3.5 and 4'' exhaust for gsx and gst

[4cyls_of_fury]

hey guys i work for a fabricating company and we have a couple mandrel pipe benders. i was thinking about making a 3.5" or 4'' exhaust (which ever will fit) but i need to know how many people would be interested before i make the first one. then ill be able to give a price and pictures. plus im also thinking about making a side exit with oval tubing for gst's. so let me know what you would like to see on exhaust the system like v-band clamps and so on.

 

[cardot33]

honestly I think a 3" is HUGE on a 4 cylinder. maybe making a slight upgrade from stock. like a 1/2" bigger than stock or something like that.

 

[skatershawn]

id say 4"..... Too big!!
The only time i see 4" turbo backs is on Big ol' diesels, twin turbo supras with straight sixes, and twin turbo skylines with straight sixes!!!

It wouldnt it cause back firing??
And Cause some backpressure drop power!!

 

[4cyls_of_fury]

id say 4"..... Too big!!
The only time i see 4" turbo backs is on Big ol' diesels, twin turbo supras with straight sixes, and twin turbo skylines with straight sixes!!!

It wouldnt it cause back firing??
And Cause some backpressure drop power!!

you dont want any backpressure in you exhaust system. its velocity that you dont want to lose. but after the turbo it doesnt matter

 

[turbo addict]

many of the supra guys are now running 5" turbo back and picking up power. I am in the process of doing a build on my 2g awd. I am looking at either 4" or bigger, maybe oval at the axle. I will have to see though. I already have a 4" downpipe and titanium muffler but it is a mid car dump and would like to carry it out to the back of the car.

 

[tim4g63fast]

I would buy some bent and straight pipe from you but I need a custom side exit for my 90 tsi awd. 3.5" is what i am looking for aft of the 90 degree down pipe

 

[ForceFedRed]

It will cost you about 2" of ground clearance. What kind of pipe are you wanting? SS or mild steel there's a HUGE difference in price.
A 4" .120 wall weighs 4.9lbs a running foot.

Actually, I have more ground clearance with my homemade 4" than my old Apex'i Dunk 3".

 

[tim4g63fast]

id say 4"..... Too big!!
The only time i see 4" turbo backs is on Big ol' diesels, twin turbo supras with straight sixes, and twin turbo skylines with straight sixes!!!

It wouldnt it cause back firing??
And Cause some backpressure drop power!!

you guys might want to do some more research, I was reading this exhaust write up by one of garretts engineers basically 4" is actually preferable to 3" with a pretty small turbo actually the key is stepping it up from the size coming out of your exhaust housing to that size gradually but also quick enough to exit the exhaust correctly.

people keep saying 3.5 and 4" are too big yet you look at evos and I see a lot of evo guys running 3.5 without problems.

 

[Jets303]

Shhhhi I think a 4'' exhaust would be too sick. Might help with lag time on my Holset. +1 for a group buy.

 

[4cyls_of_fury]

Shhhhi I think a 4'' exhaust would be too sick. Might help with lag time on my Holset. +1 for a group buy.

let me know who is intrested and ill make one and take pics and post up a price
ill offer it stainless and mild steel .

 

[skatershawn]

im not saying 3.5" and 4" is too big for everything!
but something that has a ton of power that actually needs it!

ok lets see if your engine is only hitting 200 hp and you put a 3.5" or 4" exhaust would be pointless if not a loss of power!!!
i dont even think a 3" would help!

Now i see if your pushing up to 700hp why a 4'' would work!
but
just cut the whole thing off then!!

 

[98spydert]

im not saying 3.5" and 4" is too big for everything!
but something that has a ton of power that actually needs it!

ok lets see if your engine is only hitting 200 hp and you put a 3.5" or 4" exhaust would be pointless if not a loss of power!!!
i dont even think a 3" would help!

Now i see if your pushing up to 700hp why a 4'' would work!
but
just cut the whole thing off then!!

