prop testing need help

rssteiny · 06-08-2009, 08:26 AM

I have a 2000 32 active thunder with 500 hps with a refresh to about 560 per side, my original prop is a 30 b1 labbed heavly, verry thin, i am now getting into the rev limiter at 5500 it runs 86 on gps up 3 mph from last year,so i tried a stock 30b1 only spun it 5300 at 83 mph but made the boat porpoise bad on top end, then i tried stock 32 b1s with a cupp in them im told to about a 33 only spun them 4700 at 83 mph but again porpoise bad on top end but did pick up 5 mph at 4000 rpm, my original props do not make the boat porpoise at all. im lost what to try next.

Thunderstruck · 06-08-2009, 12:20 PM

The standard 30" B1 prop, unless the pitch has been changed is about 29.25". Based on your WOT numbers with the 32 worked to 33 is way too big.

I was at your point with my project. Right now you are at 16% slip at 5500.

You have three options:

1. Change to adjustable rev limiter ignition and run the 30's.
Easier on the drives and a little harder on the driver train.

2. Go to labbed 32's. Maybe a little more speed. Probably the most expensive option of the 3 if you buy new props. Used could get even with the other two options.

3. Look at nose cones. I ran 90 mph last weekend with labbed 30" bravo i's at 5450 rpm with cones, 2 people 3/4 gas, 10% slip. Probably not much hp more that you after 3.5 summers on the motors. Nose cones cost me ~$600 doing the work myself. Nose cones will lower your WOT rpm by reducing the pressure wave in front of the bullet so that the prop gets a better bite. So you shouldn't need 1 or 2.

Come to LA and I will let you try my drives and we can drink some beer and talk boats.

Thunderstruck · 06-08-2009, 12:21 PM

BTW LA is Louisiana not Los Angeles. The Royal Purple Poker run is June 20th come on down.

audacity · 06-08-2009, 02:09 PM

DO NOT USE nose cones!

so prior to the engine work the boat was only going 83 and not pulling the current props to the rev limiter?

rssteiny · 06-08-2009, 02:38 PM

Quote:

Originally Posted by audacity

DO NOT USE nose cones!

so prior to the engine work the boat was only going 83 and not pulling the current props to the rev limiter?

yes correct

audacity · 06-08-2009, 03:07 PM

so the boat is 5mph off at the same rpm.? if the engines were loosing power then your rpm would be coming down with speed. if your speed dropped then u have problems elsewhere.

and you will know when you are on the rev limiter...it cuts out big time! those tach go over 5500 maybe 5600 and still be off the rev limiter!

rssteiny · 06-08-2009, 04:25 PM

Quote:

Originally Posted by audacity

so the boat is 5mph off at the same rpm.? if the engines were loosing power then your rpm would be coming down with speed. if your speed dropped then u have problems elsewhere.

and you will know when you are on the rev limiter...it cuts out big time! those tach go over 5500 maybe 5600 and still be off the rev limiter!

ther at 5500 to 5600 then you can here it it is in the limiter , i back off to 5400 or so and all is well, thinking i need a labbed 30 that is not labbed so thin like the 30 i have now but i concerned with why it porpoises with the other props and not the ones on the boat.

rssteiny · 06-08-2009, 04:28 PM

Quote:

Originally Posted by audacity

so the boat is 5mph off at the same rpm.? if the engines were loosing power then your rpm would be coming down with speed. if your speed dropped then u have problems elsewhere.

and you will know when you are on the rev limiter...it cuts out big time! those tach go over 5500 maybe 5600 and still be off the rev limiter!

not really 5mph off as it only ever went 86 the 1st year i had it and then slowly down to 83 or so, must have been faster where you ran it as i run on a river with no chop to help out. ive only lost 3 mph obver 4 years and i added a 4" wind screen acroos the front that may of slowed it down a tad.

audacity · 06-08-2009, 04:40 PM

the props u have are not even all that thin.

u need to first send them to throttle up propellors have them scanned. this will give me numbers i can use. anything else is guess work as the props may have changed! with my input we can get you back on track. and more if your budget allows?

second u need to look very close at the bottom of the boat.

that boat had the ability to hit 90mph no problem with the setup that was in the boat minus props.

Thunderstruck · 06-08-2009, 06:11 PM

second u need to look very close at the bottom of the boat.

that boat had the ability to hit 90mph no problem with the setup that was in the boat minus props.[/QUOTE]

Glad you jumped in. What is the deal with the bottom, who, how what do you look at? That is my next step.

If Rick's boat went 90 at one time with stock power, can the hull get a hook or whatever over the years sitting on the trailer???

Understand nose cones are controversial but they helped my boat.

Tom