<VV> Conversion to EFI: Is it really cost effective?

[Bruce Schug]

On Jun 16, 2004, at 12:08 PM, NicolCS@aol.com wrote:

*SNIP*

> gear).  The engine is a 140, so it has dual (low restriction) exhaust, 
> larger
> valves and exhaust manifolds: all of which contribute to reduced 
> breathing
> losses.

*SNIP*

Hmmm... interesting comments.

I think the dual exhausts will have a negligible effect on mileage at 
the rpm's used in an economy run or even for normal driving. 
Nevertheless, I would run them too.

The large 140 valves are another matter. Again, they won't increase 
power at the low rpm's in this example. I never thought of them as 
lowering pumping losses. They might do that. One thing they will do, I 
think, is lower the velocity of the incoming fuel mixture which will 
decrease responsiveness at low rpm's. Of course this only gets bad if 
the secondaries are opened. In other words, if you floor the throttle 
at low rpm's and open the secondaries the mixture velocity will go way 
down and the engine will not respond quickly. I think if I were to 
build an economy run engine, I'd stick with a small valve head for 
better intake velocity.

I think the trick to reducing breathing losses, which really means 
pumping losses, is to run with the throttle as wide open as possible. 
Your low (numerically) gearing does this.

What size tires are you using, Craig?

I have gotten nearly 50 mpg in an economy run using a few economy run 
tricks and a fast ignition switch ;)

Bruce


Bruce W, Schug
CORSA South Carolina
Greenville, SC
bwschug@charter.net

CORSA member since 1981

'67 Monza. "67AC140"