Question on compression in lbs running 9.13:1 comp ratio

[rxrider]

I have searched the site and the Internet but I can't find anything useful.

I'm in the works of getting my compression checked. I am running 10:1 pistons and 2 stock head gaskets giving a compression ratio of 9.13:1 according to the boost calculator.

My question is;
What compression in lbs will be normal with my 9.13:1 compression ratio?
Thanks

 

[Thomas800]

Very hard to say. The the mechanical compression ratio will effect the cranking compression but.. The intake valve closing point will have a definite effect as well. Where do you have your intake cam set? You probably won't find a formula to give you an answer. I havent done your exact setup before, but I would venture a guess at about 135 to 140. Maybe someone that uses multiple gaskets will chime in.

 

[Thomas800]

Oops. Just noticed where you live. 9.3 to 9.65 bar?

 

[rxrider]

My intake cams are set at stock setting.
When going with multiple head gaskets I had to grind the holes to move the intake cam back to stock position, all done according to mcxpress turbo install manual.

Anyone running 10:1 pistons and 0.54" headgasket did any compression testing? What have you seen measured in lbs?

 

[Skydog]

Hey buddy if they are all with in 10% you are good! Not to sure on a number but i would bet like 125 or so.

 

[rxrider]

Hi there Skydog - Thanks for your input

I'm asking this question because my friend has the same setup on his 2003 RX-1 that I have. He is a automotive mechanic and wanna make sure everything is OK inside his engine before running it with higher boost than the stock 10 lbs. This is his first yammi 4stroke ever, he just got it. He did a compression test today reading 116 lbs on the pto side cylinder. This was with a cold engine, the IC in place, throttle at WOT.

This would not give an accurate measurement I believe. Service manual tells you to warm up the engine prior to testing. WOT will not raise the carb slides, so I think he has to raise the slides manually as well, am I right?

When we have this Q figured out I will let him test mine as well

BTW Skydog - how's your apex running? any boost in the near future?

Thanks
Jan-Ove
rxrider

 

[Anonymous]

finally, got to test compression with engine hot today...

140-145 compression are my results with 9-1 shim

 

[rxrider]

mulot30th - thanks for your input.

Talked to my friend this afternoon, he will test again with warm engine, IC off, throtle at WOT and slides wide open. He said he would repeat the test with some oil added and do a second test.

Thanks
rxrider

 

[TWIN TURBO]

Glad you asked was going to post the same question. 2006 Apex new with .062 head shim along with the 2 halfs of the stock gasket 9.3:1 wide open throttle gave me 155 lbs. across the board. Please keep in mind all compression gauges are not created equal 5lbs. more or less wouldn't surprise me at all. By the way thats a cold engine.
And a big yes to holding the slides open on a RX1 for the real number.
Friend of mine just put JE 10:1 pistons no shims in a RX1 and it gave him 165 lbs. on his gauge.
all above is with stock cam timing. Rolling the intake cam back to 114 c/L would drop compression about 15 lbs. tried it for fun.

 

[Anonymous]

Glad you asked was going to post the same question. 2006 Apex new with .062 head shim along with the 2 halfs of the stock gasket 9.3:1 wide open throttle gave me 155 lbs. across the board. Please keep in mind all compression gauges are not created equal 5lbs. more or less wouldn't surprise me at all. By the way thats a cold engine.
And a big yes to holding the slides open on a RX1 for the real number.
Friend of mine just put JE 10:1 pistons no shims in a RX1 and it gave him 150 lbs. on his gauge.
all above is with stock cam timing. Rolling the intake cam back to 114 c/L would drop compression about 15 lbs. tried it for fun.

My intake cam is roller back 3.5 degree and exhaust cam is advanced about 3.5 degree

so my 140-145 compression is probably good according to your expermient.

 

[rxrider]

Thank you guys for your input, .

I'll post :exc: the results when we have tested both his and my engine.

 

[samrx1]

I have searched the site and the Internet but I can't find anything useful.

I'm in the works of getting my compression checked. I am running 10:1 pistons and 2 stock head gaskets giving a compression ratio of 9.13:1 according to the boost calculator.

My question is;
What compression in lbs will be normal with my 9.13:1 compression ratio?
Thanks

i am runniing....10/1 pistons and 2 heads gasket too....
my compression ..before start engine....145lb..

 

[Skydog]

Love the Apex BIG TIME!!! Going to just ride her stock TURN KEY!! HAHA I am going to keep the Rx1 turbo for my modded sled!

Skydog

 

[rxrider]

I had my engine tested today. With a cold engine without IC or carbs in place, (it has not been cranked since the last trip in May) it tested as follows; cylinder 1=147 psi 2=130 psi 3=147 psi 4=159 psi.

I will make another test as soon I have her ready to ride. I assume readings will change when engine has been run a few miles.

My friends sled tested close to 145 across with a warm engine, IC off and slides wide open.