I have heard and been told by differant rx7 fans that you can't get a good compression reading using a conventional tester. If this is true what type of tester do you need, and where can one be bought?
I have two rotaries, one is a stock 12a and in a 84 GSL. The other is a 13b that has been street ported and is in a Magnum GT using a rear engine configuation. If I had the proper tester what amount of compression should be expected in a fresh engine, and if I use a conventional tester what kind of reading would I get?

Hey thanks in advanced

 

i'd just spare the 50 bucks and get mazda to do it--they know what they are doing and they have the right tools...

 

Having a general idea of your engine’s compression is a great idea and if you got the $100 to get both cars done go for it!

However to use as a trouble shooting tool or maybe on a car/engine you are thinking of purchasing you can do it yourself and save time and money.

Simply get your regular piston engine compression tool and remove the schrader valve in the end of the thing. On a warmed up motor with a strong battery remove a plug and screw the thing in. (I suggest removing the coil wires or the ignition fuse or something to keep the car from firing up before the next step.) Crank the motor over while observing the gauge, it should bounce three separate times for each revolution. These are your combustion chambers. Look for the highest point on the gauge on each bounce. Remove the tester and replace the plug, and repeat on the other rotor. This test will give you a fairly accurate idea of what is going on in your motor.

I do not know what a street ported motor should read but I think it is lower than stock ports. I also do not know what a 13b should test out to.

I am sure somebody could throw those numbers this way.

Hope this helps a bit.