[DeTomaso] 351 C Compression Question

[Göran Malmberg]

Chuck
In the late 70:s we where using 351C:s in "smallblock prostock". We run
som 14-15:1 cr, allways using close heads and I wonder if the same
hp could have been reached using open chamber heads. Depending on
gas quality, Cr ratio and the range of power output, I think the difference
between the two heads will alter.
Kind regards
Goran

----- Original Message ----- 
From: <cengles at cox.net>
To: <JDeRyke at aol.com>
Cc: <detomaso at realbig.com>
Sent: Tuesday, December 09, 2008 4:06 PM
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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