IT7 engine differences

[Dano77]

As im currently stock pileing engines & parts,What are the external differences between years of engine & whats the most desirable cores to start with. 2 of the engines we have,have raised ridges around the spark plugs,2 are not raised and 1 has an auto trans flex plate attached. Interesting question as when looking for seal kits the question always asks "what year is your engine" Duh I have no clue it was in a pile out back.
Dan

[Weaver7]

Don't quote me on this but I believe you want the 79/80 intake can't remeber why since we haven't had our first gen for a few years now. I also think the 83 rotors are the lightest.

Bill Weaver
ITS RX7 #63

[Daryl]

It's been awhile since I've owned a 7. Be warned, this is by memory.

Not sure how complete, unmolested your motors are, however:

The 78-79 motors have points ignitions
80-85 distributors are electronic with ignitors mounted to the outside of the body, there may be differences in ignitors from year to year.

78-82 rotors are lower compression (teardrop shaped combustion chambers)
83-85 are lighter and higher compression.

81-85 Housings have the eyebrows around the spark plug holes.

83-85 have an oil to water cooler mounted beneath the oil filter as opposed to the type needed for racing that mounts beneath the radiator.

Seems to me there are probably some emissions/exhaust port differences as well.

Someone more knowledgeable will chime in soon, I'm sure.

[Dano77]

So no body but daryl knows the differences by loooking at a motor,come on if I show up with a 20j everyone would be able to tell. I just need to know if there is a casting number or stamp to say what it is?

[ddewhurst]

Anyone interested in a 79/80 intake manifold please make an offer.

Parts numbners

[mustanghammer]

Here are a couple of places to look:

http://www.wankel.net/~krwright/cars/rx7/manuals.html

At this site you can down load factory service manuals. This will give you part numbers that can be used for comaprisons.

www.mazdatrix.com

There are some rotor and flywheel weight listings at this site.

Earlier rotors are heavier but have lighter flywheels. Later rotors are lighter but have heavier flywheels. Counter balance weights are not the same between early (light flywheel) and late (heavy flywheels) 12A's. Those that have mixed and matched without rebalancing the assy have reported engine virbrations.

I have no idea which housing or iron is better. I am certain that a few calls to engine builders could shed some light on your questions.

A great place to look for vendors is www.rx7club.com

http://www.ludwigmotorsports.com/ - this guy is an IT racer

[johnny]

I about 10 diferent style intake manifold for 12A engine including a couple for the 77 RX3 SP wich have primary going to outer side housing better low end torgue but over all horse power is the same,, if any one need a housing ,, they are for sale, thanks

[joeracerx95]

Anyone interested in a 79/80 intake manifold please make an offer.

Parts numbners

Please save me some research time. 1) Is putting a 79/80 intake manifold on a '84 motor legal? 2) What do I gain by doing this?

thanks

[mustanghammer]

Please save me some research time. 1) Is putting a 79/80 intake manifold on a '84 motor legal? 2) What do I gain by doing this?

thanks

Answer to question 1 - YES. Per GCR page 329, C. Specifications in the second paragraph. All 12A powered RX7 made from 79 to 85 are listed on the same spec line in the GCR. This means that updating and back dating of components from 12A powered RX7s in this model year run is allowed. This would not support the use of earlier RX3, RX4, etc parts on an RX7, however.

Answer to question 2 - Don't know for sure. It has always been represented to me that the earlier manifold and the earlier carb top is superior to what came later. Currently I have an ISC early carb on a late manifold. The car runs great but I want to see if the 79-80 manifold is better. I also have a Yaw prepped late carb to play with. Guess I need to spend some time on a dyno.

It seems to me that the best way to answer your questions is call an engine builder that has been there and done that. You probably won't get answers for free....and you shouldn't....but you will get closer to the truth.

[miketrier]

I used to run a IT7 then sold it. I had a 1980 car with ISC prepared early carb and early intake meaning; 79-80. The flywheel was '82 with matching counterweight. I changed the flywheel and the '82 was considerably lighter than the original, about 7 lbs if I recall correctly. Acceleration improved noticeably. Supposedly, the 83-84 rotors are lightest and 81-82 flywheels are lightest. 79-82 rotors are same weight. I don't know about compression however. Best talk to a good engine builder like Mike VanSteenburgh at ISC or Jessie Prather at Prather Racing. I'm sure there are others as well.

[joeracerx95]

Answer to question 1 - YES. Per GCR page 329, C. Specifications in the second paragraph. All 12A powered RX7 made from 79 to 85 are listed on the same spec line in the GCR. This means that updating and back dating of components from 12A powered RX7s in this model year run is allowed. This would not support the use of earlier RX3, RX4, etc parts on an RX7, however.

Answer to question 2 - Don't know for sure. It has always been represented to me that the earlier manifold and the earlier carb top is superior to what came later. Currently I have an ISC early carb on a late manifold. The car runs great but I want to see if the 79-80 manifold is better. I also have a Yaw prepped late carb to play with. Guess I need to spend some time on a dyno.

It seems to me that the best way to answer your questions is call an engine builder that has been there and done that. You probably won't get answers for free....and you shouldn't....but you will get closer to the truth.

My interpretation of the updating/backdating rule is that in order to use the '79 intake manifold you must also use the '79 carb because together they make up the "induction system". Similarly you would need to use the later carb only with the later manifold. Are there other substantiated (survived a protest) interpretations out there?

9.1.3C "Any updated/backdated components shall be substituted as a complete assembly (engine long block, transmission/transaxle, induction system, differential/axle housing)."