mitchntx

I get a little puff of blue smoke on a hard downshift.

So, I'm yanking the heads to have them freshened. While I'm at it, I'm considering milling the head for an increase in compression.

It's a '98 LS1 casting. How much should I have milled? Will the increased compression change the torque profile, with everything else remaining the same?

I like the grunt I now have. I don't like RPMs. So, in many cases, I might be down to 3 or 3.5 pulling off of a corner.

All_Z_Way

Hey Mitch... I didn't know you were pulling it apart. Hope to see you Saturday.... then we can talk about what you are doing.

mitchntx

Not sure about Saturday ...

If I don't get my heads off tonite and shuttled to Yelvi tomorrow, I will do that Saturday.

94bird

Mitch, you're sure it's not piston rings? Rings don't cause high oil consumption only at WOT. Pullover can occur to the combustion chamber at light load if your top ring is fluttering. If this hard downshift is at higher rpm, I'd at least consider checking out your rings, especially since your heads will already be off anyway.

mitchntx

Time line ....

No smoking issues

Dec 2002
Bought a set of used heads supposedly ported by MTI.
Took them to a local shop to be inspected and freshened

Jan 2003
After a real port, and valve job, installed heads
Head guy said the guides and seals APPEARED to be OK

March 2003
First on track excursion, blip the thottle to rev match or hard on the gas after a long engine brake, get a nice puff of blue smoke.

Because it was fine prior to the head swap, using my root cause analysis training, I deduced it had to be at least seals and probably guides because that was the only thing that changed.

Still think it's rings?

94bird

Good thing you took those classes in root cause analysis training huh? Didn't realize you had just switched heads and only wanted to make sure you weren't ignoring a possible contributor. In your case you're likely right. If your heads were stock I'd look at rings too.

Elliswon

Have you already modified the PVC system so it doesn't draw oil into the intake?

mitchntx

That wasn't abundantly clear, so my bad.

And Mr. Reason would be proud!

mitchntx

No, I haven't.

Could you point me to a link that gives a parts list necessary to do the conversion?

I'm assuming you mean the LS6 conversion, correct?

I know you have to remove the valley tray and grind out a portion of a boss in the block to accomodate the plumbing.

94bird

The cheapo way I've seen that would help is just putting a catch jar in the system. All you need to do is slow down the oil vapor enough that it accumulates in a container before it's sucked into your intake system.

Hmm, noone's giving suggestions on your original question.

Elliswon

I wasn't specifically refering to the LS6 conversion...there are easier ways that involve plumbing a catch can into the line just prior to the PCV valve. I did mine with a few bucks worth of home depot hardware. Ghetto, but effective. I drain about 1/4 to a 1/3 of a cup of oil out of my catch can between track sessions that otherwise would be turned into little puffs of blue smoke. It's a lot cheaper than head work especially if the heads aren't the problem. I don't have a link but search for the catch can mod on your favorite forum(s). It's a pretty common mod.

mitchntx

Torque profile Q? Yeah, even on Tech, I'm getting nothing.

Maybe I should put 12 bolt, 200 shot, !sway bar as a sig.
Would get plenty of response then

94bird

Regarding your CR question, I wouldn't change your CR by milling the heads at this point. Another .5 in CR or less just won't make a real difference (maybe 5 HP or less) would be my guess. It'll make you more sensitive to detonation when your engine gets hot on track for those 20-30 minute sessions also.

However, I'm making an assumption you're running a stock cam still. Given your ported heads am I wrong? A larger cam will likely lessen your dynamic CR and thus giving it more CR may prove a larger benefit and your engine may still not be very detonation sensitive. If you're not running stock cam I'd highly recommend you call the cam manufacturer and ask what they recommend.

Elliswon

Give me more info like flow numbers, current CR, future CR, cam specs, bore and stroke...if other than stock and I'll run you some sims to see what happens.

mitchntx

stock Bore and stroke

Current CR 10.1 (according to chart here http://www.ls1tech.com/forums/showthread.php?t=111207 )

mill .020" to target 10.7 or 10.8

220/.558/114

I can get more precise flow numbers, but from memory they flow ~230 @ .400, 280 @ .500, 300 @ .600 ... very close to LS6 heads