High performance prop.

[theworm]

Quick question. I'm interested in changing the prop. on my 1991 40hp Evenrude to enhance performance. What kind of prop. should I be looking for, stainless or aluminum, three or four blade, and how do I tell if I have a large or small gear case on my motor.<br /><br /> Please Inform

 

[JB]

Re: High performance prop.

Unless you provide a lot more information you are not going to get anything but unqualified guesses, Worm.<br /><br />What boat? Details on the boat, load and use? What prop do you have now? What rpm and top speed are you getting now? How is your "hole shot"?<br /><br />With that information we may be able to make some useful suggestions.

 

[steelespike]

Re: High performance prop.

The prop question can be pretty involved and Im not an expert but can give you some tips.When you talk all around performance a prop is a comprimise.To keep it basic you select a prop based on pitch measured in inches. and the maximum recomended motor RPM.and what type of performance you want.<br />ultimate top speed,fantastic hole shot or somewhere inbetween.<br />You need to know where you are at now. Max<br />rpm, prop pitch and boat speed.To increase rpm you need to go down in pitch (lower number)<br />To lower rpm you increase pitch (higher number)<br />Think of the prop as a single gear in a transmission low (low pitch) gives lots of hole shot but poor top end, 2nd gear gives a little<br />hole shot and better top end and high gives poor hole shot but good top end.If you haul a lot of people and gear you will tend toward the lower numbers.Of course there are some refinements like<br />cupping that can inhance performance as well.<br /> A three blade is generally the best all around<br />prop.generally a four blade gives better low end performance with slightly reduced top end. Generally a stainless prop will give better performance.But because of their weight and toughness tend to put more stress on the drive train.And of course they are costly.

 

[Hooty]

Re: High performance prop.

My suggestion is check around and locate a good, reputable prop shop close by, hook up the boat and take it to the prop wizard, let him look at it and tell him what ya want. It's been my experience with those guys that they will work with you and try to supply you with a prop that will make you happy. <br />One thing to keep in mind though, he can't add horespower to your engine. <br /><br />c/6<br />Hooty

 

[theworm]

Re: High performance prop.

Thanks for the helpful info. I ,ve got a sixteen foot side console aluminum bass boat with all the bells and whistles attached, it planes out at a top end speed of about thirty MPH at four thousand RPM. Don,t hold me to the latter,(RPM) because I haven,t gotten the boat in the water for the season yet, so my memory fails me a little, but I,m certain of the MPH. I am hopping to enhance the top end of the motors range and get more speed out of her, is this possable. Again thanks for the helpfull information and the great analogy on the props and gear ratios.

 

[Spidybot]

Re: High performance prop.

I'd suggest you get the free booklet 'Everything you need to know about propellers' from my homepage.

 

[Bass Runner]

Re: High performance prop.

sounds like your rpm at wot is low, good average is 5500, try a lower pitch prop, if you have someone you can borrow a prop from try it, a lower pitch or smaller dia. prop won't hurt your top end if it increases your rpm, also check and make sure your carbs are open all the way, if not that will hurt your hole shot and top end. Just remember overproping is like trying to run a race with a fat woman