DIY_EFI Digest V4 #709

[Gary Derian]

With carbs, small throats meter fuel better at mid to low rpm.  With EFI the
computer meters so small throats are not needed.  What matters is port and
runner size to strike a balance between low and high rpm.  With dry
manifolds, lots of variable runner configurations are possible.  A too small
EFI throttle body restricts the higher rpm range with no improvement in low
rpm.  Torque peak and power peak are reduced and occur at lower rpm because
of this.

Power in HP = (torque (in ft-lb) X rpm) / 5252

Torque is easy to understand, how hard the engine twists.  Power has a rate
component, how fast it twists hard.  One curve determines the other.  A
gearbox trades torque for rpm, no effect on power.

Gary Derian <gderian at oh.verio.com>

> Can someone post or email me the calculation to convert ft/lbs at a given
RPM
> into Horsepower - or the other way around.
>
> And for the engine guru's,  if the Throttle Body used for an engine is
downsized
> will the Peak Torque developed by the engine increase or move to a higher
RPM
> with a corresponding loss of maximum Horsepower at redline?  After all,
smaller
> venturis are used in carburetors for the lower RPM settings,  I thought to
keep
> the engine torque up by keeping the velocity of the airflow up.
>
> Cheers,
>
> John Dammeyer