compression ratio ???????

[Highbanked Hauler]

Is there anyway to find the compression ratio other than to pull a head off and measure ? thanks...

[ChargerST]

Hard to do...

You could use a slim bore scope and see how much the piston is in the cylinder. Problem is that you probably don't know if the engine has been bored (and how much) and that the actual chamber volume (especially on factory heads) can vary quite bit from the advertised volume.

[firefighter3931]

Is there anyway to find the compression ratio other than to pull a head off and measure ? thanks...

Nope, you need to pull the head and get a piston to deck measurement as well as a chamber volume. From there we can calculate static compression. Anything else is a shot in the dark. 



Ron

[justcruisin]

Without pulling a head anything is a guess. Best guess would be to get a cranking compression reading and make an allowance for the cam. For example - a stock 440 with an 8.8:1 compression will crank somewhere around 160psi, presuming a healthy engine, but there are to many variables to be accurate. A bigger cam in the same engine would produce a lower reading.

[BSB67]

What is it exactly you are trying to determine?  Are you looking to make a change?  Trying to identify potential?......

[1974dodgecharger]

What is it exactly you are trying to determine?  Are you looking to make a change?  Trying to identify potential?......

Ali can think about is BLOWER time at how much boost.......

[Challenger340]

there is a new machine now available....
which uses sound waves to "map" Cylinder Volumes at BDC, and then again at TDC, and then digitally calculates a "static" compression ratio.

Camshaft events obviously modify ACTUAL cylinder pressures, but the Machine will give an accurate STATIC C.R.
It has become a standard Tech tool in some classes of roundy-round racing.

[Highbanked Hauler]

What is it exactly you are trying to determine?  Are you looking to make a change?  Trying to identify potential?......

 I bought this 440 engine which is supposed to have 12-1 comp. and was planning to run it on E-85.and limited use but not sure if I am going to stay with the same plan and more street use also.. The previous owner  had only (broke in) the motor and his plans fell apart and I got it. NOW he said that it was run in on 93 unleaded and when I got it set in the car I ran it on 93 also and obviously not under load. At 12-1 comp. wouldn't I have  had brutal spark knock on 93. ??  I just question 93 octane and 12-1 comp in the same sentence. I will say the new starter works hard to crank it over to start but that alone say high compression.
     I should also say the motor sounds great.

[cudaken]

Cast iron heads? 

[Kern Dog]

My 440/493 was at almost 11.0 to one and ran okay on 91 octane until I went past half throttle. I would guess that a 12.0 engine could do the same with 93 octane.

[Highbanked Hauler]

Cast iron heads?  

   Yes, they are 906's not ported. I THINK it has stainless valves, it does have double springs, 1.6 crane rockers, adjustable pushrods and a hydraulic cam (not radical)and I would have to look up the grind on it. I have not had it on the street yet and am thinking of putting it in the 500 to run it.

    The motor was bored 60 over for what difference it might make.

[Challenger340]

Cast iron heads?  

   Yes, they are 906's not ported. I THINK it has stainless valves, it does have double springs, 1.6 crane rockers, adjustable pushrods and a hydraulic cam (not radical)and I would have to look up the grind on it. I have not had it on the street yet and am thinking of putting it in the 500 to run it.

    The motor was bored 60 over for what difference it might make.

getting anywhere near 12:1 on a 906 Iron Head would probably require a substantial "dome" on the piston... which should be fairly easy to see even looking through a spark plug hole with the piston at TDC.
Look through a plug hole with a flashlight
get somebody to turn the engine over slowly so you can look ?... SEE a BIG Dome ?