What limits the size of the prop?
 

I'm running upwards of 640+ HP, actually 540 HP at 4000 RPM to 648 HP at 5300 RPM, yet I am only able to turn a 28P Bravo1 prop 4650 RPM.

It actually seems like as I push the throttle to the max, my HP drops off! Engine has less than 10 hours on it. I've taken it easy for break in, but want to run a little now!

Last year before the rebuild, I was able to spin a 29 at over 5000 RPM.

What limits the size of the prop I can turn, shouldn't it be the HP and torque? I should have enough of both to spin a 28P faster shouldn't I?

Just curious. . . and a little disappointed

What is your HP and TQ curves every 250 rpm or so?

I bet 4650 is right near your TQ peak!

4000 - 542 HP, 711 Ft-Lbs

4250 - 580 HP, 716 Ft-Lbs

4500 - 604 HP, 706 Ft-Lbs

4750 - 623 HP, 693 Ft-Lbs

5000 - 628 HP, 661 Ft-Lbs

Peak Torque is around 4650, but the HP is still going up.
With a 4500# boat, Deep V whats the recommended prop. Darin at Houston recommends a 26 Bravo 1 repitched to a 27, cupped and labbed. I agree at this point, but just like to get several opinions/ideas.

Thanks

What speed are you running at WOT with the 28"?

I would try a stock 26" and get the numbers and then talk to Darin.

Before I labbed or cupped a prop I would test the 1 and 2" shorter lowers. Maybe trying different lower units (shorter) might help more.

Shorter? I'm running a 17-1/4 X dimension already!

I am turning a 28 labbed Bravo 1 4850 in 90 degree heat and high humidity with a 575sci on my pantera 28.

Something is wrong.

I think labing that prob would get you to 5000, but maybe a labbed 27 would be even better, you would probobly turn 5200-5300

What could be wrong? Engine is strong, boat seems smooth and good. This is a stock prop no modifications.
Should still be getting the RPMs up. I'll try a 26P and see what happens.

High Tide - I ran the dyno. Did 15 - 20 pulls all the same.

What is the drive gear ratio?
Dennis Moore

Call Matt or Julie at Throttle-Up Props. These guys can get the most out of any prop, and they are the best people you will ever deal with.

Throttle-Up 727 531-2256

More Data
 

1.5 Ratio

78 MPH, GPS

4650 RPM WOT

4500# Boat, fuel and me

24' Pantera V bottom

1' Chop, 10 - 15 Passes

Engine specs are above. I should be able to turn this prop easily.

the number you are using for your x is a number that the factory uses...tell us the measurement from the bottom of the boat to prop shaft centerline (like 3 1/2")....with the shaft parallel to the running surface. the other measurement requires me to use transom angle to calculate.

you can toss HP all day long at an ill set-up boat and never go faster. I think the problem is much deeper than the prop...hummm a pun perhaps :D

Man that is only 5% slip!!! Are you sure you aren't at a 1.36 ratio? If so you would be running around 15% slip and that would be much more realistic and may explain why you are having problems turning that 28.
Good luck!
Craig

XZ 1.5 Drive on the way!!
 

I believe its a 1.5 ratio, thats what I was told by the factory and previous owner. Wouldn't it be on the serial number tag? I can verify.

I will be receiving an XZ drive next week, 1.5 ratio for sure.

If mine is a 1.5 what else could be the cause? The X dimension measured is stated above, I will measure bottom of boat to shaft this weekend.

Your Drive can not be a 1.5...
You would need a 30pitch prop to go that fast at your RPM.

My 24' Pantera only had a 305HP/454 and would spin a 24 at 4600 and go 63gps.

My 24' Superboat has a 310HP/454 and spins a 26 at 4400 and runs 66gps.

Try a 26 and you will crack 5000rpm and be going over 80mph.

What else are you dragging in the water? Trim tabs, offshore water pickup, speedo pickup? Do you have a nosecone?

Do you have any good data from before the engine was redone? That may lead you to where the problem is. Double check the tach with another shop tach or known calibrated tach. The best slip numbers I can get are about 10% with a bravo1. Good Luck

Only have trim tabs. Speedo pick up in the drive. No nose cone.

