Ive googled and can`t find my manuals for this. What is a new motors cilinder lb. compression equaling a 9-41 or 10-1 compression rating, for a standard new regular octane engine. I thought 9-41 was aproximately 145-155lb. Do new small 4 cilinder motors run near 200lb?
most new gas engines are 125 to 150 pounds of compression.
compression ratio on new engines is 8 to one or less to burn regular octane gas,..
Ds, alot of motors are 9.41 rating and regular gas, I believe. Computers retard timing when needed to prevent knock, modern engine management is allowing higher compression ratings for regular gas.
What lb. pressure would 9.41 equal, im sure its a simple formula.
hi, i rebuild several engines a year,and have been sure to keep them 8 to 1 or less . i knowsome engines from the factory are more,and show 165 pounds compression.but the way i build them,they run cooler and spark knock less.. best regards, lucas
Not entirely true. A lot of engines are over 9.5:1 these days.
The reason for this is aluminum heads - you can run several points more compression and not worry about spark knock.
-CF
Actually, I know guys that run 11:1 compression with aluminum heads - and run 93 octane no problem.
-CF
OK but what compression rating equals what lb. a factory new 9.5-1 equals how many pounds pressure with a compression tester. It has to be a simple formula.
PV=nRT ?
Having said that, all cylinders should be within 10 psi of each other.
If the highest pressure is 120 psi all other cylinders should be no less = than ~110 psi.
If all are within range, compression is usually AOK.
--=20 PDQ
-- "m Ransley" wrote in message = news: snipped-for-privacy@storefull-3133.bay.webtv.net... | OK but what compression rating equals what lb. a factory new 9.5-1 | equals how many pounds pressure with a compression tester. It has to = be | a simple formula. |
PDQ, that makes sence, thanks.
Just a guess but doesn't 9.5 to 1 mean you are compressing 1 lb to be 9.5? So if air pressure at sea level is 14.6 than compressed 9.5 it would be about 139.
The compression ratio is by volume. If there are no leaks and the valves are closed when the compression starts , then it will be 14.7 (air pressure) times the ratio.
Assume nRT remains constant (actually they don't because compression increases T which increases the pressure). So P1V1 = P2V2 or solved for V2= (P1/P2)x V1 . Actually you just assume the normal pressure is 15psi at sea level so just multiply the 15 psi by the volume change ( in this case 9.5). That would be absolute so on subtract one for the actual pressure gage.
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