Compression Help!

[evoeta]

Hey guys, this is the first rb30det ive tridd to build. Its a fairly basic one. Stock bottom end with acl bearings, standard rb30 rods and pistons which are in good order. Arp head studs. 1.3mm headgasket. and rb25det head which had been cleaned up etc. Went to to compressio test. It had no extractors, intake on and no spark plugs in any of the cylinders prstty bare and im getting about 100psi all over roughly. B

Just did the test with battery on starter motor etc any help much appreciated!!

[Ben C34]

Throttle held open during test?

Low result can also be cam timing out of whack.

[evoeta]

Timing all lines up, and no intake plenum on it.

[evoeta]

Would it be cause of the headgasket thickness? Or battery going flat slowly?

[Ben C34]

You want to use the thinnest gasket possible if you have a non neo head. 1.2 is stock ?

[Ben C34]

and engine hadn't run at all yet? so rings aren't bed in at all, run it and retest later.

[The Mafia]

Did you use turbo or NA pistons mate?

[Ben C34]

Did you use turbo or NA pistons mate?

Turbo pistons would be ultimate compression fail .

[KiwiRS4T]

Sounds like my engine. Unless you're going to pull it apart and put in some high compression pistons you may as well carry on and test it again when its been run. Thinner headgasket would help but will not make a significant difference. My compressions are all around 120 and I am making 314AWKW with a 3540R. PM me your no and I'll give you a ring if you want.

[evoeta]

Hey guys, turbo they are non turbo pistons, and sweet didnt think about rings not setting in? And tried to get headgasket and 1.3 was thinnest sta parts had. Next time will get 1.2

[Duncan]

absolutely don't worry about the compression until the rings are bedded in. and for what it's worth the motor should be warm too, as well as a healthy battery (which they normally aren't by the time a motor's been pulled out, rebuilt, and put back in)

[AngryRB]

with the above build would it be a good idea to shave the head inorder to increase the comp? 1mm?? how much piston to valve clearance is there usually?

Edited January 2, 2014 by AngryRB

[Simon-S14]

No don't shave or Deck. The cr gains is minimal