Has anybody done this? Any issues clearing the rear axle during full jounce? Pics?

 

I hope you discover the answer to this before I do!

I'm putting a shopping cart together for ubends and such. I was thinking of using the oval pipe for ground clearance -- have you given any thought to that?

 

Why? You don't need 4" unless you plan on making something like 400 ish hp with a single exhaust..

 

Well he's got a 13b-re with a GT35R. That combo can make more than 500hp

 

Yes, that's exactly what I'm shooting for. I believe 500 is achievable on my setup, so I would like to plan accordingly.

 

Ohhh lol. My old parts car had a 4" it fit fine. Was straight from dp to muffler no resonator. Probably stupid loud

 

total overkill. 4in is needed for at least 500+hp, which in of itself is total overkill in a first gen.
3in should be more than enough for any turbo swapped first gen.

 

It's very presumptuous to assume you know my goals or needs.

 

I got a 4" muffler on, it doesn't sound bad and I don't have clearance issues at all. I know this question is about a full exhasut, but at its widest point my muffler is approx 5.5" in diameter and I've never hit it on anything.

 

You said your goals were 500hp right? You don't need anywhere near 4" exhaust for 500hp. You don't even need 3" for that. I think your making things harder than they need to be.

That being said I ran 4" under the radiator into a 2.5" muffler with a 60mm WG as an exhaust dump. It's quiet and flows a ton with the dump open. Lighter than a full exhaust system as well.

Good luck!

 

Yes, I've considered oval. I ran calcs on the sectional area of different tube sizes (attached), and you'll see that the oval tubes will flow slightly less than a round tube of the same nominal size, while being 1.25" shorter (in the case of a 4"). This is all OK, but the issue is that I think the difficult area will be over the axle, and I haven't seen an oval tube that is bent around the narrow diameter. I don't think I'll have a clearance issue anywhere else, even with a round tube -- and round tubes are cheaper.

If you do want to go oval, SpinTech has mufflers that aren't much taller than the tube.

 

I didn't say what my goals were, but your setup is very interesting and innovative. I don't do drag racing, so I'll need a full exhaust.

How well does your crankcase evac setup work? Did you use a check valve?

 

Ah sorry, seems like I always miss post when using my phone. I read the 500hp statement by Dysfnctnl85 and thought it was you.

What size housing is on the gt35r? whats the minor diameter on the exh. wheel? What kind of power you shooting for? I was pushing 640 whp on the dyno through my 3" exhaust the full length of the car. I removed it and went with an open down pipe and had zero gain. Just food for thought, I can't see 4" going over those axles easily at all. Even 3 looks like it would be a bear.

Yes. I run a check valve. It works well in the revs, and even pulls a little at idle. Took this video but it's hard to see. In person you can clearly see it trying to suck the plastic bag in.

 

I'm planning out a similar build. It'll fit with some coaxing and a different rear end setup. Sorry, I'd prefer to keep the details a bit secretive, but you should find some room for this without a problem.

To the "you don't need that size piping" group of people, you have to remember that rotaries generate a LOT more heat than reciprocating engines. When you go to larger piping, EGTs go down...Talk to diesel guys. I'll also be running a 4" after I do my 3" NA setup shooting for max power stockport.

Go .120" wall, use resonators, and wrap accordingly. I still don't understand how so many RXs sound tinny...It's the stupid 1mm piping that these stupid JDM companies keep selling off as quality. That's 3x the thickness...trust me, it makes a difference.

 

I'll be watching you...

EGTs are my primary motivation.

 

Where are you getting this information from? It’s just plain wrong. The exhaust/EGT is no hotter in a rotary than a standard recip engine. In fact rotaries run cooler combustion temps than standard recip engines. Also the motor is tiny, with tiny combustion chambers displacing very small amounts of air each combustion event. Yet another reason you don’t need a massive exhaust system. Especially on an NA setup. What they do have is rapid exhaust pulses which is why they are hard on exhaust parts and can drive larger turbo hotsides than a recip of the same cubic inch.

Now I’m not saying to throw some Honda muffler on there with some 1.5” piping. But 3” exhaust is more than enough for almost all Streetable applications IMHO.

 

RacingBeat as well as a dozen threads on this forum.

http://www.cumminsforum.com/forum/98...ower-egts.html

http://www.racingbeat.com/mazda/perf...y-exhaust.html

https://www.rx7club.com/2nd-generati...rouble-657058/

https://www.rx7club.com/rotary-car-p...so-hot-492812/

https://www.rx7club.com/1st-generati...t-temp-683748/

http://www.nationalspeedinc.com/gear...rotary-engine/

http://*************.com/rotary_foru...ead.php?t=8750


What you need to understand is that both Elwood and I WILL do the 4" exhaust, he just wanted your opinion on whether or not it would fit, not criticism as to why he should go with another size.

 

i'm running 3" under the axle, and its fine, plenty of clearance. 4" would need to be oval there.

if you guys are that worried about running 4" all the way back, you should be worried about the bend over the axle too, going under = straight.

 

Oh, I understand completely. Just don’t agree with the logic behind it. Which is fine, we will agree to disagree.

Just making a point. At a certain point going bigger on the exhaust will gain you no additional HP. For the same reason a 8” exhaust pipe isn’t going to give you anymore power than 4”. If your not building up back pressure in your exhaust then you don’t need larger pipe… period. If I were trying to get the most out of an NA exhaust system I’d keep the exhaust pulses separate the length of the car with a smaller diameter pipe. 2 2” pipes are much easier to run (and make 10x more sense) than 1 4” pipe. And even that is overkill.

Obviously turbo applications will raise the EGTS a ton, but no more than a recip. In factory form mazda throws a ton of emissions equipment on and the exhaust temps can be high. (mainly the turbo models) This is done in a effort to clean up the emissions and doesn’t apply to straight pipes and racing.

An NA rotary with straight piping will have lower EGT’s than a recip of the same displacement. It’s a fact. Rotaries aren’t as efficient and spit out a lot of unburnt fuel per combustion cycle that results in lower CC temps.

Those links don’t tell us much. They seem to be worded to sell aftermarket products and are vague at best. Racing Beat makes me laugh… 2000 degrees yea right! You got problems if your seeing 2000* EGT temps. Pushing over 30psi through my 13b I’d never see over 1600*. The forum links have no factual information what-so-ever! A bunch of toddlers comparing the color of their muffler tips doesn’t tell us jack about the recip vs rotary EGT’s. Wiki search wankel engine or similar sites for real information and keep away from forum “tuners”.

 

Could you split to two-2 1/2" or two-3" pipes over the axle?

just a though, I really have no idea if it works.

 

I considered this, but I have a horizontal Watts Link, with the central pivot on the bottom of the pumpkin. I don't think a straight exhaust will fit under my Watts arms.

Can you post a pic of your setup?

 

yeah that doesn't look good... i think your link is right in the way.

i don't have pics, but i could take some

 

I even considered a side exit. At my last track day, I saw an IROC Camaro with a single passenger side flattened tip that exited just ahead of the rear wheels. It was well executed . . . and the car went like stink.