

As far as I know there are no aftermarket test pipes for the GS400.

I had a complete custom exhaust installed for the turbo setup, so we just ran 2.5 inch pipes the whole way. The only thing that I did keep was the borlas and now it looks like I may remove that in favor of a 2.5 cat back

 

A better question might be if I am alrady at my HP goals, is there any reason to replace the mufflers with a larger diameter catback system, so that all the exhaust piping is the same size?

 

Can anyone help me with this question?

 

Well, i'm sure if all the piping was the same size as the downpipe off the turbos it would help flow rather then fluctuating between small and larger pieces. If you're at your goal though, i guess the only benefit would be helping make boost quicker as the flow would be smoother.

someone with more expeirence with turbos should asnwer though, i have limited knowledge

 

Morris Cat Backs are mass produced systems. If I was you with what you have I would have some build me a Mandel Bent custom system from front to back. Big Diffrence with turbo Car. I know a guy in GA that just Built my system totally for cheaper than a CAT back. If you want the info PM me.

 

morris, I'll double check my facts, but dual 2.5 inch cat back should be good for 500 hp IIRC and dual 2 inch ~400hp


Also, GRAND MUFFLER in marietta does AWESOME work. They have a mandrel bending machine.

If you choose to go that route, let me know. I have some info that you need to know

edit... Also in a turbo system you want ZERO back pressure. It helps the turbo spool faster, so I'd go with the 2.5

Most people with single exhuasts use 3-4 inch. So dual 2.5's should work

 

Morris,

A good "guide" is an exhuast 10% larger than the turbine housing.

And 2 2inch pipes can handle approx. 600 BHP. 2 2.5 inch exhaust pipes are good for approx. 800 BHP. ( Using corkey bell as a resource )

I'd go with the 2 2.5 inch system and look at either test pipes or hi-flow cats. BUT, stay away from R/T ( random Tech) cats. They come apart on the inside

 

With turbo's negative back pressure is the enemy. If it's all 2.5 you will see benifits in spool time.

With my turbo sr 240, i ran without a down pipe and exhaust, just a dump pipe off the turbo once......insta' spool yo!!!!

 

Heck I've been so busy with work this past week that I forgot about this thread

After reading the numerous posts on the subject of catbacks, and now the technicall information so nicely provided, I have decided to go with the Greddy EVO2. I found a price of 729 on the NEt so I will go ahead and order it. I am sort of holding off till my car gets closer to completion (engine build that is). It seems that the pistons are a problem and the date has been pushed back quite a bit. I already have several thousand dollars tied up in the engine rebuild deposit and I dont want to tie up any more cash needlessly till I know I will get to drive it relatively soon.

Dr G has made a few posts about how happy he is whith the Greddy and his opinion carries a lot of weight with me.

Thanks guys..

 

PS

The Cats are long gone.

 

Well its done I ordered the Greddy Evo2 for the car 786 shipped to my shop in GA. Now all I need is 600.00 more for some headers

 

BORLA by FAR the best


especially if you dont want a total ROAR from the exhaust but want a really *****en mellow but meaty tone...



after tying Hiper/Blitz/Tanabe/Megan etc... the Borla is by far the best on my car.

 

Morris - I would sure be interested in buying the Borla's if you don't have plans for them. I just bought a '99 GS 400 that is being painted at this moment and have had a hard time deciding on which exhaust I want.