My first impression was FUCK i have rod knock... but my oil pressure is just fine, the oil is clean, and the knocking only comes typicaly when under load or just barley idle... when i accelerate or rev it sounds clean.. doesn't get worse....

My buddy said he accidently put reg fuel in.. not the high octane stuff... could this be causing it?? we are running around 10psi... on 8to8to1 compression crower rods with arp bolts and forged pistons...

I also haven't felt any loss of power.

Probably just piston slap. Do you have JE pistons?

Quote:

Originally posted by BoostedGS
Probably just piston slap. Do you have JE pistons?

yes

just about everyone on here with a rebuilt engine has this sound including me. it's perfectly normal, there have been a lot of threads addressing this. if the sound doesn't go away by the time that the engine is fully heated up then you have a problem - either it's rod knock like you originally guessed, or whoever rebuilt your engine left a piston to bore clearance that's too large. anyways, the noise should go away when the engine is fully warmed up. let me guess... it's worst when you first start up the car on a cold morning?

Quote:

Originally posted by ner947
just about everyone on here with a rebuilt engine has this sound including me. it's perfectly normal, there have been a lot of threads addressing this. if the sound doesn't go away by the time that the engine is fully heated up then you have a problem - either it's rod knock like you originally guessed, or whoever rebuilt your engine left a piston to bore clearance that's too large. anyways, the noise should go away when the engine is fully warmed up. let me guess... it's worst when you first start up the car on a cold morning?

actually it's worse at low rpm under load.... it doesn't get worse per rpm range i can usually hear it around 1000rpm to 2000rpm but fades rather quickly afterwords.... It may be the fuel im not sure though... I think just to be safe im going to drop the oil pan and check everything out.

Be careful, pushing 10psi on 87? octane is right on the edge of causing detonation. If you're hearing it at high loads & high boost, it could be detonation. Piston slap and detonation sound very different, but its confusing since you have to know which is which first.

Anyways, if it knocks when the engine is fully warmed up, don't boost anymore until you get high octane back in.

bah. thats why i never let anyone do anything with my car. bitch slap him for using the cheap gas.:nono

Quote:

Originally posted by thedawg
Be careful, pushing 10psi on 87? octane is right on the edge of causing detonation. If you're hearing it at high loads & high boost, it could be detonation. Piston slap and detonation sound very different, but its confusing since you have to know which is which first.Anyways, if it knocks when the engine is fully warmed up, don't boost anymore until you get high octane back in.

can you explain piston slap? this is all weird....
i still think im gonna drop the oil pan just to be safe.

Piston slap sounds like a diesel engine. HadesOmega has a clip on his imagestation site where you can hear the pistons slapping .

Detonation sounds like 50 marbles just got dropped into your engine, but the noise goes away immediately if you back off the throttle.

Could be valvtrain related also.

1999 Black C5
1997 Silver RS
Wiseco 8.8:1 Pistons(back to low compression!)
Eagle Rods
T3/T4 Turbo
Custom FMIC
Greddy Exhaust
390's
Most current 1/8th mile time: 8.3@90mph 2.015 60'(Nitto Drag radials, i suck)

Originally posted by Nitrous_RS1997
Could be valvtrain related also. 1999 Black C5 1997 Silver RS Wiseco 8.8:1 Pistons(back to low compression!) Eagle Rods T3/T4 Turbo Custom FMIC Greddy Exhaust 390's Most current 1/8th mile time: 8.3@90mph 2.015 60'(Nitto Drag radials, i suck)

I have already started to take the head off... well kinda i took the valve cover off im still working on getting the stupid wastegate off... my waste gate is horizontaly placed and im having a bitch of a time getting the last screw out... once that is done i'm going to be taking the turbo out and then the turbo manifold. then i will pull the head bolts and lift the head out after breaking the timeing cover. How do i know for sure if it's a valvetrain issue?

i'm really starting to think this is the case because when my engine first went the first time it was the headgasket and got nearly the same compression scores... #1 was at 80... this time it's at 60...


Any idea's?