1989 Evinrude VRO 90 HP RPM Question

[Myklle]

I have a 1989 Evinrude VRO 90 HP on a 1989 15' 6" Kingfisher bass boat with a 13 x 19 aluminum prop. It runs great but I cannot get it faster than 41mph (WOT) at 4800 RPM's with just me in the boat. It currently has a 13 x 19 alum. prop. I was reading the book I have on my motor and it states that the WOT RPM's should be between 4500 and 5500. I am right in the middle of that range. I've been told this motor should run at 5500 RPM's at minimum. My question is, how to get higher RPM's out of her? Any and all responses are welcome. Thank you in advance.

 

[SparkieBoat]

Re: 1989 Evinrude VRO 90 HP RPM Question

I prefer my motors to hit 5500-5800 RPMs at WOT, seems to be the best performance range for most motors in my humble opinion. You should increase about 200 RPM for each inch in pitch drop. I would try a 14diaX15 pitch prop on it..if you could borrow one and check your RPMs and speed you may even find a 14x13 would do well, especially if you plan on having more people and weight in the boat or pulling skiers or tubers. best if you can test with borrowed props before shucking out $$ for a new one. If you live near Savannah GA, I have a 13 and a 15 you could borrow with a deposit.

 

[SparkieBoat]

Re: 1989 Evinrude VRO 90 HP RPM Question

BTW I am assuming that your motor is running properly....

 

[Myklle]

Re: 1989 Evinrude VRO 90 HP RPM Question

The motor is running great and I live in Chattanooga, TN. Perhaps we could work something out?

 

[SparkieBoat]

Re: 1989 Evinrude VRO 90 HP RPM Question

yea just drop by tomorrow and borrow the props its only a 7 hour drive
you may find a test prop a little closer

 

[GeneH]

Re: 1989 Evinrude VRO 90 HP RPM Question

Are you certain your tach is accurate? A lot of people make wrong prop decisions based on an old cheap tach and the info it provides.

 

[trendsetter240]

Re: 1989 Evinrude VRO 90 HP RPM Question

I have a 1989 Evinrude VRO 90 HP on a 1989 15' 6" Kingfisher bass boat with a 13 x 19 aluminum prop. It runs great but I cannot get it faster than 41mph (WOT) at 4800 RPM's with just me in the boat. It currently has a 13 x 19 alum. prop. I was reading the book I have on my motor and it states that the WOT RPM's should be between 4500 and 5500. I am right in the middle of that range. I've been told this motor should run at 5500 RPM's at minimum. My question is, how to get higher RPM's out of her? Any and all responses are welcome. Thank you in advance.

You should definitely be up another 500 RPM at WOT. However, I believe a 13p would be far to low pitch for your setup. My 70 will turn a 13p 4 blade at 6600+rpm on a simlar weight 17ft boat. I have a slightly lower gear ratio than you though.

As a guess based upon the info you provided I would try a 15p 3-blade Turning Point hustler or a 17p 4 blade Solas Amita. Both inexpensive aluminium props and both will raise your RPM from where it is now.

What is the current prop make? Have you tried raising your motor up a notch or two? That can make a difference of a few hundred rpm and a few MPH.

 

[Myklle]

Re: 1989 Evinrude VRO 90 HP RPM Question

thank you to those that replied. I am going to raise the motor a notch or two and see how it does before I spend the money on another prop. I will let y'all know what happens.

 

[Myklle]

Re: 1989 Evinrude VRO 90 HP RPM Question

I installed a 13 1/4 X 17 prop last night. At WOT, the RPM's are now 5200 - 5300 at a speed of 39 according to GPS on my phone. I am going to raise the motor 1 notch and see how she does. I am a bit concerned that raising the motor 1 notch may make her a bit unstable. I'll find out in the morning and let you all know. Thank you again to those that reponded with suggestions.