Re: block decking compression question

[ortfamily@xxxxxxx]

I am no expert, but if they meant they removed 7/1000 of an inch it should not make a noticeable difference. Engine rebuilders commonly remove 10/1000 from both the block and heads to ensure that there are flat mating surfaces. It is little more than cleaning up the surfaces. I have a (excuse the profanity) Chevy 327 that I took apart and reassembled with steel shim head gaskets which are .015 thick rather than .045 to .050 that standard gaskets are without a noticeable difference. The factory used the steel shim gaskets on high performance engines, but rebuilders commonly use the thicker ones to ensure a good seal. The difference of about .035 didn't seem to make any difference. My brother once milled some V6 heads .090 and had to also mill the intake surfaces or the intake would not fit in the valley. Now that did make some discernable difference, but still not what I would call a huge difference. If they mean .007 was removed, it will likely be with no net effect. Of cour!
 se, that is my opinion and the only thing I am an expert on is my opinion. Happy motoring.

On December 1, 2004 Dan Curtis wrote:

> Many years ago I purchased a NOS AMC factory replacement block from a fellow
> who had set it up for racing by decking the block to .007, drilling out and
> tapping the head bolt holes for the larger 1/2 head bolts, removed the stock
> pistons (which I still have), installed forged TRW flattops and balanced the
> whole setup at the machine shop. When I got the motor from him, all of the
> assembly lube and oil sprayed on the engine had turned to a consistency of
> thick glue so I had it disassembled and hot tanked and then put everything
> in dry storage in separate wrapped packages.
> 
> I have been giving some thought to using this motor with the original stock
> pistons in my very nice and newly acquired 51K original 68 AMX but would
> like to know if any of you technically savvy or mechanical engineering guys
> can figure out what the resulting compression ratio would be with the .007
> decked block when using the stock bore cast pistons that were previously
> 10.2 on a block that was not decked.  Also, can anyone tell me how much was
> shaved off on a block that has been decked to .007?
> 
> I was also wondering if there is a thicker head gasket that I can use to
> make up for the block having been decked to get me back to close to the
> stock compression ratio.  As an alternative, would using  later model 58CC
> heads achieve the same result and get back close to 10.2?  With 91 octane
> out here in Phoenix, even a 10.2 compression ratio is pushing it so anything
> over that would be tough to run on our "clean burning" oxygenated gasoline.
> 
> By the way, I also have that balanced and blueprinted 69 390 that is bored
> ..030 over for forged 70 dish style piston and decked to about .008 which the
> engine builder claims will have a 9.6-9.8 compression ratio.  I would rather
> have the stock setup to restore my car to as close to stock as I can.
> 
> Any help that anyone can offer in figuring out the compression ratio on
> these engines would be greatly appreciated.  As always, I request that you
> copy your responses on the list to my personal email at d.curtis@xxxxxxxx
> .....thanks
> 
> Best Regards,
> Dan Curtis
> Cell 602 317 2018
> d.curtis@xxxxxxx
> 
> 
> 
> 
> 
> .


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