SSkeet

05 Automatic trans GTO with a 230/236 cam, stage 3 heads..

Got the AFR dailed in 13.0 across and a strange thing is happening...

the car pulls up to 5200 and falls on its face and stumbles...and strugles to get past 5200-5400. If we stay in the throttle, eventually around 5800 the power picks back up and starts pulling again.

Could this be valve float or what? The power curve is like so...
3800-5200 the power climbs as it should.
5200-5700 the power falls off nasty
5800+ it picks back up and the power can be seen climbing again up to 6800.

AFR is steady entire time and never goes lean...there is plenty of fuel.

Any ideas?

Pwebbz28

iTrader: (31)

Any KR being picked up at those RPMs?

99Fbody99

very charactoristic of valve float!

Dave

SSkeet

Made several pulls...no knock whatsoever.

I thought valve float too, but it is strange that it starts to come back to life after 5700...I guess it could still be valve float, because its not making near the power it should be.

Patrick G

iTrader: (14)

Could be the torque converter coupling up if you ran it unlocked. What is your stall and did you dyno it locked or unlocked? A graph would help in this case.

V6 Bird

iTrader: (15)

Its the tune...try fattening the car up in that area and see if it comes around.

SSkeet

It actually responded best when it was between 13.5-14.0 but that is too lean and I could not let him leave with the car tuned like that. But that did not fix the problem by any means, Im just saying the car seemed to run best there. In the 12's it was really bad and richer than that forget it.

This could be, I didnt think of it. No I didnt tuen out the converter, I imagine this can be done in real time with the scanner? Still though, this happens on the street as well so I dont think this is the answer, even though it still could be trans/converter related.

Im still leaning toward valve float but not sure...

Patrick G

iTrader: (14)

The converter does not lockup at WOT on the street and this is exactly where you'll be experiencing it. One look at your graph would tell us for sure. Got a graph?

SSkeet

PROBLEM SOLVED> He called me today, told me his pushrods were the wrong length He replaced them and readjusted his rockers and now it pulls like a beast all the way through.

Patrick G

iTrader: (14)

Great. Do you mind telling us what was in there before and what's in there now? This might keep people from making the same mistake too.

Old Geezer

iTrader: (3)

I agree. If you have to add .400 of an inch to the prods, there's something wrong elsewhere...No way are the rods that far off. If they were, the drop in power wouldn't "wait" til the engine is over 5000rpm, to show up.

silverbeast

iTrader: (16)

how in the hell were they that far off on the push rod lenght?

1997bird

iTrader: (2)

If they were .400" short, they wouldn't even be able to touch the rocker arm pivot point.

1997bird

iTrader: (2)

"George" you are so full of **** your eyes are brown! There is NO way that you can get a shaft mount rocker to adjust that far.

SSkeet

I am the one tuning the car and I just recently met him. Although I dont know much about valvetrain geometry, what he told me was that what he did was replace the 7.0 pushrods with 7.3 and we went back to the dyno....car pulls hard through well past 5200. So even though you cant adjust them that much, I guess they were adjusted enough to let the car run...it just didnt make much power with the way it originally was because the valves were not opening near their potential and also it was breaking up nasty at 5200 before the 7.3's

georgevette

no need to insult if your the one that does'nt know ****. i had to shim the bottom of the pedestal almost and 1/8 of an inch to get the whole valve train to sit higher and it stills needs a little more to make it perfect. I dont want to turn this into a pissing contest but get all your facts staight before you give your all mighty advice. Yea you know alot alright shiming is the oldest trick in the book to change your geometry.

1997bird

iTrader: (2)

Shimming your heads 0.125" is not going to make up .400" (that was your origonal posting before you deleted it), I guess now it is .300", you can't adjust the rockers that far without oiling problems. Good luck with your long lasting engine combo.

V6 Bird

iTrader: (15)

Its only lean depending on who you ask.

Put a cold plug in there. Sounds like the heads are pretty efficient and if its responding to being lean, a cold plug and going leaner will make it happy. Dont fight the feeling man. Its after peak torque and VE's are dramatically down from 100%, it cant hurt itself with a NGK8 or 9 in the plug hole. Efficient cylinder head port work wants to run leaner to make power. Put precautions in place to remove heat from the chamber and let her rip.

V6 Bird

iTrader: (15)

Makes since but I still wouldnt rule out some better tuning.

Its the part the puts you in the middle of the pack with your combination or sets you out 2 or 3 cars and everyone else chases.

georgevette

its cool man i have'nt deleted anything but now i got my problem solved all the way. I shimmed it a little more this morning and put in the 7.400 push rods
and it feels alot smother now. crisper throttle response and smoother all the way across the rpm range. thanks for contributing your wealth of knowledge to this thread and helping a fellow member solve his problem and not just being an *** and saying negative things that dont help anyone on this board.