I'll admit you said it better than I did Vance. Thats what I get for writing
stuff while I have a nasty headcold. Thats what I was getting at by saying
that the burn was more efficient when you retain more of the combustion
chamber shape. Higher efficiency through the burn results in more power. With
mild compression increases, the difference between the two techniques might
not be so obvious to the average butt-dyno, though would probably be easily
seen on an actual dyno, not only in more power but smoother power as well.
In my Ford Cortina 1600GT, the combustion 'chamber' was in the piston head and
the valve surface of the head was flat, no chamber on the head what so ever.
>===== Original Message From "Navarrette, Vance" <email@example.com>
> Raising the compression ratio by decking the block will get you
>more power than raising the compression the same amount by milling the
> The reason is that with a decked block the piston comes closer
>to the head, increasing "squish". This creates more turbulence and fuel
>mixing in the chamber, for a more thorough burn. The closer the piston
>comes to the head, the more squish you get, right up until the piston
>crashes into the head and your new motor is reduced to scrap metal.
> If you are hot rodding an engine and are pulling the block,
>ALWAYS get your motor zero decked if your head has any squish area on
>the head (Some motors have no squish at all, like the old Chrysler Hemi
>motors and some Japanese 4 valve designs). If you have no squish area,
>then it is a waste of time. But most motors have a squish (sometimes
>call "quench") area designed in so you should go with a zero deck
>height. This is why Kastner instructs you to deck the block (although he
>does not say why) when prepping your motor. David Vizard also strongly
>recommends it in his engine building books.
> Confucius say "Learn the ways of the Zen masters, oh
>grasshopper, and you will go fast"
>Behalf Of Shawn J. Loseke
>Sent: January 05, 2008 8:22 AM
>To: Foster, Stan; Derek
>Cc: 6pack (6pack)
>Subject: Re: [6pack] Compression Ratio Calculation
>The best/most mechanically efficient method for increasing compression
>begine with a zero deck height. That way more of the combustion chamber
>can be saved. When you keep shrinking that chamber shape you completely
>the burn characteristics. On race engines the pistons will actually
>proud of the blocks deck to maintain as much of the chamber as possible
>cutting the head down. My pistons stand proud of the block by .013". I
>originally looking for zero deck clearance but my machinist (who buildd
>primarily circle track motors) went a little too far. Luckily, the
>thickness of the head gasket is still enough to not cause any problems.
>Shawn J. Loseke
>Fort Collins, CO
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