ranger 374v prop suggestions

[jp101977]

Hey guys. Ihave a 1990 ranger 374v with a 1990 mercury 175 and a 6" manual jackplate. I am currently running a laser 2 25p prop. I can the motor 6000 rpms but can only achieve app. 54 mph gps at wot. I have moved the motor up and down and tried both, it is currently 3.25 below the pad, I tried it as high as 2" but it would blow out coming out of the hole. I know this boat is heavy but I think 62-63 is realistic. Do you guys have any suggestions on what prop I should try, or do you think I may have another issue? I don't want to totally sacrifice holeshot but I would prefer more top end. Thanks in advance

 

[jestor68]

Re: ranger 374v prop suggestions

Do a compression test and post the numbers.

I suspect your 1990 motor is not putting out like a fresh motor.

Check the tach for accuracy.

Your motor, with it's gear ratio and spinning a 25" prop at 6000 rpm, with a 10 % slip should be doing about 67 mph.

Something is wrong. :grumpy: And it probably isn't the prop.

Boat tests posted on the Merc web site(175 Optimax) indicate low 60's with a 24 pitch prop at 5500-5600 rpm.

 

[jp101977]

Re: ranger 374v prop suggestions

Do a compression test and post the numbers.

I suspect your 1990 motor is not putting out like a fresh motor.

Check yout tach for accuracy.

Your motor, with it's gear ratio and spinning a 25" prop at 6000 rpm, with a 10 % slip should be doing about 67 mph.

Something is wrong. :grumpy: And it probably isn't the prop.

The compression is 110 +/-4 on all cylinders
I haven't truly tested the tach at higher rpm but it is correct up to about 1500 rpms I know (didnt want to turn it higher than that on the muffs)
Maybe I need to adjust the engine height again?

 

[jestor68]

Re: ranger 374v prop suggestions

Since your numbers indicate a 29 % slip, is it possible your prop's hub is slipping at higher rpm, causing the rpm to raise and speed to drop?

Your motor is down on compression. That's a fair amount of power lose.

But that doesn't explain how your 1990 motor can turn 6000 rpm with a 25 pitch, when a new Optimax 175 can muster 5500 rpm with a 24 pitch on a like size boat.

Do you know how to check your prop hub for slip?

 

[jestor68]

Re: ranger 374v prop suggestions

I would recommend that you replace your Flo Torque hub with a Solas Rubex hub, if you suspect it is slipping at high speed/load. There are interchangeable with Flo Torque, and frankly work better. The RBX-102 is for Mercury/Mercruiser.

A tach can read fine a lower readings, and get progressively worse as the rpm goes up. You might try cleaning the contacts on the back of the tach, as they can get dirty over time and cause the tach readings to be off.

I am really suspecting the tachometer, because your gear ratio/prop pitch/ at a 10% slip and 54 mph equals a theoretical speed of 60 mph; which works out to only 4739 rpm.

 

[jp101977]

Re: ranger 374v prop suggestions

You are correct about the compression being low. I am going to check the tach first since the flo-torq is new. But it is all being put on hold since the transmission went out in my truck this morning...I reaaly do appreciate your info and will check back after that problem is solved..