Hello guys, this is my first post on here been reading these forums for a good bit now. I bought an 83' rx7 that's bone stock around June 2025, I just recently got it running right and got rid of most the emission crap. I plan on making an exhaust here in the next week or so (RB header, 2.25" exhaust to a glasspack). I want to do some porting this winter and when I discovered the half bridge thought it'd be perfect for want. I want to be able to drive this car around town through the summer and make an occasional 3 hour drive home from college. I also want to be able to take it to the track occasionally and have some pepper to put down on the pavement.
however I also have been thinking about putting a weber on it which i think would kind of defeat the purpose of the half bridge because the SP primaries would come in at the same time as the BP secondary's, therefore I was kind of thinking about going full bridge. I'm a teenager still so I want all the power I can get and don't mind sacrificing some drivability for it, I do however want to be able to take it home every once in a while and be able to drive it when I want.
I figure with a half bridge I could always go back and go full bridge if I so desire I was just wondering what your guy's thoughts were, because I want to toss a weber on the car (they look the best and seem the most simple) but I don't want to defeat the purpose of the half bridge. I just want to make sure I know what I want to do before the time comes to port it.

 

Just full bridge and put a webber on it'll be awesome. Rotarys dont have any low end power to begin with so you aren't sacrificing too much, just make sure your exhaust isn't too loud and make sure to smooth out the ports nicely so you don't catch your corner seal

 

Low end power increases dramatically with a bridge port. It feels like the engine has grown another rotor.

What you can not do, half or full bridge, is drive at low throttle openings. You can't cruise unless you are loaded enough. It took a lot of screwing around playing with ignition timing and other settings to be able to drive at 60mph. Slower than that and you need to shift to neutral, coast down, shift back into gear and accelerate, etc. City traffic actually isn't as bad because you are never driving a constant speed anyway, so all you have to do is upshift at 2000-2500rpm to get up to speed and coast down in neutral again.

Maybe you could do it with a really REALLY heavy flywheel. Whats the point of doing the port and hampering the acceleration?

I had half bridge engines for something like three years. I went full bridge in 2012 and I don't see the point of half bridge, they had the same drivability, actually better with the full bridge because I went to four throttle ITB at the same time, but the full bridge just felt better.

https://www.rx7club.com/naturally-as...s-not-1003287/

I wouldn't do a 12A though. Parts are too rare and they can't rev. The thing is that they make power everywhere but then the power just never actually STOPs. Its electric.

 

That's what this guy on instagram looks like he's doing.

 

 

Thanks for the information everyone. I know very little about what is being discussed.

I would however like to mention to the OP about glass packs. If you were being literal about the glass, it will melt pretty quickly in a bridge port, if I am remembering correctly. As a rule of thumb, all rotary's will chew up glass pretty fast. Also, if I remember correctly.
You need something with metal substrates. There is a lot of info in the FD section about this.
My apologies if I didn't remember things correctly.

 

Thank you guys I do appreciate the advice I was kind of thought full was going to be the way to go other forums just had me thinking otherwise. And thank you for the tip on glass packs I never would’ve known that

 

I repacked my racing beat mufflers with high temp fiberglass mat.

That's the other thing... the engines tolerate NO exhaust backpressure whatsoever, to make one remotely quiet enough to drive on the street you need a pretty well engineered exhaust system. Unfortunately Racing Beat doesn't sell their good exhausts anymore and hasn't for quite some time. They are thin wall stainless now, which is garbage for noise handling, the presilencers don't have the "silencer chamber" in them anymore, and the rear mufflers are chamber mufflers instead of absorption mufflers.
the exhausts DO have the same flow but at the expense of noise, tremendous amounts of noise.

The exhaust system will comprise of mufflers basically from the engine back. I dont think anyone makes a suitable rear muffler so you may need to fabricate one yourself.

 

Well good thing I like obnoxiously loud cars 😂

 

With the super quiet exhaust systems they are still obnoxiously loud.

 

one of the PP cars ive done is running a stock flywheel, and it does smooth it out a lot. it is nicer on the street, but like you say, slower

 

i've learned basically four things about keeping these things quiet, without loosing (too much) power

First, once you port the thing, there is a LOT of noise from the intake. an airbox helps a lot. with my PP car, i fired it up without the air cleaner, and my neighbor came out of his place holding his head, and when i fire it up with the airbox, he doesn't, so i've tested it properly!

Second; the more muffler you have, in general the better. i'm thinking primarily size here, and Mazda uses Volume. the FEED exhaust i'm running in my FC has a muffler that is basically the biggest thing that will fit in the car.
it is hard to find big enough mufflers in the US. the FEED and old Mazda race mufflers were 8" round by 20-22" long.

Third: the tail pipe has a big influence on the noise. my PP car is running a borla 3", and it sounds nice, but its loud. if i jam a 2x2" tip on it, its much better. and with my FC, going from the 100mm tip to the ~50mm silencer is like someone took an equalizer and just zeroed all the bass frequencies.

and Four: the pipe diameter has an influence on the pitch of the system, a bigger pipe will have more bass frequencies, and a smaller will be higher pitched. a bigger system might help keep the high pitched lawn mower frequencies down.
depending on where or if you put a collector, packaging may be a thing

 

I used a pair of 1 3/4" washers welded into the tips of my new-era Racing Beat muffler to try to quiet it down. It helped a lot, and according to datalogs, airflow wasn't hurt one bit. If it choked flow this would be noted as running richer than before (speed density based EFI)

Still too freakin' loud though so I repaired/repacked my old muffler and put it back in. The inlet pipe had rusted off so I made a new one with some selection of 1 7/8" mandrel bends and a collector.

Barely the threshold of acceptable on the road...