Rotary Miata
 

Hey all long time no see. I have been busy and I am getting close to being ready for my first race in this monster. Check out the build here youtube.com/@castellawspeed


https://cimg0.ibsrv.net/gimg/www.rx7...372750913e.jpg

Car looks great!

here is the engine bay for those that are wondering

https://cimg7.ibsrv.net/gimg/www.rx7...3742c6612c.jpg

I like your oil breather cap and coolant overfill reservoir.. . I also like how you got the wires through the firewall.

just curious, but do you have a tensioner on the alternator belt or have any issues with it being that far out?

I have an A/C mounted similar, but I have yet to finish hooking up and wasn't sure if I would need a tensioner. mine would only have one belt....looks like your has 2

It can be a bit of a pain to get tight. Depending on what you are doing this setup will be fine with 1 belt since it goes over halfway around the water pump pulley.

PS 39.5 in belt is what I am using.

Well I have now been told that I am offically to loud with the side exit. I had a insert in the exhaust before and it cut the performance so much that the engine would rev all the way out.

Any ideas on small bullet mufflers that can quiet the car down?

Supposedly blew a 113db at 10' on what I believe was someone checking on a cell phone.

maybe a custom lava rock muffler? search for that if you don't know about it...

did some searching that is very interesting. also came across some info that Borla makes racing rotary exhaust. might give that a shot if i can get it to fit. they are 2in in diameter bigger than my current muffler.

I have decided to attempt to build my own muffler. I have ordered the following:

3ft 4" dia SS tubing from summit
3m 3" dia SS perforated tubing from the UK since no one in the US seems to make already rolled perforated tubing
1/2"x24"x60" ceramic fiber mat that supposedly can survive up to 2600F sustained.

I am going to make a video of my whole process and hopefully figure out some way to make it rebuildable and servicable.

Go bigger than 4" on the can though. That's giving you less than 1/2" of absorption material. Bigger is better with absorption mufflers, as in cubic volume. Also, oval or irregular shaped cans tend to cut sound better than round ones.
Also as to the absorption product you have, it may or may not be ok, but rotaries are brutal on mufflers. It's not so much the heat but the pulses. You may want to make it rebuildable. Most people use stainless steel wool at least on the first few wraps on the perf tube if not the whole lot, but it's $$$.
Sick looking car btw. Looks very purposeful and well done!

Bullets aren't really going to do much. I run Borla XR-1 400373 and 400374s in series depending on the car. Haven't ever been flagged at the track other than Laguna.

^^you have an NA PP engine like he has or a turbo?

and for anyone else not reading the thread first, he can’t easily go bigger than a 4” OD for reasons that also were already stated.

edit: my apology, didn’t realize he had two threads on the same subject, those discussions were in this other thread:

https:/www.rx7club.com/race-car-tech-103/sound-limits-1163796/

however …

it would have been more considerate if you had told me sooner, since you knew I was already pulling everything together for you at all my own expense and effort as we had discussed, having already purchased it all and then being told of the new plan.

I don’t think your plan is going to work, but hope it does and wish you the best, despite feeling like you gave me the shaft.

what I had for you has no packing to replace or needs any maintenance, but oh well …
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Update:

The 3ft bullet muffler I built has lowered my idle db by 8dbs and I no longer have to wear 2 sets of ear plugs.

here is an album of the full build of the car. I update it regularly.

http://www.facebook.com/media/set/?s...3067557&type=3

glad to hear it worked out, seen a lot of MX-RXs started, but very few ever completed.

think mine would have worked out better for you, but life goes on and no hard feelings over what was only a mild annoyance at the time.

please keep us updated.
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Thanks sorry i didn't get back with you. i needed to get it done and you had been quiet. I may still get the design you have if this one dies since this is already my 3rd attempt at an exhaust to keep it quiet.

https://www.racingbeat.com/RX7-1986-...sal-Parts.html

Hopefully there wont be a round 4 for the exhaust, but If you need quiet...

Sadly those are to large for the exhaust channel I have built. Had one on my RX-7 and it was super quiet compared to this thing.

exhaust backpressure is a P-Port engines worst enemy.

did you try dynoing it with/without yet?
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