On Mon, 16 Sep 2002, Peter Macholdt wrote:
> I missed the issue with David's article. Would you look and tell me which
> month is printed on the cover so that I can get a back issue (is it worth
> the $7.00)?
I think the issue was the September or October issue.
Is it worth $7? Hard to say. I suppose if you save more than $7 by doing
your own porting job the answer would be that it is "cost justified".
:-)
The gist of the article is 7 rules of porting. In summary (my
translation), don't hog out metal with no reason. You get more benefit
from removing material where the charge is moving fast, so focus there.
Shrouding of the valves plays a big role in flow, there was some stuff
related to that. More on shrouding a bit later.
That's pretty much it.
There were some interesting charts that show that a certain amount of
porting gained the biggest amounts and then more hogging produced no
measurable increase in flow. So - access to a flow bench is a pretty
important part of the equation.
This stuff takes time. Lots of time. So if you pay someone to do it,
you're paying for thier knowledge and thier time.
Regarding valve shrouding, the A series BMC motor seems to (by the example
in the article) benefit quite nicely by relieving the area around the
valves in the combustion chamber. BUT - there are issues around this, one
of them being sealing between the head/block. So, you might be able to
decrease the shrouding and get better flow, but you might not be able to
keep a head gasket in the motor from failing. That'd be a serious
tradeoff. But the point of the comment - it would be interesting to get
flow numbers from some of the folks that have put in oversize valves (aka
PRI and others) to see if they really do flow better.
> I also like David's book "Tuning Standard Triumphs". It was a great help
> during my rebuild this past winter. Anyone know if real, printed copies are
> still available? I downloaded mine from the web and had it spiral. It
> works, but I'd still like a real copy.
The book is out of print. There's also a lot of fluff in there (like the
section on the ideal TR cylinder head, like we're all going to go out and
built our onw cyl heads from scratch...)
But FWIW, copies of the book show up on eBay from time-to-time. Be
prepared to pay some $$$, though. Frankly, the internet downloaded version
is worth about what you paid for it (IMHO). There's some good info, but
it's not all good and the info can be found elsewhere.
> TIA,
> Peter
> '68 TR250
C ya,
rml
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