Mr Helmholz - simple model

[Todd....!!]

Gary what's a CVT...?

ALSO a TOP FUEL dragster is still traction limited, doesn't have more
than one gear, and the clutch slides the entire run...

LATER!

Todd....!!

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Gary Derian wrote:
> 
> I race go-karts which use centrifugal clutches so I have done some thinking
> here.  If you change your gears, you have changed your top speed at max rpm.
> If you are pulling stumps, use as low a gear as you can but still set the
> clutch stall at max torque.
> 
> For a drag racer, not traction limited, you need to maximize the "power
> under the curve" for the 1/4 mile and must choose a gear that does this
> without blowing up the engine before the traps.  Once you are close on a
> gear, the clutch setting can be calculated.  Since a sliding clutch
> transmits all the torque input (there is no where else for it to go) and
> converts power into heat, it stands to reason the more torque input, the
> more torque output.  Therefore set the stall to the max torque rpm.  If you
> want to change your gearing, you still must set the stall to the max torque
> rpm.
> 
> For a drag run with a sliding clutch (again, not traction limited), start
> out at max torque rpm while the clutch is sliding, as speed builds up, the
> clutch will lock up and rpm increase to max power rpm and beyond.  At this
> point, you can shift gears if you have them.  One would hit the traps at an
> rpm between max power and the rev limit.
> 
> This is only for a sliding clutch or fluid coupling.  A snowmobile uses a
> CVT so does not absorb power.  For this case, operating the engine at max
> power rpm will be faster.  A torque converter multiplies torque and absorbs
> some power so it operates somewhere in between.
> 
> Gary Derian <gderian at oh.verio.com>
> 
> > On Thu, 20 May 1999, Gary Derian wrote:
> >
> > > If one has a sliding clutch, it should be set to hold the engine at max
> > > torque rpm, not max power rpm.
> >
> > I disagree, because of the effects of gearing.
> >
> > A hypothetical engine makes 300 ft.lbs at its torque peak of 4000 RPM.
> > At that RPM it makes 228.5 HP.
> >
> > Let's say it makes 201.3 ft.lbs at its HP peak of 6000 RPM.  At that RPM
> > it makes 230 HP.  This is an engine that could probably use a new cam. :}
> >
> > Even so, once gearing is taken into consideration, it is better to use the
> > HP peak.  You can have a 33% lower gear ratio at the higher RPM, which -
> > more or less by definition - outweighs the decrease in torque at the HP
> > peak.  Once we gear this engine down by 1/3 it makes the same 300 ft.lbs
> > of torque that it did at its torque peak.
> >
> > But let's say we have an engine that doesn't have its torque fall off so
> > badly.  Let's say, instead, the engine makes 220 ft.lbs at 6000 RPM,
> > instead, for an HP rating of 251.3.  This engine, when gearing is taken
> > into consideration, can generate an effective 328 ft.lbs of torque - a
> > noticeable improvement.
> >
> > This is why engines are rated mostly in HP.  Torque is of course the most
> > important component in acceleration, but what RPM the torque is generated
> > at is just as important.  HP is a better measurement of torque at RPM,
> > although of course a full printout of the torque curve is the best :}