Need prop advice

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TRL WGN 1

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So, this is my first post. Have been reading lots of prop posts since I purchased my new to me 88 25hp Evinrude back in June. My 10 1/8x13 aluminum is in pretty bad shape (chunks missing, one blade bent forward slightly, etc.)

I took the advice of all I had read and installed a Tiny Tach so I could get an idea what the engine was doing.

My boat is a 16' Lowe Big Jon. I usually have myself, wife, and two young kids with us, but will occasionally have fewer or more.

With my chewed up prop, the engine is turning anywhere from 4900 (with two adults and three children) to 5280 with two adults only. According to GPS the boat is averaging 23 mph with a maximum so far of 25 mph.

I know I need to get a new prop, and plan on keeping this one for a river spare but don't know if I should just get the same thing or something different? It seems that my RPM's would be higher now that the prop isn't as efficient as it should be, or will my RPM's be the same with the same replacement but just gain speed?

Any advice or insight you can give would be great!
Thanks
Kyle
 
I have an 88' 25hp that I converted into a 30hp. You want your RPM to be 5500 (25hp) with the lightest load you can run and it doesn't seem like you are getting there with the 13 pitch. Don't be fooled by thinking that chewed up prop is costing you more than maybe 100rpm unless it is REALLY chewed up. Also it will not kill your motor to run 100 rpm or so over the 5500 when loaded light, just make sure you are running 50:1 mix.

At 4900rpm, 2.15: gear ratio, 23mph GPS you have an 18% slip which is not good. At 5280, 2.15:1 GR, 25mph you have 17% slip also not a great reading. Ideally you want to be 15% or less.

I would highly suggest putting an stainless prop on. Unless you run in bad water that you hit stuff a lot. You could easily go down one pitch to a 12 which would bring your RPM up about 200. If you go with SS then you will gain another 100rpm or so just due to the performance characteristics of stainless.

You are probably not going to gain any top end by dropping in pitch but you will gain in holeshot, prop slip should go down and your motor will run at a healthier RPM. Because 4900 is to low for that motor, ideally 5250-5500 is where you want to be.

Remember dropping 1 pitch gains around 200rpm, going up in pitch you lose around 200rpm
 
Johnny thanks for the reply
I have read your posts about your conversion and have deeply considered that route myself prior to the prop change but decided I may be best off to just get a prop for now
Didnt know if the possible increase in speed was going to be worth the cost and extra fuel consumption?
Yeah I didn't know how much I was loosing in speed and rpm having the prop chewed up
I have considered ss but didnt want to spend the cash and not get the right one
 
If your patience you might be able to find a nice used one on E-Bay.I have purchased quite a few of my props from their.
 
Well it all depends on what you are looking for. The conversion will not gain you any holeshot really. But top end will increase 2-3mpg and maybe more depending on if you can go up another pitch after the conversion (which you probably will). Where you would gain the power is mid-range and top end. Most likely you would never see less than 25mph after the conversion and may be able to get to 28-29 depending on weight in the boat. If you did the conversion I would suggest a 13 SS prop. If you are looking for holeshot then I wouldn't suggest the modification since it will not change much if any.

There are SS props out there at a reasonable price.......$150-180 bucks for your motor. I run a 10X14 pitch SS new saturn solas prop that I paid about $170 after shipping for. It is not a top of the line speed prop but does very well all around and will outperform 99% of the aluminums made.
 
that 28-29 is about what I had figured with the 30hp conversion

I had read online that the 25hp rpm range was something like 4800-5200 with peak power at 5k while the 30hp range was like 5400-5800 with peak around 5500

is this incorrect? I couldn't find the factory specs anywhere for proper rpm range

my biggest concern on the conversion is all the different info out there. I know what you used work and was right on, but I am finding it isn't that easy to find a late 35hp carb (I have found intakes just not carbs)
when did they switch from manual chokes to primers?

I thought I could just get a later (meaning same era as mine) 30hp carb, but was told the only difference in those carbs is jetting???????
 
Got the OEM 25hp 1988 manual right here in front of me. 4500-5500 rpm for the 25hp and 5250rpm is where you will produce peak HP. The 30hp ranges from 5200-5800 and peak is at 5500.

The primer carbs came out in 84' I believe (I can recheck if need be). The carbs that I know will work on yours is the 1984 35hp, 1985-1989 30hp. And no it is not just the jetting that is different, it is the different size venturi.

I would be happy to help you with the conversion as I have helped around 20-25 people on different sites. I get PMd about this mod all the time still : )
 
thanks for the information

You have already helped me with previous posts

finding the parts is the hardest part of the conversion from what I can tell

know anyone that has gone with the choke carb and gone with the old style choke? any opinions on that?
 
Yes I considered doing that myself before I found the correct carb. I am positive it can be done with a little extra work. The setups are not easy to come by, especially since I know a few guys still searching ebay for them. But if you search really hard you can usually find them in a month or less. I will see if I can find something for ya. Also shawnfish has a parts place that may carry these parts also. I will try and PM him again and see if I can get the used parts wharehouse info
 

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