Prop Question

[BrianLucky13]

I have a 1988 Johnson 90 horse on a 16 foot lund. My prop on there now is a 13 X 19. I have a another prop that is brand new and its a 13.25 X 17. I wanna put the new one on cuz its not all banged up.

What I wanna know is will it fit and what it will do to my speed and hole shot???? I can go about 44 mph now but wouldnt mind going a little faster if you know what I mean!!!!

Thanks a lot guys!!!!

Brian

[LMITOUT]

What are your max RPM's with the old prop when trimmed up? Going with less pitch will increase your RPMs and may put you over the maximum recommended by the motor manufacturer. If you're already at max RPM then the only thing the new prop will do is probably help the hole shot. Not sure what that extra 1/4" will do though.....it may neutralize the effect of the lesser pitch to some degree so you might be able to get away with dropping the pitch and not increasing the RPM's as much as just dropping the pitch and leaving the diameter the same as the old one.

You'll have to see if the prop will clear the cavitation plate too, which is easy to determine if you already have the new prop.

If it has the clearance, then bolt it up and take it for a spin and see what it does. Watch your RPM's though so you don't overrev the engine.

[BrianLucky13]

I have no clue what the rpms are. The prop cam off my dads 90 horse Johnson too.

So what your are saying is ill have more rpms and a better hole shot but less speed???

Thats kind of the opposite I want cuz I already have a great hole shot.

Thanks a lot that helps!!!

[LMITOUT]

It's possible you could pick up some speed......if you're not at max RPMs with your current prop, because then you can rev the motor a little more and get a little more speed with the new prop.

If you're already at max RPM's with the old prop, then you'll go over the max with the new prop and you probably don't want to do that. You'll still have a great hole shot, but will have to watch the gauge to not overrev the engine.

Another thing that could happen is you'll "blow out" with that high-revving prop and it won't help you at all.

There are a lot of variables and the best thing would be to try the other prop, if possible, to see how it performs.

On my boat the engine came with a 17P prop and it wouldn't rev and the hole shot wasn't the best. I dropped one size pitch and it's a completely different boat now. It jumps on plane and I gained about 600 RPMs and a handful of MPH too, not to mention it handles a lot better. In my case the RPMs were well short of max so I had a lot of room for improvement. Now it's on the upper end of the recommended engine RPM and runs like a champ. Also have to mention I went from a 4-blade to a 3-blade which makes a difference too.

[BrianLucky13]

Ok thanks a lot. Should I hook up a tach then to see what my RPM's are cauze i dont have one now.

Also what do you think the max RPM's are for that motor????

[marine_man]

Yes, I'd hook up a tach to find out where you're at. That's about the only way you'll sure you're not running past the recommended RPM range.

Max WOT RPM for your motor is 5500.

Good luck!

marine_man

[BrianLucky13]

Thanks a lot!! Now I just gotta figure out how to hook a tach up. To bad my truck got broken into a couple days ago and the tach I was gonna install was stolen!!! Some people!

Thanks again!

Brian

[pfluemis]

Some makers, like Mercury, Evinrude, Johnson, change the diameter of the prop with the change in pitch. Has to do with the performance of the prop. Both props you listed are correct "stock" size props. In "theory", you should see a quicker holeshot, less top end, and slightly more WOT rpms with the 17 vs. the 19. This is with all things remaining the same. Changing motor height, trim angle, and the load in the boat will effect the performance. Engine condition and state of tune will also effect what happens to performance with each prop. Given the fact you are getting 44 MPH with the 19p, it sounds like the motor is running well and is puting out good power. The 17p is a good prop on that combo for general use, but being more desireable for pulling tubes and ski's than WOT speed. A 20p, in "theory", is going to give you more speed. Depending on how much "added weight" you have in the boat, your combo might struggle with a 21P.

FWIW, the props that are availible in "stock" form for the motor are 15p x 13 3/4", 17p x 13 1/4, 19p x 13", 21p x 12 3/4", and 23p x 12 3/4" aluminum or SS props. There are aftermarket props that might be different sizes. I know the aftermarket has a 20p prop for the motor. That would not be a "stock prop" but might give better performace than a 21p or 19p prop, depending on setup.

[shamalex72]

Brian, let me know when the next time you will be around. I have a 13x19 stainless you can try.

[BrianLucky13]

Thanks a lot Pfluemis!!!

Troy, whens the next time youll be fishing on Alex???? I would maybe take you up on that offer. Seems like when I get something from you I catch big fish!!!

Thanks

[shamalex72]

I will probably try it out there this weekend.