EFI Head Volume

[Mark Romans]

Hi Bruce:
Lingenfelter's book on modifying small block chevy engine's on page 47-48
says that "A performance piston-to-head clearance is usually between .040
and .045 inch. This quench area is too small to support combustion, service
instead a more useful function. As the piston approaches top dead center,
this tight area tends to squirt or squish the air/fuel mixture in this area
into the open combustion space. This violent action produces turbulence that
acts like a very efficient blender. This blending action helps homogenize
the air-fuel mixture and supports more efficient combustion.  Dyno testing
has proven that improving the piston-to-head quench area from .060 inch to
.045 inch will improve power even when the compression ratio remains the
same.  It is even possible to optimize the quench and increase compression
without suffering detonation problems! This is because improving the
homogenization of the mixture in the chamber reduces the tendency for lean
areas in the chamber to promote detonation. "

I have my piston to head clearance set at .039 inch!
11.0 to one with efi, aluminum heads and 92 octane unleaded!
Mark
-----Original Message-----
From: Bruce Plecan <nacelp at bright.net>
To: diy_efi at esl.eng.ohio-state.edu <diy_efi at esl.eng.ohio-state.edu>
Date: Tuesday, April 06, 1999 7:49 PM
Subject: Re: EFI Head Volume


>
>----- Original Message -----
>From: Marc Piccioni <mpiccioni at attcanada.net>
>To: <diy_efi at esl.eng.ohio-state.edu>
>Sent: Tuesday, April 06, 1999 8:42 PM
>Subject: RE: EFI Head Volume
>
>I've heard comment that, there is actually a chance to reduce detonation in
>a wedge chamber (specifically the SBC), cause of the turbulence.
>Bruce
>
>
>> True, as the quench area increase so does the likely hood of detonation.
>> /Marc
>> ----------
>> From: Greg Hermann[SMTP:bearbvd at sni.net]
> Subject: Re: EFI Head Volume
>> >I thought the aluminum vette heads and the early powerpack heads were
>> >the only ones with chambers that small.
>> >Any others?
>> >Shannen
>> >Mark Romans wrote:
>> >> The stock cast iron head is 58.5?  Whoa, I thought it would have a
>bigger
>> >> chamber than that.  Thanks for the info.
>> >> Also quench area is critical in preventing pre-ignition
>> Make that "DETONATION"!! Different animals.--Yeah, I'm being picky
>tonight!
>> Greg
>>  so he would rather
>> >> increase the combustion chamber volume than shim the head up.  Thanks
>again.
>> >> Mark
>
>