Zero Deck and valve clearance
Elder User
Joined: Aug 2001
Posts: 962
Likes: 2
From: Collierville, TN
Zero Deck and valve clearance
Hmmmm...our math is a little different. I have an Excel spreadsheet I set up some time ago for calculating clearances and compression ratios on FE engines. Assuming a stock (10.17") block, I come up with a piston-to-deck clearance of 0.016" using those pistons with a standard 390 crank (3.78" stroke). 1.89" (throw) + 6.488" (rod length) + 1.776" (piston height) = 10.154". That's 0.016" "down the hole", and a total of 0.057" from piston top to head at TDC with a .041" compressed gasket. With 72 cc Edel 6006 heads, and roughly 5 cc of space for the valve reliefs, you have a static CR of 10.1:1.
Offset grinding the rod journals .010" would make your throw 1.90" and stroke 3.80", right? The piston would move .010" higher, resulting in a piston-to-deck clearance of .006" and a CR of 10.4:1. If you added yet another .010" of throw (3.82" stroke), you'd have the pistons .004" ABOVE the hole at TDC, which gets you darn close to that .035" optimum "quench" space you wanted. Static CR is up to 10.6:1. Incidentally, that 3.82" stroke also gives you a nice round 400 cid.
I can't advise on whether or not that's a good idea. I have no experience offset grinding cranks. DF and others here talk about it from time to time, and I understand it can be done if your machine shop knows what it's doing.
Offset grinding the rod journals .010" would make your throw 1.90" and stroke 3.80", right? The piston would move .010" higher, resulting in a piston-to-deck clearance of .006" and a CR of 10.4:1. If you added yet another .010" of throw (3.82" stroke), you'd have the pistons .004" ABOVE the hole at TDC, which gets you darn close to that .035" optimum "quench" space you wanted. Static CR is up to 10.6:1. Incidentally, that 3.82" stroke also gives you a nice round 400 cid.
I can't advise on whether or not that's a good idea. I have no experience offset grinding cranks. DF and others here talk about it from time to time, and I understand it can be done if your machine shop knows what it's doing.
Cargo Master
Joined: Aug 2000
Posts: 2,931
Likes: 12
From: SW Michigan
Zero Deck and valve clearance
Tom, it looks like Karlsd's math is right on the money. If memory serves, Bill Ballenger has this combination in his truck and he has the 057 clearance. I like the way you think about the offset grinding. Keep in mind however, that some shops don't know how to do it. And to gain .010 in throw, you would have to cut the rods down to .020 size. Another option you have is cutting the decks on the block .010. Your machinist might be cutting the decks anyway........ so why not ask for the .010 off each one? After a while the intake doesn't fit as well when the heads or the block have been decked alot. the solution is to cut the intake face of the cylinder heads the same amount as the decks. Don't ever cut the sides of the intake manifold- if your shop suggests this, get a new machine shop. I think you have lots of clearance for the valves but it is always safest to check anyway. DF
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