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transmission idle speed - how low is too low?

B

bobct

Advanced Contributor
Jeff, just saw your comment on the other thread. When I switched to 4 blade props, I lowered my idle quite a bit to reduce my forward speed in gear. It just seemed a little too fast when coming into the slip. I also wanted to reduce the clunk when it went into gear. Both transmissions sound exactly the same before/after the change.

Anyway, I have my idle set at around 550-600 in neutral/out of gear. Is that too low? I have noticed a whirring sound from both since I made the change about mid way through the season. I assume that's gear noise I'm hearing. Definitley no rattling noise which I guess is pretty common at to low and idle. By having it set so low, what exactly happens to the gears?

My engines sound great at these low idle speeds or I wouldn't have made the change. I thought the primary reason for having a higher idle was to eliminate the risk of stalling but maybe not.


Bob
 
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Very low engine speeds make it hard for the torsional dampener to do its job. Every piston stroke at the ignition point causes the engine crank to jerk. Both the dampener and the flywheel work to reduce this jerk. BUT, your ears are a good judge of rattle and gear chatter. If its quiet at dead slow forward, there should be no issue.
 
You want to set the idle speed in gear, fully warmed up...like DD said, too low and you will hear the damper rattle.

if the engine is in good shape, there won't be much drop when going into gear....velvet drive says all shifting should be down w/ RPM < 1000.
 
My twin 1990 454's idle at 575 but jump up to 600 when I put um in gear. Everything is smooth, no rattles, plenty of idle speed.
Nightstalker
 
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