On Thu, 4 Aug 2005, SHANE Ingate wrote:
> Hi All,
>
> Whats the story on Circle B heads?
Circle B is the foundry. That's most of the story.
> I mean, I know that have a lot of
> material between the ports so that they can be opened up more than the other
> heads, but what years were they manufactured?
It's not the material between the ports that matters, it's the thickness
of the casting - e.g. the material between the combustion camber and the
water jackets, etc. - that matters. With the Circle B heads, you can
theoretically grind more material away and not be as concerned about
making thin spots in the head. In other words, you can "hog 'em out".
> I have a Circle B head that
> come from pre-1971 cars as it has the big valves (1.45"/1.28" in/out). What
> other difference are there between the early and late heads?
Early _US - SPEC_ heads have narrow port spacing for the intakes. All
other heads are like the PI heads with the wide intake port spacing.
The narrow port heads were sent to the US for the 69, 70 and 71 model
years. Starting with model year 72 (roughly CC75000), the US got the PI
head. They also used the narrow port heads for the TR250.
I'm curious - with the 1.45"/1.28" valves, is there much "shrouding"
towards the outside of the combustion chamber? Now that my rules have
changed, I could legally run the big valves, but when I looked into this
in the past, I recall the the valves run very close to the edges of the
combustion chamber... I'll bet there's lots-o-HP to be unleashed by doing
some grinding in that area! Does anyone have any info that they can/want
to share about this?
> Will the early
> heads match up to later intake and exhaust manifolds?
The intakes for fed. spec. early heads only match up to the fed. spec.
early head and the intakes for late heads only fit up to late heads.
The exhaust port spacing is the same for all years, but the downpipe
configuration changed from a single pipe to the double pipe for the 72
model year. So, other than the downstream exhaust config, the exhaust
manifolds are interchangable.
> Thanks in advance,
>
> Shane Ingate in Maryland
regards,
rml
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