Turbo1

I need help designing the exhaust for my new track car.. a 92 miata with a 13B big bridge in it.

51ida's, S5 internals, 4 port (obviously), everything lightened/balanced, dual disc clutch, stripped out car (1700lbs), yada yada yada.

2" Primaries I'm assuming... but where do they merge into 1? 2.5"or 3" ? we don't really have a noise restriction on the track, but I need to try and keep it reasonable. Also may see the street once and awhile for some hooligan weekend drives.

I've searched and searched, but I can't find anything decent for an answer. Most are just speculation and rumors...

Help me!

diyman25

check this link http://www.awrracing.com/awr.html or call them for more detail

speedturn

iTrader: (1)

The length of the exhaust from motor to collector is definitely a topic of debate. I have been racing rotaries since 1983, and I have seen short 15", medium around 27", and long around 100" lengths. Currently I am running an ISC stainless header with 88" length to collector on my 13B peripheral port, and my buddy with a 12A PP motor is running an SDJ header with about a 27 to 30" length to collector, and he is making massive power too.

Your collector needs to merge down to a throat of around 2.25" ID diameter, then expand back out to 3" diameter pipe for the rest of the system.

speedturn

iTrader: (1)

http://www.sdjmotorsports.com/Headers.htm

wrankin

go check http://www.improvedtouring.com/ in the forums section and see what the mazda drivers are doing in ITA (12A) and ITS(13B). I believe that a lot of those guys are running full dual almost all the way back with a Y-pipe and silencer at the end.

How are you routing the exhaust? (since the miata normally vents on the drivers side).

-bill

DriveFast7

iTrader: (1)

My 12a J-bridge put 205hp to the ground @ 8800rpms. ISC stainless header JetHot2000 coated. Racing Beat's dual presilencers side by side (same ones used on street cars. They're straight though, only take 1-3hp away, fit and last). The pipes are 2". Bend pipes up and over rear axel. Merge together via Flowmaster dual 2.25" -> single 3". Into a Supertrapp with 3" inlet and 23 5" discs.

Peoples will say not to go with supertrapp but that's another story and my dyno numbers are above. The lava rock muffler is the best but very expen$ive. Cheaper alternative is to buy a Borla or other such muffler and cut it open and put Home Depot BBQ lava rocks in there and weld it up.

I measured and it merges around 125" from exhaust port which is fine per Racing Beat's catalog which I reccomend getting.

Makes way too much noise for the street even when I use 5 discs which chokes the motor big time. But it is QUICK.

diyman25

mm... just check the ISC site. just wonder what is different between them and racing beat one ?



hey drivefast7, did you drive you car on street?



Need to put more develop time into my rx7 now. so for PP from what I got from racing BEAT you need short system right. because the one I got on my 2 gen uni body car I think is too long(need to measure it for sure.) how do you know your system is too long or too short ?????

thanks in advance

speedturn

iTrader: (1)

The ISC header is better than the Racing Beat header. I own both, I know.
The RB header makes too sharp a turn, too close to the engine exhuast port. The ISC header comes straighter out of the motor, and has larger radius turns, so it flows better. The ISC header is made from thinner wall stainless steel tubing, so it weighs less than the heavy wall RB header.

RussTypeS

iTrader: (3)

I've never used the ISC header, but I have an old RB one on my race car (just a stock 12a). the thick wall on the RB helps it hold up to the high exhaust temp. My old one has cracked from the heat before, but i would hate to think what would have happened if the metal was any thinner.

then again this may not be an issue with the ISC header as the RB one only cracks right at that sharp bend where all the heat is.

im not saying the RB one is better, its just something to keep in mind....

MPM

Are you rerouting the exhaust to the left side like the original Miata layout(for more room) or modifying the floor pan to make it fit on the right side? I was involved in a rotary engine transplant into a miata and the exhaust is a compromise at best. I can't imagine the ISC racing header having enough room. We had to cut an old rotary engineering header up just to make it fit along with the redone floor pan in the passenger compartment. Its collected about 18" out and is a tight fit all the way to the back. A long primary header could fit but you'd have to redo more of the floor pan and firewall to do it right. That will require some additional bracing in the firewall area to keep the unibody strength up.

DriveFast7

iTrader: (1)

Stainless steel holds up to heat better than mild steel, so you can use thinner walled stainless and still take the heat and abuse of rotormotor. BUT I have noticed that the stainless header is a little louder in the engine compartment but no biggie.

My RB header cracked right at the sharp bend too. On the pipe for the rear exhaust port. I do think if I had more exhaust hangers it wouldn't put so much stress on that bend and might have lasted longer....

DIYMAN, haven't driven the rex on the street since 1999 right before the registration expired and I needed a Test Only Smog :-( Here's my webshots site including 2 pics from SS6:

http://community.webshots.com/photo/...99266323TkbdBR