Glenn...
STOP!
DON'T SHAVE IT YET!! I screwed up in my calcs as I went back over
them, and found I'd messed up somewhere - Sorry... 8^( If it's
already too late you'll end up with 11.5:1 or something! Ping city. I
hope your machine shop isn't open this time of night anyway! I think
the correct amount would be around 0.048" and assumes flat-top pistons.
You may or may not have dished ones. The best way, is to cc the head
after all the polishing takes place, and then determine how much you
want to take off. Sometimes, if the block is "decked", you will end up
with "pop-up" pistons, and that'll throw these basic calcs out the
window. Joe Curry sent me the following note, so your results may
vary...
Joe Curry wrote:
>
> Peter, did you take in to consideration that his engine apparently
> already has the higher compression pistons instead of the stock "dished"
> ones?
>
> When I first built Huxley's engine, I used a head that had been shaved
> an incredible amount (best I could tell about a quarter of an inch had
> been removed). I was using flat top 9:1 pistons and the result was
> about 260 pounds of compression all the way across. I could not find a
> fuel with enough octane to keep it from pinging, even with the timing
> set much further back than it should have been.
>
> As a result, I got a stock head and had it recone and now I have about
> 180 psi across.
>
> I also discovered since then that the stock 1300 head is something on
> the order of 1/8 inch shorter than the 1500 head. I suppose it is to
> compensate for the shorter stroke, but it sere seems extreme. I have
> often wondered what effect that particular head would have on a 1500
> engine without any shaving.
>
> Regards,
> Joe
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