2.5,3.0 and 3.5 inch exhaust. which one will suit me better?
 

Here is my current situation and my setup.

i have a bnr stage 1 right now, and i have a bnr stage 4 sitting on my desk.

I have a 2.5 inch bonez down pipe to an rx7.com crush bent connector pipe to a 2.5 inch resonated mid pipe to an apexi gt catback.

my current problem im having is that i am unable to controle boost. on some days it wants to reach for 12 psi and on some days it only wants to go to about 9. on the dyno, its even worse. it doesnt matter what i set my manual or my electronic boost controller, it always wants to do whatever it wants on the dyno and hit the same psi no matter if we unplug the waste gate or not.

my question is this. should i invest in a 3 inch or a 3.5 inch exhaust for my bnr 4? will i benefit from just having a larger downpipe and mid pipe? will the 2.5 inch catback ( it goes from 2.5 inch to 3 inch) restrict me at all?

if i do want to go and get a full exhaust, what is the normal pricing for something like this? in the 600 to 1000 dollar range?

little bit more info on my car
s4t2 engine with s4na rotors. stock top mount, haltech e6x with 55cc and 1600cc injector combo with full paralell ss fuel system and walbro 255 intank fuel pump.

i guess what im trying to ask is what exhaust size should i pick for my bnr stage 4

I would say 3in or bigger. Or 3.5in downpipe into 3in exhaust. There have been some dyno tests that show not only better spool but horsepower increases as well.

SirCygnus,

any restriction after the turbine hurts spool and ultimate power. the turbo is a pressure diff device. exhaust back pressure vs boost level. anybody that tells you you lose torque or HP from too big of an exhaust on a turbocharged engine is mis informed.

you might have have boost control issues though if your wastegate (in this case internal) is too small.

cheers

Kenn

2.5 is too small, at least for the DP.

3.0 is just right

3.5, while actually matching up with your cat back, is probably a little big.

would a 3.5 inch downpipe to a full 3 inch catback be a better idea? i dont want to limit my potential with my exhaust here.

now that we are on the subject, what wall thickness would be suggested?

Hmmmm...

I'm considering running a BNR Stage 1 with a big free flowing exhaust.

You're saying that you're getting uncontrolled boost on your 2.5 inch exhaust with a BNR State 1? Are you sure your wastegate and actuator are fully operational?

yes and yes.

3 is fine...3.5 really won't give you THAT much better power and response with a BNR.

What are your noise constraints?

street car, so nothing crazy.

Copy this system. Have it fabricated locally 100% fucking proven. Designed by me in conjunction with my fabricator. Muffler suggested by rx72c years ago as a proven quiet powerful setup for BNR size turbos (most turbos gt35r or smaller).

For catalytic converters.

I just had a 4" body metal 200cell put on a 1jz-gte (vvti, stock ct15b turbo). Smelly on cold starts.

I also just had a $550AUD 5" body SMB 200cell put on a S15 black top SR20DET (vvti, gt28r ball bearing factory turbo). The S15 is not smelly even cold and has a LOT of catalytic converter. Its seriously big.

Anyway for my 7 I use the same rear muffler and no cat. The JZX100 and S15 I had an additional drum centre offset middle muffler put in. JZX sounds awesome got rid of the drone the previous blitz exhaust had. JZX100 is still using 2.5" dump pipe moving up to 3.5 or 4" once we get the full TO4 turbo on that car.

S15 has a very slight drone at some RPM's we plan to fix that with some 262 duration cams.

Anyway the stock FC turbine housing/wheel with no backcut combined with a nice big muffler even in 3" mandrel can still REALLY fricken quiet at 800rpm idle.

http://i1085.photobucket.com/albums/...ESAYEE/2-1.jpg
http://i1085.photobucket.com/albums/...E/DSCF1055.jpg
http://i1085.photobucket.com/albums/...E/DSCF1054.jpg
http://i1085.photobucket.com/albums/...E/DSCF1002.jpg
http://i1085.photobucket.com/albums/...DSCF1001-1.jpg
http://i1085.photobucket.com/albums/...E/DSCF1004.jpg
http://i1085.photobucket.com/albums/...scf1512uq2.jpg

what muffler is that? oddly nobody in the usa makes a muffler BIG enough for a 1st gen

i built mine 3.5 and honestly its gonna be easier and cheaper to go with 3. im running an sc370 and i luv how it feels with the big exhaust but for a BNR stage4 i think it would be an unnecessary expense.

jobro, i have no idea what you said, but from the looks of it, you did tell me anything.

