[Diy_efi] compression ratio

Greg Hermann bearbvd at mindspring.com
Sat May 11 13:50:16 GMT 2002


>You also need to consider the basic efficiency of the head design.  Some
>combustion
>chambers have almost no detonation (hemisphere and pentroof),

Bzzzzzt!!--

A hemi chamber is one of the worst for burn time and detonation. They can
be helped if pistons with a dome shape that creates squish around the edges
is used. Dual plugs also help a _LOT_.

A pentroof (four valve is not terribly good, either, although better than a
hemi because of the central plug location. The cloverleaf version of the
pentroof (four squish areas around the edges) is considerably better.

 and others are
>overly prone (mostly stock heads with small volumes).
>
Closed chamber "stock" (American V-8) heads are generally better than open
chamber heads. (More squish)

>Generally speaking, the less timing you can run to make power, the more
>efficient
>the head.  If you're dialing in 18 degrees base timing to get power (like stock
>5.0s), you're prone to problems.  But if you can run 8 degrees and get
>decent power
>on 89, then it's a better head (like the TW).

True.

Greg
>
>--Perry



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