Top Speed?

[Ktown]

OK, I know I have been asking a lot of questions, however I have another newbie style question.  I was reading a recent post dealing with prop selection and realized that my boat is not getting the kind of top speed that most everyone else is getting.  I typically only see between 31-33 (on the GPS) at full throttle, even in calm conditions.  I also don't remember generating more than about 4500 RPM's.  Most top speeds seem to be in the 40's and seem to generate at least 5500 RPM.  Is it possible that I need to adjust my throttle cable?  I don't mind cruising at a lower speed (probably saving gas money), but would like to have the ability to get to shore quicker when the West Texas storms come rolling-in!

[westtx]

The engine's max RPM is 6,000 and you should be able to turn close to that. Do you know what size prop you're running?

[Ktown]

I have a 4 blade 13x13 1/2  LH  1 1/8" .  Hope this isn't a bigger problem!

[skiboarder]

Mine is a 13x13 right hand and it goes about 50 with just me in it,the rpms are about 5800. Sounds like somethings not right

[Bitzco]

That 13.5 is a lot. The higher that number, the slower you will go. I had a 14.5 on my boat when I bought it. It could pull stumps, but only ran at about 4k rpms. I had lots of control over speed but couldn't go fast. The guy I bought it from was running over 2k in ballast on a small lake. He wanted hole shot and not speed. I traded that prop for a 3 blade acme and now get to about 5800 rpm and 40 mph at WOT (look guys I used a technical term). You have an SX like me and they have a different gear ratio than the other Toyotas so you might want a similar prop. Somewhere in here I outlined my prop making decision and the size of the ACME I settled on. You may want the same one or something a little different if you want more top end speed or are going to use a lot of ballast. Mine seems like a good compromise between speed and hole shot. You can't have both.

[cyclone]

If you are wakeboarding with extra ballast beyond stock (I would be:) I would go for stump pullin' You'll save a lot of gas just getting on plane quicker.

I rarely see water conditions where I could run at 35+ for very long. Couple of miles at the most, and for that I wouldn't care about losing top end. Just my .02

[westtx]

The higher the RPM's, the better the holeshot. I'd call ACME and have them set you up to turn as close to 6,000 as possible with your setup and the altitude at Amistad. If you can't turn at least 5,000, you're going to damage the engine at some point.

[Rambling Wreck]

Although this has turned into a prop discussion, I would like to throw in another thing to consider - the ever so popular "change your plugs" recommendation. I have a pontoon boat powered by a Mercury outboard. Right after I got it, the max rpm and max speed dropped siignificantly. It ran just fine otherwise-no rough idle, nothing. On the suggestion of a mechanic, I changed the plugs and that was the problem. I find it hard to believe that a 4 cylinder enginie could run so smoothly on 3 cylinders but that is what was happening.

[Ktown]

 :)Thanks for all the input.? I didn't realize the gear ratio was different on the SX!? I am real happy with my hole shot and not worried about the loss of top end speed,? I just want to make sure nothing is wrong with the boat.? If I don't get over 5,000 RPM's will I damage the engine?? I assume my prop is stock, so why would it come with a prop that might cause damage to the engine?? I will probably change the spark plugs soon and compare the difference.? Anyone have any idea how long the plugs in these boats normally last?? Thanks again for all the help!

Ktown

[toyotafreak]

Fed and cared for properly, the plugs are rated to 1000 hours (yes, that's 100K miles in the SC400).

One bad bag of fuel and you're making a hundred dollar trip to the spark man.


Wish I could remember where I heard this, maybe OJ props, maybe TMS...one of the biggest killers of marine engines is over-propping them. Lug them and suffer the consequences. However, there's a TON of guys running around at 22 mph heavy - if that ain't lugging...

[extruop]

Wow, now I am really confused.   I just got through telling / reading in other threads that the smaller pitch prop (smaller second number) would increase rpm.  My WOT on a 13 x 13 is barely over 5000.  I am going smaller (13 x 11.5) to increase my WOT RPM and hopefully get a bit more torque out of the hole.  Am I thinking bassakward?

Bitzco?  Did you say you ran a 13 x 13.5 around Salt Lake and said it was good at holding low speeds?  Do you have the higher ratio trans than the 1.26?  What prop are you running now?

[westtx]

Smaller pitch = higher RPM's. You're doing the right thing dropping to the 11.5

[Ktown]

OK, I checked my performance today and I am seeing the numbers below on my GPS (my speedo shows about 2-3 MPH faster).

3000 RPM - 21 MPH
3500 RPM - 26 MPH
4000 RPM - 29 MPH
4500 RPM - 32 MPH
4600 RPM (WOT) - 33 MPH

That means I am at least 1400 RPM from redline.  I ordered the spark plugs, but after reading Bitzco's previous post, I think my boat just may be prop'd poorly.  Bitzo, I found your old thread and see you are running a 449 (13 X 12 5/8).  Looks like you gained over 1000 RPM's from the new prop, and at less than one on the pitch change?  Any other SX folks with a similar situation?

I found the Acme prop online for about 315.00 from a company called board-it-up!  Anybody used them before?  Also, should I get the Acme weekend saver kit (wrench, hammer, and harmonic puller, and spare parts (nut, key, and cotter pin)?  Or are there better kits out there?

Thanks everyone for the help.

[PSullivan3]

I would just make sure it is new and not recondioned.so you know what you getting (paying for)

[Capt Rick]

Also check to make sure when at full throttle it is fully open on the engine throttle position sensor....
I also have a prop puller for $122.
Capt Rick