EatMyShortsRacing
Well-Known Member
- Joined
- Jan 8, 2003
- Messages
- 1,254
For those who didnt go into the CMB 80 needle thread the topic sorta strayed to induction issues with the CMB especially relating to disc clearances. Now the way I was taught was that the disc engines SHOULD be better for lots of reasons.
Firstly the area inside the drum is added to the crankcase volume meaning the amount of vacuum (fuel/air draw) and pressure (fuel into cylinder) generated in the crankcase is decreased. This is supposed to mean a performance reduction.
Secondly I was under the impression you could get more duration out of a disc induction engine than a drum induction engine. (this could be wrong...)
Thirdly the drum would produce lots more drag (unless bearing supported and then this would also affect the integrity of the crankcase seal)
So I would be assuming that the recent switch to drum induction motors must be for one of two reasons. Either the drum seal is better than the disc significantly to offset the loss of pressure due to bigger effective crankcase volume - or the reliability of the drum is desired. This I am thinking from the older Picco disc days where shearing the disc pin meant goodbye engine.... or are they just easier to make???
Firstly the area inside the drum is added to the crankcase volume meaning the amount of vacuum (fuel/air draw) and pressure (fuel into cylinder) generated in the crankcase is decreased. This is supposed to mean a performance reduction.
Secondly I was under the impression you could get more duration out of a disc induction engine than a drum induction engine. (this could be wrong...)
Thirdly the drum would produce lots more drag (unless bearing supported and then this would also affect the integrity of the crankcase seal)
So I would be assuming that the recent switch to drum induction motors must be for one of two reasons. Either the drum seal is better than the disc significantly to offset the loss of pressure due to bigger effective crankcase volume - or the reliability of the drum is desired. This I am thinking from the older Picco disc days where shearing the disc pin meant goodbye engine.... or are they just easier to make???