KingKiller

iTrader: (7)

Hey guys,

My friend's 2004 GTO seems to be down about 50rwhp.

-6sp
-Kook 1-7/8"
-SLP LM2 catback
-MSD Wires
-NGK TR5 plugs
-Cam: 226/234 600/600 112+4

Here is the dyno graph. The dotted black lines are a headers only GTO.



You guys have any ideas why the power is so low?

DACTARI

iTrader: (1)

Have to ask-- same dyno? both runs SAE corrected?

KingKiller

iTrader: (7)

Same dyno yes, not sure whether the numbers are corrected or not.

Darkman

iTrader: (2)

Any other symptoms - Codes? Misfire? Valve Float? or other atypical behavior?

KingKiller

iTrader: (7)

Nope, that's what's weird. No codes, no misfire, no valve float. Idles well, you can tell it's not the stock cam.

Darkman

iTrader: (2)

Regarding the absence of codes - does it have a tune that turns off any of the usual codes (other than the post-cat O2 sensors)? It is tuned for the cam is it not?

KingKiller

iTrader: (7)

I don't have any visibility into the tune, but Don from Slowhawk racing did it and he has a very good reputation from what I've heard. I don't know that any important codes have been turned off.

Darkman

iTrader: (2)

Tuners typically do not turn off codes without being asked to do so. Given that, I would check the compression and fuel pressure to start.

KingKiller

iTrader: (7)

Compression test showed all over 165. Leakdown test showed about 8-10%. AFAIK air/fuel was fine, the tuner would have noticed if it was going lean.

Darkman

iTrader: (2)

Did the tuner have any ideas?

Does it have catalytic converters?

KingKiller

iTrader: (7)

Tuner thought maybe the cam was off a tooth, or the lifter pre-load is wrong. Has 7.400 pushrods. No cats.

Darkman

iTrader: (2)

The push rod length does sound short since it is stock and the cam likely has a smaller base circle which would suggest 7.425" minimum length. Having said that, measuring the preload is the only way to determine whether the push rod is too short. Secondly, a push rod that is significantly too short would cause a lot of valvetrain noise and sometimes even low oil pressure.

I am not sure whether having the cam one tooth off brings about other symptoms other than the visibile problem you have, which is missing power.

Burken01

iTrader: (88)

More importantly was the cam degreed?

Who did the install

JakeFusion

iTrader: (7)

I'm betting it's off a tooth.

KingKiller

iTrader: (7)

hmm so what would be the result of too short of a pushrod? would that reduce the effective cam lift/duration? We'll have to see if we can measure the preload.

A local LS1Tech member who is well known for his success with the LT1 motor did the install. I've never been involved with degreeing a cam, but from what I understand to degree the cam you have to have adjustable gears and this car has fixed gears.

KingKiller

iTrader: (7)

It certainly seems like a possibility based on the dyno-graph. The installer said he saw coolant on one of the plugs last night and believes it's a headgasket issue. If that's the case my friend is just going to wait to pull the heads until he's ready to install his new heads. It's just hard to swallow considering the compression and leakdown tests came back good and the car doesn't use any coolant.

Darkman

iTrader: (2)

The symptoms of a short push rod vary. If it is only a little short, preload is inadequate to allow quiet operation, but it will not necessarily affect cam lift or duration because the lifter will fill with oil to take up the difference. If the push rod is signicantly too short, there is no preload. With no preload cam lift and duration can be affected but there would be a lot of valve train racket and it would be very noticeable. Oil pressure can also be erractic. Beyond that (even shorter push rod) there would likely have been valvetrain damage on the dyno at high rpm.

As an aside, most cam installs are done dot-to-dot and without the cam being degreed in. I am not saying that is the best method, but it is the most common.

KingKiller

iTrader: (7)

Thanks, that makes sense. His motor isn't noticeably loud. I think it's quieter than the 05 I had.

This install was done dot-to-dot.

Darkman

iTrader: (2)

Well, unless someone else has another idea I would consider pulling the timing cover to verify that it is not off by a tooth. Having it off by one tooth is not an uncommon mistake. There just aren't any symptoms pointing to other issues.

KingKiller

iTrader: (7)

As far as the preload goes...how much preload should I be looking for?