Cold Compresion Figures, On A New Engine Very First Start

[daneldridge23 15]

hi

 

im nearly ready to start my car but before i go mad i want to do a compression test, what sort of numbers do you think i should expect to see?

 

its a brand new rebuilt 1.9mi16, it will be cold and not run in at all, so im not expecting high, but maybe in the region of 140, 150

 

what could i expect?

 

dan

[welshpug 1,627]

depends how well you've built it, a good 16v xu should see 210+ easily, however I don't see the point of a compression test before even trying to start it?

[daneldridge23 15]

i have done work to the head welsh pug, just wanted to make sure i am getting compression lol. over thinking and putting of the inevitable first start i suppose!

[kyepan 291]

turning it over by hand will give you an indication of how much compression, and help you spot any serious issues like lifters stuck open, or valves not sealing. Although if it's got new liners / honed liners and new rings, it will go from virtually no compression to full compression within the first 100 miles.

 

do it after 100 if you want to get a 90% figure, then again after 1000 for a near full figure.

 

also depends on how you break it in (opens can of worms) i used the warm it up and run it hard method

Edited May 2, 2012 by kyepan

[petert 554]

I agree, should be 210 with standard cams. A compression test will determine if it's worth starting!

[daneldridge23 15]

thought id let you know i got

 

214

212

216

216

 

whart does that give me as a ratio?

 

and that was very first turnover and cold

 

Dan

[Mad Scientist 106]

That's nice and healthy. I wouldn't take the numbers as gospel though. Unless your tester was about £400. The important thing is they are in the right ballpark and all very similar. 10% difference between cylinders is said to be acceptable. It's also important that they all "jumped" up the same as you turned it over. (i.e. with successive revolutions of the engine)

[daneldridge23 15]

cool now just need an exhaust system and can hear it properly!