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Custom 4" Exhaust Help

felixy69

By felixy69,
in Engines & Forced Induction

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felixy69 Rising Star

felixy69

Posted
Posted
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

mufflerpic1_150.gif

and

Ultra Light muffler

SSmuf-2.gif

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

is it just for more ground clearence ?

straight_x3.jpg

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DCIEVE Mentor

DCIEVE

Posted
Posted

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 Rising Star

saliya

Posted
Posted

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 :P 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

psi Experienced

psi

Posted
Posted

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 Rising Star

felixy69

Posted
  • Author
Posted
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...

rb26s13 Mentor

rb26s13

Posted
Posted
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

R31Nismoid Grand Master

R31Nismoid

Posted
Posted

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

rb26s13 Mentor

rb26s13

Posted
Posted
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 Grand Master

MBS206

Posted
Posted
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...

R31Nismoid Grand Master

R31Nismoid

Posted
Posted
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

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