3inch Or 3.5inch Exhaust

[alwaysdreaming]

hey all

quick question, am getting turbo back exhaust but dont know wich size to get,

is there going to be much diffrence and how so?

how much have people spent on there turbo back exhausts?

thanks heaps everyone

[G-Money]

depends on what power your aiming for. unless your looking for heaps of power stick with the 3" or you might loose a bit of back pressure(bad)

[WARLORD]

3.5 all the way if you are going to put a bigger turbo in the future .

[alwaysdreaming]

im not aiming for much over 300rwk at the end of the day, thats along way away yet though.

only looking at mide sized turbo as ill be using it for some drifting so need good spool.

got any ideas for a good turbo based around those needs.

thanks for your response guys, all new to this so any help is much appreciated.

gezza

[BHDave]

for 300 i'd be leaning towards 3.5inch.

Back pressure? How the hell is that myth still being perpetuated? It's an NA myth too, incidentally, not turbo.

[nisskid]

Back pressure? How the hell is that myth still being perpetuated? It's an NA myth too, incidentally, not turbo.

what exactly do u mean by this?

[Cjmartz2k]

for 300 i'd be leaning towards 3.5inch.

Back pressure? How the hell is that myth still being perpetuated? It's an NA myth too, incidentally, not turbo.

x2!!!

I'm going to have to create a word document and save it so I don't have to type this explination over and over and over and over.

FOR N/A......

"Backpressure" is always bad. You want appropriate sized pipes for your power lever and desired rpm range. Smaller pipes equal higher exhaust gas velocity (EGV), but more "backpressure". If the pipes are too small, it will choke out the motor on the top end, but pull better low end until the smaller pipes become a restriction. Higher EGV helps pull the air behind (along with exhaust gas pulses) out of the motor thus helping said engine make more power. If you have a huge pipe on a honda, the air is almost stagnant in the exhuast and it kinda "bumps into itself" on the way out. If you have huge pipe (slow EGV) and put a big kink in it to create "backpressure" (restriction), you will have the worst of both worlds (like most honda guys, especially when they also realize they drive a honda ).

BOTTOM N/A LINE-----SMOOTH, STRAIGHT, APPROPRIATE SIZED PIPE IS BEST!!

FOR TURBO.....

EGV and exhuast gas pulses don't matter (after the turbo) because the exhaust already has one big arse restriction messing with the exhaust gas pulses and EGV......YOUR TURBO!! For turbo cars, the bigger/straighter the better, for any power level. Now taste and common sense, that's a whole different story

Edited January 25, 2008 by Cjmartz2k

[R31Nismoid]

upto 300rwkw 3"

350rwkw 3.5"

400rwkw 4"

Is a basic rule to use.

G-Monkey - backpressure is the enemy. You need to do some more research.

[alwaysdreaming]

thanks for your help guys, probably go wit the 3.5 just to make sure, i wanna get it as close to right first time.

3.5 alows me to dable in the 300+power range.

in ideas for turbos though?

thanks heaps

Gezza

[geraus]

I currently got a Greddy/Trust 3" catback then connected to my 3" front Greddy/Trust pipe with high CATCO 3" high flow cat, Then my 3" dump-split pipe from the turbo. A good free flowing exhaust will have the RB sounding great, turbo lag will be reduced, and power gained throughout the rev range. The new exhaust should start from the turbo with a dump pipe either a 3" open bell mouth or better still a split dump to separate the gases from the turbine and wastegate. The sound is excellent sounds tufff man ... my mates 33 has the same trust/greddy system as mine but then just a str8 pipe through omg i can tell ya it sounds meannnn. From this mod you should get good gains.

