joecar

Yes, I agree, the vid with the vacuum gauge is the best clue so far.

zacht

iTrader: (18)

wow! what a crappy problem....im sorry i got nothing for you...read the whole thread and find it interesting!

im subscribing to see the results! sorry to hear its been going on so damn long!

but...did i read you over headed the old heads (currently on the car) and havent tested the valve springs???

dtfastbear

Thanks for the compassion. I'm going to be soooo happy when it is finally resolved!

Over heated the new heads, which is why the old heads are on the motor currently. Starting to be enough things pointing to valve float that I should probably just get some new ls6 springs and swap them out. That's like $80 and an afternoon, right? The history of the old heads is a mystery, since i got that motor used.

The Alchemist

iTrader: (19)

Without a doubt, get the old factory springs off the heads and put a set of decent springs on there.

I gaurantee that if you check the currents springs, you're going to find more than a few that are quite a bit softer than factory specs.

While you're at it, put in a better set of pushrods as well since they are cheap. You'd be surprised at how easily a pushrod can flex under high rpms. Valvetrain stability is critical to producing cylinder pressure, and cylinder pressure is torque.

dtfastbear

LS6 springs and comp cam chromoly pushrods ordered this morning. I also got a generous offer of installation assistance and a valve spring compressor tool from a local LS1tech reader! Looks like I'm good to go. Will shoot for installing the springs in the next couple of weeks before my next race at the end of October. Damn, I hope this is it!

Cheers,

Dean

dtfastbear

OK, a seemingly positive development...

I changed the valve springs this morning to new LS6 springs and the stock pushrods to comp cams chromoly pushrods. A couple of observations:

1 - The proform LS1/6 valve spring tool is great! It sure made things easy.

2 - The springs coming off the car were completely shot, I think. Some of them were as much as a 1/16" or maybe more shorter than some of the others. Does that mean they're totally worn out? I don't have a spring rate checker.

3 - One of the symptoms that was pointing us to valve float was that after we'd rev the engine up through the "stumble zone", it would burble and run like crap at idle for a couple seconds. The theory is that the lifters would pump up when the valves floated, causing the valves to not close all the way for a few seconds at idle. With the new springs, THIS NO LONGER HAPPENS. Even if we would hold the car at 5500 rpms - the middle of the problem zone - and then cut the throttle, the car would idle perfectly immediately.

So, I'm cautiously optimistic. I won't know if we've really solved the problem until I either run the car on the dyno or get out on the track. I'm going out on the track in two weeks. Then we'll know.

As a side note, I took off the small borla muffler and fitted a short magnaflow race muffler and the car sounds totally awesome. I can't wait to get it back on the track!

Thanks for all the ideas and support along the way, guys. I'm hoping we've nailed this one.

Cheers,

Dean

dtfastbear

Only 4 more days until I get this thing on the track and will know definitively if we've solved this problem! I'm very excited...

dtfastbear

Valve springs fixed the problem! Power dip GONE.

Thanks to everyone who contributed ideas along the way. It would be easy to be super frustrated that I didn't try new valve springs earlier in this "journey", but I'm just so freakin' happy that it's fixed I just don't care about how long it took.

Whew. Now, onto getting the suspension right.

Cheers,

Dean

The Alchemist

iTrader: (19)

It's great to hear that a long running problem was fixed in the end with relatively low cost. I'm sure you had plenty of frustration and sleepless nights, but in the end, it worked out.