I am about to do a little hybrid set up with 1983 gen1 sidehousings,REW rotorhousings, RX-8 rotors and counterweights. The engine is for a customer who shall compete in rallycross in September. The engine made 259 hp 6 years ago with a 51 mm Weber,RB headers and MSD 7AL2 with distributor. Now my new goal is 270 hp with some more porting and new improved exhausts ports and the higher 10:0 before 9:2 cr. Now i wonder if anyone has used the RX-8 rotors and seen some hp gain? As i can see it the little flanc cuts improves duration and fills the streetports earlier which improves gas filling and some more hp? But is there any drawbacks when you also have a bridgeport to? Hope to have the engine on a Superflos dyno in about 2 weeks.

/Lasse

 

on the rx8 rotors

 

Why? Is it becausse of the rotor flancs being 0.5mm shorter? Or is it the flanc cuts being to narrow of duration? Another question to you Manny is, why not RX-8 rotors please explain!

/Lasse

 

well, there is a lot f machining to be done to get the rotors to be used in the earlier 13b's. the compression ratio was more used for emissions than power.

you could just use the rx8 e-shaft (.5 lbs lighter!) and stat gears (much stronger and better for higher revs) with the s5 (89-91 9.7compression) rotors and have them lightened, beveled (like the rx8 rotors), and balanced.

the side seal placement and apex seals are a big problem to fit them in the earlier 13b's the cost will not equal the power. try what i posted. and you'll love the results...

 

Just noticed this thread. Figured I should chime in since I have a 13B Bridge with RX8 internals. I know it's not Gen1, but you might run across some of the same issues.

(There is another thread about it here if you want some details: https://www.rx7club.com/naturally-aspirated-performance-forum-220/full-bridge-port-crazyness-740643/ )

We did the build in an effort to try something new, plus finding good S5 rotors was hard and expensive, where as RX8 rotors are relatively cheap and plentiful. Even with the extra work, the RX8 rotors worked out to be cheaper (but I got a good deal on the rotors.)

2 main issues with fitting them:
The RX8s are of course all side port, so the RX8 Apex seals are not as long and strong as RX7 seals, and the lands on the rotors are not as deep. We had to get the lands for the seals machined with an electronic discharge wire cutter to allow fitment of the Racing Beat RX7 Apex seals.
The other issue was the side seals are positioned differently, and as such, the corner seal would fall into a standard bridge port template, so my builder had to create his own and shift things over a touch.
Also, had to use the uncut RX8 side seals and take them down by hand to get a nice tight seal.

The engine works and sounds great, and I'm happy with it. But having some issues with tuning (and between work and a new house, haven't had any time to work on it so far) with what look to be fueling issues at high RPM. Not a lot of cars like this out there, so we are basically just guessing when it comes to the Carb tuning, but we'll get it figured out.

I don't think we are really going to make a lot of extra power with the RX8 rotors, so, if you aren't just looking to try something new, and can get good RX7 rotors for a price where there is no cost saving, the extra work may not be worth it. That part is up to you.

 

I was on the Super flow dyno yesterday,but with bad results 3 side seals were stuck in the RX-8 rotors, causing bad compression. Engine started ok and idled at 2000 rpm for 20 min then let it cool off for 1/2 hour then it was hard to start and then suddenly the engine become unstable and would not take load. Did compresion test and at 180 rpm front housing was 6 bar or 90 psi but rear only 2 bar or 30 psi The NRS ceramic seals looked great and according to the Mazda compressoin tester it should have been 8 kg (120 psi) at 300 rpm. Now i'm switching to S5 9:7 cr rotors and beweled them like the RX-8 rotors,balance the package and go for the dyno again I choose to use the FB side housings becausse they were machined and hardened

/Lasse

 

Yeah, I haven't heard to much positive feedback on using rx8 rotors. Like sen2two said, just use the rx8 eshaft and 9.7 N/A rotors. Alot less hassle with better results.

 

from everything i've read (by people who have actually done it), i must echo what Redshft posted. it can be done and it can yield good results - good, not spectacular - but it's probably not worth it unless it's just something you want to do for the sake of doing it.

 

Sorry to pop your bubble, but

I am pretty sure the 83 Irons will not work with the REW housing, there would be no place for the water seals.

I cant picture it in my head, but i beleave that the water seals are in the rotor housing on the older motors (83 and older) and I know that the newer motors the water seals are in the Irons.

You just need to check that before alot of work/planning

 

There are rotary shops that cut the water seals in the 13b rotor housings for you ..

Hope that helps you confusion...

 

Cool, didn't know that one

 

what happened to the build

 

Which Rotor did you use?

 

From my research you have to be very aggressive with timing when using rx8 rotors. The different shape of the combustion chamber effects the burn rate and as a result standard timing numbers no longer produce optimal power.

 

in MI?