ArcticZ28

iTrader: (14)

Finally got my 6.0 block tuned and on the dyno last weekend. First off, it was not making very good power at all, dynoed ~350/353 with a real restrictive exhaust (shorties + catted Y + LM). But my real concern was a consistent drop in the graph at ~4200 RPM's, then there would be smoke (a good amount) coming out of the exhaust all the way to 6300 where we stopped. I'm just wondering what the hell is going on with this. It happened on all 3 runs at the very same spot as well. A/F was perfect and we even tried leaning it out to no avail. For a bit of info on this it's a 6.0 bored .060 over, forged bottom end with -2cc dished pistons, 244/248 .635/.627 112 +4 cam, Cometic .045 head gasket, stock LQ9 heads, ported TB, LS6 intake, etc etc with the restrictive exhaust system. What could possibly be causing this? I'm stumped.

conan

iTrader: (5)

What type of valve springs? Maybe valve float.

1fastWS6

iTrader: (3)

Do a leakdown and compression test first.

BrentB@TEA

valve float was what I was thinking also. Or spark knock.

ArcticZ28

iTrader: (14)

The springs are brand new PRC duals. I put the whole PRC kit on the brand new heads no more than 200 miles ago. What is spark knock exactly? All I know is that my tuner said there was no knock retard that he saw. I realize it could be the piston rings, but this engine supposedly had only 1300 miles on it when I got it and was in perfect working condition. That's what doesn't make sense.

Ron@Vengeance

iTrader: (51)

"Engine" and shortblock are two different things

Lemme know if I can help you out with anything man.

ArcticZ28

iTrader: (14)

Yea, just the shortblock had 1300 on it, the heads are brand new and so is everything else basically.

Cammin - I sent you a PM a bit ago about which route to go, didn't get your response though.

ArcticZ28

iTrader: (14)

Update - We were getting knock retard, but we were pulling timing like crazy and it was still pinging/detonating. It was burning oil so it's gotta somehow be getting past the rings or something, being that we checked the PCV return lines and it was bone dry, nothing was getting into the intake.

DaddySS

I was going to say PCV, since burning in the upper RPMs is often the result of greater oil volume in the heads and then getting sucked in. I would run it with the PCV plugged just to be sure. This will also let you see if there is blow-by in the rings as you will see lots of smoke/pressure coming from the vent.


The knock retard is because oil in your A/F mixture effectively lowers the octane.

ArcticZ28

iTrader: (14)

There wasn't a drip of oil in the PCV tubing, I checked that for sure. But yea, the lowered octane from the oil causes the detonation which I'm getting. I just have to figure out where the hell the oil is coming from and why.