Brand is 'hurricane'. 20 inches long, 6 inch by 8inch oval barrell. 3" offset inlet, 3" centre outlet. As I said I've put 1 on my 12A turbo RX-7, 1 on a SR20DET (s15 rear muffler) and 1 on a JZX100 Toyota 1jz-gte vvti model chaser. It has shut all 3 cars up. I know rx72c has used them on rotary cars before he was the one that made me aware there were off the shelf truck/performance mufflers available relatively cheap. I think rx72c's 700whp GT42 car used to use one before it got such a big power setup. Used to have pictures.


I just told you everything. If you can't find good mufflers then send someone who can get good mufflers green paper things and have a good local to you tradesperson BUILD (not bolt-on chinese/japanese) you a nice exhaust.

That muffler is good for 500 rwhp + I have tested it many times on rotaries I've seen one on one particular car for over 6 years and is still intact

can not find any info on this muffler. i was gonna go with a magnaflow.

Well trawl the magnaflow catalogue for the biggest centre offset (NOT chambered) muffler you can fit.

As we are saying 6x8x20 is enough to shut up a turbo rotary with a small turbo and small mild port.

just to be dumb about this, that 20x6x8 muffler is 960in3

magnaflow has a 5x11x22, which is 1210in3

and i could run a pair o dynomax's (2x2.5") 4.5x9.75x20 for 877in3 for one and 1754in3 with two.

is there anything special about the hurricane that would make it quieter than anything else? or is it just the right size, and well built?

20x6x8 IS the right size for an FB

I may have mis quoted the size. It is actually 10"x7"x20"

You have room for 10"x8"x22" if you really want to push the area. It is nothing special it is just an appropriate muffler to use on performance cars in general.

Its probably only a glass pack too (can't be 100% sure) but that has not stopped it lasting 2 years so far. And as rx72c said he got 6 years out of one.

Thats about the best I found find in 2 minutes. Make sure you measure and contact your fabricator to make sure he can make it fit.

http://www.magnaflow.com/02product/s...e=main&id=9111

ah excellent that helps a lot!

and yes, i'm trying to make the front half of the car out of radiator, and the rear half out of muffler...

That's what you told me to do! :)

I can tell you the results from my car with BNR Stage 4 turbo.

Racing Beat Rev II 3" turbo back= full 14psi boost at 3,800rpm.

JIC Spec 90 3.5" downpipe/midpipe to RB Rev II 3" "Y" pipe and mufflers= full boost 14psi boost at 3,400rpm.

In addition the 3.5" downpipe/midpipe made more boost from 1,000rpm up making it much nicer to drive around town.

Full JIC Spec 90 3.5" turbo back (one rear muffler)= full 14psi full boost at 3,400rpm but WAY TOO LOUD to use any boost without getting everyone's attention including the police. Sounded great at full throttle with earplugs and helmet for short periods of time.

Maybe had a little more top end power than with 3" RB rear or maybe just sounded really fast, hard to tell.

For best low end power you will do well to create as free flowing an exhaust as possible and if you have boost creep problems add restriction at the very rear of the system until you get the wastegate situation sorted out. This way you still get the great spool of a free flowing system at low rpm.

For noise control you should split the exhaust and use 2 mufflers at the rear in an FC as you are lucky enough to have the space there for it.

If I were to do the exhaust over again I would buy two cheap ($339 each w/ free shipping) ebay 3" ss turbo back single exhausts and modify them into a full dual 3" turbo back exhaust with a little cut and weld.