Viv,
I see that Peter Green has already given you the original head thickness (3
41/64" per Blowers Manual). The additional info re compression ratios can
be calculated from the Special Tuning section for stages 1 and 2. I went
through the numbers in an EXCEL spreadsheet and came up with the following
(adding in my own Stage 3):
Stage Amount Head Combustion
Compression
Removed Thickness Chamber Ratio
Std 0 3 41/64" (3.6406) 35cc 6.2
1 3/64" 3 19/32" (3.5938) 32cc 6.7
2 3/32" 3 35/64" (3.5469) 28.5cc 7.25
3 1/8" 3 33/64" (3.5156) 26.5cc 8.6
The max that can be removed is debatable. I have heads that have been cut
by 0.090 and 0.150". They still seem to be structurally sound, but I
started having problems fitting pieces like oil return pipes, dynamo forks,
etc. These calculations also assume standard flat top pistons. Once you
introduce pop ups, its a whole new ball game. If you wish to do your own
calculations, the formula is given in Blower's Special Tuning section. And
don't forget to include gasket thickness. It all affects the answer.
I found myself in the situation with high pop up pistons and thin heads. I
was heading towards making a diesel. I have had to have 1/8" solid copper
head gaskets made to keep CR down to the 9.2 - 9.6 range.
Pete Thelander
pthelander@earthlink.net
> [Original Message]
> From: <viv@trax.co.za>
> To: <mg-mmm@autox.team.net>
> Date: 5/16/2006 4:56:41 AM
> Subject: PA Cylinder Head
>
> Can someone tell me the standard measurement of an unskimmed
> head?
>
> Is it usual to take a bit off to allow for modern day fuels? If so, how
> much is normal and what CR should this give?
>
> Thank you.
>
> Viv
>
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