[Diy_efi] compression ratio

[TVS]

> >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_.

Yes, take the Jaguar XK engine. These use something like 45deg BTDC of total
advance. The early engines used offset ports to produce more swerl and I
beleve this helped quite a lot.
But a dome shaped piston gives a terible surface to volume ratio for the
combustion chamber.

> 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.
I beleve pentroof chambers normaly need around 28deg of total advance so
they much have a quick burn, but as you say, the central plug location helps
a lot. Toby


_______________________________________________
Diy_efi mailing list
Diy_efi at diy-efi.org
http://www.diy-efi.org/mailman/listinfo/diy_efi