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.

http://www.minibite.com/america/malone.htm

compression ratio on new engines is 8 to one or less to burn regular
octane gas,..

http://www.minibite.com/america/malone.htm

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

http://www.minibite.com/america/malone.htm

wrote in message
...
compression ratio on new engines is 8 to one or less to burn regular
octane gas,..

http://www.minibite.com/america/malone.htm


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

"CFster" wrote in message
news:SISZf.5864$IZ2.51@dukeread07...

wrote in message
...
compression ratio on new engines is 8 to one or less to burn regular
octane gas,..

http://www.minibite.com/america/malone.htm


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.

In article 12433-44380DE0-234@storefull-
3133.bay.webtv.net, says...
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 ?

9.5 atmospheres to 1.
1 atmosphere = ~14 psi.
9.5 X 14 = 133 psi.

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.

--
PDQ

--
"m Ransley" wrote in message ...
| 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.

"m Ransley" wrote in message
...
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.

"calhoun" wrote in message
...
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.

"m Ransley" wrote in message
...
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.



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.

MikeP wrote:
In article 12433-44380DE0-234@storefull-
3133.bay.webtv.net, says...

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 ?

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.