Shaving the head, how much is too much?

[keith0alan]

We used some seriously cut heads on the race car. After matching the squish area and combustion chamber volumes the compression ratio didn't get that high. We used premium pump gas. I believe the real magic is managing preignition with the squish area. Done right is reduces the flame propagation distance in half compared to a sloppy chamber that would be produced by only using a thick head gasket. The down side is of course that it is very labor intensive but the results are quite impressive.
There are several ways to achieve acceptable results in a street car and I wouldn't call any of them wrong. It is a balance between time, money, skill, and results.

[rbhenderson]

We used some seriously cut heads on the race car. After matching the squish area and combustion chamber volumes the compression ratio didn't get that high. We used premium pump gas. I believe the real magic is managing preignition with the squish area. Done right is reduces the flame propagation distance in half compared to a sloppy chamber that would be produced by only using a thick head gasket. The down side is of course that it is very labor intensive but the results are quite impressive.
There are several ways to achieve acceptable results in a street car and I wouldn't call any of them wrong. It is a balance between time, money, skill, and results.

Is there a good reference on the squish area/machining you did? Do you have any pics you'd be willing to share?

[redroadster]

Headgasket thicknesses varied greatly
I like Victor gaskets had the graphite like composition

[keith0alan]

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I didn't really photo document the process but here are some pics. The top one shows the grease from the piston top transferred to the head. This lets you know where to remove material from the head. The process is repeated many, many, many times.

[JT68]

Very nice work Keith, there is definitely many hours per chamber in that especially if you are CC'ing every chamber to match each other. Basically man-days.

Here are some real-would numbers for everyone:

I just did a quick measurement the CC of an aluminum head that is cut .060" The smaller 1&4 chambers were 41cc. The stock domed pistons would certainly hit the head on chambers 1&4. Would be close on 2&3. An iron head might be different since they are different castings.

41cc gives a static CR of 10.3 so if simply ground out to clear the piston, (call it 42cc) the static CR is just over 10:1. That is pretty hi for 93 octane without modern electronic engine management. (and 1 full cc is a lot of grinding!)

My guess is you removed enough material or your cam timing put it in the 9's of you are not detonating on 93. Again, very nice work and a labor of love!

The last track R16 we did had forged domed pistons and Carrillos's. It was just under 12:1 (Like 11.8:1) and we started with an NOS head (47 cc) because of the big piston domes. It was a 3main and engine dyno'd at 144hp with race headers. It was not a crazy camshaft and was very happy on 100 octane and was raced a couple years before it was torn down.

Most the 5main racing 1600 engines didn't get much over 135/140 and as I recall Col Joe got into the high 150's (w/3 mains) with many grenades along the way. Good times!

Of course STROKERS present a bigger problem with shaved R16 heads since with flat tops and that 41cc head you are already at 10.5...add some overbore and its getting out of hand quickly. (add the factory domed R-piston and it is pushing 12.5:1 LOL)

There is also another practical limit on cutting the R head, but I'm not sure what number that would be. At some point the water passages where they meet the HG get pretty thin and start to lose enough crush for the Hgasket to seal-they start to weep and erode. Guessing around .100" cut, but that is just a guess. Hope this helps!

[keith0alan]

This guy has forgotten more than most will ever know. Not Datsun but great to watch. https://youtu.be/nCU6xXPR8pw?si=zeR-yPhCrcwHKsrz

[JT68]

yep, that guy is great, lots of good info. He works on all kinds of wacky stuff too-very entertaining! Note what he said about porting-there is little reason to go nuts with it. Our flow bench work shows little or no gain from retentive port work-clean up the castings-not much more is needed on Nissans.

[martinmmartinezc]

So, I've got this head that's been through the wars. Shaved it 60 thou already, and it's 22 thou warped. Considering some more carving to fix the mess from a head gasket party gone wrong. Wondering how low I can go without hitting oil or water passages.