[Diy_efi] Timing table change needed with CR increase?

[Gary]

As long as it is understood that excessive (by the stds. on many) quench
distance alone will not automatically lead to anything in the way of knock
probability. Stated another way, a given engine does not necessarily
require or need any predetermined figure for quench distance. There are
several factors that determine the probability of an engine's combustible
mixture to detonate. I consider combustion chamber/piston crown design
to be more influential in determining detonation probability.

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.

GAS

----- Original Message ----- 
From: "Mike V" <efi at dyakron.com>
To: <diy_efi at diy-efi.org>
Sent: Tuesday, January 30, 2007 9:47 AM
Subject: Re: [Diy_efi] Timing table change needed with CR increase?


> Agreed.  A typcal felpro SBC gasket is .039in thick.  IOW, your piston 
> should be at or a few thousanths above deck when at TDC to achieve proper 
> squish..
> mv
>
>>I would like to add that most squish is lost because the piston top is 
>>below the deck.  You need ~ .035-.040 from the piston to the head - 
>> >>measure it - or ping could be a problem. TomS