Milling Alum GN-1's

[StageII86]

Hey guys,

Champion advertises 46cc chambers out of the box on these. I'd like to see about 40-41cc's to get my build where I'd like it CR-wise. I plan on CC-ing the chambers on these heads anyway just because they are 2nd hand and we may alter the volume some after the valve job.

Who has milled their aluminum GN-1's, how much, and any issues?

Thanks,
John

 

[Eticket]

have you thought about just going to a thinner head gasket and milling just to get it perfectly smooth? I think the later castings have thicker deck surfaces... older ones, you want as much meat as possible.

 

[TurboBob]

smaller dish in the piston?

Bob

 

[Nick Micale]

We have cut alum heads down to 41cc only because they needed that much for a good clean-up.

It is not an issue, but it leaves very little more to cut if they ever need it in the future?

 

[StageII86]

Bob,
Best idea, yes, would be pistons with less dish. I'm working with the Diamonds and they are 29.5cc, but they're what I got as they were in this motor when I bought it. I may price another set and factor what I could get out of these to sell them.

John,
Originally I was calculating with a .035" but now I'll likely use a .027" to drop a hair more volume.

Nick,
Thanks for the feedback - that philosophy is sound for sure.

I talked briefly with Tom at champion yesterday and have decided (if I stay with these pistons) on likely running the .027" gasket, cutting the heads maybe .010-.015" max, and living with what that yields which should work. Fwiw, Tom is not a fan of removing much if any off the decks of these heads.

Thanks for all of the input. I got feedback from some great sources in this thread!

 

[Nick Micale]

One option is to use the 1984-5 factory steel shim turbo head gasket which is .018" when installed, and we have done this many times.

 

[bison]

I personally would never remove material off the deck and or heads unless I was trying to correct a flatness issue. There's very little gain in CR when removing from the heads anyway. A lot of removal does little. Pistons are cheap and easily ordered with any dish you want. Chasing after .3:1 CR makes little sense if you are considering removing material to achieve it.

 

[StageII86]

One option is to use the 1984-5 factory steel shim turbo head gasket which is .018" when installed, and we have done this many times.

With sealant or no? the GE1200 or the 4400?

They hold up well?

 

[StageII86]

Bison,

I hear ya. This was champions sentiment as well. Gonna get them flat, and cc to see where we are. Then I'll evaluate from there.

Thanks for the input.