Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
#21
Registered
Re: Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
rm,
If the same motor is n/a and has 12 inches of vacuum at idle and then you add a blower and it has 12 inches of vac at idle then no difference correct? I do agree that a blown application off of idle is different. Vacuum is vacuum with or without a blower dont you think?
If the same motor is n/a and has 12 inches of vacuum at idle and then you add a blower and it has 12 inches of vac at idle then no difference correct? I do agree that a blown application off of idle is different. Vacuum is vacuum with or without a blower dont you think?
#22
MarineKinetics
Platinum Member
Re: Does a Crane"741" Cam With Silent Choice Cause Water Reversion?
HP,
Simply stated manifold vacuum is not the cause of exhaust reversion. This can be seen by a mild (duration) cam with less overlap that does not revert and hold, say, 18” manifold vacuum, where a more aggressive cam, with a higher duration and the resulting increase in overlap will have a greater tendency to revert water and only carry say 10” manifold vacuum. We reverse engineered this concept as it pertains to blower motors. While exhaust reversion is a design/engineering consideration when building a motor, only in the marine environment is exhaust reversion a mechanical factor due to the fact that many marine engines utilize cooling systems that place water in the exhaust tract. We know the consequences of water entering the combustion chamber due to reversion. The running engine, from carburetor to exhaust tips, is a series of bi-directional pulses and pressure differentials. Exhaust reversion occurs during the overlap period when the entire tract, from carburetor to exhaust tip, is open and under the correct conditions these pulses bring the discharge (and water) back into the combustion area. It appears that the supercharger being placed in this tract disrupts these bi-directional pulses enough to counter exhaust reversion. If anyone has experienced reversion with a blower motor I would be interested in the specifics.
Bob
Simply stated manifold vacuum is not the cause of exhaust reversion. This can be seen by a mild (duration) cam with less overlap that does not revert and hold, say, 18” manifold vacuum, where a more aggressive cam, with a higher duration and the resulting increase in overlap will have a greater tendency to revert water and only carry say 10” manifold vacuum. We reverse engineered this concept as it pertains to blower motors. While exhaust reversion is a design/engineering consideration when building a motor, only in the marine environment is exhaust reversion a mechanical factor due to the fact that many marine engines utilize cooling systems that place water in the exhaust tract. We know the consequences of water entering the combustion chamber due to reversion. The running engine, from carburetor to exhaust tips, is a series of bi-directional pulses and pressure differentials. Exhaust reversion occurs during the overlap period when the entire tract, from carburetor to exhaust tip, is open and under the correct conditions these pulses bring the discharge (and water) back into the combustion area. It appears that the supercharger being placed in this tract disrupts these bi-directional pulses enough to counter exhaust reversion. If anyone has experienced reversion with a blower motor I would be interested in the specifics.
Bob