Wondering if anyone has any suggestions for how much to take off the head to boost comp up a bit. Whats the limit for piston to valve clearances and will lowering the head affect timing chain tension and the rocker arm position very much? Hoping to get the comp up to around 9.5. This is using a 4k-c head. Otherwise I'll get a burette and dial gauge and work it out. Cheers :)

Talk to the guy doing the machining. Let them work it out. If they stuff it up then its their problem.

15-20 thou. nothing startling and it doesn't seem to affect rocker geometry.

 

I had combustion chamber volumes of 31ml stock & an area of 30sq cm. Its educational for you to work out yourself and compute how much to remove.

Also its good to double check incase it has been shaved before.

Did you calculate what your new CR was Altezza? I might as well calculate it, do it once do it right, right?

Yep-

 

Combustion chamber 31cc from a pipette.

Head gasket 79mm x 1.5mm gives 7.35cc

Bore and stroke 75 x 73 gives 322cc

 

So compression ratio is piston down to piston up

 

31+7.35+322 to 31+7.35 or 9.4:1

 

I traced around the combustion chamber with mm square graph paper and counted the squares to get the head area, then calculated how much to take off. 20thou takes it to 9.75 : 1.

 

Substitute the 5K's 80.5 piston size into it gives an instant 10.5 to 1 compression with them.

There's plenty of downloadable CR calculators, personally I wouldn't go off anyone's advice unless they're the engine builder. So many variables to this calc, you'd rather know for sure what you're aiming for.

 

The only hard bit is measuring head volume anyway, the rest can be done with a vernier easily enough

Could someone clarify what the stock CR of a 4K is with reference to a reliable source? http://www.kp61.net/forum/showthread.php?t=475 here it says its 9.1 for a 4kc, 9.4 for a 4ke. I have done my calculations, but using 9.1 as the CR which seems to be the genreal consensus for a 4kc. Also Keith did you include the piston volume in your calculations? I worked it out to -1 cc, if 9.1 is the correct compression ratio. My head cc measured 33ml using a syringe and brake fluid

My Gregory's manual says CR is 9.0 to 1 I thought it was 9.4, but it seems that is the 4KE figure. It probably varies between countries too.

 

I didn't give the piston a volume, being a flat top, but in reality I'm sure there is a small volume there as it is not completely flat and doesn't necessarily come up dead level to the block top.

 

Then again, making cheap mass-produced cars with castings for combustion chambers probably has errors of several cc between cylinders, never mind between motors.

 

Your 33cc works out fine for a CR of 9.0 Isn't it 8.98?

I'm a engine recondition by trade and you need to work out your cc volume in the head then work your compression ratio then shave your head to get comp you wont.. its about - .007" per cc

If you where in wa id be happy to help