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View Full Version : PROP & MAX RPM...????



Christopher Gentile
06-26-2000, 07:03 PM
I just switched my prop on my 16 from the 21 pitch ski prop to the 24 pitch stainless that came with the boat. However the boat still seems to reach max RPM and I still have throttle left..? The powerplant is a stock merc V6 4.3 with a Alpha 1 out drive. Im told the max rpm@WOT is 44-4800rpm. Has anyone ever come across this before. I still have not opened it up yet due to this barrier.
Advise and comments welcome. New owner. Ps Love this boat!

Varyak
06-26-2000, 07:48 PM
Chris,
I've got the same boat with the same drive train. Stock prop allows the motor to rev to about 4800rpm as advertised. Perhaps the throttle assembly is not rigged properly. Keep in mind that there are lots of moving parts inside the throttle, and back at the carb. Do you have a 2-bbl, 4-bbl , or EFI? EFI's have an electronic RPM limiter to keep the engine together. The carbs will only flow so much air at wide open throttle. Have you advanced the throttle with engine off to observe what happens at the engine? You don't want to over exert the butterflies on the carbs. You may have to remove the flame arrestor to watch the butterflies internally. Same with the airflow control on EFI.
Mark

Barry Phillips
06-27-2000, 07:35 AM
Chris: your 24pitch prop seems like a
lot for a 4.3, my 350 is proped with a 23.
Who is the prop manufacture and what
model is it? The newer Donzis I've seen
came from the factory proped with 23s.
SO-SLO

AVickers
06-27-2000, 08:57 AM
RATIOS

My guess is that the 4.3 has a different drive ratio than the 5.7... Perhaps 2:1 as opposed to 1.5:1.

That's why it can spin a steeper prop.

Varyak
06-27-2000, 11:15 PM
Actually, after chatting with Chris directly, his V6 is the 4bbl version, 205 HP. The 24 pitch would probably be right since my 2bbl 190hp V6 came with the 23 pitch. The reduction ratio is listed as 1.81 for the Alpha that comes with these engines. BUT his real problem is still deciding if the throttle control is properly rigged and if it is advancing correctly. He may also not be comfortable with all of his trim settings yet; the boat has hull trim tabs as well. Cavitation? Drag? I suggested he experiment a bit more and let us know...