[DeTomaso] 351 C Compression Question

[JDeRyke at aol.com]

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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