[DeTomaso] 351 C Compression Question

[cengles at cox.net]

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
>
>