12A rotor weights and compression ratios
 

There is much debate as to the various weights and compression ratios of the 12a rotors in the first gens. Mazdatrix lists from 76-82, the rotors were 10.15 pounds and 9.4:1 compression ratio. They also say that from 83-85, they were the same compression ratio but they went down to 9.6 pounds (these figures include the bearings but no seals).

I think they are wrong. I have seen the difference between a 79-80 rotor and 81-85 rotors and i know that the compression ratios are different. The 79-80's, I have been told, are 9.1:1 and I know that there compression dishings is deeper and wider. What I am uncertain about its the weight differences. I was under the assumption that the 79-80's were the heaviest, lowest compression rotors, and from 81-85, they weighed the same and had the same compression ratio.

If anyone has WEIGHED the rotors personally, and could tell me what year they changed weights, it would put my mind to rest. The more research I do, the more I find that the information out there is both vague and faulty. Mazda themselves said that the horsepower was 100 on the later 12a's when they infact went up to 115.

I hope someone has personally tested and can tell me.

When I crack open my '85 engine I'll let you know what I find. I've got a dis-assembled '81 engine already.

i got my 84 rotors all cleaned up, ill clean up one of the 82 rotors and weigh them at the post office, wanted to see if anyone had already done that to save myself the work...

The 84-85 are inded lighter than the 81-83 rotors. By about half a pound. Just need to find a set of 79-80 now

First and foremost the 79-80 rotors do not have lower compression than the later 12A rotors. They're 9.4:1 just like all the other 12A's. Take a gander at a factory manual for the '79-80 model years if you have any doubts. There is NO reason to doubt the technical specifications provided by Mazda for the introductory years of the RX-7 without evidence. Secondly where exactly is your evidence that the later 12A models had 115 hp? If Mazda had indeed squeezed 15 more HP out of the 12A, they would have updated the specifications, especially in the face of competition from other automakers outpacing the RX-7 in terms of HP and speed.

The worst thing about forums is misinformation being passed off as fact. Here's a fact:

Mazdatrix has built more motors than you will ever do. This is not a flame, it's a fact. If they have rotor weights listed, you can be sure that those weights are accurate.

Any speculation on your part is just that, especially when you discard technical information provided as 'vauge and faulty' with no evidence to back up your claims. Kinda sounds like your theory about steam cleaning a rotary and the killer carbon from the 5/6 ports on FC rotaries.

If you have EVIDENCE to back up your claims, present it. Otherwise label your speculations as such, not as fact.

any ways, i have 1980 rotors...... ill wiegh one, then as a set.... Ill tell ya what they wiegh (later today)


so tell me what the 81-83 and 84-85 wiegh and we will be set....

That's '83-85. Not '84-85. '83 engines use the same lightweight rotors as the '84-85.

I have an '83 engine - it has the light rotors and the same flywheel as '84-85.

I havent forgotten, but shit keeps getting in my way... just shit load of free work I keep getting stuck in..... shit...


Well, I will get it asap....

Laters, Andrew