These are the numbers from a 93 FD I'm thinking of purchasing. Test was done by a mazda dealership using a mazda tester. This is the car's original engine and is not ported or modified in any way. What do you guys think? Good to go or do you think I'm looking at a rebuild in the near future due to the variability in the first rotor?

1st: 7.4 6.3 6.9 (6.87 average)
2nd: 7.3 7.3 6.5 (7.03 average)
(numbers are in kg/cm2)

Thanks in advance!

 

Here's a pretty please bump.

 

From the FAQ:

28) What should the compression be?

Compression test results are reported as six numbers: 3 per rotor. (This is not the same as the compression ratio). Higher, more equal numbers are best. The original Mazda specs dictate 8.5+ kg/cm² as new (121+ psi), with 6.0 kg/cm² (85 psi, 690kpa) being minimum acceptable. Maximum difference should be 1.5 kg/cm² (21 psi, 150kPa) from the highest to lowest value. It is important this test is carried out using proper equipment and under the correct conditions for rpm and engine temperature. Mazda dealers are generally reliable for performing this test, so long as they follow the procedures precisely.

 

I did read the faq and searched quite a bit (robinette, RR, etc) so I guess my question is this. Is it the average per rotor that needs to be above 6.0, or if one face is below 6.0 you're already screwed? Plus I've seen that the intrarotor variability is supposed to be less than 1.0 (which in this case is 1.1), so how important is that?

 

The engine is worn, no doubt about it. Is that a bad thing? That depends on how you look at it.

Will it need a rebuild? Yes, at some point.

Is that point now? That depends on you. If you plan to slap a ton of mods on the car and make it go "fast", then yes that point is now.

Can you drive on a worn engine? Sure, it's not going to be as strong as a fresh engine, but it will go.

 

Thanks for the reply Mahjik. I think it may be FD purchasing time. . woo hoo!

 

Just my opinion, I agree with Mahjik, but I believe the engine has a tendency to flood easier under the 7kg mark. I could be wrong, I don't have any scientific data to back that claim up, just my experience with an old first gen GSL-SE. I have a Mazda compression tester, and it ran with one face right around 7 and the other two around 6. It gives me a hard time now and again with starting. It want's to flood pretty easily. I think if it were in a better state of tune, it would not be such an issue.
Anyway, that's my .02

 

Sorry the thread jack, but in general, how much difference have people seen between the mazda tester and a piston tester?

With the valve removed, one piston tester I have sees 85 psi per face, seemingly even on my current motor, this one has a 14" hose.

A different tester which has no hose, just an adapter which bolts into the plug hole, that goes directly into the gauge, so it is maybe 2" from the rotor housing, sees over 100 psi, still nearly even.

any thoughts on this

 

How many miles are on the motor? Just curious...