I'm going out today to verify gear ratio, I'm positive its 1.5. I have another tach, I'll try it, but the one in the boat seems right as the engine is definately not up in RPMs at WOT with the 28P

Definately a 1.5 ratio. I can't get a good measurement on the drive, looks like 5-3/4" - 6".

Any other ideas?

If your propshaft is that deep, its WAY TOO DEEP. You sould be in the 3"-4" range. If the X is really at 17 1/4 then it should be in that range. My X on my notched transom 28 is set at 20 1/2. I have a 3" drive spacer that lowers the propshaft 3" and does the same thing as changing the X to 17 1/2. My propshaft is 4" above the bottom.

4" above the bottom???

Stay with me on this little story...
 

Pantera24,
Two years ago when I was putting my boat in the water for the first time I was using 30" pitch props. I had a set of 28" props that I had JUST sold before I tested the boat to a guy in NJ because I knew I wouldn't need them. At about the time I sold the 28's I had JUST purchased a pair of brand new York labbed 32" props prior to testing the boat because I felt they were what I needed! Come to find out on the mainden voyage I could only turn 4900rpms at WOT(wide open throttle) with 30" pitch props----I was shocked and confused! So I called up the guy with the 28's and asked if he wanted to sell them back to me and he wasn't going to be able to get his boat running that year anyway so he sent them back and I put them on untill I recieved some brand new 28" York labbed props! I knew I couldn't turn the new 32's so I didn't even try them and Joe Skrocki (Audacity) bought them from me. The labbed 28's put me up to about 5200-5300rpm. About 6 weeks after I had been running the boat we found out that the throttle linkage wasn't opening up all the way and was cheating me out of about 100hp or so. So, after ALL the prop testing, $$$, TIME, AGGRIVATION, I have sold both pairs of the 28's still have the 30's and now own another set of 32" labbed props. The 32's turn at about 5500-5600rpm---which is what I originally needed to begin with! :rolleyes:

So do yourself a favor and check the throttle linkage FIRST before you go crazy on wasting your time and $$$ on other stuff! :crazy:

BTW, My boat is a 32' Active thunder and I had a pair of dyno tested 540's that were making about 630hp @5400rpm when all this was going on. So at the time I was just about as confused as you are now!

KAAMA - that is GREAT advice. I wish I had all the hours back in my life from working on stuff and then I found the SIMPLE problem!

Especially from those stupid snowmobiles!

That is the exact same advice that Jo from Pantera just gave me. I checked the linkage and it appears to be at the exact location as when I pulled the motor, according to the digital photos I took. But it may need adjustment.

I will attempt to adjust it this week when I can get the boat out. I'll be both pleased and pissed!!!

I hope its the throttle/linkage as the motor runs smooth and strong, as it did on the dyno. Just too low of RPM with a moderate prop - 28P. And on the dyno under load I could pull up to the soft touch limiter 5400.

Thanks for the "Story" it may have saved some real aggravation for me!

Kirk

Kirk, did you do something different to the motor or did you decide to dyno it just to see wht it had? What exactly is your motor? Supercharged or NA?

I would think you should be running low 90's in the right conditions! I love those Panteras.

Is your engine making the same power in the boat as it did on the dyno? What is different? Exhaust, fuel pump, water pump ect. I had one MPI engine dyno at 600 but when put in the boat she ran pig rich and made no power. Did you look at the plugs? What are the engine specs? Fuel pump, tank pick up size? Is the engine getting enough air?

I agree with GEOO, it's usually best to try and dyno with the same equipment that you will using in the boat i.e., carb, distributor, fuel pumps, ignition boxes, etc, etc....even the type of fuel you plan on running. When I was at the shop of the guy who was doing my dyno testing, I brought in 2 different kinds of fuels in 6 gallon gas containers. Anyway, it can be the little things when transfering the engine(s) from the dyno to the boat. Some installations have more problems than others while getting the bugs worked out and getting it dialed in properly is all a part of it as you know.

Soon, you will be able to enlighten someone else who's having problems with your experiences that you have had with setting up your boat. Selling used or un-needed parts and giving helpful advice to others--- I believe that is one of the better reasons of what this website was initially intended for. :)

Everything is the same, fuel pump, water pump etc..except the exhaust, but it is open with Imco Powerflow Manifolds.

The intake air and throttle position are the (2) I need to check. Plugs look very good, actually I dropped down in temperature range and got too much soot, so i went back up.

