What Exhaust

[Lukas 33]

Hey guys

I was looking into getting an inline 3" varex put in the car so it wasnt to loud around town etc however I have a 3" back to just after the cat where it splits off into 2 2.5" (so it looks). It is an r33 gtst s1 with an rb25/30. I am looking at making about 360kw or so and was told that my 3" wont be up to it. The turbo is a GT35R with a 0.82 rear. It has a 4 bolt 3" outlet. I currently have a 3" front pipe from turbo to cat, a hollowed out 3" cat and then the two 2.5" pipes onwards.

I was looking into just getting a 3.5" cat and 3.5" cat back exhaust and putting in one of the inline 3.5" oval varex somewhere in there.

What I would really like to know is will the 3" pipe from the turbo to cat and then the 3.5" cat and 3.5" cat back be fine to support that kind of power?

I was reading on these forums that 3" would be fine but then others say it wont so Im stuck in the middle. What exhaust would you guys recommend from cat back where I can just cut in and add the 3.5" inline oval varex.

Cheers

Lukas

[R31Nismoid]

360rwkw = 3.5" all the way through from the dump to the rear tip, with at least a 4" Cat.

Honestly, Varex mufflers have a shit sound mate, i would just get two decent mufflers if you want a quiet and decent flowing exhaust.

It is exactly how i had mine done planning for upto 380rwkw at a max.

Rule i've been told to use

3" upto 300rwkw

3.5" upto 350-380rwkw

4" 400rwkw+

[Mandingo]

Yeah what he said talk to any decent exhaust joint and they will be able to help you out with a legal setup.

Edited December 9, 2009 by Flipmo

[Lukas 33]

360rwkw = 3.5" all the way through from the dump to the rear tip, with at least a 4" Cat.

Honestly, Varex mufflers have a shit sound mate, i would just get two decent mufflers if you want a quiet and decent flowing exhaust.

It is exactly how i had mine done planning for upto 380rwkw at a max.

Rule i've been told to use

3" upto 300rwkw

3.5" upto 350-380rwkw

4" 400rwkw+

Oh ok so I should be right putting a 4" exhaust from the turbo back? Just didnt know how i would go getting it down the little hole in the engine bay or how a 4" exhaust would go when the turbo outlet is only 3" Is it even possible to get a legal exhaust at 4"? f**king didnt budget for a bigger exhaust. Fcuk! How much do you think a 4" inch system would cost to get put in? Might have to pull some money out my a$$ by the looks of it

[Lukas 33]

And how much would a 3.5" system be? I dont think it would be worth going 4" unless I decide to go crazy and get a t04z

[R31Nismoid]

3.5" will be cheaper, but not by much.

If you are not going to change turbo, 3.5" will be ok.

4" and legal... very very hard. 3.5" is hard enough to get legal, 4" just poses more problems.

Either way you won't be legal with a Varex - you'll need two big solid mufflers, they wont be cheap

[Lukas 33]

Yeh well I think 3.5" is the go if it will be legal. I will see how the stock exhaust goes and maybe I will just get it tuned mildly until after the christmas and new year are over. Will update this thread with how the exhaust holds up for future reference. Thanks ash

[bozodos]

Is it really essential to have an exhaust with that large a diameter? I thought in the past when this was debated that it turned out that 3" was pretty much ok for everything, that it came down to the combination of cat/mufflers moreso than the pipe diameter itself.

[Lukas 33]

Is it really essential to have an exhaust with that large a diameter? I thought in the past when this was debated that it turned out that 3" was pretty much ok for everything, that it came down to the combination of cat/mufflers moreso than the pipe diameter itself.

Well I dont know. I thought if if the turbo was 3" outlet and I had a 3" dump, hollowed out cat and the rest was all good to flow fine then it would be fine. But I have been reading and apparently it is better to have a greater pressure difference on either side of the turbine. So if I had a 4" exhaust the exhaust gas will want to go from high pressure to low pressure (ie Manifold to dump pipe) faster than it would if I had a 3" exhaust. As there is a greater pressure difference. This in turn would obviously reduce spool time and free up top end power. DO NOT QUOTE ME ON THIS. This is just my basic understanding of why you would go to something so huge.

