what o/s valves to use in a 4K & comp. ratios

**ToDa30/4** · 19-07-2006, 02:22 PM

ok what oversize valves have been used in 4K's ,did u have to mod the stems & i want 9.8 to 1 comp ratio ,how much do i need to shave off the head .cheers dave

**Billzilla** · 19-07-2006, 04:17 PM

On the race 3K I used to run many years ago, we used 39mm inlet and 33mm exhaust valves. But the bore was 79mm.

**oldcorollas** · 19-07-2006, 07:44 PM

modding stems is for weight reduction = revs.

why such a low CR.

you can (and should) calculate the amount yourself, by measuring the volume of the combustion chamber after you clean it up and deshroud the valves, and compare it to the new bore size.

**ToDa30/4** · 20-07-2006, 12:50 AM

Originally Posted by oldcorollas

modding stems is for weight reduction = revs.

why such a low CR.

you can (and should) calculate the amount yourself, by measuring the volume of the combustion chamber after you clean it up and deshroud the valves, and compare it to the new bore size.

yep ,weight & length maybe ,gemini ..? ones are used i think by some folks / ..9.8 to 1 ,reckon i was writing out loud. yes need to cc it LOL 10.1 to 1 might be the go!

**oldcorollas** · 20-07-2006, 01:34 AM

3K head on 4K block? free 10:1 and easier to get higher and have good chamber.

i believe someone used laser valves... dunno what model... in a 5K head... thinner stems, not much stuffing around, can't remember the size

but worth looking at

**ToDa30/4** · 20-07-2006, 03:50 AM

also the 4K-C head is 8.5 to 1 ,i was musing cb4/cb4a springs ,o/s valves ? ,clean up the head & it would be good for a SC12 s/charger @ 0.5 bar with efi later.. Fitted on the 4K block that im building now set up to run with a single 40mm DCOE on a 3K-H head with extactors & 1.75"ish system ,tighe #113 cam ,electric dizzy ,10 mm leads ..et all.