Custom 4" Exhaust Help

[felixy69]

i have a T78 with rb30/26 in a BNR32

looking to make a custom 4" exhaust from turbo back.

question is..should i include a muffler or should i make it stright out.

disadvantage ?

and i guess i'll be using 321 SS stainless steel from burns

any thoughts or experience on that ?

should i also use heat wrap on this tubing ?

i see that on Burns Stainess's page, they have many selection of mufflers like

DR-1 Drag muffler

and

Ultra Light muffler

also using oval tubings. what's the effect of this ?

is it just for more ground clearence ?

[DCIEVE]

I would certainly be using a muffler and making sure it is straight through and at least maintains the exh id... that is assuming you dont mind the noise. If you do want to quieten it down, as an example a mate with a 4" has two rather large straight through magnaflow race series mufflers and that is imo very quiet at light throttle/cruise, as opposed to my 3.5" with a single 4" muffler which is deafening no matter what your doing.

btw that drag muffler is a merge collector design for aspirated drag motors (ie straight of headers)

[saliya]

Hey,

With that turbo and a 4" straight-through I'd guess you'd be at about 110-115dB. That's pretty loud.

You might want to have a listen to something that loud before you decide to do it; if you're

getting a full custom system done you'll save a lot of time and effort (and money) if you decide on

the configuration before you start They go harder with less muffling; but you can probably knock

10dB off that with minimal flow restriction, and another 8dB with only a little more restriction.

I'd probably try to get it down to about 95 using the best flow-vs-noise tradeoff mufflers you can find.

Below that mark on 4" I think you will notice the difference.

No experience with that vendor of stainless. I think you have to weld 321 with 347 so that may be a concern.

Heat wrap: no idea; I'd probably wrap the manifold but not worry about the exh. side. It's a _big_ pipe.

The oval tube is for more height clearance - you have more width + less height used, but similar area.

Hard to do 'the bends of your choice' with it though because it's indexed.

Round is easier, and you can fit a round 4" under a 32 with 100mm clearance everywhere

at SK's suspension GB ride height (minor relief needed when passing over the rear driveshaft area).

Regards,

Saliya

[rb26s13]

dont use 321.. its not needed just use 304 grade stainless.. half the price of 321 and does the exact same job.

[felixy69]

dont use 321.. its not needed just use 304 grade stainless.. half the price of 321 and does the exact same job.

wouldn't 304 crack after along time ?

[rb26s13]

wouldn't 304 crack after along time ?

for a turbo back exhaust system i doubt it ive never had one crack on me or any of the cars ive done

all the systems ive done have just been 1.6mm 304 grade stainless.. works perfectly find never had any crack leak or anything

[felixy69]

for a turbo back exhaust system i doubt it ive never had one crack on me or any of the cars ive done

all the systems ive done have just been 1.6mm 304 grade stainless.. works perfectly find never had any crack leak or anything

1.6mm meaning 16guage?

[GeeTR]

Gauge -> mm for steel

15 -> 1.702mm

16 -> 1.524mm

Edited June 7, 2008 by GeeTR

[psi]

I use 304 for 2 reasons, 1 is cost, 2 is for availability of the material and bends, flanges.

I can often buy ALL the bends and straight right off the shelf!

Cracking is usually tracked back to thermal stress. Often where 2 pipes meet and they are running at different temps and/or lengths.

Like dump pipe and waste-gate join. Make sure you add a flexi-pipe! If in doubt, check out any decent GTR front pipes!

I wrapped my pipe until it had left the engine bay..

Help ya any?

[felixy69]

I use 304 for 2 reasons, 1 is cost, 2 is for availability of the material and bends, flanges.

I can often buy ALL the bends and straight right off the shelf!

Cracking is usually tracked back to thermal stress. Often where 2 pipes meet and they are running at different temps and/or lengths.

Like dump pipe and waste-gate join. Make sure you add a flexi-pipe! If in doubt, check out any decent GTR front pipes!

I wrapped my pipe until it had left the engine bay..

Help ya any?

i thought flexy pipe was a good idea..but some say it's not important and it's only important on FWD cars.....but gtr has FWD too...

[DCIEVE]

fwd as in east west motors....

[Adriano]

You will need a flex pipe on the wastegate pipe if you are going to plumb it back in

[rb26s13]

I use 304 for 2 reasons, 1 is cost, 2 is for availability of the material and bends, flanges.

I can often buy ALL the bends and straight right off the shelf!

Cracking is usually tracked back to thermal stress. Often where 2 pipes meet and they are running at different temps and/or lengths.

Like dump pipe and waste-gate join. Make sure you add a flexi-pipe! If in doubt, check out any decent GTR front pipes!

I wrapped my pipe until it had left the engine bay..

Help ya any?

your lucky.. i have to order all mine in majority of the time

[MBS206]

Build it 3"

It'll still flow enough. Trust me.

[R31Nismoid]

3" - 300rwkw

3.5" - 350rwkw

4" - 400rwkw+

Thats a 'general' rule for exhaust size.

Yeah a 3" will 'flow' 350rwkw, but put a 3.5" on there and you'll see the benefits right away.

You can easily get two mufflers, plenty of places sell 4" ones these days, plentiful on the market.

Will still flow brilliantly and have a nice note, without being a massive noise/drone box

[Roy]

I would be trying to thinner in wall thickness then 1.6wt. Way too heavy for an exhaust, maybe the dump pipe and front pipe will be fine in 1.6mm, but after the cat you can drop it back to 1.2mm

[rb26s13]

I would be trying to thinner in wall thickness then 1.6wt. Way too heavy for an exhaust, maybe the dump pipe and front pipe will be fine in 1.6mm, but after the cat you can drop it back to 1.2mm

thinnest my supplier has is 1.6 in 4inch and 3.5.. can do 3inch in 1.2 tho if your that concerned about weight.. you can go titanium.. but that will cost an arm and a leg...

[MBS206]

3" - 300rwkw

3.5" - 350rwkw

4" - 400rwkw+

Thats a 'general' rule for exhaust size.

Yeah a 3" will 'flow' 350rwkw, but put a 3.5" on there and you'll see the benefits right away.

You can easily get two mufflers, plenty of places sell 4" ones these days, plentiful on the market.

Will still flow brilliantly and have a nice note, without being a massive noise/drone box

Seen enough ~400RWKW cars, with ZERO gain from a 3" to 4" exhaust...

[rb26s13]

Seen enough ~400RWKW cars, with ZERO gain from a 3" to 4" exhaust...

majority of the restrictions on cars with 3" exhausts is either the muffler or the cat.. a well made 3" will flow 400rwkw chasing much more than that tho it is worth steppinh up to 3.5 or 4

[R31Nismoid]

Seen enough ~400RWKW cars, with ZERO gain from a 3" to 4" exhaust...

Of course a car with no mufflers, ext gates not plumbed etc etc will do it.

Road cars, with a level of noise legality surrounding noise, ride height and so on, simply not going to happen