DBKZ06

Seeking any advice because we can't seem to diagnose the source of my problem.

Background
Car was in good condition putting down ~480rwhp prior to Friday, 422ci w/ LSx Intake and TPIS 90mm TB.
Went to the shop to put in 1.8 rockers and an LS2 TB in search of better drivability.

Did the wiring for the LS2 TB and put in the rockers and put the car on the dyno.
First pass made 406 rwhp Obviously not an amount that's gonna get tuned out.

A/F was good, no knock, timing was good, fuel pressure good, etc. Later we threw back in the original program and the TPIS to rule out if it was TB related. Still made about 408rwhp. Then it started throwing MAF and TPS codes, going into reduced engine power, so we knew it wasn't the LS2 TB. Fooled around with the wiring and got the reduced engine power to go away. Took the valve covers, did a leak down (2%) and checked cylinder pressure(low- took about 5 cranks to get to 140), so we reset the rockers. Sure enough they were a bit outta wack, and that solved the cylinder problem. But put the covers back on and ran it and the car still made 419rwhp and no torque.

At that point we gave up because everything mechanical seemed good. So I'm back with my original tune and TB, plus 1.8 rockers, and I'm down about 70rwhp. Still throwing the p0101 maf code. Anybody experience anything like this and could it be internal? The gut feeling is screwing with the wiring for the LS2 TB caused an issue between the info shared from MAF and TB causing a precipitous loss of power, but it's scary thinking maybe something in the motor went down. Still drove home 300 miles with nothing exploding.

Ideas?

BTL FED

iTrader: (9)

How big of a cam where you running, and how much lift could the valve springs support. If the valvesprings werent up to the task of the higher lift you could have floated the valve's and one could have kissed a piston.

Tony Mamo @ AFR

iTrader: (13)

You are probably experiencing valve float...common with 1.8 rocker installs on aggresive hydraulic roller lobes. Put your original rockers back on and see if your power comes back....problem solved if it does, if it doesn't then you can spend your energy looking for other issues. I doubt it's the TB, but anything is possible.

Good luck....

C_Williams

I agree with Tony -

FWIW - At A&A Corvette we've done some back-to-back tests, aftermarket vs LS2 TB, and not seen losses.

Good luck,

Charlie

DBKZ06

The cam is 248/248 111lsa and with the 1.8s I was told the lift should be in the .603 range. Is that really that aggressive for 1.8s? I kept the stock rockers around so we'll probably throw those back on next. I'd be bummed about wasting the 600 bucks on the rockers if that's the problem.

Also, if it is causing valve float, what would that look like on the dyno? From what I was seeing it appeared that there was no point where the power began to drop specifically...

Thanks for the help guys.

Gman2002Z06

What was the original lift specs on the cam with 1.7 rockers...You say you figured that you had .603" of lift after the 1.8 rockers were added, but the cam has 248 degrees of duration...That would mean that the lift with 1.7 rockers was only .570"...That doesn't seem to go along with a cam having 248 degrees of duration...I would have thought that size cam would have been in the .600" range with the 1.7 rockers, 1.8 rockers would have put you at about .635" lift and if this is true, that is alot of lift with that size of LSA...Are the pistons flycut deep enough to handle that much lift...If not, you may have bent a few valves over...

Recheck your original cam lift specs and let us know what they were...

Peace...Gman

DBKZ06

Gman,
I was told the cam was designed specifically for 1.8 rockers, and with the 1.7s it was in fact only in the .570 lift range. We just didn't get ahold of the rockers at the time of the original install, so the car was running with less than ideal lift, which is why the power was a tad low. I agree that it seems strange to have a cam with that type of lift with that amount of duration, but this is what I was told.

Thanks,
Dave

Gman2002Z06

That does seem strange, but if they ground the specs relative to you using the 1.8 rockers, then the .600 lift would be right based on that...Still, even with the .600 lift, when the motor was built, were the pistons flycut for clearance...With the 111 LSA, I would think that you may have some problems at .600 lift...May have been why at .570" lift you didn't have a problem...Hopefully this is not the case and it is only a wiring/MAS problem...

Peace...Gman

Mike94ZLT1

iTrader: (3)

Is this Dave Bannister by chance?

edit: Yes it is. Where did you take your car to to get this work done? You still aren't trekking all the way to Toronto are you? (It's Johnson, by the way)

DBKZ06

Depends on who's askin, although I've got a pretty good guess

Mike94ZLT1

iTrader: (3)

I'd go with your gut feeling on this one Hmm... guy named Mike, drives a 99 SS, a Blue one at that, who identified you by your engine and initials... thats right! It's Jason ***, in disguise!