[alwaysdreaming]

I currently got a Greddy/Trust 3" catback then connected to my 3" front Greddy/Trust pipe with high CATCO 3" high flow cat, Then my 3" dump-split pipe from the turbo. A good free flowing exhaust will have the RB sounding great, turbo lag will be reduced, and power gained throughout the rev range. The new exhaust should start from the turbo with a dump pipe either a 3" open bell mouth or better still a split dump to separate the gases from the turbine and wastegate. The sound is excellent sounds tufff man ... my mates 33 has the same trust/greddy system as mine but then just a str8 pipe through omg i can tell ya it sounds meannnn. From this mod you should get good gains.

lol im getting excited already, havent even got the thing booked in yet.

how much did that all cost, ive been quoted around 2300 for a full custom 3.5inch and new manifold.

think ill get it made so i can swap the cat in and out for track use.

thanks for your help.

[GeeTR]

Before you make you decision on a custom, rem a name brand setup could v.well hold its value when / if you go to sell it.

Purchase a good, large cat to start with, so you don't have to change it out at track meetings (and save on the yellow stains on the rear bar)

[alwaysdreaming]

Before you make you decision on a custom, rem a name brand setup could v.well hold its value when / if you go to sell it.

Purchase a good, large cat to start with, so you don't have to change it out at track meetings (and save on the yellow stains on the rear bar)

if a race performance shop did the custom build would i be acheiving better performace, as i dont think im going to be selling it?

[GeeTR]

if a race performance shop did the custom build would i be acheiving better performace...

If the custom was still tucked to the floorpan, didnt drop too low (read - not a dead straight pipe to the back) stayed the same diameter; then I wouldnt think it would gain much over a name brand dump, down pipe [cat] then cat back no. Tis my opinions only.

Its a cost thing really. For ~300rwkw 3" is fine. It'll keep the raw materials and cat costs down a lil

Edited January 26, 2008 by GeeTR

[alwaysdreaming]

alright, thanks for your help GeeTR, ill see what the guy reckons about going straighter.

although its street driven now it most likely to be converted to full time track eventually and id prefer to get things done right the first time.

im also looking at turbos rated between 475-600hp but i need something with a good spool as my end intent is to use it for drifting, any idea for one that will get me a bit over 300rwkw but acheive good spool? been looking here http://www.slidingperformance.com/catalog/index.php?cPath=25.

[GeeTR]

600hp = 360rwkw'ish race?... go 4"

I'm building a 4" dump & gate into a r32, at the mo, which isn't fun while keeping AC in the car.

[alwaysdreaming]

600hp = 360rwkw'ish race?... go 4"

I'm building a 4" dump & gate into a r32, at the mo, which isn't fun while keeping AC in the car.

not yet, its my only car for a while but definatley race car once iv got another car.

4" will be to big until i get close to that sorta power wont it?

haha who needs ac when uv got windows.

was looking at the gt30r or the gt3071r, but im still learning about turbos and am kinda reading some of the info with out knowing what it impacts.

thanks heaps mate

Gezza

[SirRacer]

Im in NZ and here a massive issue is actually getting mufflers to fit that sort of exhaust (3.5 inch +)

If any of you Aussie blokes dont mind linking a few sites i wouldnt mind ordering a few.

Cheers

[Al]

GT30R would be my pick for 300rwkw. It's the smallest turbo that will make the power, but will still be a little laggy on an RB25.

If you are serious about drifting, consider the HKS GTRS kit. I made 270rwkw: Head porting, Tomei cams, std manifold, std plenum. Had a great power band, great package to drive.

I have since cracked a piston, at a track day, so have upgraded to an rb30det, using the same 25 head, but with ETM manifold, GReddy plenum, and a few other upgrades. The GTRS was going to restrict the flow of the rb30 so i upgraded to a GT30R; smallest turbo recommended by a few "experts". Once the build is complete i should see about 300-330rwkw, with better response than a std high-flow on an rb25

[RB30-POWER]

3076 is a far better turbo, has the smaller compressor wheel to better suit the turbine wheel.

if you go 3040, you would be better off with the 3540, that way you don't have the restrictive hot side and can make full use of the large gt40 compressor wheel, even if you went with a smaller ar housing, it would still be more efficient.

people are really beginning to realise what a mismatch the 3040 turbo was, especially when tuning on pump fuel.