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  1987 Mercury Black Max 150: New Gear Case Loses 10-MPH

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Author Topic:   1987 Mercury Black Max 150: New Gear Case Loses 10-MPH
jdizzie posted 07-27-2012 11:43 AM ET (US)   Profile for jdizzie   Send Email to jdizzie  
On a 1987 Black Max 150, I was getting about 39.5-MPH top speed using a 15 x 17-pitch aluminum Quicksilver propeller using a FLO-TORQ hub kit. I hit a rock and wrecked the propeller and lower unit. I installed a new SEI lower unit and a Michigan Wheel 14.25 x 17-pitch stainless steel propeller with a fixed hub. Now I'm only getting about 30-MPH top speed. Does the [change in propeller] diameter [of 3/4-inch] really matter that much? I'm considering a four-blade 15 x 17-pitch aluminum Quicksilver propeller, but I thought the stainless [propeller] would be better. Assume weight and conditions are equal.
L H G posted 07-27-2012 03:27 PM ET (US)     Profile for L H G    
Did you buy the correct gear ratio in the SEI unit? For your engine, it should be the 2.0:1 ratio. Even though I do not like Michigan Wheel propellers, the propeller should not be the problem. It sounds like something else is wrong.
Teak Oil posted 07-27-2012 03:41 PM ET (US)     Profile for Teak Oil  Send Email to Teak Oil     
What is your [engine speed] at 30-MPH?

Larry--what higher gear ratios were available for that V6 gear case that he might have received?

jdizzie posted 07-27-2012 04:30 PM ET (US)     Profile for jdizzie  Send Email to jdizzie     
Yes, 2:1 gear ratio from SEI. That's what Mercury told me as well. However, none of my gauges have ever worked since I've owned the Revenge, four years now. So, I have no way of telling [engine speed].
jdizzie posted 07-27-2012 04:34 PM ET (US)     Profile for jdizzie  Send Email to jdizzie     
The [boat speed] is coming from [a GPS receiver]
jimh posted 07-28-2012 10:36 AM ET (US)     Profile for jimh  Send Email to jimh     
It is impossible to analyze performance if the engine speed is not known. The decrease in boat speed with the new gear case and propeller might be simply due to the engine speed being much lower than it was with the original gear case and propeller.
jdizzie posted 07-28-2012 12:17 PM ET (US)     Profile for jdizzie  Send Email to jdizzie     
I can't wait to put a 200hp Honda on this rig.
outragesteve posted 07-28-2012 08:56 PM ET (US)     Profile for outragesteve  Send Email to outragesteve     
I agree with Larry: Possible wrong ratio. Easy to check: The flywheel should turn 2 times for every 1 turn of the prop in forward gear. Ignition OFF!!!
brisboats posted 08-03-2012 10:08 PM ET (US)     Profile for brisboats  Send Email to brisboats     
Sure appears that SEI has given you the wrong ratio.
brisboats posted 08-03-2012 10:11 PM ET (US)     Profile for brisboats  Send Email to brisboats     
Forgot to add, Mercury 200 hp 2.0's and 2.5 liter typically have a 1:87:1 ratio. Not sure what SEI uses but they do have a one size fits all mentality on the mercruiser lower units.

B

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