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Cylinder Head Thickness vs Compression?
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TOPIC: Cylinder Head Thickness vs Compression?

Cylinder Head Thickness vs Compression? 15 years, 8 months ago #3970

  • Weston
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Can anyone give me measurements for actual cylinder head thicknesses vs compression with early pistons and a turbo headgasket?

My cylinder head has been shaved by an unknown amount, and now I need to get it rebuilt again because the last shop didn't know WTF they were doing. I'm trying to figure out if this head is even going to be legal to use at this point, so I need some way to find the actual compression ratio by measuring the head thickness.

Thanks
#22 - Red 1983 Porsche 944 - Rocky Mountain


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Re:Cylinder Head Thickness vs Compression? 15 years, 8 months ago #3973

I should have a head here for you if you need one ....

Re:Cylinder Head Thickness vs Compression? 15 years, 8 months ago #3982

Weston,

It's not quite that simple. If a shop has already been in there, they have dressed the seats and sunk the valves. I have a spreadsheet to tell me how much you need to shave the head to overcome the valve sinking and to otherwise increase the CR. If you can give me the valve lengths, tip heights and head thickness I can approximate the cc's in each chamber.

If you have the tools, cc the head and give me those numbers. Either way I can tell you how much you need to shave.

HTH.
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Re:Cylinder Head Thickness vs Compression? 15 years, 8 months ago #3983

One more thing.....

Don't give up on a head. If the tip heights are out of spec, new seats can be installed which have the added benefit of increasing your CR.
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Re:Cylinder Head Thickness vs Compression? 15 years, 8 months ago #3994

  • 944cer
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Hi Weston, I have an old head if you need one. I was told any shop should stamp on the head how much they shave off. Thet did on mine, I think it was along the side down by the shaved surface.

Re:Cylinder Head Thickness vs Compression? 15 years, 8 months ago #4002

  • Weston
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Thanks. The only number I see stamped on this head is "542"... not sure what that means, if anything.

The valve I pulled out is 111mm long, tip is 4.5mm, and the machined surface on the head is 23.0mm on both ends. I'm just using a metal tape measure, so there's a little margin of error here. I'm mostly concerned with making sure this head will be legal after another resurface, rather than shaving it down any more for the purpose of power. I have early pistons, so I would think that I have some room to play with, but just want to be sure.



Thanks!
#22 - Red 1983 Porsche 944 - Rocky Mountain


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