The lowest I'd seen was closer to .020, you also have to remember that the lt1 isn't a zero deck number the pistons are in the hole quite a bit so a thiner head gasket is usually pretty safe on these motors, i'd be more concerned about the possibility of blowing the gasket than piston valve interference (assuming the valves are properly controlled but that isnt really a headgasket issue). And I do believe the original poster has a stock engine so he should be pretty safe with the thinner headgasket.

 

Mine's at 0.030" even on this build.

 

You are either measuring quench incorrectly or you should be working with Reher-Morrison. At 0.020" between the piston crown and the head it will self destruct in no time. 30 is just BARELY possible. Are you figuring the gasket thickness or the quench? At zero deck, quench = gasket thickness. If the piston is proud, you need to subtract from the gasket thickness and add if it is in the hole.

Rich

 

I love this man and I'm proud to say it!

 

yeah mine is .005 in the hole on a .027 cometic (so it might compress to what a .026?). i think i spoke to you about it before rich , or someobody else.

 

Yeah. That is close but doable if you are good or lucky 20 is not no matter how lucky you are unless you are running at 4,000rpm or something. Again, is it even desirable to go that close? If so, not by much IMHO.

Just curious, did you measure it at 5 in the hole?

Rich

 

that fell on the engine builder . when the motor arrives i will mic it though. then put the heads on and turn it over a few times with some playdough and mic it also. i am kind of nervous about doing it but i belive in the gentleman that set it all up. i also trust the builder to do what he said he would/did do. we shall see.

 

piston 0.001" in the hole, 0.030" cometic, so 0.031" quench. I forgot that my block wasn't decked exactly at zero.

 

If those measurements are correct on all 8, it will probably be ok as I am figuring it is not a high revving (7,500+) setup. When they get down into the <30 range you start to see marks where the piston has "kissed" the head on teardown. This does not give me a warm, wet feeling, but whatever turns you on!

The variables that determine minimum quench (leaving aside what is the most desirable quench) are primarily the rod, rod bolt, piston bore clearance, piston weight, stroke, and rpm range. We are talking steel rods here, so the rod issue is largely moot. But even steel rods will stretch, and the heavier the piston the freater the stretch. A piston with loose skirt clearance will rock in the bore, decreasing clearance. The force on the rod is going to increase as the square of the rpm and the longer the stroke, the higher the piston acceleration. When you start getting to the 0.030" range, you had better measure every hole. There are going to be variations based on the quality of the parts and the machine work. Due to "stacking" of tolerances, you may find a couple of thousanths difference even on a good build. If an error was made in the wrong direction and you were aiming for 30, you could easily end up with a big problem.

I guess I have made my point, but I wouldn't try for closer than 0.035" in a street motor and more like 40 in a high rpm race motor.

Rich

 

i will measure all 8 and measure all 8 with clay with the heads tq'ed down. thanks for the warning rich , i will try to be cautious. later gents

 

measured all eight...all exactly the same. revving to 7k max.

 

My set-up is very similar, all my pistons measured .005-.006 in the hole, and I'm running the .029 impala gaskets...

 

Be careful how you measure. I don't think using clay is appropriate to measure quench - I believe it will yeild quench numbers that are several thou too large. I don't know what the accepted method is, but based on what I needed to do to get my measurements to even come close to my engine builder's measurements, I think a different method is called for.

When I measured mine, I found it was a bit tricky to get repeatable numbers, and the results varied by up almost 10 thou depending on how & which time I measured, on my pro built zero-decked shortblock. At first I simply used a dial indicator on a bridge to measure height of the piston centers, and got .004 to .009 in the hole depending on which hole and which time I measured it. Pushing the pistons down on the .004ish holes would bring them closer to the .009 holes. I thought, WTF, what kind of crappy build is this. Then I calmed down and realized I was probably measuring it wrong.

I realized that I needed to push UP on each piston from the bottom of the crown while measuring to get a relatively consistant zero-deck result, or else the piston measured several thou further in the hole. This makes sense; it is due to the way the bearing clearances were stacking up, and pushing up on the pistons is the way the engine will see it running.

Rocking the pistons while measuring caused a bit of variation, too, several thou at the edges. Fully rocking a piston while pushing up on it could cause the edge of the pistons to go a couple thou proud of the deck, but considering the pistons grow when hot I think worst case stackup hot would be close to zero-deck with full bearing clearance stackup and piston rock. By the end of my dozen or so measurement rounds the results were repeatable within a couple thou per hole, but that's the best I could do.

While the motor is running, bearing clearances are added to the part dimensions and part stretch (I didn't consider oil film thickness). Using the clay method, those clearances would not be included, since the pistons would be pushed down to compress the gaps, and the results would show more piston-to-deck clearance than the motor would see running.
If you push up on each piston at TDC while using the clay maybe that method would work ok.

That's how I interpreted what I saw, but I'm not an engine builder, and I've never even played one on TV. We could all no doubt learn more from a real builder's comments on how to measure.

 

You guys crack me up. Much ado bout nothin'. Just what do you think you are going to gain by using a thinner gasket. If you screw it up you are going to pay big time. On the other hand, there doesn't seem to be much to talk about any more except problems. And messing with the quench is a good way to spawn threads about "gee, I wonder how that happended"

 

This makes alot of sense to me, and now makes me nervous about my measurements of .005-.006 in the hole cause I measured the same way you did at first. My machine shop told me that it was zero decked but I took it upon my self to double check them... maybe I measured wrong too....and maybe I should ditch my impala gaskets and buy a set of Felpro 1074s just to be safe before I start this thing for the first time......