Is this Compression okay? w/o open throttle
07-28-02, 09:05 PM
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Is this Compression okay? w/o open throttle
I'm looking at buying an FD, and i just got a compression test on one.
Numbers were 6.0, 5.9, 6.0 on front rotor and 6.0/5.9/6.4 on the rear rotor.
It was turning at 260rpm. The throttle WAS NOT depressed, and the motor wasn't hot, it was semi-warm. Basically just taken out of a parking spot and driven into the garage. Not really hot.
ANy thoughts? Not sure if the motor is good, or on the end. The chambers are very even which is good, and very even from front rotor to rear rotor. Any comment is greatly appreciated. Thanks.
The MAIN question is how much is compressin affected with the throttle closed?
Danny
Numbers were 6.0, 5.9, 6.0 on front rotor and 6.0/5.9/6.4 on the rear rotor.
It was turning at 260rpm. The throttle WAS NOT depressed, and the motor wasn't hot, it was semi-warm. Basically just taken out of a parking spot and driven into the garage. Not really hot.
ANy thoughts? Not sure if the motor is good, or on the end. The chambers are very even which is good, and very even from front rotor to rear rotor. Any comment is greatly appreciated. Thanks.
The MAIN question is how much is compressin affected with the throttle closed?
Danny
07-28-02, 09:57 PM
#3
Weird Cat Man
I own a graphing-type rotary engine compression tester... based on my experiences with MY cars, I have this to say:
Having the throttle closed makes your readings up to 0.5 lower. (approx) Having the engine not fully warmed up can also hit you for about another 0.5 or so at most. I would predict that the same engine when fully warmed up with an open throttle might get around 0.75 higher (at most) on all those readings... but then again, what do I know?
Those numbers don't necessarily scream "new engine" to me, but they don't say "run away" either. However, I would be very interested to see the PATTERN of the pulses on that rear rotor. (This is why I prefer the graphing type). If it's a consistent "high-low-low-high-low-low-high-low-low" you might have a cracked apex seal on the rear... but without more info it's impossible to tell.
See my webpages on the topic for a little about my experiences...
http://www.zeroglabs.com/rx7/compression.htm
http://www.zeroglabs.com/rx7/compression2.htm
Regards,
Brian
Having the throttle closed makes your readings up to 0.5 lower. (approx) Having the engine not fully warmed up can also hit you for about another 0.5 or so at most. I would predict that the same engine when fully warmed up with an open throttle might get around 0.75 higher (at most) on all those readings... but then again, what do I know?
Those numbers don't necessarily scream "new engine" to me, but they don't say "run away" either. However, I would be very interested to see the PATTERN of the pulses on that rear rotor. (This is why I prefer the graphing type). If it's a consistent "high-low-low-high-low-low-high-low-low" you might have a cracked apex seal on the rear... but without more info it's impossible to tell.
See my webpages on the topic for a little about my experiences...
http://www.zeroglabs.com/rx7/compression.htm
http://www.zeroglabs.com/rx7/compression2.htm
Regards,
Brian
07-28-02, 10:15 PM
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thanks for the info.
is 0.5kg that big of a difference? I forget what the specs were exactly.
I'm thinking that the motor isnt' that bad since all the numbers were very even from chamber to chamger and from rotor to rotor. There are many factors that can affect a compression test, but nevertheless...slightly low numbers.
Danny
is 0.5kg that big of a difference? I forget what the specs were exactly.
I'm thinking that the motor isnt' that bad since all the numbers were very even from chamber to chamger and from rotor to rotor. There are many factors that can affect a compression test, but nevertheless...slightly low numbers.
Danny
07-28-02, 10:31 PM
#5
Weird Cat Man
Yeah 0.5 isn't a huge amount.... *Technically* speaking, the manual claims that 6.0 is the lowest you want to see on a warmed up engine with the throttle open... BUT there are TONS of cars that drive just fine making sixes across the board. Another telling sign is how much vacuum the car pulls at 750 RPM idle speed. If it's stock-ported and it's only pulling like 14 inches, that's not so good.. if it's got a big street port and it's at 14, that may not be a big deal...
B
B
07-29-02, 12:56 AM
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usually when the compression test is performed, engine rpm can range from 250rpm to 340rpm. When the engine is warmed up it usually sees more compression.
With the factory mazda digital compression checker, you should see the 3 compression chambers with readings within 0.5 or less difference. In this case, your numbers looks pretty even.
6.0-6.5 for cold compression is acceptable, expect about 7.5 or more when its warm. If 6.0 after the car is completely warmed up, then it might be a little weak. Usually a 40-50k miles engine has about 7.0-7.5 readings when warm. Newer rebuilds can range from 7.8 and higher.
With the factory mazda digital compression checker, you should see the 3 compression chambers with readings within 0.5 or less difference. In this case, your numbers looks pretty even.
6.0-6.5 for cold compression is acceptable, expect about 7.5 or more when its warm. If 6.0 after the car is completely warmed up, then it might be a little weak. Usually a 40-50k miles engine has about 7.0-7.5 readings when warm. Newer rebuilds can range from 7.8 and higher.
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