Question about reversion and superchargers
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Question about reversion and superchargers
Ok, after reading a bit about reversion on pb's thread, you've got me wondering about whether having a supercharger changes the chance of reversion. Does running a blower decrease the chance of reversion? I realize this is probably not an going to be easy to answer, but as I'm a newbie at supercharged engines I need all the help I can get.
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My guess it NO. This is a problem that only happens at idle or just off idle. If the motor has a blower or NA the motor is in vacuum when at idle. Camshaft design & exhaust type are the only items to worry about.
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Indirectly, yes. A correctly cammed supercharged engine will have a camshaft with less overlap so the supercharger doesn't blow the air/fuel mixture straight through the cylinder and out of the exhaust when both valves are open at the same time (valve overlap). Most supercharger camshafts have either a wide LSA or less exhaust duration (some have less exhaust duration than intake duration).
The stock GM marine camshafts used in the 454/502 Mercruiser Magnum engines make fine supercharger camshafts. They have a wide LSA at 115.5 degrees and 224/224 degrees of intake/exhaust duration. Very little valve overlap!
Dennis Moore
www.mooreperformance.org
The stock GM marine camshafts used in the 454/502 Mercruiser Magnum engines make fine supercharger camshafts. They have a wide LSA at 115.5 degrees and 224/224 degrees of intake/exhaust duration. Very little valve overlap!
Dennis Moore
www.mooreperformance.org
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I won't know exactly what cams are in these engines until I disassemble them this fall. The engine builder (the previous owner's engine builder) isn't inclined to give out the cam specs to me, and I can't blame him for that. He did pass a some spring information to me when the previous owner asked him what I should buy to replace them. Isky 8005A, which is a fairly light spring, 130 lbs. on the seat I think, and .600 lift cam max.
I"m going to have one of the engines dyno'd before disassembly to se what kind of numbers it's making.
I"m going to have one of the engines dyno'd before disassembly to se what kind of numbers it's making.
Last edited by Crazyhorse; 09-13-2003 at 02:00 PM.
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By the way, the engines are 509 cid, J&E flat-top pistons, Merlin rectangle-port heads, custom-ground hydraulic flat-tappet cams, 1050 Holleys on B&M 250 blowers. I had the heads freshened right after we bought the boat this past spring and the engines have performed very well. But gee, we all want just a few more horses, right?
#6
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2 kinds of reversion.
Exhaust reversion (that pulls water into the cylinders)
Intake reversion (that causes air to oscillate back and forth thru the carb, double-fueling it and making it slobbery rich at low engine speeds).
A blower will reduce or eliminate Intake reversion (draw-thru will eliminate it - blow thru will reduce it).
A blower will have no effect on exhaust reversion (versus the same engine with no blower).
Exhaust reversion (that pulls water into the cylinders)
Intake reversion (that causes air to oscillate back and forth thru the carb, double-fueling it and making it slobbery rich at low engine speeds).
A blower will reduce or eliminate Intake reversion (draw-thru will eliminate it - blow thru will reduce it).
A blower will have no effect on exhaust reversion (versus the same engine with no blower).
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Yeah, they seem to idle much better. I'm assuming that's because of the reduced intake reversion, probably partly due to the decreased overlap too. I could be wrong though. I'm new to blower motors.
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Originally posted by mcollinstn
A blower will have no effect on exhaust reversion (versus the same engine with no blower).
A blower will have no effect on exhaust reversion (versus the same engine with no blower).
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"A blower with 5psi of boost will charge the cylinder with 5psi of positive preasure"
This all well & good except when you are at idle. Intake maniford is in vacuum, thus air is not being forced into the cylinders
This all well & good except when you are at idle. Intake maniford is in vacuum, thus air is not being forced into the cylinders