[Fot] Camshaft recommendation

[Larry Young]

"it seems most of the better cam grinders these days have some very 
fancy software".  -  That has not been my experience for TR cams, maybe 
for SBC cams. - Larry

On 2/22/2020 3:28 AM, Enquiries Road & Track wrote:
> 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 <mailto: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
>     <mailto: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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