The_7

racing beats race rotors for the 12A are modified 74-75 rotors - are these lighter than the 81-85 12A rotors?

Sk8r_dude

donno...if i rebuild, i want renisis rotors, no word on if they'll fit yet...

hornbm

dont know if theyd be lighter, but the comnpressions would sure be a hell of a lot lower.

The_7

really? why? im building an n/a so anyone know where i can get some lightweight, normal comp ratio (or maybe a lil higher), 12A race rotors?

1987RX7guy

iTrader: (3)

The RENESIS is a 13B so I don't think the new rotors will fit a 12a.

REVHED

From looking at the RB website it seems like the only thing they do to the rotors is install the circlip. If you're worried about the compression you can have this same process done to any rotor you want as well as lightening and balancing.

But, I'd find out the compression first. I can't seem to find any numbers on the 74-75 rotors but I know that all 76-85 12A's have the same compression.

The_7

well stock compression is fine for me because when you raise compression you drop displacement. im really interested in lightening tho, what is actually involved in the rotor lightening process?

REVHED

These are some lightened rotors. You can see where the material's been removed.

diabolical1

iTrader: (3)

come again?????
the crude explanation is that they basically grind away the sides of the rotor that seal against the intermediate housings. they just leave contours of the original material so that they can support the side, corner and rotor o-ring oil seals.

they do them in pairs and for extra money they can balance your rotating assembly, but you'll have to send the shaft, flywheel and main pulley with the rotors.

EDIT: okay, Revhed provided pictures while i was responding, so there you go ...

The_7

how much do stock 81-85 12A rotors weigh?
how much approx. weight can you lose safely before the rotors become to fragile?

diabolical1,

to raise the compression of the engine you can have a smaller indentation in the faces of the rotors. this decreases the volume at BDC and TDC by the same amount, therefore making the compression ratio higher. but since you have a smaller indentation the displacement drops.

Rx7carl

http://www.mazdatrix.com/faq/rotorwgt.htm

Ahhhh, thats the million dollar question. Anyone who really knows the answer to this will not tell. You dont want lightweight rotors anyway dude, unless you just hit the lottery?

mwatson184

I disagree with that displacement and compressions statement. There will be an equaly smaller volume at both bdc and tdc when you raise the comp, so when you subtract to get the displacement it will turn out the same as with the lower comp. The volumes will be lower, the disp will be the same.

The_7

isnt displacement volume at bdc?

mwatson184

Nope displacement is simply the difference in volumes.

Think of it in non car terms, what does it mean to displace fluid in a bucket? The bucket has marks to measure volume, and the fluid is at 4 liters. You have an empty 1 liter bottle and stick it inside the fluid, it will raise to the 5 liter mark. 5-4 = 1 liter difference, or 1 liter of displacement.

-Marques