At 8:57 PM -0600 9/25/2000, Scott wrote:
>should I stick with a later head or go
>with one that doesn't have the smog ports... What SU's should I use
>if I'm going to run a hotter cam at rebuild and will I have enough
>room to put them in with the crossflow?
From what I know, head, carb and cam choices depend on a lot of
engine things, like compression ratio and where (RPM) you want the
power band to be. You should look at your engine as an integrated
system. A lot of nifty changes may make sense if you are running
flat out on the track, but aren't necessarily good at street RPMs,
where you want your torque and HP at the low end as well. (From my
experience, a rough, lumpy idle and bad gas mileage in an overly
"trick" street engine can get old after a while.)
Variables include the valve size of the new head (does a '76 block
have cutout valve pockets, or will you have to have that done in the
rebuild if you use large valves or a higher ratio rocker arm?),
chamber capacity of the new head, and the flow characteristics of the
new head.
Two books that might best inform your decisions are "How to Powertune
Your MGB 4 Cylinder Engine", by Peter Burgess, and the Vizard book on
modifying the A series engine, which has a lot of the basic thought
process and theory in approaching engine mods. See also Doug
Jackson's www site: http://www.mgbmga.com/tech/index.html
I don't know how similar different crossflow head manufacturers
products are, but Burgess makes the point that the crossflow heads he
has tested flow less well in some ways than a well-prepared standard
head because of the obstructions that are part of the design.
The basics for increasing HP seem to be good gas flow, through good
aerodynamic port shape (though not necessarily smooth walls), bullet
shaped valve guides, tapered/thinned intake valve backs, unshrouded
valves (head mod.), good compression, a good cam, and a good flowing
muffler. Second level improvements include bigger carbs, headers,
and higher ratio roller rockers with better valve springs. And there
is always the 1950cc engine.
IMHO, I would get a standard aluminum head and trick it out with the
help of a machinist with a flow bench. Put the extra money into work
on the eventual rebuild--things like engine balancing. Good luck,
--
Chris Attias
Aptos, CA
'64 MGB
A file that big?
It might be very useful.
But now it is gone.
|