[Fot] Camshaft recommendation

[Enquiries Road & Track]

it seems most of the better cam grinders these days have some very fancy
software for examining the motion of the valve for any cam/valve train
being proposed. They can easily calculate the critical acceleration and
deceleration limits for any valve train mass and its not hard to 'plot" the
motion of the cam/valve lifter, even if they did not create the actual cam
being studied.   Ive done this on my lathe with a data capture system,. Ive
just finished a major exercise with one cam maker on my Toyota 4AG race
engine where I suspected valve train harmonics were responsible for a
broken cam (actually snapped in 2 at peak rpm) . valve spring makers  like
PAC in the USA are known to have such software.

it seems like many TR cam profiles were created in the ancient past,
possibly more by trial an error than serious maths. Thats not to say they
are wrong/bad, but rather there is a more modern alternative that might
have a place. Some cam makers may be using such approaches with TR cams,
but I suspect many are just churning out what they did 30 years ago. .

Terry O'Beirne


On Sat, Feb 22, 2020 at 2:14 AM Larry Young via Fot <fot at autox.team.net>
wrote:

> Yes, the down side to a smaller clearance is that the seat-to-seat
> duration and valve overlap will increase causing a loss of the low end.
> This page > http://tildentechnologies.com/Cams/Tip_Lash.html shows a case
> where the duration would increase about 32 degrees to about 4x86 = 344
> degrees. I like to call this the "tuning fork effect" it sets of all kinds
> of vibrations which can cause the valve to jump off the lifter and bounce
> off the seat at closing.
>
> I did not intend to imply most smack the lifter, just that many do. This
> is a good reason to thoroughly measure your cam profile. Most stuff on the
> web talks about valve springs as the only cure for valve float issues.
>  - Larry
>
> On 2/20/2020 6:51 PM, van.mulders.marcel at telenet.be wrote:
>
>
> Larry, you say most camshafts smack the lifters hard. Will a smaller valve
> clearance relieve this a bit? Has it disadvantages to set the clearance
> smaller than recommended?(except that the valves will run hotter)
> Marcel
>
>
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