[DeTomaso] 351 C Compression Question

[tony DiGiovanna]

I had one engine builder say it was his experience that he could get more
top end power out of open chambered Cleveland heads than closed chambered
Cleveland heads, presumably from less valve shrouding that ensues.  However
low end performance is often less due to decreased cylinder turbulence
during compression.

Opinions are like a......

-----Original Message-----
From: detomaso-bounces at realbig.com
[mailto:detomaso-bounces at realbig.com]On Behalf Of cengles at cox.net
Sent: Tuesday, December 09, 2008 10:06 AM
To: JDeRyke at aol.com
Cc: detomaso at realbig.com
Subject: Re: [DeTomaso] 351 C Compression Question



Dear Jack and Tom,

I have in my files an article from some hot rod magazine about two allegedly
comparable and similar 351C engines. One was built with quench heads and the
other was built with open chambered heads. They alleged that the open heads
made almost as much power as the quench heads. Interesting. It goes against
conventional wisdom. It might be true and it might not. I have been educated
that the dyno "tests" in many publications bear as much similarity to the
real world and does the view from government! My suspiscion is that properly
chosen components can permit reasonable power from open heads, but less than
quench.

Warmest regards, Chuck Engles


---- JDeRyke at aol.com wrote:
>In a message dated 12/8/08 12:30:48 PM, tborcich at msn.com writes:
>
>>I have read conflicting reports that the Open Chamber heads had better
>>flame travel because the plugs were not shrouded the way the quenched
chamber
>>plug was, but I have also read that the open chamber head was more
susceptible
>>to detonation.
>>
>Engine builders know a lot more about flame travel etc now than they did 40
>years ago, thats forsure. The open chamber is in fact more suceptible to
>detonation, so you must back off ignition advance to compensate, and that
ireduces
>the power output. But the main power builder is the compression ratio, and
with
>an open chamber, its not physically possible to get much compression unless
>you use domed or lumpy pistons. And once thats done, the dome or lumps
changes
>the way the flame front propagates- usually for the worse. Its all quite
>exotic and for our old motors, what it mostly means is, one just can't get
enough
>power outa open chambers without a whole lot of trouble, dyno-tuning and
>expense (like adding a blower). But even an amateur like me can get cheap
power out
>of a closed chamber head.
>As for the dished piston, my August build '72 engine had cast flat-tops,
>which I still have around in my shop, along with the original open chamber
heads.
>My understanding is, dished pistons weren't used until the smog laws got
>really restrictive in late '73 thru '74, for the last run of Clevelands in
the U.S.
>Cheers- J Deryke
>
>
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