Got a question about jets. If I increase the jet size will I increase the HP? Adding more fuel for more compression and hp. I know I have to watch temperature but if I tape up the flywheel housing to increase temp, is there any benefit of increasing the jet size? Or should I just keep everything open and put the jet that keeps my temps good? Any info is appreciated. Thanks
there is something called stoichiometric. This is real tough reading, but you might get something from it.
http://en.wikipedia.org/wiki/Stoichiometry#Stoichiometric_ratio
if your
current jet size is ideal, making it bigger, thus a richer mixture, will more than likely decrease the horsepower. The opposite is also true, make the jet smaller, a leaner mixture, will also hurt the horsepower.
Taping up the shroud has 2 effects, one, that might be good, means the flywheel will be pumping less air, as pumping air takes horsepower away from the power to the ground. It will raise the temperature of the engine, measured with a CHT, which really doesn't tell you very much. If the engine is hot, that will thin out the air and give you less horsepower. People tell me I'm a screwball, but the ideal way to check the temperature is the EGT. (Exhaust gas temperature) this tells you what's going on
inside the engine.
There is always an ideal air/fuel ratio. The air density, as it changes, changes the ideal air/fuel ratio. If the air density is higher, more air gets pushed into the engine, and this requires more fuel to maintain the ideal air/fuel ratio. The opposite is also true. If you now have a .039" jet, and the air density changes 5 points, either up or down, a change in jetting size of .001" would be called for. A change in air density of one point, would call for a jet change of .0002". Not very practical, nobody has jets with that small a change in diameter, but the numbers don't lie.
Now it is possible that you have a jet that is currently to small for the current air density. In this case, putting in a larger jet might help, but only because you are currently lean.
The best way to determine jet size is track testing. You have a stopwatch, right? Once you find the ideal jet for your setup, using an air density gauge will tell you when, or if, you should put in a bigger or smaller jet. It really depends on how serious you want to get.
From the desk of
Al Nunley
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory. (Al Nunley)
