insightful

this is a load of crap, i think you mean the compression release button which is in the gauge itself and not the one in the hose. if you are getting readings that low doing it the proper way then your gauge either sucks or your engines suck.

peejay

I know what I mean.... If you remove the valve from the hose, the hose depressurizes with every stroke. That is why the valve is in there in the first place.

Let's say the hose is two feet long and is 5/16" ID. Or let's say 60cm by 8mm because we're about to calculate CC. 8mm circle is roughly .50 square centimeters, times 60cm long is 30cc of volume in the hose.

A 13B has 654cc of swept volume per chamber. If it has 9:1 compression, then the ratio between BDC and TDC is 9:1. The clearance volume is always there, so if we call the clearance volume X, then TDC is X and BDC is X + 654. So therefore, 9X = X + 654, 8X = 654, X = 81.75cc.

With that in mind. Removing the Schraeder valve effectively increases the clearance volume from 81.75cc to roughly 111.75cc. Doing the math backwards (well, forwards), this makes your 9:1 compression 13B have 6.8:1 compression.

You don't think that will have any effect on compression readings?

This is exactly why there is a Shraeder valve. With a piston engine you crank the engine for four or five pumps because you have to build up pressure in the hose. The first pump on a 180psi cranking compression engine will be only about 50 or 60psi, most of the compression is wasted in filling the gauge. Piston engine compression testers can be used for a "general idea" of engine health but are NOT to be trusted for hard-and-fast numbers! And the most accurate compression testers have a digital sensor that threads right in with no hose, so there is zero additional volume.

Kenjiryan

so the way I should go is to buy a new rx8 starter and swap the rx7 nose on and try cranking it? I'm heading to napa now.

Kenjiryan

I bought a new rx8 starter and I'm getting a much faster cranking speed but still sounds the same way as in just cranking like there is no spark or fuel present. I'm bumping fuel into the compressionm chamber and checked my Leading spark plug for spark. should I be seeing a really bright spark or just a little spark?

Kenjiryan

I got it to make a pop now with the faster rotation speeds..... but still nothing significant...

Kenjiryan

I took off all spark plugs and blew out what ever was inside of the engine and tried cranking it over with a bit of starter fluid. It instantly started to hickup and buck then it came to life for just a second!!!! it's far from anything but this is a pivotal moment for me..... I'm now gonna move onto why my injectors arn't grounding out.... but as of now I'm really, really happy!

silverTRD

iTrader: (36)

It sounds like you have some other issues needing fixed before you continue.
First off, if you remove the schrader valve it will only read the pulses from each side of the rotor, it wont build psi to read total compression, so 55 psi isn't bad. Someone correct me if I am wrong.
I had this issue once as well, but my issue was because I was a new newb and didn't remove a plug in the other housing slowing the cranking down.

Have you flooded at all? I bet you're not building compression as your housings are dry. Try putting oil in housing. You can remove the upper intake manifold or do what I did and use a RC car fuel bottle and squirt it into the spark plug holes that way you don't have to disassemble the top of the motor just to get oil in.

Good luck

fendamonky

iTrader: (6)

I seem to recall that compression initially improves as an engine is broken in. That being said, you cannot really blame minor cracking near the plug holes for low compression. I would look to seal clearances or general build quality to find the "fault" of low compression LONG before I'd accuse a good/decent condition rotor housing of being to blame.

Did you buy all new hard/soft seals when you rebuilt the engine? (or) Are you reusing the seals from the old motor? If you're reusing seals, did you test them all thoroughly to ensure that they're well within spec? How much clearance did you have for your hard seals? etc., etc., etc.

As silverTRD suggested, it sounds like you've got a LOT more going into your engine woes than you can pin on a merchant who sold you some fairly standard parts from half a world away... Just saying

Kenjiryan

Thanks guys but the car is sold.. glad I'm getting how much I put into it back but sad cause my dream car is going away... I used new OEM 3 price seals with the build though.

insightful

wonder where these people are even finding the 3 piece stockers...

mazda stopped making and selling them a decade and a half ago.

Kenjiryan

I got them with the car when I bought it's the guy was sitting on the car for a decade