[Diy_efi] Timing table change needed with CR increase?

[Gary]

Bob, embossed steel shim gaskets they were. The two offered were
.016" and .019" thick. # xxxx336 and # xxxx708 rings a bell, but 
memory is questionable after having my bell rung a couple of times. 

Actually, that was a trick used by racers as well; to double up on those
gaskets for purpose of better hi-compression sealing and durability. 

GAS

----- Original Message ----- 
From: "Robert W Hughes" <rwhughe at oplink.net>
To: <diy_efi at diy-efi.org>
Sent: Tuesday, January 30, 2007 1:49 PM
Subject: Re: [Diy_efi] Timing table change needed with CR increase?
> 
> Back in the old days Chevy used to ship the hyper 327s and 409s 
> with two headgaskets per side, cut an advertised 11.25:1 down to 
> about 10.25:1. I seem to remember these as being the thin beaded 
> steel gaskets.
> 
> Robert W. Hughes (Bob)
>
>> With the 90s LTx variety of 350, GM defied accepted rules by altering
>> the CR on a particular engine/head combo solely by increasing the head 
>> gasket thickness. OEM GM gasket choices were a pre-compressed
>> .029" and .049". In the process, the quench distance on typical OEM
>> assembled engines could exceed 065". That generation of SBC can be
>> considered to be respectably knock resistant, PCM ignition retard
>> capability notwithstanding.