On Fri, 28 Jun 1996, Dave Gropper wrote:
> 1. X-flow heads is why 1275S Mini's MOOOVE!!!
>
> 2. Better efficiency and more HP is why Formula I, Formula III
> and others use cross-flow heads.
>
> 3. Cross-flow heads give better fuel/air mixing, increase turbulence
> in the cylinders, better combustion flame-fronts, and better exhaust
> gas scavenging.
>
> I know that's correct, because I read it in a book!!!
> (Incoming!, watch out for the flame wars!!)
I would add to this a couple other little points. Usually, with LBC's,
when you're talking about going ffrom stock to crossflow (and on the B I'm
pretty sure this is so), you're also talking about going from five to
eight ports. This is the root of the biggest improvement: you get more
even mixture distribution and better port shaping with one port per
cylinder instead of 1/2. Additionally, one port per cylinder allows the
use of resonance tuning in the intake and exhaust, something that is all
but impossible with siamese ports. All this is independent of the
crossflow/no-crossflow question.
What the crossflow head specifically gets you, in addition to the reasons
Dave mentioned here, is room for more optimal port sizing and shaping,
more flexibility in combustion chamber shaping, and - last but not least -
they remove a very large heat source (exhaust manifold) from beneath the
intake manifold and carbs, allowing a cooler intake charge.
FWIW, I can't think of a modern engine that doesn't use a crossflow head,
unless VW's 8-valve engines are still non-crossflow.
Hope this helps!
Michael Chaffee
mchaffee@staff.uiuc.edu
[Note new address]
CCSO probably thinks I'm working right now. What do you suppose they think
I'm saying?
|