James Carpenter wrote:
> Have you ever noticed how the acceleration (kick in the back) the same as
> second, if not better in second.
> If I am doing 2500 rpm in 1st, and descide instead of going chainging into
> second to flaw the accelerator untill 5000rpm, the proformance and kick is
> realy poor. Try it in second and you get a much better kick.
>
> Strange and seems to defy all laws of physics. Except that the flywheel
> saps loads of energy to spinup, so it takes a predefined time to spin up the
> unloaded engin. This is added to the spin up time of the car for all the
> gears.
>
> The net result is that you find the spin up for first and second almost the
> same, but second covers more MPH. And so the acceleration can be better in
> second, even though ist give you more hill pulling power.
>
> Anyway I wan't a lighter flywheel to give me a more peppy responce. I
> currently have a Doly 1500 engin in my car, with Spitfire carburetters. Is
> a Spitfire 1500 flywheel lighter than the dolly. I also have a Herold 13/60
> GK block (for sale) is the flywheel for this lighter than the Doly 1500 or
> Spitfire 1500.
>
> OK it's been 2000 miles since a complete bottom end overhaull, and I don't
> want to take the engin apart again to do any work on it. Can I take the
> flywheel off the crank and have it balanced and lightened without doing
> anything to the crank. Or do I need to give the engenering works the whole
> lot?
>
> How much can be taken off before it starts to effect the tickover i.e. you
> have to raise it above 800 rpm.
>
> It seem to me this is a very effective, and invisible way of tuning an
> engin, giving better fule economy, not brakeing any emmissons laws, and a
> smoother running engin.
>
> How much does it cost in the UK?
>
> James
I suspect something else. If you want to know how fast the engine will "rev up"
do a Neutral Engine Run Up from Idle to Redline at Wide Open Throttle. The time
required for this to happen should theoretically be the fastest available
acceleration for the engine. This is true for Fuel injected and constant area
carbs.
However, with Constant depression carburators such as the SU or ZS, the driver
does not truely control the rate at which the engine receives fuel and air. The
carburator piston is vacuum actuated. Its the piston and needle valve position
which control the amount of power produced by the engine. This is why the
piston spring and dashpot oil have such an influence on carburator performance.
I suspect that your strange physics are due to the performance characteristics
of the constant depression Carburator, not the weight (more accurately described
as the rotational inertia) of the flywheel.
Patrick Barber, Allen Park, MI
70 Spitfire MkIII FDU89984L
Visit My Triumph Website at http://www.geocities.com/motorcity/pit/7864/Triumph/
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