rx7learner

My first 12a blew a coolant seal. I disassembled it and posted pics of the rotor housings which were in very poor shape. I bought a low milage 12a from a member and just installed it instead of doing the rebuild. My old 12a was "supposedly" ported and recently rebuilt by MazTech in Largo (based upon the original owner)... but it still blew the coolant seal a few months after purchase and based upon the housing condition... I figured I was lied to about the porting and the rebuild.

I saw a 12a in craigs list local today for 75$. I figured I blow that in the movies... worst case scenario I would have fun doing the breakdown. I go pick it up and the guy gives me the alt, the nikki, a newer water pump, wiring harness, bags of other parts... and I look at the motor... and the housings look new... it looked like somone did a rebuild. I asked whether he did a rebuild and he said no... he said he bought it to put it in his vw but lost interest when he found it had no compression on the rear rotor.

I took it home and drained the oil and saw coolant... by the time I finished the teardown it looked like the housings were fairly new (no flaking, no end wear, and the coolant passages looked fresh. When I pulled the oil pan the bottom of the engine was clean.

Then I compared 1 of the plates to my old and to my surprise my old plates intake port looks like its about half inch bigger than the one I just tore down. All of the old plates had the same porting. Then I looked at the rotor housings old versus new and saw a huge difference in the exhaust ports.

Based upon the pictures could someone tell me what type of porting was done on my old plates & housing?

Is the idea of using my new housings that arent ported with my old end plates that are ported... a bad idea?

Could I make a template from my old housings exhaust port, and remove the exhaust sleves (such as was done in the old housings) and use my dremel to match the exhaust port? or is this really hard to do?

I know... alot of questions... but I'm just excited that I have good housings now...

Ay help appreciated... Thanks in advance...

KansasCityREPU

iTrader: (9)

Looks like what is generally called a "Street Port"

rx7learner

Thanks. I'm going to try to match the exhaust ports since my original engine performed well (good idle and response). Will make some templates.

Need to research how exhaust porting its done... I'm assuming its easier than porting the plates because rotor housings are aluminum. Still have some reading to do...

Hope the dremel will do the job.

trochoid

iTrader: (6)

Not to hot on that exhaust port, buy the RB porting template instead and study up over at NoPistons.com, engine building and porting section, on how to properly port an exhaust.

locopr1

Depends on what your goals are whether it is worth porting the exhaust. When you open the exhaust ports your timing is changed. exhaust timing is advanced, causing loss of low end torque a tradeoff for top end HP. IMO the factory ports are good enough if you have a good header/exhaust system in most cases.

rx7learner

Trochoid, is there anything particular about that exhaust port that you are not liking?

Maybe its my pic... Please let me know becuase it appears like its not symetrical in the pic...

Those exhaust ports with those intake ports felt like they made good power and it was Mazsport (not Maztech) that did the porting.

trochoid

iTrader: (6)

That's why I suggest you study porting over at NP, that way you can reconize what's right/wrong with the ports. What I see wrong first is there is no beveled edge on the exhaust port, that's a big nono. As far as size/shape, I would need to see them in person, or have them compared to other porting side by side.

rx7learner

Thanks... I'm looking at NP and studying........ Great resource!

rx7learner

Just need some final cleaning... but after reading over at NOPISTONS.COM I learned that there are many opinions on the exhaust porting.

Obviously Judge Ito is a master, however this very knowledgeable resource Lynne had a post regarding how he felt it would be necessary only in applications where over 8k rpms is frequented.

After contacting Judge Ito he recommended that I ship the housings to someone who could port since I never had done before...

I decided to try with my Dremel and I matched the port to the exhaust sleeve (PeeJay did the same on one of his posts)... Not going all the way up... keeping it more square on top (similar to the pics on mazdatrix) and putting in the angle at the closing end so that my apex seals dont wear because of a sharp closing end. I did not change the opening end. I also did not use templates but I made sure both matched.

P.S. everyone mentions the importance of eye protection but I would also like to mention gloves and long sleeves because those shards of finely shredded aluminum itch like fiberglass.