black sunshine Posted June 21, 2007 Report Posted June 21, 2007 Curious as to why I get more compression with the "short" threaded insert than the one with the same amount of threads as a spark plug. I would have thought it would be the other way around, considering there is less room for the air to "squish". The results were pretty significant, too. 10psi difference. Someone set me straight, or tell me to go fuck myself at least Quote
ToomeySheeLE Posted June 21, 2007 Report Posted June 21, 2007 (edited) Go fuck yourself... does that help? You bring up a very interesting point.. hope to read a good explination.. As I would think the same as you, taking up more space in the combustion chamber should raise the compression.. Makes you wonder how to get a "true" reading.. Most likely since your spark plug threads are close to the length of the once adapter that would be the best bet as far as believing one reading over another.. As far as octane requirements, definitly go with a mix of race gas if your in doubt... I just detonated my new motor.. nothing sucks more... too be safe i plan on running a mix if im over 150psi as I want to go +4 on the timing. Good luck Brad Edited June 21, 2007 by ToomeySheeLE Quote
blowit Posted June 21, 2007 Report Posted June 21, 2007 Go fuck yourself... does that help? You bring up a very interesting point.. hope to read a good explination.. As I would think the same as you, taking up more space in the combustion chamber should raise the compression.. Makes you wonder how to get a "true" reading.. Most likely since your spark plug threads are close to the length of the once adapter that would be the best bet as far as believing one reading over another.. As far as octane requirements, definitly go with a mix of race gas if your in doubt... I just detonated my new motor.. nothing sucks more... too be safe i plan on running a mix if im over 150psi as I want to go +4 on the timing. Good luck Brad The reasons should be simple. If you have schrader valve at the end of each test lead, one valve is failing you. I have said before that they are critical for accurate testing. If no valves, you are not going to be accurate anyway but the reason would be displacement in the tube. One must be a shade shorter than another. Fluid dynamics would not lie on this one. You are right about the longer lead giving a higher number. It should if things are working like they should. Switch the valves in the two leads and see what happens. Brandon Quote
Snopczynski Posted June 21, 2007 Report Posted June 21, 2007 Its more accurate with the smaller adapter of the two because as the piston goes down every time the compression is released from the head and dumped out the exhaust. So basically the amount of space attached to the spark plug hole is easier to fill when its has less volume, thus being more acurate. You typically always want to check compression with the shortest adapter setup possible. Thats why a lot of automotive testers have a rubber nub on the bottom that you just push into the spark plug hole and hold. Quote
MILO Posted June 22, 2007 Report Posted June 22, 2007 Its more accurate with the smaller adapter of the two because as the piston goes down every time the compression is released from the head and dumped out the exhaust. So basically the amount of space attached to the spark plug hole is easier to fill when its has less volume, thus being more acurate. You typically always want to check compression with the shortest adapter setup possible. Thats why a lot of automotive testers have a rubber nub on the bottom that you just push into the spark plug hole and hold. hmmm... i was always told to use the long reach adaptor on the shee cuz it's more like when the plug is in. i would think that you want it to be as close to reality as possible. Quote
blowit Posted June 22, 2007 Report Posted June 22, 2007 hmmm... i was always told to use the long reach adaptor on the shee cuz it's more like when the plug is in. i would think that you want it to be as close to reality as possible. I think he is referring to the extension tube and not the threaded termination end. Brandon Quote
Snopczynski Posted June 22, 2007 Report Posted June 22, 2007 I think he is referring to the extension tube and not the threaded termination end. Brandon Bingo. The less volume in the tube or even the extension for that matter is going to make the reading more accurate. Quote
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