Armilite
Well-Known Member
Ok, I'm convinced, Fuel Injection is the best way to go to eliminate Carb Ice problems, and to lower your GPH use, and gives you a smoother running, better starting Engine. Now, with running say a Single Throttle Body to keep it Simple, and Cost down, and turning Max 6800rpms, what Size/CFM Throttle Body do we need, based on these common CC, 2 Strokes used on Planes? Is there a Formula based on CC/RPMS used?
I do know using a Single Carb vs a Dual Carb on Rotax's can make 2-3hp difference on 377/447, and 3-4hp difference on a 503, and 5-6hp difference on a 582UL. These Sled/Ultralight Carbs seem to be rated by Size 30mm, 32mm, 34mm, 36mm, 38mm, 40mm. They don't give a CFM rating. Most Rotax UL Motors seem to run 34mm, or 36mm, Carbs. Like I know the 377UL use's a Single 36mm Carb to make 35hp at 6500rpms, as does the 277UL that also use's a 36mm Carb to make 26hp at 6250rpms.
Using this CFM calc:
Carb CFM Calculator
So a 277UL(268.72cc) at 6800rpms at 83% requires:
CFM REQUIRED 32.26517774305556 100% VE
CFM REQUIRED 26.780097526736114 USER 83% VE
CFM REQUIRED(ROUNDED) 32.265 100% VE
CFM REQUIRED(ROUNDED) 26.780 USER 83% VE
So What CFM is a 30mm, 32mm, 34mm, 36mm, 38mm, 40mm, Carb?
Rotax SIZE/CFM
185UL = 184.16cc
277UL = 268.72cc
377UL = 368.33cc
447UL = 436.57cc
503UL = 496.72cc
462UL = 462.83cc
532UL = 521.15cc
582UL = 580.67cc
618UL = 616.96cc
670 = 668.97cc
Kawasaki
292 = 292.46cc
340 = 339.29cc
400 = 398.2cc
440 = 435.8cc
I do know using a Single Carb vs a Dual Carb on Rotax's can make 2-3hp difference on 377/447, and 3-4hp difference on a 503, and 5-6hp difference on a 582UL. These Sled/Ultralight Carbs seem to be rated by Size 30mm, 32mm, 34mm, 36mm, 38mm, 40mm. They don't give a CFM rating. Most Rotax UL Motors seem to run 34mm, or 36mm, Carbs. Like I know the 377UL use's a Single 36mm Carb to make 35hp at 6500rpms, as does the 277UL that also use's a 36mm Carb to make 26hp at 6250rpms.
Using this CFM calc:
Carb CFM Calculator
So a 277UL(268.72cc) at 6800rpms at 83% requires:
CFM REQUIRED 32.26517774305556 100% VE
CFM REQUIRED 26.780097526736114 USER 83% VE
CFM REQUIRED(ROUNDED) 32.265 100% VE
CFM REQUIRED(ROUNDED) 26.780 USER 83% VE
So What CFM is a 30mm, 32mm, 34mm, 36mm, 38mm, 40mm, Carb?
Rotax SIZE/CFM
185UL = 184.16cc
277UL = 268.72cc
377UL = 368.33cc
447UL = 436.57cc
503UL = 496.72cc
462UL = 462.83cc
532UL = 521.15cc
582UL = 580.67cc
618UL = 616.96cc
670 = 668.97cc
Kawasaki
292 = 292.46cc
340 = 339.29cc
400 = 398.2cc
440 = 435.8cc
