Expert Advice Needed:

[mattbenselin 0]

Hi

 

When my head gasket started to fail I took the head off and discovered that my engine block was a DKZ with dished pistons and a presumed CR of 9.2:1 as standard.

I rebuilt my cylinder head having a Piper 285 cam shimmed in, 3 angle seats cut, etc and a skim. Now I spoke to Neil at DES who said that the original depth of the compression chamber on the head was (I think) 7.5mm from the head to block mating surface as it came out of the factory. He used an excel tool to work out that if I had 1mm skimmed off the surface it would bring the CR up to 10.2:1, so I had it skimmed and it turned out the head had only been skimmed once or twice before.

 

Since then the head has sat patiently waiting to go on the block whilst I sort out my carbs and I have started to think is my CR good for the cam? I know there will be issues with valve to piston clearances if more is skimmed off.

 

How crucial is getting the right CR for the cam? Will 10.2:1 be ok or do I need to go higher? Can anyone comfirm that my CR is actually 10.2:1?

Any more info or advice would be great, thanks

[Tom Fenton 1,542]

You need to accurately measure the head chamber volume, anything else is just educated guesswork that may or may not be correct.

[mattbenselin 0]

Thanks Tom so I can do that and work out the exact volume of the chamber on the head. What about the block would I need to measure the volume also with the piston where?

So once I have done this I know my CR, but I also want to know what the ideal CR is for the cam and spec and if what I have now or think I have now is going to work well?

[Tom Fenton 1,542]

Yes ideally you need to measure the chamber volume at TDC, you should know what your bore and stroke are. To be absolutely accurate you also need an idea of your head gasket volume. Then you can work out your CR. As for cam then see what the grinder recommends is a good start.

[mattbenselin 0]

By grinder do you mean the guy with the skimming machine? When I had it done before he didn't know what would be best just did what I asked, thats why I'm asking here.

[Tom Fenton 1,542]

No, I mean the grinder who ground the cam. So Kent/Piper/Newman/whoever did it.