Thanks for the ideas. I'll let you know what I find.

I would double check your tach. That 5% slip number is still a little suspect to me. 78 MPH would make sense at 5000 or 5200 RPM, but at 4650 it doesn't add up. Also did you dyno the motor with the same exhaust and all accessories on the motor? Dyno headers and no accessories could easily be 50 to 75 HP. Personally I don't think 78 MPH with 650 HP is all that bad in a 24' vee. Just my .02. Good luck and keep us posted!!

Kirk,

How did you verify it was a 1.5 ratio? Did you actually check it by spinning the motor or did you look at the tag an the drive. I was thinking that maybe the previous owner switched to a 1.36 when they did the motor work. That would explain why you can't pull a 28 and how you're getting 78 mph at 4650 rpm!


Just a thought.

I'll pull the boat tomorrow and hand turn the engine and count. I hope its a 1.36 but doubt it.

What would the benifit be by going to a 1.36?

Before big pitch props (30+) were available, there was no choice but to change the drive ratio.
There is also a school of thought that the lower ratio gear set is stronger. Bigger teeth and less of them...

Kirk,
Your tach is either way off, or you have a 1.36 ratio.
With 650HP, you should be able to go 85-90mph.
Slap a 25 Mirage plus or 26 Bravo I on that baby...

Keep us updated please,
Happy Boating!!!

Tried a 27P Ballistic today:

73.2 MPH GPS @ 4800 RPM

Turned the motor slow with ignition disabled and tried to watch prop spin, almost a complete revolution, appears to be less than a 1:5 ratio. If this is true, even with a 1:36 gear why can't turn more RPM with the HP/torque I have? Accoring to the prop calculator, I should have a 1:5 which gives me 7% slip.

Wether I have a 1:36 or a 1:50, I should have enough HP to swing a 28P faster, shouldn't I?

Hey Kirk,

Long time! I am sorry to see you are having trouble dialing your boat in. This much I can help with. The drive was never apart and is definitely a 1.5. As you are aware I was running what would appear to be a little less HP and torque, at much higher speeds turning that 29 Mirage + that I had on the boat. I understand you lose a few mph in fresh versus salt but there is obviously other issues. I personally never liked the bravo props on the boat either which may also be costing you a tad in speed too, but I will say what you probably already suspect, there is somethign wrong with your dyno numbers. You should be running much better with that kind of HP. I am sure that Jo would confirm this. Anyway, good luck ironing things out. I miss the boat in a big way.

Regards, Mark

Hi Mark!!

The boat runs and handles awesome, just should have better top end. I remember you told me that you didn't care for the Bravo 1. What prop worked good for you? I tried a 28P hydromotive, too much stern lift.

My latest test was a 27P Rapture:

73.2 MPH @ 4800 RPM

Any ideas on what could be limiting my HP and RPM?

Hope all is well with you. What type of boat are you running now?

Kirk

Years ago in 1983, I had a friend who modified a 330hp engine in his 24' Pantera. The boat was a 1978 and had a TRS drive (1.50 gears) and tranny! With the engine mods he made 486hp @5300rpm on the dyno with dyno headers. Once the engine was in the boat, he went with a GIL dry exhaust system. With the same prop (23' 3-blade Cleaver) we guessed that the boat ran about mid to upper 70's at about 5400rpm. What ever the REAL speed was we don't honestly know---but it was FAST and he took the boat down to Florida and embarassed a lot of people who thought they had some very fast boats back then! It was an all white boat and in 1984/85 he sold it to someone in Kentucky somewhere.

I know every boat is different, but with my friend's 24' Pantera in mind----and I could be wrong, but I believe it seems that your boat should be running much faster and turning more RPM than what you are now.

I agree and am gettin very frustrated. I'm borrowing a scan tool next week to verify timing, RPM and everything else.

The motor is very strong, huge hole shot and pulls the boat easily up to full throttle. Just cna't get the RPMs up. I pulled the flame arrestor to verify full throttle when the sticks are forward, it looks fine.

Any other ideas?

Also measured the bottom of the boat to the center of the prop shaft - 5-3/4"

Try with the flame arrestor off and the engine hatch propped open slightly with a 2x4. What else are you dragging thru the water? speedo pickup, offshore water pickup, trim tabs? How much extra weight do you carry? tools, skiis, etc?