Measuring Compression Ratio
 

Is there anyway to measure the compression ratio of a motor that is fully assembled, besides taking it apart?

if you do not know the specs on the components the answer is no.

Thanks Mike!

Yep as said, specs ( CC's of head, piston dish or dome, deck height ect ) Good luck


John jr

Just say 10:1. That's what everyone says when they don't know. LOL.

Yes,

http://store.katechengines.com/whist...ster-p174.aspx

You'll have to find a local shop that has one.

Jeff

wow,never seen one of those.i cant see to many shops spending that on one when most engines taken to a machine shop will soon be torn down anyway.

Mike,

They are utilized mainly by sanctioning body tech inspectors to verify the legality of compression limited class engines.

Bob

if you have done enough engines and know the cranking compression of similar engine specs you can kinda guess..example my suburban is a 8:0 to 1 compression and my cranking psi is around 130.. my boat is 10; to 1 and its around 165 psi..

i can see a tool like that being useful for that.

Thanks Jeff,

That is exactly what I was thinking of, But definitely a lot cheaper to just disassemble motor etc lol. Figured in today's day and age they had to have some technology for measuring the ratio. But like you said I'm sure some high end machine shops have them.

There are many shops that build spec engines. This is what the sanctioning body uses to check compression.
The engine builder will use it to make sure it passes before it goes to the customer.

If you pay 25,000 for an engine and inspection time comes around after the race, it better be right otherwise the engine builder will look pretty stupid.

Jeff

a engine builder can figure the compression ratio useing simple math and should not need this peice of equipment imo.

Nobody needs it. If the tech inspectors are using it, it makes sense that you use it as well for that added security.


Jeff

i called 6 shops in the chicago area and none of them had one.that makes me think they are not vrey commonly used,atleast not in my area.

I'm curious how it works. Okay so you can calibrate it with a provided jug of known volume, but what does this have to do with compression ratio? So an engine exhausts a certain amount of air on the exhaust stroke, ok well if there is no valve overlap and none goes out the intake, it all goes out the exhaust and the volume can be measured, so that times the number of cylinders is the engine displacement. So how does it figure compression ratio? I'm not questioning that it works, just how it works?

Look for big names in area that build heavily restricted 2bbl engines. If none look for Crate Engine / Spec engine builders. Like the Chevy 604 and 602's.

Back in my day (few eons ago) just track inspectors had them.

Quote from the link given on 1st page of this thread:

there are a couple builders in indiana that do a lot of stock car engines,maybe they have one.

i believe if you take the rocker arms off and then put engine on tdc you get a measurement,then put the engine on bdc,then take another measurement,the difference would be the compression ratio.i dont know this for a fact because i have never seen one of these .

My typing must be invisible. LOL.

SB, I read your response quoted from the website (which I already looked at). Thats like saying how does a car engine work...easy, you turn the key and it starts....haha. I was just wondering if someone knew what measurements it takes, like it measures how much air to pressurize the cylinder to a certain psi at TDC and then BDC and can then calculate the chamber volume somehow?

SB is correct, the vast majority of the Whistlers were utilized by sanctioning bodies (SCCA_NASCAR_APBA etc) for validation of CR in the field (competition events). In the shop environment stacking tolerances works equally well. See Katech spec sheet attached.

Bob