tanmanski

This is unrelated to my other open thread.

My '95Z had an unfortunate run in with a tree one foggy December night a couple years ago. I just got around to tearing it down for salvage (parts to be posted in for sale soon) and obviously will be saving the stroker motor and tranny, both of which were in good shape at the time of the wreck.

The 389 was professionally built by a race shop with a good reputation and it ran like a raped ape. I think dyno was 410 or something close to that, before fine tuning.

When I took the heads off everything looked good, nice clean chambers, good valve seats, all roller rockers and lifters good, but...

There were TWO head gaskets on both sides. I have never seen this before and it seems like a really bad idea. There was already some indication of "blow by" on one cylinder, so I know I woulda had a head gasket issue if it had been run much longer. I know WHY they probably did it - lack of valve to head clearance with big cam AND 1.6 rockers, or too high compression or maybe both.

My question is, how to put it back together correctly? I'm assuming they already had the thickest head gaskets they could find...I suppose I need to bolt it together with modeling clay in the chamber and actually measure valve to piston clearance right? Allowing for thermal expansion, float etc, what's minimum clearance?

How do I calculate theoretical compression ratio? Measure cylinder head chamber volume and?

If its just a matter of ditching the 1.6 roller rockers for 1.5 I can probably live with that. I never did get a good number for total intake and exhaust valve lift so I've got no base numbers.

OR, if properly torqued ( a couple of the "bitch" head bolts weren't at specified torque) is double head gaskets no big deal? Just slap two thick ones in, torque it really well and go?

thanks guys

97WS6SCharged

You need a bunch of measurements to calculate the compression ratio. Bore, stroke, chamber volume, piston compression height, gasket thickness, piston volume. You can Google for the actual formula as it's a bit involved.

As far as your gasket question goes... Don't use 2 gaskets. Check your PTV clearance with clay and then decide from there. If you need a thicker head gasket then I would look into a custom gasket from Cometic.

tanmanski

cool, thanks, I didn't know about custom thickness head gaskets

Chimera96

the 2nd point would mean the 1st one is false assuming they installed 2 head gaskets vs someone after they built the motor

you need to do a clay test to see WTF valve to piston clearance you have. IIRC a stock AL head gasket for LT1 is .050 thick. iron heads used .029 thick ones

tanmanski

Yeah, it was disappointing to say the least. I can only assume the shop owner had one of his junior guys assemble the engine and for whatever reason he didn't report an issue to the owner and tried to "fix it" on his own. Even when you think you've got a shop you can trust, unless you're there watching every step, you can get less than what you expect. At least I caught it before something expensive got ruined.