Exhaust routing

All,

I'm working on putting together a new exhaust setup. I'm relegated to the stock exhaust manifold, and 2.5 inch pipe before the rear axle.
For muffling I've got 3 inch inlet/ outlet dyno max ultra flo (round). From there it seems simple; just connect the bits, right? My questions are:
A) How much power do I lose going over the axle instead of under the axle?
I would go under the axle except I'm worried about getting the car on and off the trailer. (I already use 2X10's with the "stock" 4 foot ramps and jack the nose of the trailer waaaaay up) Any war stories or reassuring words for that? Has anyone else ran into this probelm? If so, how did you solve it?
B) Will this setup have any problem meeting 103 db? How about 90 db? With the 2.25 inch pipe and the dynomax super turdbo on it now, the thing is very, very quiet. with a 2.25 inch side pipe (no muffler exiting in front of the rear wheel) its pretty loud...
C) Any guesses on power gains?

thanks all!
Marcus

I can't give you an idea of power gains, although when I built my system, I was given the impression that rotaries are VEEEEEERY sensitive to exhaust backpressure, so I went under the axle.

It's been about 5 years, and the pipes are showing the abuse. Not from the trailer though! From my taking to the grass and curbs to aviod "incidents"! The part that rubs getting on the trailer is the very back of the muffler. It projects too far down.

Besides that, straight is easier. But weld on a rub plate just for giggles.

With a header, my sound is always around 101 or so.

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Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]

Many of the fast cars in SEDIV go over the axle. It's what's recommended by SDJ and sold by ISC. My only other advice is "GET A HEADER"
IT7 #99

Thanks for info guys,

I'm going to size it up when I put the thing on the trailer, and stare at it soome when its on lift at the shop.

Now for the dirty secret!
I can't run a header, becuase its actually a NASA Pro7 car (running in Norcal) I intend to get my feet wet, and maybe run a season next year of NASA, before building another IT car to run in SFR SCCA. This gives me a year to begin learning the limits and get comfortable in the car.Then, I can transition over while my brother spends a year in NASA. Two years from now, the goal is a two car attack; maybe an IT/ enduro car and a wreck Miata.
For the record, pictures of the car here:
Http://www.miller-motorsports.com

(Ducking the inevitable stoning)
Marcus

[This message has been edited by Marcus Miller (edited June 23, 2004).]

Quote:

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Originally posted by miketrier:
Many of the fast cars in SEDIV go over the axle. It's what's recommended by SDJ and sold by ISC. My only other advice is "GET A HEADER"
IT7 #99

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Any idea why SDJ and ISC both recomend going over the axle?

I use an ISC exhaust. As far as I know the reason they built their new exhaust over the rear axle is because it has a three inch pipe running all the way back instead of two 2 inch pipes. It helps a lot with ground clearance and the axle wont sit on it when I jack the car up. Plus its a whole lot easier to work with.

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Jeff Ryan
SeDiv IT7 #47
"My tires are gone, the brakes are shot, but the nitrous I still got"

my exhaust used to run under the axel. for the longest time i fought a problem with locking the right rear under braking untill i figured out the the exhaust was a droop limiter. I lowered the hangers and the braking problem got better. I have since redone the exhaust over the axel. while i can not be sure about power, at least i can change springs without unbolting the exhaust.
dick

Marcus,

The Pro7 exhaust is a big compromise at best. The best all around exhaust we ran was into a 3" dynomax and turn down infront of the rear axle. That is the setup we ran on Mike Tolmans(ps2 champ,Pro7 champ) car for years and we never down on horsepower. I used to run a Racing-Beat turbo2 pre silencer which was 2.5" straight through turned down before the axle. It lacked a little torque out of the corners but would pull the whole front straight at Thunderhill. We ran a similar set up with 2.25". It was awesome out of the corners, but ran out of go at S/F.

If you are trying to make an exhaust that will work when you change to IT trim, I would go mandrel bend 3" over the axle.

Good luck,
Eric

By the way we never had a problem with sound even at Laguna.

[This message has been edited by wlfpkrcn (edited June 24, 2004).]

Thanks for the help and ideas everyone!

Eric, you didn't have any problems with overheating the components under the car by running a turn down, I take it?

I tihnk I'm going to have it bent 2.5 inch with a flange so that I can try the turndown in front of the rear exle, in the future.

thanks!
Marcus

Marcus,

We never had a problem with exhaust in the car or overheating of components under the car. Initially my exhaust ran out the side in front of the RR tire. I just ended up banging the exhaust on everything and changed over to a turndown.

Marcus, you gonna get your license soon?

Hey Eric http://Forum.ImprovedTouring.com/it/smile.gif

PaulC
#33 PS-1 RX-7
NASA NorCal

Hi Paul!

Since we are talking Pro7. Has my car been out at the track this year? It is red with a single white stripe. Similar looking to the California's Best car. Someone called me a while back and purchased it from the guy I sold it to. He said he was going to run NASA events. Just curious

Paul, I'm thinking of running Bondurant this winter, then the SCCA school in the spring

Bondurant; because I've always wanted to, the SCCA school since its nice and condensed. I'll keep my fingers crossed all goes well, and I'll be racing next year.

Eric, It might have been in Reno, I looked through my pictures, but didn't see it. That car might be the only car I don't have a pciture of... (Naturally!)
Marcus

"It might have been in Reno"

That is very possible. The guy I talked to lived in Sparks. Atleast it is being used.

And its on! http://Forum.ImprovedTouring.com/it/smile.gif

The old muffler:
http://images.miller-motorsports.com/misc0...04/P7030191.JPG

What's left of the old pipe:
http://images.miller-motorsports.com/misc0...04/P7030202.JPG

pretty straight:
http://images.miller-motorsports.com/misc0...04/P7030203.JPG

Over the axle:
http://images.miller-motorsports.com/misc0...04/P7030217.JPG

The muffler(1):
http://images.miller-motorsports.com/misc0...04/P7030218.JPG

The muffler(2):
http://images.miller-motorsports.com/misc0...04/P7030220.JPG


Sounds great, fits well, a definite improvement over the previous system, maybe not ultimately the most powerful, but good enough for now.

Thnaks for all the help!
Marcus

[This message has been edited by Marcus Miller (edited July 05, 2004).]