WOT question...

[texanaustinite]

1997 Regal 1700 SLR with a Volvo Penta 3.0 4 cylinder engine and a SX stern drive.

Specs say WOT is between 4200-4600rpm. Why does the tach go up to 6000rpm? From 4600-6000rpm it is highlighted in red. Is it safe to rev it up into the red zone for short bursts of acceleration? Spedometer also goes up to 60mph. From 45mph on up, it's in the red zone. Could the boat even go 60mph?

 

[Don S]

Re: WOT question...

The manufacturers of the tachs and speedometers have know idea what type boat or engines they will be used on.

 

[texanaustinite]

Re: WOT question...

What exactly is meant by Wide Open Throttle? Does that mean that it is the max the engine can run or the max you should run it?

I've read that WOT is when the throttle is in its forward most position, i.e. horizontal. If that's the case, I'm reaching WOT (4400rpm) with the throttle 2/3 of the way down. I haven't been brave enough to push it all the way.

 

[Esox]

Re: WOT question...

In the case of your boat when the throttle is "wide open" the engine should be turning between 4200-4600 rpm. If it's more than that you are most likely underpropped.

 

[45Auto]

Re: WOT question...

WOT is the throttle pushed as far forward as it will go, with the boat in forward gear and going as fast as it can. Don't be surprised if you don't see a whole lot of difference in speed between 3/4 throttle and WOT.

 

[steelespike]

Re: WOT question...

The instruments are no doubt available for other applications with a face painted to match the rpm/speed requirements.It's not ok to exceed the red line.Normally the boat will be propped to not exceed rpm red line.Sometimes to improve low end performance the prop may allow to much rpm.In these cases throttle sould operated to not exceed red line.If a boat will not reach recomended wot rpm the cause should resolved.
Don't be afraid to go wot and observe your rpm probably will be right on.
If it goes over just don't let it stay there more than a few seconds to see where it
settles.If it appears to be shooting way past say 200 rpm or more then throttle back.

 

[QC]

Re: WOT question...

Dude, like wow . . . in your other thread I thought we were talking about top speed. I see now that maybe we weren't. You need to tie these two threads together in your head . . . There is no discussing props without a WOT run. As is kinda alluded to above WOT is wide open throttle. Which technically has nothing to do with your control handle position. It is the intake "throttle" being wide open, which hopefully happens with the handle all of the way forward . . . WOT should deliver every ounce of performance your engine has that day. Also, kinda means it has to be running perfectly for it to be usable info. Anyway, if you're propped right, it will not exceed 4600 RPM whatever you do in gear. There is no need to go up there out of gear, so, uh, like, don't . . . Anyway, you must be "brave enough to push it all the way." It is the only way to select a prop . . . If it goes over 4600 for this test, then OK, but no too much more than 4800 or so. If it is trying to go over that RPM easily, then you are waaay under propped (too little pitch). If it is just barely going over, then you are just about right if you are lightly loaded, and still under propped if you are heavily loaded and it is going over. What you should be trying to achieve is somewhere around 4500 - 4600 with a typical load . . . And that's how we figure out propeller selection.

 

[texanaustinite]

Re: WOT question...

QC, I guess I'll give it a short burst to see what it does next time I go out. Which will be Tuesday afternoon. I'll have two teens, two little ones and myself, so it will be a typical load.

I tried one of those "prop wizards" on a website and it recommended a 21 pitch prop for my boat. Is there a place where I can rent a prop to try out before I buy one?

Better yet, is there anyone in or near Austin that has a 21 or 23 pitch prop with a 19 tooth spline and would let me try it?

 

[rndn]

Re: WOT question...

Some marinas will allow you to test a prop prior to purchase. Find one that does and after you find the proper size please purchase from that marina as a courtesy for letting you try his props.

 

[QC]

Re: WOT question...

Make it a loooong "burst". Get it trimmed up as far as possible. Move the kids around to allow you to trim out. Preferably in the back . . . Ya gotta do this dude . . . take a valium, no wait, take a chill pill and give her all she's got. We all do it. We have to BTW, the manual says you can do it forever, although it will shorten life. Commercial fisherman do it from day one until boom (a year or two later). I leave mine there for 5 minutes or so, once in a while, no biggee. I had a 3.0, bought it new in 1984, ran WOT all the time. BIL still has it, head's never been off. Rock on

 

[45Auto]

Re: WOT question...

