View Full Version : Propellor upgrade
Father of 5
09-02-2005, 08:02 PM
I have a 98 Outback with the original OJ prop. The prop has some dings and a few rough edges on the ends of the blades. I believe it is a 13" 12 pitch (stock). I want to upgrade the prop partly to reduce RPM at cruising speeds. We ski on some large lakes and with fuel getting higher I could use the efficiency. I don't want to over do it though and loose all the low end torque. The boat has no issues pulling me up on one ski. Most of the sites I have seen ask what the maximum RPM is for the motor. My 5.7L MPI will easily rev all the way to 6000 RPM and probably beyond. I don't use all the throttle travel to prevent over reving the motor. Is there a rev limiter on these motors? What is the maximum safe RPM for the motor? Can I run a 14" prop (how much clearance do you need on the hull)? Will a four blade versus a 3 blade prop affect top end or just low end pull? Are there any props to avoid?
09-02-2005, 08:49 PM
As far as I know, the 5.7 should rev to between 4400 - 4800 rpm. 6 grand for a stock GM V-8 is twisting it pretty good.
Hope this helps
09-07-2005, 12:21 AM
Take a look at ACME. I have had two separate boat guys tell me that the ACME 3 blade is the best choice for my 1999 Mobius (5.7L Carb, Direct Drive). Once you picka manufacturer, tell them what you have and they will tell you which prop to use. If you use anything other than their recommended I would think you are asking for trouble.
I would not use a 14 inch prop.
The money you save in gas may not be worth the damage you could do to the engine/tranny if you misapply a prop.
09-07-2005, 06:46 PM
Std prop, 13 inch, 3 blade or 4 blade, difference isn't huge.
I'd keep the old one as a spare, along with a new nut and key ( old prop can be sent away and reworked if bent ).
Agree with Buttafewcoe, as these motors don't seem to have limiters, and emphatically REALLY shouldn't turn up above 4200 or so. Its standard GM iron. It will blow, and several guys here have blown them pulling barefooters.
My truck has one of the same vintage, and it has a rev limiter somewhere around 4400.
We use ours as a tractor for towing skiers and boarders. Anybody with us that wants to run above 40 mph can find a jetski somewhere to get off on.
09-08-2005, 07:59 AM
I was thinking.............in neutral you prolly can rev way up, but in gear and pulling, does it still want to rev 6k? You may have some sort of slippage thing going on.
Hope this help
09-08-2005, 11:55 AM
The o.e.m specs. call for a 13x13x1" 3 blade prop. The 12 pitch you have is contributing alot to the high rpms. I suggest starting with this one, and note the differences. Brian Raymond
Father of 5
09-11-2005, 11:34 PM
Thanks for the info. I was on the lake Saturday and the boat easily revs as far as I want it to. The 6000 rpm seems pretty high to me also even for a roller cam engine. I slalom and I would also like to barefoot so 40+ MPh is a consideration. I do not want to blow this thing up because I am sure a short block is at leaat $3 grand. The transmission doesn't seem to be slipping. You know in a straight drive car you can see the slippage because the tach revs more than the acceleration you feel. It just seems that above 3000 - 3500 rpm there is no much more speed or at least it is not linear. I have sent in a spec sheet to Michigan wheel and Tacoma prop for a recommendation, but I don't know What Indmar says the max RPM is and I can't find it in any of the owners manuals or on the face of the tach. Got any ideas?
09-12-2005, 09:16 AM
I'm runnnig my 05 LSV at 41 mph and 4100 rpm with the throttle fully pressed (325 hp MPI). This is lower than the max spec but the same as I expected based upon boat mag boat reviews. Does anyone get up to the max 4800 rpm that the engine is rated IAW the manuals SC says top end is 4600 rpm, Indmar says 4800 rpm?
While I'm asking stuff, how exactly do you do what I've heard called a bat turn, you yank all the way around 180 and the boat comes to a stop inside the straight away wake.
Off to tennis, then swim team meet. I'll be home by 9 pm - IF I'm lucky.
Last edited by: smokedog2 on 06-21-05 14:55:05
I posted this back when. The numbers are from the manuals. My manuals are with the boat. I never got a good answer on the speed/rpm diff but 6000 is too high.
Search smokedog2 and engine to fing the whole thread.
Father of 5
09-12-2005, 08:55 PM
Thanks for the tip on the old string. I found it. I also heard back from Tacoma prop in WA state. Tacomapropellor.com. Real helpful. He felt like I am probably running the right prop. He suggested I send it to him and they repair it in the shop. He said they could also add some cupping to the prop which would give 3-4 mph on top. He was willing to set me up with a new prop but didn,t think that would be neccessary. It is always a good start when the first option recommended is the most economical. I guess in about a month when I winterize I will pull prop and see how it goes. I have also tried to contact Indmar and get a number from them. Most of the new motors redline between 4800 & 5800 rpm for the LT-1 so I would guess my redline should be about 4600 - 4800. Probably more in the 4600rpm range if you don't want to throw a rod. We will see how long it takes to get a response. It is also nice to know Skiers Choice tries to take of their customers ie. the string on lemon laws. Boats can be hard enough and expensive enough without quality issues. I hate to see someone struggle when they have a new boat with 0 hours.
I had another thought. It sounded like from the old string you actually hit a throttle stop at full throttle that prevents going any faster than 41 MPH. Is there a throttle stop some where on the throttle body or is there an adjustment to limit throttle control travel?
Thanks for the help, I'll let you know how the prop repair goes...
09-13-2005, 08:01 AM
It is my understanding that there is a throttle feature to prevent you from redlining. I do not know exactly how it works but the throttle crashes down and the motor drops to idle. A heart stopping feature the first time you do it.
It might be adjustable. Over the summer my speed has creeped up without adjustment.
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