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U12 Bluebird, Pintara & Stanza => performance and handling => Topic started by: SleepaTi on Feb 3, 2008, 02:11PM

Title: ka24 head shave ..how far to get 9:1 CR?
Post by: SleepaTi on Feb 3, 2008, 02:11PM

how far has ppl gone when getting their ka24 head shaved?

i want to get the comp up to 9:1 but dunno how far (max limit) i have to go on the shave to get the CR i want

i have standard (0.50) pistons

Title: Re: ka24 head shave ..how far to get 9:1 CR?
Post by: SleepaTi on Feb 27, 2008, 09:26PM

results are in, 30 thou off the head & 20 thou off the block yielded a cr result of 8.8:1

close enough lol

Title: Re: ka24 head shave ..how far to get 9:1 CR?
Post by: SSS on Feb 28, 2008, 08:05AM

Did you get the pistons flycut to match the .020" that was taken off the deck height of the block?

At TDC the highest part of the piston sits flush with the deck (effectively 0 deck height clearance).

I'd suggest that you have higher than 8.8:1 CR. I'll do some calcs and post back here.

Title: Re: ka24 head shave ..how far to get 9:1 CR?
Post by: SSS on Feb 28, 2008, 08:16AM

I'd suggest that you would be around 9.5:1 static compression.

stock sohc chamber volume is 68cc
stock piston dome volume is -4cc

you removed 4.7cc from the chamber volume & 3.1cc from piston dome volume.

Assuming that the piston was flycut to have 0 deck height (which it should, otherwise the pistons will be 0.508mm above the deck), chamber volume is brought down to 63.25cc and piston dome volume is -0.8cc.

Chucking that in a CR calculator with 0 deck height and a 1mm thick HG gives me 9.5:1.

Title: Re: ka24 head shave ..how far to get 9:1 CR?
Post by: SleepaTi on Feb 28, 2008, 11:39AM

it needed 20 thou to get the pistons reaching 0 deck height as i had all the rods resized, the pistons were untouched

Title: Re: ka24 head shave ..how far to get 9:1 CR?
Post by: SSS on Feb 28, 2008, 11:53AM

Ah, gotcha.  :)