On Tue, 28 Oct 1997, Jim Barbuscia wrote:
>
> Bob,
>
> Very good, and pretty much what I had suspected would be the case with
> Webber carbs. Except the gas mileage issue, I would think a properly
> tuned engine would only consume more fuel when you actually "got on it".
Well, you have to remember that you are now capable of moving more air
through your engine. Unless you improve the volumetric efficiency, your
just moving more air through. The bottom line is that your mileage will
go down. I'm pretty sure this is because with the triple Webers, you are
using an "individual runner" style manifold instead of a "common plenum".
The IR style of manifold is probably a bit less efficient because each
cylinder is "on its own" to produce the pressure change pulse to get the
fuel to atomize. And at normal road speeds, the efficiency is probably
less than at higher speeds. Note: I'm pretty sure this is one reason that
having a perfect ignition systems is very important to triple Webers...
Also note that I tuned for power, that means 10 BTDC initial dynamic
timing with 30 degrees total advance. If I tuned a TDC and 30 degrees
total advance, my milage might be a bit better, maybe 19 MPG. Overdrive
would help a lot, and with the webers you have plenty of power for the O/D.
Now, if you really want to make some power... start playing with the
volumetric efficiency... let's see: Cosworth pistons , ceramic coating of
_everything_, computer controlled fuel injection..., titanium bits, fully
ported heads, increased compression ratio... Then you might get better
mileage, but you'll spend a lot of money that you'll never get back from
fuel savings... And, if you did all that, the .410 lift cam and 280
duration would be too little - how about .550 lift and 290 duration: 200
plus HP, but no idle....
>
> -jimb
>
regards,
rml
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