Autograss ? Assume this isnt a Chinese Windscreen replacement Co, or a compulsive police informant, but some form of autosport I've not come across. Please illuminate this ignorant fool.
Thanks P
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Lol. I never expected to laugh at reprofiled cam shafts. Thanks Pezzer.
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Adam
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My pleasure - I'm sure theres one in there about funny cigarettes too but I'll quit while I'm ahead :-)
P
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Autograss is probably the least well known of UK motorsports but has the most participants. It is very basically oval racing on grass / dirt tracks.
www.loosenet.co.uk/nasa/
In some of the classes, you'll see inovation, engineering, and moneys worth which would make many respectable circuit formulas look dull.
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Aha, didnt know that this was called Autograss, have seen these being towed aroung and had assumed it was some sort Banger or Stock car racing. Looks like fun !
Thanks P
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Look at the clss tens - Upwards of 400 horsepower, in not much more than a glorified go kart, on a quarter mile dirt oval - Yea, thats fun!
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---------8<-------
Now bear in mind that the valve gear is most highly stressed at low RPM (hence most cam belt faliures occur at cranking speed or idle).
At the much higher engine speeds used in race engines, a reprofiled cam should be fine.
---------8<-------
I can't really agree with the whole of this point of view.
At start up, there is a lot of friction between the poorly lubricated parts of the valve train. However, as the engine speed rises, the inertia force of the valve begins to dominate (force proportional to speed squared) the spring force remains remarkably consistent, simply being a function of the valve's position (until really high speeds when the spring surges!).
The complicating thing about this inertia force is that during times when the valve is decelerating in an absolute sense, the contact loads are lighter at high engine speeds, however, while the valve is accelerating in an absolute sense, the valve contact loads are higher at high speed.
The reason why cam belts tend to fail at low engine speeds is because here any torsional crankshaft oscillations due to partial misfires, roughness, etc, result in a large, oscillating, camshaft drive force.
I would argue that for high engine speeds, the re-profiled cam is at a disadvantage, besides its inherent, radius driven, contact stress disadvantage, but also due to its poorer dynamics, which are really only shown up at higher engine speeds.
Number_Cruncher
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The complicating thing about this inertia force is that during times when the valve is decelerating in an absolute sense, the contact loads are lighter at high engine speeds, however, while the valve is accelerating in an absolute sense, the valve contact loads are higher at high speed.
Please excuse my paragraph of complete twaddle and nonsense above. What I meant to say was:
The complicating thing about this inertia force is that during times when the valve is reaching the end of its opening motion, and beginning its closing motion, the contact loads are lighter at high engine speeds, however, while the valve is beginning its opening motion, and reaching the end of its closing motion, the valve contact loads are higher at high speed.
Apologies for any confusion caused.
Number_Cruncher
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Sorry for the delay....been away.
This weekend sees the biggest event in our calendar,the Mens Nationals.
For information,see the link below,and then follow the further link at the top of the page for the Mens Nationals.
If you want some spectacular action,then come and see for yourself what it's all about,and then perhaps post back on this site afterwards.
www.yorkshiredales.uk.net/
To get there,take the A1 north,and come off at the B6267 Thirsk split,just after the Quernhow cafe,and at the bottom of the sliproad,turn left,and keep going for about 3 miles.
From the North,come off at the B6267 south,and then double back under the A1,and again,follow the road.
I personally compete in Class 4,which is 1130cc max,with unlimited mods.
However,probably the most spectacular class is 7,where twin bike engine saloon cars,usually Seicento's or Cinqucento's because of their lightness,are usually the favourite.Not surprising with one engine on each rear wheel!!!!!
Class 10 is twin bike engines in a sort of a go kart chassis,and these are quick as well.
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