At 9:26 PM -0600 10/3/2000, owner-mgs-digest@autox.team.net wrote:
>How about cross flow heads?
IMHO, I wouldn't mess with a cross flow head unless you want the "gee
whiz factor" when opening the bonnet/hood. Rather expensive, and I
haven't seen any airflow or dyno data that support it's superiority
to a well prepared conventional head in street use. See Burgess'
comments about airflow problems with the Derrington version. Seems
like block design limits airflow.
Personally, I'd put money into a well prepped aluminum standard head.
Good heat transfer/less chance of overheating, no chance of spending
a lot of work on it only to have it crack on you as an old iron head
might. And aluminum is a little easier to work with if you (or your
machinist) are careful about it. I bought a complete head from
Pierce Manifold because I wanted to get back on the road after
burning a valve on what turned out to be a cracked stock head. It
had the smaller of the stock size valves, and I will probably be
changing them for larger ones the next time it comes off.
Desirable head mods might include large valves, airflow mods to the
intake runners, Rimflow or tapered back valves, "bulleted" high
quality bronze valve guides, carefully shaped combustion chambers of
equal capacity, unshrouded intake valves (opening up the backside of
the chamber around the valves). This work is best done by someone
with a flow bench and some experience, although it can be done as a
DIY project. On an aluminum head, I added stainless thread inserts
for the manifold studs and sparkplug holes, as insurance against
things stripping out when properly torqued multiple times.
See the following pages:
http://www.mgbmga.com/tech/index.html
(No commercial interest, etc...) Doug Jackson has done a LOT of
research and testing, and has a lot of info on his site about his
results. See also the Vizard book on mods for the BMC A series
engine. Burgess swears they are different from the B, but a lot of
the logic / theory of modification is similar.
If you can afford it, get new SUs. SUs can't be beat for most street
motors, and rebuilding old ones can be less than successful on really
worn out carbs. Throttle shaft reamers aren't always precise, and
there isn't much meat on the carb body to work with. You could
invest a lot in a rebuild and still have leaky carbs.
Have fun. Cheers,
--
Chris Attias
Aptos, CA
'64 MGB
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