rx7 exhaust routing

[benracin]

I'm going to be changing the exhaust on my car. Currently it exits before the rear wheel, passenger side with a super trapp. I was wondering how many people go over the axle, how many under, and with one pipe to the muffler or two?

I have a fuel cell in the back and it looks like it would be difficult to run pipes over the rear axle and not hit the thing. I could fix this by moving the cell more driver side, but that seems like a lot of weight on one side of the car (driver + fuel). I know I've seen some that just run it straight back under the axle. Does that cause some probs jacking the car up? I'd hate to damage the headers by yanking around on the exhaust.

Thanks folks!

Ben

[Speed Raycer]

I've got 3" that runs from the header collector all the way back, over the axle to a Flowmaster muffler.

That being said, over the course of the season, or maybe next winter, 75% of it is getting changed. The current exhaust pipe is too low and drags loading and unloading (heat sheilds were still on the car when I got it) and the header is a RB street header (collects into one pipe). I'm going to run two 2" pipes and collect them just before the axle. Not the best, but much better than the current setup. I'm also thinking about adding some length to the headers up at the exhaust ports. Everything I've heard about the rotary is the longer the exhaust, the better.

Also, make sure there are plenty of exhaust hangers. The header should NOT be supporting the weight of the exhaust pipe. I believe Mazda suggests like 5-7 hangers or something like that. Remember also, that the pipes will grow quite a bit so you don't want them to be so rigid that they become stressed when hot. Mine had one hanger back by the muffler. It was truly a hanger. Nothing but a 1/2" bar bent into a hook I added a couple more.

How big is your fuel cell? My 10 gal. cell leaves plenty of room.

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Scott
It's not what you build...
it's how you build it


[This message has been edited by Speed Raycer (edited February 27, 2004).]

[benracin]

As far as I can tell it's a 15 gal. I think it might fit, but it's going to be close to the cell. I think some folks place some heat shielding on the cell to keep those temps away. But how close is to close? I know the previous owner had an exhaust system going all the way back with double pipes going back and over the axle then merging right before the muffler. I have those pipes and muffler actually. I don't know if that exhuast was pre fuel cell or not though.

[Scott Nutter]

This is what I run, a Racing Beat header (2 to 2) then the Racing Beat mid section with presilencers then two pipes straight, well slightly bent, under the axle and out the back.

I have hit 100db, but then again I am a turd, and shift @7200, well that's when the light comes on

Jacking the car up is usually not a problem because I jack the rear up from the pumpkin.

[lateapex911]

Ben, you're a second gen car, right?? Or am I confused?

If a first gen car, then....I run under the axle. The pipes get beat up when Madison forces me off at the kink on No Name, but thats ok, going straight is rumoured to be the better power producer.

(And when you have as few as these engines have, you want to count every last one!)

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

[benracin]

Yep, it's a first gen. I think straight just might be the way to go. Seems fairly easy to make. Can you still lower that side of the axle if you need to though? Maybe un-hook some of the exhaust mounts after things have cooled off?

[lateapex911]

Yes, it does limit axle droop on the right side, but it's rarely an issue.

I have a bracket right there, and in the back to drop the system. 4 minutes and you're good to go.

(But, plan on it getting a bit ground under there....are you good with a MIG?)

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

didnt we already do this guys? heres the under the rear end duals.

http://www.calclub.com/gallery/showphoto.p...&cat=500&page=1

[Allen Brown]

7's....In the photo of your dual setup...Is this a separated duals (one pipe for one rotor), or do you have a merge location of the dual pipes and it then separates back to duals?

Under the rear seamed to bring my GSL-SE to life...

there separate although a crossover I have considered.

[benracin]

I've got a 1st gen. I've seen some use exhaust tape for that under the axle area to try and take some of the ground hits. I wonder if welding on a little nub of like re-bar or something would help this. Like a bump stop.

[lateapex911]

Originally posted by benracin:
I've got a 1st gen. I've seen some use exhaust tape for that under the axle area to try and take some of the ground hits. I wonder if welding on a little nub of like re-bar or something would help this. Like a bump stop.

Yes! A skid plate is in order!


