2G: what exhaust are you guys using?

[Silkworm]

Custom, Apexi, Racing Beat, Mazdatrix, HKS 50mm, etc?

More to the point, what have you done to get your particular exhaust below sound limits if that's an issue for you and your region? Laguna Seca's got some serious restrictions, and I'm worried about it..

PaulC


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[plank]

We have a custom exhaust this year. What we did was do a straight through glasspack right behind the header pipe and then did a 90 degree turn right before the rear wheel so it comes out the right side. We fabricated two tips, one straight and one with a supertrapp. While we have not had any sound tests and in this area only waterford hills has serious sound regulations, the supertrap is quiet, my guess is we will be well under 90. Of course all our sound readings are on the left side of the car, so I guess having it out the right side will help on the readings.

Not too sure how long the glasspack will last given the high heat of the rotary. The tips come on and off in 10 seconds, we fabricated two quick release pins to put them on and off.

Dick Plank

 

[Aged racer]

Mitch Piper at Rotary Performance in Manassas, VA, fabricated a system for my 2nd Gen that uses (1) of the Dynomax mufflers available from MazdaComp. He ran a straight pipe from the header flange to behind the rear end, installing the muffler at the end of the pipe with a 180 degree reversible outlet (sound control is on different sides at Summit Point and VIR). This is what the R/P guys used at Summit, and they set the pace (aside from the odd E36 BMW). Evidently the theory here is a long, straight system adds to mid-range power. I forget the exact decibel readings, but it was well under the limit (albeit louder to the ears in the garage at home).

 

[NoRaceCarYet]

The old formula that used to be the big deal was to run 2 pipes, from the end of the 2 pipe racing beat header out towards the rear of the car, then collect them a foot before the rear wheels and go straight under the axle into a megaphone or supertrap (or better than that) muffler... Also building it out of super high grade thin wall stainless steel tubing was supposed to make the most power.

This was also the loudest configuration.

Some would also add an "H" pipe at some pre determined location to mix the exhaust pulses to help scavange the exhaust from the pipe, but I never learned where that H pipe was supposed to go and even if it was necessary.

I plan to run a single pipe to behind my seat, about level with the axle, with a down-turn at the end. But, I am building a Pro7 car, and we use the stock manifold, and with this configuration this exhaust is cheaper and makes as good power as any they've tested - just ask Dave Mazdatrix Lemon. 7's Only in Bakersfield, CA created this type, it works very well and with no muffler makes about 90 decebels.

K

[This message has been edited by NoRaceCarYet (edited February 11, 2002).]

 

[Karl Bocchieri]

I used to run a 3" pipe right from the outlet of a RB header to a single Borla oval muffler in the stock location and a 90 degree spout turned to the opposite direction of sound control. When they realy started to pay attention at LRP I had to put a 3" bullet muffler under the floor boards to make it quieter. The borla was about $200 and the bullet was a special order all Stainless Steel packing model about $100.

After reading some, I decieded to try two 2" pipes, colected to 3" just before they go over the axle into a stainless steel dynomax with the same 90 degree spout.
I think the 2 pipe system has more torque without losing anything in top end. I have no dyno numbers to prove it, but it seems to pull harder at low rpm (4000-5500). It also fits better under the car.
I found that putting a straight pipe (about 3 or 4 feet)on the muffler exit realy quiets it down. I'm trying to figure a way to bend up a 3" pipe to cross under the back if the car under the spare tire hump, and exit on the other side. I figure that the 4 foot of tubing after the muffler would solve some of the noise problens.

 

[BALLZOUT]

Karl, I belive you about the pipe extendo and if I could shave off some sound I will, these things are stinking loud, I ran on my test track ( limited use hwy.) for about an hour w/out a helmet and almost lost my sense of hearing. I will do the cross over trick, but I've got a better plan...I'll run the 3 foot of exsaust out side the bumper, that way when it gets real super hot on the last lap and second place is trying to make a move on me, I'll early brake and melt his urethane bumper to my car so he'll be stuck behind me till the checker !!!Rick

 

[Silkworm]

Thanks for the answers guys.

PaulC