that's what i've been trying convey, that the only explanation is that someone fucked up the comp test... but they keep looking for some unimaginably improbable explanation.



i agree with you, there is no way that much carbon has built up in a recent rebuild without numerous other symptoms surfacing.

 

Symptoms such as?

 

excessive carbon build up enough to increase the compression ratio that much?

as a guess, your plugs would be fouling and look like **** and you would have increased wear on the seals and housings. stuck seals, carbon lock... you would know something was wrong.

if you are asking what symptoms i am referring to because you doubt me, feel free to prove me wrong... my statements are only based on common sense and math, not experiences.

if you are asking because you're scared it might be the reason for you high compression numbers and your car is running fine otherwise, i wouldn't sweat it.

 

I'm asking in general because i have no idea about compression tests, and i don't have any other symptoms with the car.

 

symptoms such as: a blown motor

 

Compression ratio only changes static compression numbers a couple of psi one way or another. Even the 9.7 and 10:1 rotor engines only make 125psi of compression under optimal conditions.

Sounds like this test was done 1) on a cold motor and/or 2) at higher than standard cranking rpm, and/or 3) with oil in the chambers. IF you spin a rotary fast enough it will generate higher compression numbers. If you put a compression gauge in a rotary and towed it down the road with the clutch popped at 20mph, you'd be spinning 2-3k rpm and you'd see way higher compression.

The specs given are only for cranking compression at the given rpm of 250. Use of a battery boost can increase cranking rpm. Testing a cold engine will also raise numbers...rotaries make more compression cold than hot. This is why borderline engines start right up when cold, but have hot-start flooding problems when trying to restart warm...the compression drops just below the flooding threshold when hot, and raises just above it when cold.

Any oil in the chamblers during the test will yeild an artificial high number as well. So if you inject oil or atf before the test you are not running an accurate test. The oil takes up the gaps between the housing and seals and makes for a tighter seal with zero blowby. I've seen 40psi added by injecting oil and running a test, but once it burns off the compression goes right back to where it used to be. This is another reason not to test a cold motor...by design, there is some oil drainage that pools up at the bottom of the chamber when the rotary has sat for several hours (omp injection drainage, seep-by from non-moving oil control rings that are trying to hold thin oil in mid air). So testing a cold motor stirs this pooled oil up, again sealing the gaps and making for artificial high numbers.

I have NEVER seen a rotary test higher than 125psi hot, at the specified 250rpm. I have tested a LOT of engines as you might imagine.

 

There is a theoretical limit even when the engine is sealed up well with oil: for 9:1 it would be 9 bar (130.5psi), for 10:1 it would be 10 bar (145.0 psi). His numbers are above that.

Dave

 

I don't know how much temperature would cause the numbers to jump that high, but i know that the techs never drove the car before doing the test. The car sat on the lot for a day and a half.

I appreciate the info about these things as well.

 

[QUOTE=rx7twinturboboy]I don't know how much temperature would cause the numbers to jump that high, but i know that the techs never drove the car before doing the test. The car sat on the lot for a day and a half.QUOTE]


That's your answer right there. The FSM clearly states that you should warm the car up to operating temperature before performing a compression test.


More info here:
http://www.fd3s.net/compression_test.html


There might be a temperature correction chart listed in the FSM, but I can't say for sure as I don't have a copy with me at the moment.

-s-

 

I usually see 5-10psi higher on a cold test versus a warm test on the same engine, regardless of the actual compression numbers. So if an engine measures 115 hot it might measure 120-125 cold. Or if it measures 95 hot it might measure 100-105 cold.

 

You can idle the engine to get it warm. It doesn't have to go anywhere.

I'm not aware of any temperature correction. There is a correction for RPM and I think altitude, but that's it.