ok just curious here. ive got a motor that has 225 even compression (11:1 static). i recent did a leakdown and was getting 8-13% leakdown. it was getting into the crankcase on all cyls so im assuming rings. the leakdown results were even between cylinders.

since its ***** cold out, the car had cooled off by the time i did the test. i mean it wasnt ice cold but around 100-120 degrees, just enough that i could hold my hand on the motor and not flat out burn myself. how much would the temp. affect my leakdown results? enough to bring that 10-12% down to 5-7%? just curious.

 

in all honesty 10% leak is about normal....as far temp effecting results, it really depends on the condition of the motor...a worn motor is going to have greater clearances and therefore leak more when cold; ie piston to cylinder

 

.....the motor has 1000 miles.......

 

Things expand when there warmer, but either way 13% is not that bad.

 

I would think it also depends on what type of pistons youre using. Some alloys that require .003" will probably "leak" a bit more than some factory cast pistons which have a tighter PTW clearance...
Interesting though...Never did a warm vs cold leakdown test before....
Let us know what you find please!

If you are familiar with your cam timing enough, you could probably do another leakdown with the pistons halfway and at BDC to see if theres any difference...

 

i would try the leakdown with the motor at running temp since thats the way it will act when your driving around, things should tighten up, then come back here and post your results.

 

hot vs cold will make a difference but not that much, your not supposed to do a leakdown test when warm really but.

 

a warm engine is def going to have less leak because of the ring being expanded and nice warm oil in the oil ring but you want to leak down test a cold motor because some problem can be covered up by warm oil everywhere and youll catch them in a cool engine

 

hmmm interesting. i was always under the impression that compression and leakdowns should be done at normal operating temp, as thats the conditions in the cyls when driving.
good thing i posted this as im learning more.

the pistons are 84.5 rs machine itr copies. piston to wall is .0015 as recommended by rs machine. the ring gaps were .017" top ring and .022" bottom ring

 

compression test you do hot, leakdown cold; besides the point above, its mainly so you dont shock the hot cylinder with cold air