measuring piston to deck clearance on 440 source dished piston

[68-500]

I agree.

 

[Paul_G]

If I had a way to measure the actual deck height it would answer some questions. How much was the deck cut at the first shop? What is the actual deck height now?

My guess, the first shop zero decked it. Then after the thing popped out a freeze plug and cooked the engine they had to cut it some more, along with the heads. Then they had the pistons sticking out of the holes and sent it anyway with 12:1 compression.

I dont have the stock crank, pistons and rods or I would put them in and measure where the stock pistons are at now.

 

[Kern Dog]

I have a couple of comments.....

. the stock head at 78cc is, 11.06:1. No wonder it detonated itself to death in 5000 miles.

How heavily milled was that stock head? I've cc'd a few and uncut open chamber heads are often near 90 ccs, I had a few come in around 86 ccs after a few resurface jobs.

I seem to remember Kern Dog trying alp kinds of things to get his stroker not to detonate. He finally solved it. HE STUCK FAT HEAD GASKETS IN IT.

Oh yeah...I was close to 11 to 1 with aluminum heads and with anything less than 110 leaded gas, it would knock. I tried several things to eliminate the knocking but it wasn't until I went with thick head gaskets that the knocking stopped.

Not sure what KD had going on with his engine. We’re discussing Paul G’s engine.

Yeah, but like anyone smart, 33 looked to things from the past to solve a problem in present day. This is something that seems to be LOST on some people today. The reason we study history is to try to avoid making the same mistakes over and over.

 

[gkent]

Someone has cut the deck quite a bit to be proud 0.012”.

440Source pistons are measured on the large flat surface - NOT the bottom of the dish or any raised portion. Yes, you want to measure on the pin centerline or close to it - if that means at the edge of the piston that's fine.

FWIW the pistons on my 526 are .016 out of the hole - they should have been .009 IN the hole !! Since my block was not finished for MLS gaskets, I used .062 SCE copper gaskets with a stainless fire ring in them. NO issues.

I have Indy aluminum heads. I figure compression is around 10.5:1 - give or take. I run 36* advance and 92 or 94 octane unleaded gas.

Its worth noting that all the compression numbers piston manufacturers give are based on the block manufacturers "blueprint" deck height and stock gasket height with the cc volume of whichever head you're running. So to achieve the advertised compression ratio with a specific head you have to adjust the head gasket thickness based on the piston relative to the final deck height. In a nutshell, you want the head mounting surface (including the gasket) at the same height a stock head would mount. Block deck surfaces should always be measured. Any deviation + or - should be corrected with the head gasket.

 

[dvw]

If the pistons are a true .012 out of the bore I would .050-.060 hg. And have the chamber in the heads and the dish in the pistons enlarged to get to the desired cr. More than .050 quench distance your opening the door to detonation again.

Personally I believe quench is overrated. Does it help with detonation, yes. Will it overcome insufficient fuel octane, poor chamber design, compression to high, camshaft to small? No. Is there is a difference between a .038" gasket at zero deck vs an .050" gasket at +.012" deck? Yes, the positive deck will have the dead area above the ring closer to the deck which is a small benefit, though very little. In this case that compression would still be too high. I'd run the thick gasket and get the compression down. At tthat point it won't care if it has quench. Many race motors run no quench. Especially boosted and nitrous stuff. My race motor runs zero deck at 15.1-1 with a .060" gasket. Just have to match the fuel to the compression ratio. In this case 10.3 using an aluminum head on 93 octane will never detonate.
Doug

 

[Paul_G]

I have a couple of comments.....


How heavily milled was that stock head? I've cc'd a few and uncut open chamber heads are often near 90 ccs, I had a few come in around 86 ccs after a few resurface jobs.

I dont know how much was cut from the heads by the first shop that screwed it up. The machinist who has them now is going by cc volume. One head was much less than the other. I am calling him today and will get the actual numbers.

 

[PRHeads]

I like the “buy a new bare head” plan(as long as the head to be reused is still close to 78cc’s).
Pair that with the 27cc piston out of the hole .012” and a cometic .051” gasket.

(I get 9.93cr for the above combo)