Vince,
Thanks for posting BTU numbers. Bottom line is that no matter how light and efficient a gasoline engine is, more power is still available by running alcohol (especially when nitro is added). The benefits generally realized by spark ignition gasoline engines vs glow alcohol engines is the ability to more accurately control the combustion - spark can be adjusted to be at the optimal time at any RPM, and will occur more accurately and consistently - this lends to better fuel economy/efficiency. This is exactly why glow engines converted to gas don't make as much power, and why glow engines converted to spark ignition (ie, YS 170 CDI) make more power.
Regards,
Dave
ORIGINAL: vbortone
Dave,
Probably the reason is explained in this web site:
http://www.smokemup.com/tech/fuels.php
They compare the gasoline, methanol and nitromethane. Probably the information gives a good reasons why we use nitro in glow fuels. The table 1 gives the total energy that could be delivered by IC engine for each fuel. Clearly gasoline is the lowest one and probably this is a good explanation why it does not work well in small displacement IC engines. Her the numbers from table I:
Total Thermal Energy delivered in IC engine (BTU)
Gasoline 53,176
Methanol 67,545
Nitromethane 125,412
Vicente ''Vince'' Bortone