I decided to make this thread for some of the people who have the some concerns and questions about 4in exhausts. My personal issue is that right now im considering going to a 4in and ditching my straight 3in but im trying to see if its even worth it for me. i currently have a t04r with a 1.0 divided hotside on my fc that im fairly sure will put out 500whp at 20psi. The exhaust comes into play after that because i want to run my car on some road courses so im looking to lower back pressure, egts and make the turbo more responsive. Problem is this is a semi daily driver haha. I drive this car alot because i love it haha

and for those considering going to a 4in 304ss v-band exhaust with 1 resonator and 1 muffler your looking at 500-600 (unless you have hookups) in quality parts alone thats not counting labor if you have to have a welder make it.

 

You could always do a 4" downpipe & midpipe then taper down to a 3" catback. This will make it more street-able and won't cause a restriction. It will still help with spool/power & lower egts. The Exhaust gases cool the farther they get from the turbo, and then condense more. As they condense they don't require as big of a pipe. If you have a open wastegate, I seriously doubt you would see any difference with a 4" catback. I've tested it on the dyno myself.

 

I'm doing the exact same thing converting my exhaust to 4" (as well as new manifold). Lets just say its more then 500-600. Same reasons as you, looking for more response and lower backpressure and more rwhp is always good. Open wastegate is just too loud in a rotary for me >_>

thewird

 

I am considering a 4" exhuast for the race car, using 4" SS for the downpipe with a short "midpipe" to it, then making a 4" aluminum section into a can muffler in the rear. The aluminum tubing is a slightly thicker wall and helps absorb some of the exhaust harmonics, while being lighter than SS tubing.

 

Ah yes this is one other thing forgot to mention i DO want to recirculate my waste gates into my exhaust. some ppl may think im crazy but i hate the sound of open dump tubes

 

I would be scared to make part of my exhaust aluminum. A melting exhaust would be kind of funny though haha

 

I did a 4" bell-mouth downpipe for someone as an experiment and it worked out quite well. I tapers back to 3" halfway down to the horizontal ground bend.

4" exhausts are not for everyone. You will be getting exhaust tickets and dirty looks from damn near everyone. Depending on your HP goals you might want to really think about this decision. I've never brought a girl in my FD somewhere without them complaining. Needless to say you won't be getting many dates but all your fiends will gladly hitch rides with you...

 

I got a 4in DP for stock twins tapered down to 3.5in before the midpipe then 3.5in resonated midpipe and 3.5" catback with 4" dolphin tip all from SMB in Australia.

It's very quiet IMO and I daily drive the car a lot. Of course once you go WOT and higher rpm it gets loud!

You could get a 3.5" midpipe and cb and have a 4" tapered to 3.5" dp custom made for your turbo. It's what I plan on doing if I ever go single.

 

Hey Thewird, I'm in the same boat. I've already ordered a muffler through summit, but need to order bends, some v-band sets and straight tube. Where are you planning on ordering from? PM me, maybe we can hook up a shared order to cut costs, I'm down in the GTA often enough...

-Taylor

 

I have done a few aluminum exhaust rear sections and it works pretty well where you have to have a full exhaust. Its not cheap though. Never have had one melt, but they will get pretty banged up if driven over a curb or something.
My exhuast surrently is 3" from turbo to can, and its likely fine, but 4" would probably work better.

 

just started fabbing a new manifold and 4in down pipe. i'll post pics when i'm done.

 

Trots*88TII-AE*, I already have everything I need. Borla multi-core XR-1 Muffler (Giant Oval) for on midpipe for sound suppression and an ebay titanium muffler on the back for weight savings. Plus all 4" v-band connections. I actually expect this setup to be quieter then my current one.

thewird

 

Aluminum is fine. after all we have aluminum housings and most pistons are aluminum. just dont use aluminum with a really angled bend near the motor where the exhaust will focus a lot of heat on it.

 

burns stainess 2stage mufflers make some significant difference in sound if you wanna go for 4inch. they cost more than the usual mufflers but they are very nicely made.

i use 2 2stage mufflers on my setup. one is 17inch long and the other is 23inch long. its a bit loud but acceptable

 

To recap if you get a 4 inch downpipe and taper it back to 3 inches you can notice better spool, and more HP? I know every system is different but can anyone take a guess at the difference say 5HP and boost comes on 200rpm?

Just curious for my next setup.

 

my power goal is 500whp (responsive) and right now i have a 3inch straight to a n1 muffler WHICH SEEMS TO do nothing. i planned on going 4in with a 30in magnaflow to a vibrant 20in muffler. possibly 2 of the 30in magnaflows (1 as a resonator other as a muffler) if i could fit it. I was hoping that a setup like that even with the 4inches would be quieter than my 3in straight.

Ill consider aluminum too for an exhaust dosent sound half bad

 

any video or pics??

 

I've had a girl say she enjoys the ride the ride due to the vibrations (solid mounts and 1000 pound suspension). So I guess it depends on the one lol.

thewird

 

To recap if you get a 4 inch downpipe and taper it back to 3 inches you can notice better spool, and more HP?

Yes, increasing the downpipe diameter alone can really help turbo spool.

I data logged my TII before and after.

3" RB REV TII turbo back exhaust = full boost by 3,800rpm 4th gear on my set up

3 1/2" JIC Spec 90 front pipe (downpipe and presilencer/cat section) to same RB REV TII Y-pipe and mufflers = full boost by 3,400rom 4th gear.

I used 4th gear full boost data log point reference because it is easy to be consistent getting this data, but where you really feel the better spool is around town in the lower rpms.

Before I had the full JIC Spec 90 3 1/2" turbo back on and it was just too loud for the daily driving the car was doing.

I lost very little spool using the RB rear section and could spend a lot more time in boost with a quieter exhaust.

 

I currently have a turbo mani and downpipe made by Elliot at Turblown.net, 3.5 in SS all the way back.. Borla underneath and magnaflow out back.. its actually fairly quiet but sounds damn good. WG is to atmosphere but will be going back into the exhaust. I have a gt35r also from Elliot and divided housing.. i think its 1.01 but not sure maybe Elloit will remember. I hit full boost (which is 7.5 lbs until next spring) at right around 3000 maybe a little less. The WG is too loud tho. I have had a few girls tell me that they just about wet thier pants when i started boosting and the wg opened up tho

 

some pics... not sure how much louder a 4 in would be

 

http://www.youtube.com/watch?v=DdH67h7DEB8


http://www.youtube.com/watch?v=1dt9jl8f9lU


thanks to Elliot!

This might help you make some decisions.... maybe not i know 4 in is a bit larger.

Don't mind the retarded commentary by me... I made the video to show a judge when i was getting out of my illegal exhaust ticket... so I kinda exaggerated.. I have hobbyist plates etc etc... blah blah..

 

I'm also trying to decide on an exhaust system for a GT35R T4. Options are:

4" all the way
4" dp + 3.5" system
4" dp + 3" system
3.5" all the way
3.5" dp + 3" system
3" all the way

 

I just saw this today while I was at the book store. 3.5" is the way to go and 4" is over kill! In the test, they gained 103 rwhp from 3" exhaust to 3.5". Same boost level and decreased spool time by 200 rpms. Great read with dyno results to back it up.



http://www.modified.com/tech/modp-11...ech/index.html

 

Looks like 3.5" all the way like I wanted in the first place, only bottlenecks being the hotside exit and 3" HKS muffler.