I checked mine tonight and it read 110-120 front and rear, the needle was bouncing too fast for any accuracy.

I wonder if the number will go up any if I did the ATF trick. The engine has less than 40k on it. It definitely feels very strong, when it's running right.

About a year before my GTU died it showed 80 in the front and 85 in the rear.

 

I think 120 to 130.

 

Yours is good. Usually anything above ~110 is good.

Mike

 

WOOOHOOOO!!!!

My engine is gonna last forever. Now I just have to track down all those other retarded bugs under the hood.

With my luck I'll be posting about my engine popped tomorrow morning.

 

It's impossible to say whether the numbers you quote are brilliant,average or worse than average because you don't quote the test conditons.If you look in the Mazda manual you can see,for example,that the compression varies by 25psi per 100rpm cranking speed and 28psi between sea level and 3000ft altitude.Having said that since you are in Florida and assuming about 250rpm cranking speed,the test done at normal operating temperature and a reasonably accurate gauge I agree with the previous correspondent.

 

i had my n/a tested at JR rotary in august for the hell of it. i got 130 something on the front...and 120 something on the rear. according to Ito, a brand new 89-91 n/a motor straight outta the plant should have 150...

 

Well, I've owned a worn out rotary, and this one. This one feels much better. The first time I started it when I test drove it I could tell, just by starting it.

I doubt the numbers are "brilliant", but good enough that I'm sure the engine has a lot of life left in it. I really don't feel like replacing the engine any time soon.

 

It would be nice to be able to get a brand new engine straight out of the factory.

 

The highest compression I saw was on an 86-88N/A Mazda rebuild was 9.0Kg/cm2(which is about 127psi).

 

My engine is a Mazda rebuild. The dealer did a real shitty job of installing the new engine, this happened before I bought it though. I'm still trying to track down all the bugs they left over. I think I've about got the car whipped.

 

Why is the rear always (usually?) lower than the front? ANd why is it usually first to go?

 

Somebody gave me a good technical explanation of that once, but I'm afraid that I forgot.

 

the best explanation ive heard of why the rear is usually the first to go has something to do w/ the balance of the motor . i guess its not as good in the back. i wouldnt be surprised though if it also had a little something to do w/ the cooling of the motor also. ive heard of a lotta piston motors that always loose pistons that have the least cooling capablity(like the farthest back ones)

 

Actually, now that I think of it, the explanation I was given had a lot to do with the cooling of the rear rotor.

 

A few other threads have mentioned it having to do with the oil injection delivery. The system isn't set up to provide equal delivery, so since the rear is further away, it gets a little less than the front.

Running pre-mix can compensate for the problem.

 

I run premix. The only major drawback that I can think of is the extra carbon buildup. That and you have to run fuel system treatment at least every 5000 miles or the injectors will get clogged up.

 

When my friend's motor blew it was the front that went bad. It was pretty neat: Every apex seal broke, and all of the rotor faces had big grooves in them.

 

Count me among those who've had the front go first .. happened last Friday. I'm not sure how the housing looks yet, but it's got almost zero compression (barely nudged the needle). However, I'm going to look at another tonight that's got a rebuilt w/~30k on it. Anyone know the % discrepency between a normal compression tester's reading, and the actual compression of the rotors? I read it somewhere but can't remember where ..

Dave

 

How much premix are you using? When I had my oil metering pump hooked up I ran 4-5 ounces per tank. When I took the motor apart 2 years ago to rebuild it it looked very good inside.