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

[miketrier]

ISC and SDJ both use a single 3" pipe that goes over the axle. Their cars seem really fast in SEDEV. I had a 2-2" setup that went over the axle and changed to the 3" at the end of last season but haven't raced with it yet. I am using the same single dynomax ultra muffler on both. I prefer going over the axle to avoid dragging and damage.

[RX767]

Ben,

The exhaust was an issue two years ago when I noticed a crack leading to a hole in the bottom of my header while prepping the car for a race. The Racing Beat header I ordered would not line up with the three inch single pipe exhaust that came with the car. After talking to people at various Mazda suppliers/prep shops, I went with the following set-up:
- Racing Beat header
- two 2 1/4" pipes (Racer Parts Wholesale)
- Flowmaster collecter prior to the axle to single 3" (RPW)
- Various 3" inch exhaust pieces from a NAPA supply room that made the best trip over the axle.
- Connect to muffler that came with the car

I have never had a sound violation. Also, unless you have a lift or are extremly talented with a mig, take it somewhere to have it welded. After rolling on the ground and complaining incessantly for a couple of days, my wife was sick of listening to me and talked me into it. It was the best $100 I spent.
When I installed a fuel cell and G-Force's panhard suspension piece, I needed to have the 3" parts taken apart and readjusted. I also have a heat shield installed between the exhaust and the fuel cell. Be careful with what you add to act as a skid plate so that it doesn't look like the 4th of July under the car to initiate a Black Flag. With whatever setup you go with make sure the exhaust is supported under the car for those off course excursions. I was able to reuse the stock J-hooks and rubber eights for support.

Bill Emery
Glen Region
ITA#23

[benracin]

I think when the guy before me put in the cell he kind of put it more towards the passenger side so going over the axle would be pretty interesting.

I just remembered a good question though. Isn't there a top secret formula for how long the exhaust is supposed to be? Like "it needs to be X number of inches to work the best". Of course I could be asking for some really top secret info. I promise I won't tell anyone though. And I've currently using the RB header so it will probably be a two pipe into a single pipe deal.

I just can't wait to be rid of the supertrapp. Although it's neat to sound like an airplane, it's not really that manly.

[joeg]

I just can't wait to be rid of the supertrapp. Although it's neat to sound like an airplane, it's not really that manly.[/B][/QUOTE]

"Manly"??? As in a chainsaw?

Here we go.....

[ddewhurst]

While the GOOD guys are talking about their exhaust systems I have a question. Does everyone weld the system pieces from the header to the out end or are some people using other methods ? Example IIRC one house showed a three piece system including the header. Weld it all or other methods ?

Have Fun
David

[lateapex911]

Ben, shoot me an email regarding the proper length....

My system has flange at the header, two pipes to a slip fit into a collector. I welded threaded fasteners to the sides of the two pipes, and use allen cap screws to attach the muffler collector to the pipes. And a hanger at the back of the muffler.

And using the term "muffler" for that big tube of rocks has got to be the most tortured use of the word ever! Sheeesh! With a flashlight I can see the exhaust ports!

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

Originally posted by benracin:
I've got a 1st gen. I've seen some use exhaust tape for that under the axle area to try and take some of the ground hits. I wonder if welding on a little nub of like re-bar or something would help this. Like a bump stop.

mine has never touched the ground, dirt yes, asphalt no. I was playing with my rear brake bias on a friday practice and went for a wild ride
in the dirt, lucky I didnt flip it.

David, mines all welded except the flange, should you catch it anything(car trailer), slip on's with clamps might pull off.

[theenico]

Supposedly, the magic formula for the twin pipe setups is to use multiples of 2 ft. For example, the systems I have built use a twin pipe header (2' primaries) and 4' long pipes (for a total of 6 ft. from the exhaust port) to a Burns 2 into 1 merge collector and 3" diameter pipe over the axle to the standard Dynomax ultra flow (filled with lava rocks)

As a side note, don't use aluminum rivets for the cover panel on the "modified" muffler. It makes a huge mess if the car backfires

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Nico
KCRaceware (816) 257-7305
[email protected]

[This message has been edited by theenico (edited March 08, 2004).]