Matt_S3_RX7

Hi guys just wanna know what are high compression rotors? and where would they be used? what advantages would they have over normal?

Im planning a EFI NA 13B BP and looking at all the ways i can cut out the fat (lightening) yet keeping the engine strong. Any suggestions?

rxtasy3

iTrader: (2)

those high compression rotors u speak of would be the N/A rotors, ranging form i think 9.5-9.7 to 1. the low compressions rotors would be from the T2(turbo) and were i think 8.7 or maybe 8.5. not sure of the yr but i'm thinking somewhere in the late 80 early 90 that had the lightest N/A rotors.

clean85owner

S5 NA FCs had the highest compression rotors, they are also the lightest, IIRC.

Matt_S3_RX7

Cheers for the replies but im still confused.

Im only aware of the High compression rotors from reading this forum, i havent heard mention of them in any of my ref material.

Im interested because im looking at buillding a 13B EFI BP or Extend Street Port, with lightened everything. (series 5 turbo engine is what i have in my posession at present)

Engine building is new to me and id like to use the best parts for the job. so the whole "high/low compression rotors" has confused me?

Do factory NA engines have High and factory Turbo use Low?

Just here to learn. Cheers fellas.

Matt.

trochoid

iTrader: (6)

Correct, NAs use high comp rotors, turbos low. The S5 NA would be your bet choice for high comp, low weight.

mikewoodkozar

What about the RX8 rotors? Arent they the lightest of the bunch with high comp?

orion84gsl

iTrader: (5)

I have heard that the RX-8 has the lightest rotors too, but good luck finding a set without removing your shifting arm and clutch leg for payment.

Matt_S3_RX7

Hmm RX8 rotors huh? i never thougth of that. Ill look into it. Is the price a bit outrageous? what are RX8 Rotors going for?

Jeezus

iTrader: (4)

I think they are around 4-500ish a pair. Check the RX8club.com, I think there was a guy selling 2 rotors complete, but need a few side seals to finish for like 300.

markusj08

iTrader: (1)

Well here is what i have. Yet hey are for 12a.

Race Rotor on the top. (higher comp)
Stock Bottom.

Matt_S3_RX7

Just checked mazdatrix, they have a light weight rotor kit for $2200. thats plenty-o-cash.
Wonder how they would go in a series 5 13BBP (injection perfection EFI) with a lightend ec shaft and flywheel?

derwankel

I have seen lots of "discussions" and mentions of this person or that person maybe thinking about using RX-8 rotors and even e-shaft. It seems to me that one can get pretty darned close to, and perhaps even better NA HP output from a set of ported 12A irons, ported exhausts (peripheral housings ala 84-85 GSL-SE) and RX-8 internals (rotors, stationary gears, e-shaft) with superior exhaust flow.

I am not aware of any OEM rotors with higher compression than the RX-8. My question is, has anyone actually done this ... used the RX-8 internals that is? It seems to me that if nothing else, the RX-7 community stands to gain considerably from the RX-8 production of better (lighter, higher compression) internals.

I am no expert by any means, but I am wondering if there is some engineering reason this has not been done. Perhaps it has, and I just have not seen the posts.

Matt_S3_RX7

Agreed.

I also havent seen or heard of any. IF a 13BBP can achieve such high HP with pretty much just porting modifications what could a lightened modern internal engine achieve?

Crit

iTrader: (6)

Well let's get this RX-8 stuff figured out. If they move on with the 16X and the trochoid grows, the RX-8 will be the last possible source of good frankenrotor parts.

I don't know what the extra control ring does in an old set of irons, but someone figure it out, let us know, and we can all move on to what will be the pinnacle of guts-swapping. It's kinda cool being able to see the end of the road for internals as we know them.

derwankel

So I took the liberty of posing my question to Racing Beat and here is their reply:

It is possible to use the RX8 parts in a '84 Rx7 housing set, but there are problems: The rotors fit, but the shape of the 2mm apex seals is incorrect (wrong radius for the rotor housing); The statiionary gears fit but the front requires different thrust parts assuming you use the RX8 front balance weight and the rear requires machining either the gear or the rear housing for an o-ring; and the eccentric shaft fits but has larger clearance on the main bearings; And of course the entire assembly must be balanced.

We recently built an all-aluminum peripheral port intake engine with RX8 internals. The results hinted that it might make slightly more power, though that was not sure. The engine definitely needed less ignition advance than is normal for that type of engine.

Jim Mederer


When in doubt, ask an expert ... Thank You Jim!!

Matt_S3_RX7

Hey thanks for that, you have saved alot of people alot of time and money.

Its a shame that these particular internals are not as compatable as i assumed, but it answers the question why we dont see so many.

So has anyone here Have or Built a 13BBP EFI NA with lightend internals? im interested to know how much reliable power you can get at the wheels without turbo.

mikewoodkozar

^ That is good to know, if i were you i would go with S5 NA rotors

trochoid

iTrader: (6)

If you plan on boosting the S5 engine, use the low comp S5 rotors, tuning will be easier along with a greater margin of error for mistakes. If staying NA, find a set of S5 NA rotors. While you can make more hp with NA rotors at a lower psi, many times it's not worth the risk unless you or your tuner has plenty of dyno tuning experience.