RE: 2.0 L Rev Limit

["Brian Shorey" <bshorey@domain.elided>]

>  I recently installed a rebuilt 2.0 L. twin-spark (1989 from an Alfa
75) in 
> my '74 GTV.
> Having looked up the factory specs on the T.S. engine I found that
maximum hp 
> of 148 is acheived at 5800 rpm. That being said, why would anyone want
to 
> overrev an engine if you know at what rpm maximum output lies? Curious
to 
> know.

Ego?

There are (at least) a couple of reasons why you'd want to rev higher
than red line (or the RPM where you achieve maximum HP).

First, the RPM where you achieve maximum hp is not the optimal place to
shift.  Assume that HP climbs as you approach the 'maximum hp' point,
and declines afterwards.  You want to find shift points that keep your
motor revving equally (assuming you have a bell curve HP chart) on
either side of that maximum hp point.

So, if you went from 500 RPM lower than your 5800 max hp point to 500
rpm higher (5300 rpm to , that would give you overall higher usable
power than is you used a band of, say, 4800 rpm to 5800 rpm.

Another situation in which you might want to extend beyond the upper
limit of your useful rev band is when you might be approaching the end
of a straight, and taking the time to shift costs more than simply
letting the engine rev a couple, or a few, hundred rpms higher.

bs

p.s.  Torque curves figure into all this as well, in fact your optimal
rpm range may very well be better off factored against the torque curve,
as opposed to hp curve.
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