GBM wrote:
"RW Salnick" wrote

Assuming we are talking about a 2GM, displacement of say 600 cc, idling
at 1000 RPM, it is pumping 0.6/2*1000 = 300 liters/min of air out the
exhaust pipe. This is approximately 10 CFM - not bad for idle and a
small engine...


bob,
If the 2GM is a 4-cycle engine, is the above correct if it only draws in
air every other revolution?

Shouldn't air flow to engine room be calculated to keep temperature down ?
As the combustion air temperature goes up, engine efficiency goes down - I
read somewhere that power loss could be 11% if temperature rises from 80F to
150F.

Perhaps having the exhaust fan run all the time the engine runs would be a
good idea?

GBM

Correct - that is why I divided by 2 in the equation. I doubt that the
engine room temperature would reach 150 F under normal conditions
(although the engine external surfaces certainly could). If it did get
this hot, improved ventilation is certainly in order!!

The amount of air we are discussing here is a little more than what
would fill a 2' x 2' x 2' cube. On the small boat we are discussing
here, I am guessing that the engine compartment is pretty small and
crowded, and that the 10 CFM flow, at engine idle, would completely
replace the air in the engine compartment every minute or two, or less.

bob