Maxthe7man

Bringin this thread back to some sort of sanity..


To the hardcore builders, what do you think is the most overlooked part of the assemble upon rebuilding, I would think the greatest cause of low compression on rebuilt motors would be not lapping the side plates and shitty side seal sealing.. When you think about it, thats alot of real estate to seal on the sides of the rotor. Only a few shops have the ability to lap the side plates,maybe thats difference between a 150 psi motor and 70 psi motor..Max

Dragon

That is a good point, but I think a engine that had that low of compression due to side seal sealing issues would also have quite a bit of blow-by past the oil control rings as well, especially at high rpm...

any time you come out in to the corner seal ride area on the side port or up on the exaust port you increase overlap and will loose cranking compression. ie. a brige ported engine won't idol at 1000 rpm and will show very low compression on a compression check. But will make power to 10-12k rpm where the side port will fall off at 7500-8k or so..

Resource

I pulled on the ZO6 spraying a 100 without a boost controller yes.

Thanks for reminding me of my great kill.

radkins

I got dibs on Kyles useed motor!

Chronos

something tells me Resource is to these Forums what AIDS are to humans.

It sounds like you have some serious rotary tuning expertise. Let's take a look at Resource's thought process in creating such an amazing machine...

"RX-7's are SOOO bling! I gotta have one! Ok, I wanna go fast in a straight line because that's what I'm good at! Let's see...all I need is a big turbo and lot's of nitrous. Wow! I was able to "pull" on a stock car while only sacrificing 4/5ths of my car's life!! YAHOO!! Let me reminisce on my eXtr3mE 0wn4ge and str33t r4c3r prowess..."

Maxthe7man

I would say Dragon, you are probably 100% correct with that, the place that built the my 13bt that just bit the bullet, as far as I know, does not have access to side housing lapping equipment, therefore the sideplates probably went into the motor unchecked and unlapped, at any boost above 14 psi, I had tons of oil coming out of the the breathers on the motor, from excessive blow by, and only 70 psi per rotor shortly before death..
I know what you are saying about the overlap and port duration.. In a piston motor, as we increase camshaft overlap and duration, as a rule of thumb, we raise the compression ratio in order to stop the motor from being a low rpm dog, and hard to start, now in a rotary, this would seem to be the place to start using 9.4: or 9.7:1 rotors in large port applications, it would also most likely help pull the power band down a bit from such stratospheric levels.. low compression rotors are good for high boost, however like you say with large ports, you need to recover the cranking pressure somewhere..
I have a set of 9.4:1's and was considering a partial bridge, this may be the time to try it out..Whaddaya think?
Max

Crashunit

Thanks for all the advice everyone and especially Dragon for the write up on AIM . I've decided to just go with the OEM 3mm seals, due to cost, time (which I dont have alot of), and the fact is even if I still get ceramic seals, there's still no way to tell if it will last any longer, and Id rather just do another rebuild concidering the cost of the seals, maybe next time. I really actually wanted to do alot more this time around, like pinning it and other things, however, my car is on a schedule, so I'll have to do them later, but thanks for all the help.

-Marvin

boostedyellow7

wer are you haveing the motor done at?

phatdex

2mm mazda seals are the best. 3mm seals dont seal as well as they cannot flex as much. Ceramic seals are good for NA engine but not for turbos as they cant handle detonation.
My mechanics car makes 466rwKW, which is about 600 and something horsepower plus 15% to make it dynojet on mazda seals.

fdracer

so what's the consensus on lapping the side housings when rebuilding the motor for better compression and sealing. none of the engine builders here in socal seem to care much about lapping them unless their way out of spec.

Chronos