[Fot] Six cylinder cams

[Duncan Charlton]

Larry’s comments make me wonder the precise intended purpose of the engine mentioned by the original poster.  “Track days” might mean different things to different people.  Does P. J. want a good flexible power band, or does he need an ultimate dyno horsepower figure?  Does the motor have the gear set to be able to take advantage of an engine with very little low-end torque? How high among his priorities is the ability to be able to drive the car back on the trailer at the end of every track weekend?  Lack of sponsorship and cash prizes mean that I must find the setup that maximizes the fun/cost ratio.

Duncan


> On Oct 31, 2015, at 1:34 PM, Larry Young <cartravel at pobox.com> wrote:
> 
> 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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