I'm trying to figure out the actual compression ratio of my motor, results were 210,215,210,215 across the board. Anyone have the formula or that could just tell me what it is?

 

does not work like that.
you didn't say your motor specs.. but those are pretty good numbers for the typical car.

 

motor is a b16a2 block b16a2 head
stock headgasket, no milling of the head, stock b16 rods rs machine ctr pistons 81mm

 

It is impossible to calculate your static compression ratio based on compression test numbers. The intake valves do not close at bottom dead center so cam timing has a lot to do with what results you will get from a compression test. However, I agree that those are satisfactory numbers that you got from your compression test. When doing a compression test you want the numbers to all be as even as possible, the absolute value is of little importance.

 

Actually, I think he gave enough information that if someone were so inclined they could make a spreadsheet they could calc the maxium possible dynamic compression ratio in PSI. Many of the basic dimensions are published in a common Helm manual.

77mm stroke
81mm bore
134mm rod
42.7cc, combustion chamber
6cc piston dome
.66mm thick head gasket
use something like 40˚ABDC intake valve closing event.
and since he's close enough to sea level you can probably just use standard temperature, humidity and pressure for the atmospheric conditions.

Yeah, it'd be a bit of a pointless exercise though. Those are good enough numbers for a 10:1 engine anyway. ;D

 

You may be able to estimate it using that information but as you said that might be a pointless exercise. The only way to accurately measure the compression ratio is with a burette. Not that I would expect many people on this forum to know why it is important to know the exact compression ratio.

 

well i'm thinking of boosting the motor that's the only reason I want to know the exact cp ratio. I remember reading somewhere that 240psi across the board on all cylinders is equal to 12:1 cp ratio but didn't have facts to back it up, and it is the internet so who knows if it's right. my friends stock gsr with 98,000 miles came out to 180-190 across the board and a stock gsr cp is 10:1 so I figure mine is low 11's in the cp ratio.

 

Take a look at the first page of this huge thread, it should give you a good idea.

https://honda-tech.com/forums/showth...pression+ratio

 

If you really want to know the exact compression ratio, you will measure the head CC's, the piston/block CC's, the headgasket CC's, and the displacement and do 5th grade math to find it. It is not very hard.

 

There is absolutely no correlation between your cranking compression pressure and your static compression ratio. The engine does not begin building compression until the intake valves are closed so cam timing has a big effect on what your cranking compression pressure will be. Even if you knew when the intake valves closed there are too many variables to determine what the cranking compression pressure would be. You need to remove the head and cc the engine if you want to know your exact compression ratio.

 

don't care enough to go through all that, especially since the car is my DD:/

 

But you care enough to just toss a turbo on your DD engine without building it right?

 

haven't put the turbo on yet, i'm just thinking about it. I intended on keeping this setup all motor never intended on boosting it. i'm sure a cometic HG will lower it to a safe range, I talked to my tuner and he will keep it conservative for the safety of my motor.