It wouldn't be a loss of power. With a turbocharged engine, any exhaust is a restriction and hurts performance. You're thinking about non-turbo cars and the need for back pressure in the exhaust system. But with a turbocharged car, all the back pressure we need and more is created by that huge restriction hanging off our exhaust manifolds. Any restriction after the turbo only hurts spool and potential flow though the turbine.

 

[habitatguy187]

Why is everyone saying 3.5-4" is too big? You can't buy any aftermarket exhaust (besides ebay) for $400, so it doesn't matter. And of course the turbo is all the back pressure you need, with a 4in exhaust after the turbo the pressure drop would be amazing and would rock spool up.

3.5" and 4" is just excessive for most people. You'll make more money if you can find a way to make a system that competes price-wise with the 3" eBay exhausts.

There's not much out there for 1g fwd exhausts, especially cat-backs (which is why I put a muffler on my downpipe and dump under the car) Even the downpipes on ebay are $40 more than a 1g awd downpipe, you might be able to make some money there.

 

[4cyls_of_fury]

if i make a 4'' exhaust for fwds it would have to be side exit with oval pipe. do to the fact that it has to go over the rear suspension.

i plan on making one for a gsx next weekend ill post up pics whens its done

 

[canada4g63]

my car sits to low for a 4" i do have a 3.5" old school buschur exhaust on my gsx.

 

[Rob10_99]

You making that for your 99 or a 1g? =D

 

[Jets303]

Pics would be nice. Also a price and date of completion.

 

[95GreenGSX]

I'd be down for a full 3" catback, no muffler for my 98 GSX. Let me know on some prices and pics.

By winter i'd like a 3.5-4" one also.

 

[4cyls_of_fury]

well i have a gst, but ill be making it for a 96 gsx. im just waiting for the donor car to buy a stock rear bumper cause he has a body kit and i want to make sure everything lines up. i also have a 93 gsx donor car so if everything fits good on the 2g ill be making it for the 1g. im still waiting on tooling for 3.5'' so its only 4'' for now. i'll figure up some prices this weekend. the first sell will have to be a group buy.

 

[bullitt0713]

some kids that have turned to the big turbo diesels might choose a bigger than 3" exhaust, it would be feasible to fabricate it to clear a rear axle and drivetrain, but the customers looking for such a exhaust would be far and in between, but i am interested in seeing what one would sound like... maybe a 4" tip for sure, i have seen quite a lot of people welding those on recently also.

 

[Imback]

We have full blown race cars running 4" piping there is no need for that on a street car. And if it's a race car why even bother with a cat back. I give you props for trying but after all is said and done you wouldn't be much cheaper then getting one made at a local header shop. And if your wondering how i would know this. It's because that's what i do for a living. Good luck

 

[habitatguy187]

We have full blown race cars running 4" piping there is no need for that on a street car. And if it's a race car why even bother with a cat back.

Contrary to popular belief, a 3.5 inch exhaust will help performance on a 16g car.

 

[jdombrow]

you should make somebends for people, I'd be interested in a 3.5 or 4" u-j bend

 

[JusMX141]

3" is actually too big for most DSMers, and is responsible for most (if not all) cases of boost creep.

4" is downright retarded for any car with a turbo flowing less than 90 lb/min.

 

[habitatguy187]

3" is actually too big for most DSMers, and is responsible for most (if not all) cases of boost creep.

4" is downright retarded for any car with a turbo flowing less than 90 lb/min.

I don't remember where I read it but there was a guy on here claiming that he picked up 15 or so hp on the dyno with a 3.5" catback with a 16g , he was trying to max it out though and was flowing a lot of air.

Take away the boost-creep factor and what do you think about bigger exhausts?

 

[turbo addict]

I don't remember where I read it but there was a guy on here claiming that he picked up 15 or so hp on the dyno with a 3.5" catback with a 16g , he was trying to max it out though and was flowing a lot of air.

Take away the boost-creep factor and what do you think about bigger exhausts?

it depends. If you are running 15psi on a stock setup no. But if you are trying to run 40+psi with cams and intake manifold, then yes, there is a very big pressure differential before and after the turbine wheel and WILL make a difference. same goes with a bigger intake to the turbo as well.