Like QC says, find a stretch of clear water, shove the throttle as far as it will go and let it run! There's not an auto-destroy switch at 4601 RPM. If it starts to go over 4600 for a couple of seconds then pull the throttle back. If it's capable of more than 4600 RPM on your current prop put some more pitch on it. My guess from your other thread is that you'll never see 4600 RPM.

 

[texanaustinite]

Re: WOT question...

Well... like I said, I'll try it tomorrow. I'm a bit nervous about it. Are you all certain it won't damage anything?

 

[QC]

Re: WOT question...

Dude, we are positive. There is no other way for you to choose a prop. None. Forget the prop selector

 

[texanaustinite]

Re: WOT question...

I've decided not to do it tomorrow afternoon but rather on Thursday morning. There's too much traffic in the late afternoon and almost none in the mornings. Much better chance of finding perfect water.

 

[texanaustinite]

Re: WOT question...

Will have to wait for a while. Here's why: http://forums.iboats.com/showthread.php?t=225174

 

[daniel2229]

Re: WOT question...

When I got my boat this year, the dealer explained how he pitched the prop and matched it to my 3.0 Merc. He ran the boat light - by himself with a 19 pitch prop and ran it up WOT. I think he knew already what RPM's this model would take. I was told not to go much above 4500 RPM's although I have taken a couple of short bursts at 4500. I generally cruise between 3000 and 4000 when pulling a tube. That is plenty fast enough to hurt someone on our really rough lake.

I personally am not fond of running any engine at full bore. I would never dream of taking my car out on the highway and running it up to even near redline and holding it there. Most cars will run above 110 MPH, but if you did that everytime you went out on the interstate, you would be replacing engines as frequently as those "Good Old Boys" in Nascar.

That is just my two cents worth.

 

[texanaustinite]

Re: WOT question...

Boat is fixed: http://forums.iboats.com/showthread.php?p=1507084#post1507084

I took out again for a test run and it did just fine. I was a bit hard pressed to find glass-like water. There was a bit of a breeze and some strongish drafts between the cliffs (Lake Austin).

I did find some not so rough water, said a little prayer, then opened her up...

...I was able to reach 45mph @ 5000rpm, (again, I'm running a 14.25 x 19 prop). I'm happy with that... for now.

Would a 21 pitch prop give me a bit more top end speed?

 

[salty87]

Re: WOT question...

this is the part where you verify the factory spec's for WOT...earlier in the thread someone posted 4400-4600, i think (i don't know the exact number it should be), so you want to be propped to go no more and not really much less than that rpm when you have it floored. that means you've got the right match of prop for your engine. the speed it equates to is something you learn to live with or spend $$$$ on.

 

[QC]

Re: WOT question...

You thought we were serious and you ran it wide open? Holy carp!!!

Nahh, just kidding you, good job getting good numbers

I think your 4200 - 4600 is correct. If so, you could go to a 21 although you will lose some hole shot (acceleration). As long as you were not super duper light during your test (low fuel, alone, no ice chest, no stuff) then you would probably be OK with a 21. If you were heavy or typical, then absolutely you should at least try a 21. Might be worth 2 MPH which in this game is a lot. Kewl

 

[45Auto]

Re: WOT question...

As QC says, you would probably be lucky to gain a couple of miles per hour. I had a 19 and a 21 pitch prop for my last boat. The 19 (factory) would do 50 mph at 5200 with an extremely light load. The 21 would also do 50 but could only turn about 4900 rpm. The 19 was noticably better for wakeboarding, tubing, etc. If I left the kids home and just went cruising with the wife I would put the 21 on it. It cruised a couple of mph faster and the feeling was like shifting your car from 4th to overdrive. Felt like the engine was just loafing along.

If I were you I would definitely try a 21 (borrow, steal, etc ..) with the performance you're getting. If you can find one cheap enough it might be work buying it and switching props depending on your intended use of the boat that day. It's also very handy to have a spare prop! Last summer my 19 spun the hub when we were up the river about 10 miles, nobody else anywhere around. Was pulling the kids up and all of a sudden it was like the boat went into nuetral. Was very glad I had the 21 and a prop wrench on board that day!

Good luck!