My question to everyone else is. Will I be able to still make about 320rwkw on an rb25/30 with type a poncams and a gt35r 0.82 rear with a 3" exhaust?

Edited December 10, 2009 by Lukas 33

[R31Nismoid]

The only thing you need to worry about is enough flow, if you don't have enough, or its slightly impeading you'll have issues. Sometimes you wont even notice.

Like the car still might make power, but be down 20-30rwkw and you'll never know and just say "right, thats what it made so be it". Its not until you then upgrade the exhaust, or drop it and do a run and then see that there is some still hidden inside.

Its not like having 4" on a setup making 250rwkw is going to offer anything over a 3" exhaust.

You will be struggling for 320rwkw with a 3ltr. It can be done, no doubt people have done so before.

But as i said above, you might find that 320rwkw with 3", might jump instantly to 340rwkw if you changed it/dropped the exhaust

Only way is to try it as the maths would be a nightmare

[Lukas 33]

The only thing you need to worry about is enough flow, if you don't have enough, or its slightly impeading you'll have issues. Sometimes you wont even notice.

Like the car still might make power, but be down 20-30rwkw and you'll never know and just say "right, thats what it made so be it". Its not until you then upgrade the exhaust, or drop it and do a run and then see that there is some still hidden inside.

Its not like having 4" on a setup making 250rwkw is going to offer anything over a 3" exhaust.

You will be struggling for 320rwkw with a 3ltr. It can be done, no doubt people have done so before.

But as i said above, you might find that 320rwkw with 3", might jump instantly to 340rwkw if you changed it/dropped the exhaust

Only way is to try it as the maths would be a nightmare

Yeh I have taken basic fluid mechanics and thermodynamics at uni but there is no way in hell im going to be doing those calculations!

Well we will do a run with the 3" and do a run with it dropped before the cat and see the difference it makes I would LOVE the bigger exhaust but there is always a trade off. Have the car only make 300kw with the 3" so I can drive the car home to see the family at xmas time OR put the car in for a 3.5 or 4" exhaust and catch a bus home to see the family while the car is being done.....anyway it all comes down to the test. Which reminds me I had better give the mechanics a call.

Cheers

[bozodos]

could always run it just off the front pipe over xmas

is there any commercially made 4" exhausts, or would you have to get one fabbed up?

[R31Nismoid]

^ a lot of them tend to hang fairly low, which can be a problem

I would go with custom personally. Get it tucked up nice and high.

[Lukas 33]

could always run it just off the front pipe over xmas

is there any commercially made 4" exhausts, or would you have to get one fabbed up?

HAHAHA Yessssssss

yeh I think I am just going to get one fabbed up after the christmas and new year break and when I have some more moneys laying around. Might get a new manifold, bigger rear housing (depending on response and power output) and then get the exhaust done at the same time. Depending on how much extra money there is I might go for some new cooler piping and throttle body at the same time. Ah well time will tell.

R31nismoid - Yeh I dont really want anything hanging too low. Ive driven too many cars where every speed bump and driveway is "fcuk am i gunna scrape am i gunna scrape...shit!". I would like it tucked up nicely but being 4" I will have to see how much they can do

Almost home time! 9 mins till knock off time

[willyu]

^trust me, it's a pain!!!

[rasonline]

Like R34Nismoid says 3.5" probably the most practical bet. Best solution in between.

[Lukas 33]

Like R34Nismoid says 3.5" probably the most practical bet. Best solution in between.

I am thinking of going a t04z in the future and maybe making about 400rwkw. Do you think a 3.5" will still be ok or should I just do the t04z and 4inch turbo back at the same time?

Cheers