Cutting lots off 12V head

9724VF350

9724VF350

Tractor Guy
Joined
Mar 2, 2010
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Anyone try cutting roughly .100-.150 off a 12V head to unshroud the valves? Haven't cut a head up in the bandsaw yet, but looking at the water jacket openings it seems like it should be thick enough to live.

Flycutting and really thick injector washers would be obviously necessary, and it would end up increasing compression and low lift flow, cylinder pressure would go up for both reasons.

With the injector angle it would make the material in between the injector hole and the valve thicker, maybe slightly less prone to cracking there.

I'd think it would be a better alternative to just milling/grinding around the valves and losing compression in some cases.

Seems like a good setup for a street truck with a big camshaft, or in my case a puller just wanting more air.

Thoughts?
 
is extending the just valve seat itself an option, then flycutting the pistons?
 
OrangeNV said:
is extending the just valve seat itself an option, then flycutting the pistons?
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Thought that over pretty hard, the OD of the seats would have to be fairly big to get it up far enough to fully unshroud, head would be pretty thin between seats, Valve length/ installed height would change, seats are potential meat grinders.
 
Ive got one cut in half if you want a picture, 24v though?
 
Have them both on the bench cut up. The 12v is around .565" to .581" and the 24v is .472" to .479" There may be more or less material in different spots but that is the common thickness. I have cut up to .080" with no issues.

Zach
 
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Ok, they start at the bottom. Sorry for not typing anything inbetween them. This was the first time using photobucket and uploading.
 
Hamilton Cams said:
Have them both on the bench cut up. The 12v is around .565" to .581" and the 24v is .472" to .479" There may be more or less material in different spots but that is the common thickness. I have cut up to .080" with no issues.

Zach
Click to expand...

Due to the application of the first one I'm just going to stick with .080 off since it will be getting thin under the 1/2" pipe plugs under the intake.
Any suggestions on valve relief depth with one of your 181/210's, std head gasket and about .010 off the block?
 
After a bunch of measuring and figuring, on a combination that does not actually need valve reliefs, cutting .080 off the head and .080 flycuts you get rid of 4cc's. Don't seem like much, but it's enough to go from 16:1 to 17:1 A .020 over head gasket is a 4.5cc gain and the negative difference is pretty noticeable there.
Not to mention the cylinder pressure gain (mostly at cranking speed for starting) from the little extra low lift flow.

On a engine that needed .020 extra clearance for valves, doing it with a head gasket based on a 65cc/16.13:1 figure, it would put you at 15.15:1.
Cutting .080 off head and .100 flycuts would put you at 16.86:1
Huge difference in driveability.

The base 65cc I pulled out of my arse because it was close.
Piston bowl diameter will change figures slightly. the smaller bowl diameter will mean less of a change since you are taking more cc's of aluminum out with flycuts.
 
How do you lose 4cc of compression volume by shaving the head and removing material from the piston. Do the valves protrude that far into the cylinder after to reduce the volume that much?
 
Tate said:
How do you lose 4cc of compression volume by shaving the head and removing material from the piston. Do the valves protrude that far into the cylinder after to reduce the volume that much?
Click to expand...

The material cut out for the valve reliefs is not the full diameter of the valve. Some of it hangs over the bowl of the piston.
 
your wasteing a lot of time shaving the head. you wont gain enough low lift flow to even notice any power difference. if your wantin to raise compression then it aint a bad idea but IMO its a lota work for nothin. as for your question with a 181/210...thats just duration numbers. what kinda lobe lift you running and what piston? you wont know how much flycut youll need until you get your head torqued and check valve clearance.
 
lenahan05 said:
your wasteing a lot of time shaving the head. you wont gain enough low lift flow to even notice any power difference. if your wantin to raise compression then it aint a bad idea but IMO its a lota work for nothin. as for your question with a 181/210...thats just duration numbers. what kinda lobe lift you running and what piston? you wont know how much flycut youll need until you get your head torqued and check valve clearance.
Click to expand...

I know that's just duration, that's why I asked Zach directly since he's the one that engineered the cam.
It is mostly a compression thing. (at least it kind of went that direction) In my application I'm just trying to bump it up some. Don't remember lobe lift, not that that will tell much anyhow. Pstons are 286210's. With the block decked .010 and the head/valve relief crap I'll end up at 19:1-19.5:1.
Cut .080 reliefs in a piston today to check clearances, then cut as necessary on the ones I'm gonna use.
I know low lift gain is gonna be minimal. Full power/boost you'll never notice it, it's at starting and low/no boost that it'll come in to play.
 
Instead of cutting off the head. Why wouldn't you just cut seat pockets and press new seats in the head. That way you can put the seats higher in the port and un shroud the valve that way. You will probally need longer valves tho.
 
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