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MG MGB GT V8 Factory Originals Technical - Deck Height and Piston Specs

Ok here's the story.

A while back I bought some Silvolite buick pistons #1718 for my 88' RR engine. They were advertised at 8.8 Compression ratio.

After I got them installed, I cc'ed the pistons and combustion chamber. and calculated the CR. I got 7.775:1

My numbers are:
Piston dish. 14cc
Combustion chamber 33cc
Deck height .067"
head gasket .045" (felpro composite)
piston compression height. 1.845"

Glenn Towery said the buick pistons are a half point lower than advertised. so the 8.8 I have is a 8.3, that in conjunction with my thicker head gasket took my CR so low. He recommended to deck the block for .010 deck height

Now my question is. Do the rover pistons have a higher compression height than buick pistons? If I can get a piston with a higher compression height than what I have, I can avoid decking the block.

.067" deck height is quite a bit. What is the thickness of the standard tin head gaskets? around .020" ??

It is my understanding that the squish height (deck height + head gasket) should be around .040". This way the fuel mixture is pushed towards the center of the piston for easier ignition.

I've already been told that the rover and buick pistons have the same compression height. If that were the case, everyone would be having the same problem I am with low compression.


Michael Hartwig

Mike, go back & read the E-mail I sent & I said to take .040 off the block (will raise comp. 1 point) & make sure the piston is .010 below the deck height & with the steel shim (thin) head gasket the piston will not hit the head. The rover, buick piston are close to the same comp. height. I do this to just about all the motors (3500, 3900, 4200, & 4900s) I put together to get the comp. up were thay will run. 8-1 3500 = 135hp! 9-1 =165 & will burn 89oct.
Glenn Towery

Ok I understand that, I guess then my question is why buick/rover used such a large squish height?
Michael Hartwig


Should he also shave .028 from the intake manifold for proper fit?
George B.

George, It is up to you, It will bolt together as is & if you need it to match for the port work you can cut on it, but I will not cut on the stock buick manifold for it is thin were it bolts to the head
Glenn Towery

My guess is that the Rover pistons have less dish in the crown - the Vitesse 9.75:1 CR are actually flat.
Chris Betson

This thread was discussed between 08/12/2002 and 12/12/2002

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