sperkins

Stock '99 LS1 with headers. 352RWHP before a serious over rev bent a few valves at the NASA nationals race in Sept.
I swapped one cylinder head (stock to stock - both crappy 853 castings) and upgraded the valve springs to PAC1218's on both sides.
Since then, the car is noticeably down on power. I haven't had a chance to re-dyno, but my data shows a loss of 9mph on the back stretch at Rd Atl. 148mpg in the heat of the August summer vs 139mph this past weekend where the December air was perfect - cold and dry.

The cyl head was from a low mileage car known to be in great condition. It was from a friends car that ran strong before he swapped heads and cam.

Is it possible that switching the valve springs may be the main culprit?

Jason

I dynoed 363 3 years ago, and have spun the dog sheit out of my engine ever since. Put fresh valve springs in and dynoed 365 this year. I'd say the fresh springs helped maintain the hp level.

RX-Ben

With those baby springs, it should be neglible at most. Even with big boy springs, many builders find no difference.

http://ls1tech.com/forums/generation...e-more-hp.html

At that speed - 9mph is a lot of hp (like adding a serious wing). Are you showing decreased acceleration in the lower ranges? Anything else odd?

drivinhard

down 30 hp, still whipped most of the TTA field

something was for sure up, I have run with your car a lot, I've never closed in on you like that.

I'd recommend just leaving that motor in, as is

brkntrxn

Hell, I'll buy it. The thing won't die!!!

davidfarmer

unless the valves are floating, which I think you'd notice, I wouldn't expect there to be that much of an issue. The springs just need to be stiff enough to keep the roller on the cam at all times, and enough seat pressure to make a good seal (for a few milliseconds)

varkwso

My similiar problem in August was oil from the valvecover going into the air bridge and fouling the MAF. I doubt it is your springs. You could have tweaked a ring and lost some compression. Have you done a leakdown test?

sperkins

The MAF is at the air box though?? You're saying the oil was going upstream through the bridge all the way to the MAF?

Negative. My gut feeling is that there's a valvetrain issue on the other side of the engine. I checked the push rods on that side when I installed the springs, but didn't do a compression test. It's possible there may be valve damage over there, but there were no bent push rods and the valves stayed up when I used compressed air in the cylinders to install the springs.

varkwso

I poured oil out of air bridge....

drivinhard

get on it

travisnd

Old motor that gets the snot beat out of it.... I'd check the compression first then move on to the next steps.

And Jeff's right... if you're really pressurizing the crank you can push lots of oil into the intake to the point it'll drip out of the filter. There's a reason I have two catch-cans installed.

Luckily mine's an '01 so it just burns the oil and doesn't give it a chance to make it to the intake... it just makes it to the rear bumper

Z06Tracker

Yep, like Jeff and Travis, I was also pushing oil out the filter.