Decking block, impact on intake manifold fit

[Jack O.]

Hi,
I was told by the person I purchased my car from that the block had been decked twice. Once by the previous owner whereby most of the stamped numbers where removed and then again by him. The end result is that the block has been decked enough to remove all the stamped numbers. My question is what affect does that have on intake manifold fit? It would seemed that decking the block would result in a narrower gap between the heads. When a block is decked does the engine builder use thinner head gaskets to maintain fit or do other things have such as mill the intake to maintain fit? The reason for my question is that I've swithed the intake and had some leaking at the front and rear where it mates to the block. I didn't check the fit to closely without a gasket to see if the intake fit cotrrectly.
Thanks,
Jack

[Mark S. Lovejoy]

Re: Decking block, impact on intake manifold fit

Jack,

The intake may need machine work depending on the amount of material removed from the block. Most machinists know what to do. Some engine builders will make up some of the difference with thicker (not thinner) head gaskets. I have seen a chart with deck height to intake angle data, unfortunately I can't find right now. It will be difficult to determine intake fit with the naked eye, the change in mating surface angles are very small.

Deck height is easily measured and all good engine builders start with that. Should you have any doubts ask a machine shop to measure for you.

Hope this helps.

Mark

[Jack O.]

Re: Decking block, impact on intake manifold fit

Thanks Mark. It does help. Unfortunately I'm not rebuilding the engine so I'm limited on what I can check or have checked. I also no longer have the original intake to check that was on the engine when it was rebuilt. I would think the prefered method would be to use thicker head gaskets so you don't have cut on the intake but I'm sure there is a limit to how thick you can go.
Jack

[Clem Z.]

Re: Decking block, impact on intake manifold fit

i have cut heads up to .060 and all i did was elongate the bolt holes in the intake. with stock engines this do not cause any port alignment problems

[Mark #28455]

stock gaskets vs composite

the stock steel shim gasket is less than .020" thick. The Fel-Pro composite gaskets are about .039" thick, so if you decked off .020" and switched to the composite gasket, there would be NO difference in the intake location. For big block engines, Fel-Pro also makes gaskets about .050" and .060" thick.

Mark