67 Size Engine Head Volumes?

[Mike Rappold]

I was thinking of machining several head buttons for a MAC 67 to try. Was curious what volume of the head buttons others found works well - even if not on a MAC? This would be 50 - 60% nitro fuel in an outrigger application.

Also what about head clearances?

Thanks in advance.

Mike Rappold

 

[steve wood]

I was thinking of machining several head buttons for a MAC 67 to try. Was curious what volume of the head buttons others found works well - even if not on a MAC? This would be 50 - 60% nitro fuel in an outrigger application.

Also what about head clearances?

Thanks in advance.

Mike Rappold

there is more to it than that

transfers,exhaust,bore,stroke, head clearance,etc,to get the compression ratio you are looking for.change one and the ratio changes.marty's program will give you the info

 

[Marty Davis]

I was thinking of machining several head buttons for a MAC 67 to try. Was curious what volume of the head buttons others found works well - even if not on a MAC? This would be 50 - 60% nitro fuel in an outrigger application.

Also what about head clearances?

Thanks in advance.

Mike Rappold

Mike:

Steve is correct, but I run 185 timing and my head button is .55cc and clearance is .013" which comes out to 9.6:1 CR.

 

[Mike Rappold]

I agree there is more to the equation. I am trying to get a general idea of the range people have seen works.

Mike

 

[Tom Foley]

Good info ...need a bump in my Mac 67 !!

 

[Terry Keeley]

Here's some specs for the CMB:

http://gallery.intlw...album=70&pos=88

The original "bathtub" head was 0.60cc but I like the newer "hemi" at 0.53.

Been playing with volumes as low as 0.44cc on my SAW boat and 70% nitro.

I run about 0.012" on everything.

Would be interesting to see what your Eagle Tree says about the head temp and EGT's with different heads.