leakdown and compression test results... pretty good?
01-14-2002, 01:37 AM
#20
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It's all in the maintenance. Things like K+N's don't help either if they're not properly cleaned and lubricated. Maybe its dumb luck that these cars were in such good shape after so many miles. One was bought for $1600 and the other $3400 because of the miles...
Maybe its just that the owners were honest and didn't have the speedo replaced. Gotta watch some Porsche sellers...just like Porcupines but with the ***** on the inside...lol
BTW - motors usually run best when the clearences (at least rings to cylinder wall) are at their greatest because of the friction reduction. Sounds like you probably need a set of rings - but check the head first as its much easier to pull.
Maybe its just that the owners were honest and didn't have the speedo replaced. Gotta watch some Porsche sellers...just like Porcupines but with the ***** on the inside...lol
BTW - motors usually run best when the clearences (at least rings to cylinder wall) are at their greatest because of the friction reduction. Sounds like you probably need a set of rings - but check the head first as its much easier to pull.
01-14-2002, 04:20 PM
#21
Drifting
By the way - was anyone else preached to about the priority of having all compression values within 5% of each other over the actual PSI results in terms of importance?
(or was it 10%?)
(or was it 10%?)
01-14-2002, 04:49 PM
#22
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p951guy - Have you looked at your cylinder walls with a borescope? It's possible they're scored, and that will low your values considerably. My own 951 had 87K miles and was horribly scored from previous owner negligence and subsequent oil and air contamination. If you're not the original owner of the vehicle, you can't be 100% sure what happened to it before you got it.
For what it's worth, all four of my cylinders were scored equally, so my leakdown/compression numbers would have been "similar" across all four cylinders.
Have yours checked out visually and see if you can determine what the problem might be. Also, as mentioned previously, make sure your block is up to operating temperature to ensure the cylinder/piston sizing is correct, and the cyliner walls nominally lubricated.
If you're running REALLY hot power on that engine, you may be getting lower numbers due to exhaust valve wear. Might be getting close for a valve job.
Greg
For what it's worth, all four of my cylinders were scored equally, so my leakdown/compression numbers would have been "similar" across all four cylinders.
Have yours checked out visually and see if you can determine what the problem might be. Also, as mentioned previously, make sure your block is up to operating temperature to ensure the cylinder/piston sizing is correct, and the cyliner walls nominally lubricated.
If you're running REALLY hot power on that engine, you may be getting lower numbers due to exhaust valve wear. Might be getting close for a valve job.
Greg
01-14-2002, 10:24 PM
#24
Rennlist Member
As has been said make sure the engine is up to operating temperature. When you have the cylinder pumped up take off the oil filler cap and put your ear close to it. If you hear a hissing sound odds are that the rings are bad. The air is getting past the rings and into the case, thus the sound. Next, again with the cylinder pumped up, listen to the tail pipe. If you hear noise then you probably have valve issues. Obviously if you hear it in both locations then both are problems.
As to power, mine made 290 at the rear wheels with 30% leakdown and 120 psi compression and only 5 hrs. on a $9000 rebuild. Helps to not put std. rings in a first over engine. Keep in mind when that gas explodes it is not the same as a static number.
Alan
As to power, mine made 290 at the rear wheels with 30% leakdown and 120 psi compression and only 5 hrs. on a $9000 rebuild. Helps to not put std. rings in a first over engine. Keep in mind when that gas explodes it is not the same as a static number.
Alan
01-16-2002, 03:51 PM
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Hi Guys,
don't how I missed this earlier, it's an interesting one. I'm just going to mention a couple things I agree and disagree with. Not trying to harsh anyone:
plugs out = good
engine warm = good
leakdown within 5% on all = good
compression within 5% on all = good
throttle not open = bad (for compression)
throttle not open = doesn't matter (leakdown)
yes, turbos will have a much lower static compression ratio. 150 is prett common for most motors that are around 8.0-9.0 or so.
Nicely, for some of you guys, turbos run better with marginal compression, than do normally aspirated models. The turbo will run weaker than with good compression, but not horribly. Normally only poor at idle.
Back on the WOT topic. OK, I'm not a Porsche motor expert per-se, but a motor is a motor. On quite a few cars, and countless motorcycles (I have a repair business) that I've worked on, the throttle must be open. On a motor that normally should be 145-150 (and tolerable down to 130-135 if well matched) I'll normally get from 100-110. This is true on any motor I've dealt with. I can't imagine what the exception would be. Perhaps turbos are less picky, since the turbo can force more air around the gap of the throttle plate, but that seems a stretch.
If somebody knows for a fact this is wrong (i.e. you've done it both ways yourself and have seen no difference in value) not just hearsay, then I'd honestly like to know about it. My experience is that everytime one thinks they know 'all' there is about some small subtopic, they are (or at least I am) proven wrong. So, seriously and honestly, set me straight if I have a big gaping hole in my engine knowledge.
(it would be nice, but embarassing, since I've done small articles for a magazine on compression and leakdown testing before)
later
roger
don't how I missed this earlier, it's an interesting one. I'm just going to mention a couple things I agree and disagree with. Not trying to harsh anyone:
plugs out = good
engine warm = good
leakdown within 5% on all = good
compression within 5% on all = good
throttle not open = bad (for compression)
throttle not open = doesn't matter (leakdown)
yes, turbos will have a much lower static compression ratio. 150 is prett common for most motors that are around 8.0-9.0 or so.
Nicely, for some of you guys, turbos run better with marginal compression, than do normally aspirated models. The turbo will run weaker than with good compression, but not horribly. Normally only poor at idle.
Back on the WOT topic. OK, I'm not a Porsche motor expert per-se, but a motor is a motor. On quite a few cars, and countless motorcycles (I have a repair business) that I've worked on, the throttle must be open. On a motor that normally should be 145-150 (and tolerable down to 130-135 if well matched) I'll normally get from 100-110. This is true on any motor I've dealt with. I can't imagine what the exception would be. Perhaps turbos are less picky, since the turbo can force more air around the gap of the throttle plate, but that seems a stretch.
If somebody knows for a fact this is wrong (i.e. you've done it both ways yourself and have seen no difference in value) not just hearsay, then I'd honestly like to know about it. My experience is that everytime one thinks they know 'all' there is about some small subtopic, they are (or at least I am) proven wrong. So, seriously and honestly, set me straight if I have a big gaping hole in my engine knowledge.
(it would be nice, but embarassing, since I've done small articles for a magazine on compression and leakdown testing before)
later
roger
