wrote:

What type of volume would you expect to use on a small piston engine
say an 80 CID Harley Evo v-twin?

Let's make some horrific assumptions about RPM
and volumetric efficiency. We know that 1 gallon
per minute works for 540 cubic inches. Therefore,
for a 80 cubic inch engine under the same conditions:

(80 cubes / 540 cubes) x 1 gal/min = 0.15 gal/min

Note that we run our direct-drive aircraft engines
at less than 3000 rpm, otherwise our prop tips go
supersonic, and that's a whole different world.

I suspect your RPM might be a bit higher than ours,
lets say 6,000 rpm or twice ours, so that would double
(maybe) your exhaust gas flow, therefore you might try
0.30 gal/min flow, which is a bit aggressive, but I
suspect might work quite well.

When running smoke, you need to have the throttle
open, making power and RPM. Smoke doesn't work
well at low power settings - no exhaust gas flow,
and the stacks are cold.

Hope this helps - I can guarantee it's worth what you
paid me for it! :-)

--
aboyd