[DeTomaso] 351 C Compression Question

[Göran Malmberg]

There has also beeing discussions about Hemi shape heads, in fact it has
been discussion about any single factor about piston-head shape. Making
each features appear as the single important one. No matter which is the
best quench shape, the walves will dictate most of it. Hemi chambers suffer
from beeing very large, 170cc, but it is a nice burning chamber shape if we
only look at the burning as such. Add a compressor and the hemi starts to
shine as a "burner". Take at a look at model airplane engine chambers, that
has no valve or incomming head runners, free to shape things as they want.
We have one chamber shape that is great for burning, one for quench, one
for swirl, one for compression and one for piston dome and valves. All of
these components will be of different influence depnding on the overall 
engine
build. Not very easy to get right for us then.
Goran

> 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
>
>
>
> **************
> Make your life easier with all your friends, email, and
> favorite sites in one place.  Try it now. 
> (http://www.aol.com/?optin=new-dp&
> icid=aolcom40vanity&ncid=emlcntaolcom00000010)
> _______________________________________________
>
> Detomaso Forum Managed by POCA
>
> Archive Search Engine Now Available at http://www.realbig.com/detomaso/
>
> DeTomaso mailing list
> DeTomaso at list.realbig.com
> http://list.realbig.com/mailman/listinfo/detomaso
>