In Kas' latest book there's an approach to unshroud the valves by sliding
the head a bit--milling the head bolt holes into slots. Looks like it would
unleash some performance for not much work.
-----Original Message-----
From: owner-fot@autox.team.net [mailto:owner-fot@autox.team.net] On Behalf
Of Robert M. Lang
Sent: Thursday, August 04, 2005 10:38 AM
To: SHANE Ingate
Cc: fot@autox.team.net
Subject: Re: TR6 Circle B heads
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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