[Fot] Six cylinder cams

[Larry Young]

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)
>
>