That is an interesting article, but only speaks to one side of the
issue. I always say that you want to pick an intake duration for an RPM
range that you're willing and able to turn. We all know what happens to
a stock TR4 crank which sees >6,000 on a regular basis. Some guys want
a cam good beyond 7,000, but they are just not willing to push it that
far. Nowadays I'm more of a street car guy, but still like to have
power. I don't believe the choices should be to do nothing or go all
the way to race specs. From 1968 on Triumphs were severely detuned to
pass emissions. Compression ratio and duration and hence cam overlap at
TDC were reduced. For example, the early TR250/6 had 193 degrees
duration (measured at 0.050), while the TR4 was about 215 and the early
PI TR5/6 was 226. It seems crazy to rebuild a street car of this era to
the original specs. Bumping the compression ratio by a point and
increasing the duration to something like 210-215 will make the engine
the way it would have been without emission restrictions. I would not
feel guilty about polluting the planet, since most of these cars see few
miles annually and most of the other pollution controls (e.g. ignition
retard) probably quit working years ago.
- Larry
On 10/29/2015 7:25 AM, Duncan Charlton wrote:
> Cam specs and static CR are interactive. This will give you a rundown if you
> are not already knowledgeable about this subject:
>
> http://www.crankshaftcoalition.com/wiki/Cam_and_compression_ratio_compatibility
>
> Duncan
> (Texas)
>
>
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