what year 12a is best?

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ok pony up guys, what year for best rotors,housings,fly/counterweights,intakes
 
Common practice is 84-85 motor (lightest rotors), 79-80 carb &intake (intake is slightly better, carb must stay with intake per the rules) and some would suggest the 82 flywheel and counterweight because its the lightest. I would argue that the 84-85 flywheel and counterweight have a lower moment of inertia and work just fine, although the big clutch from the 84-85 weighs a little more. Most suggest the 79-82 oil cooler setup, although the 83-85 water to oil intercoolers can be made to work.
 
Dave, if 81-82 flywheel which you can use with 79 rotors is lighter wouldnt that be the bomb?
 
The trick is... finding a 79 Motor with Rotors worth using. Dave L. has more parts than anyone around here, he would have trouble I bet..
 
All rotors from mid 70's to 82 weigh the same. Approx 1/2 lb more than the 83-85 rotors. Look for the engines that had a water to oil intercooler sitting under the oil filter. They have the lightest rotating assembly. If you want to use the 82 flywheel, you have to use the smaller clutch and change to the 82 counterbalance. Should really rebalance everything also, but apparently works ok for most people if you don't. I think that the 83-85 flywheel is probably ok, as it probably weighs a few lbs more but takes less energy to spin it because the weight is not located as far out from the center. I may be the only person who thinks this way, as common folklore suggests you should use the lighter flywheel.

The flywheel and clutch do not have to belong to the original year motor, but don't try putting light rotors in an older motor, sorta illegal and all...
 
which of these has less rotating weight

(1) 79 rotors with 81 counterweight/flywheel.

(2) 84 rotors with 84 counterweight/flywheel.
 
In most of the Pro7 engines we have built we are using the heavier 79-82 rotors. We like the shape, and consistancy, of the pocket in them better than the 83-85's (*NOT fully tested yet). The power we get seems to be ok.

The 79-80 side housings seem to work also - they have a slightly smaller port cross section (in the front and rears) than the 81-85's. Our view (*NOT fully tested yet) is that it helps bottom end torque.

We prefer the lighter 81-81 flywheel and front counterweight, and the lighter/smaller clutch.

But remember!! the important power gains are in correct jetting and timing -- which have been different on EVERY engine we have built.

(*) By that I mean we found a combo that works, and have NOT been willing to buy the parts, assemble an engine, break it in (for MANY hours), and do full dyno runs to find out if 83-85 rotors, and 81-85 side housings make LESS power. I am not at all sure they do.
 
thank you Dave and Dave, but you didnt answer the question though.
which of these has less rotating weight

(1) 79 rotors with 81 counterweight/flywheel.
(2) 84 rotors with 84 counterweight/flywheel.
 
Oh, BTW. Everything else being equal, I would do what Lemon says. He's built more engines than I've seen, and my stuff blows up anyway. My point is that weight and polar moment of inertia are 2 very different things.

Dave- Interested in finding out how the new rotors and housings work if someone else is buying the parts?
 
you will find out because thats what im going with.
84 rotors/81 fly/counter/79 housings
heres why.

quote from mazda comp

"The combination of 1981-82 flywheel and 1983-85 rotors is recommended because they are the lightest stock components available.
The complete rotational component group (eccentric shaft, rotors, flywheel, counterweights must be rebalanced when changing any of the components".
 
Correct me if I'm wrong, but somewhere in the GCR there is a section specifying the definition of an updating/backdating system and its relevance to engine balancing. As I remember, it says that the flywheel, eccentric shaft, rotors, and counterbalance are considered one system (or the piston equivalent). That means you can't legally mix and match different years of rotating engine parts.
 
oh, didnt i mention this was for the E/P 7 im putting together?
no actually my ITA/7 has to have a claimer motor that a group of us have agreed to, but I plan on doing what Dave L is doing this year and run some pro7(which the above is legal for) and E/P stuff as well this year, have four cars might as well.






[This message has been edited by 7'sRracing (edited October 25, 2001).]
 
Here we go again!
wink.gif


Engine is one assembly, clutch and flywheel are another assembly. Engine may be "balanced and blueprinted", and any "harmonic balancer" is permitted. Given that most of us are cheap, its easier to leave it however it is, and probably doesn't much matter for a stock motor. Recommended motor for ITA has traditionally been late model motor with 81-82 flywheel and counterbalance. I would guess that that came from people reading the rules and reading published weights, then assuming they had the best combo. Depends on where the weight is located relative to the center whether that conclusion is correct. Probably couldn't measure the difference if you tried, so I always stayed with the original flywheel despite it being 3 lbs heavier. Dave may have a valid argument for the rotor depression, plus the older rotors could go in the front or rear, whereas the new rotors are front only, rear only. I doubt if it makes a lot of differences, although it does seem like the different rotors like different timing.
 
Whoa boy! He's one of us. You know, the other Rotary Rich. (long story) Calm down and keep an eye out for that miller wabbit guy. Then use the rope...
 
Having never been in a position ($$) to just assemble and dyno ANY engines to "see what they do", we tried to learn as much as possible, as soon as possible, early in the Pro7 program. (Had never dreamed we'd need to try and get power WITHOUT a header, have to keep the shutter valve butterfly, and no carbon seals).

Rotating weight versus polar moment of inertia ARE two very different things - NEITHER one of which shows up on a normal (old and cheap) engine dyno !! (We use a 30+ pound flywheel on the dyno).

I assumed the lighter 83-85 rotors + lighter 81-82 front counterweight and flywheel would be the hot ticket (it's what we have told customers for years). Funny thing is, it still MIGHT be better ON THE TRACK! However, ON MY DYNO, the first engines we did, which had 83-85 rotors, wanted a LOT more ignition timing, and still were a few HP short of the later ones we built with 79-82 rotors.

Once we arrived at a "best" combo (on dyno), that is what we needed to stay with for customer engines (and my own).

(BIG) However, having now finished a year of these cars/engines (Pro7), and knowing what is in each of the engines we were involved with (built and/or dynoed), I can GUARANTEE that driver, tires, chassis, jetting, etc is a LOT MORE important than rotor / flywheel combo. --
 
thanks Dave and Dave, we haveta watch them wabbit varmits sneakin in here and such, ya know their a few parts shy where it counts of a real racecar.
besides have you ever seen a rabbit run on its front legs?

[This message has been edited by 7'sRracing (edited October 25, 2001).]
 
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