How much faster
 

OK it's been pretty dead around here so here is my next project for the winter. My prop center is about 6 1/2" below the pad on my 24' Aero, 24 degree dead rise, 7' beam, bravo 1, 1:36 ratio, nose cone and no tabs, currently Whipple charged 383 sbc, 750hp, current speed with a 21 pitch quicksilver 48 3 blade is 73mph @ 5500 rpm
What should my optimum depth be? If you were doing it, what direction would you take? shortie or recut the transom and move engine up, And how much mph sould I expect?

Re: How much faster
 

ttt

Re: How much faster
 

If your prop is stock?there is 2 to 3 mph to be gained there ,Not sure about cutting the transom and moving the motor up .Sounds like alot of work and would need to be done perfect,As far as your depth, I am sure others here can help you better than I .Give me a call on your prop and I will gladly let you know what can be done if anything,Darin

Re: How much faster
 

It is likely a 23" prop with 17% slip. If it is as 25" you would have nearly 25% slip at your speed. I'm not sure why your slip is so high but you could likely improve that some with a 4 blade prop. It sounds as if your drive is already pretty deep and raising the drive would usually make the slip worse. Someone with more knowledge of your hull and set-up will have to chime in here.

Good luck.

Re: How much faster
 

If you are really making 750HP you should be able to turn a much higher pitch than 23 or 25. I haad a pantera, now owned by another member, that was making 600 or so HP with a prop centerline at around 7 below and I could turn a 29p mirage to a speed of 93.4 on gps. Seems to me you might have other issues unless you are banging the rev limiters on your currnet set-up

Re: How much faster
 

Scarabman,
I'd like to know more about this Pantera that went 93.4 mph
Length?
Drive?
Drive Ratio?
Exhaust?
CID?
RPM?
Thanks in advance for any reply.
Russ

Re: How much faster
 

How much does that boat weigh? Something is not right if you have 750 HP. I've run 74-75 in my 24 Superboat with only 385 HP. I never measured where my propshaft is. I'd go out and get a measurement but my outdrive is off right now. Good Luck.

Dave M.

Re: How much faster
 

dave
Setting up a similar boat. Any way you could get me the crank height from the bottom of the boat. What drive do you have and do you have a pad on the bottom. Thanks, Mike

Re: How much faster
 

1) Something is wrong with your HP/speed ratio unless your boat is filled with lead.

2) Hard to recommend prop heights when you haven't let us know what trim angle gives you best GPS speed. Generally, you can guess that ANY performance boat application will benefit from a higher drive height if top speed is your only concern but there is much more that comes into play.

3) Finding somebody willing to "rent" you their shorty for testing shouldn't be that big of a deal, especially if you are willing to do it on the offseason.

My guess is that a shorty will help you. You'll need to combine prop changes and testing also, but I think you'll be better off with a shorty.

An Imco +3 box maybe an even better solution, but it will require external steering as well. A shorty and a box are both about the same price, but hydraulic steering is pricey.

Re: How much faster
 

I'll go out and try to measure it in a while. I have a V shaped pad with a small single step. Here's a pic.....

Re: How much faster
 

If I measured correctly the crank centerline is 16.5 inches above the bottom of the V. Hope that helps.

Dave M.

Re: How much faster
 

I have the straight version 24' Superboat (No pad or step).
The crank centerline is around 18" above the bottom of the V.
That should put the prop shaft about 5" below the bottom of the V.
Dave's prop shaft would be 6-1/2" below with an X of 16-1/2".
I would try a 4 blade Bravo I prop first.
If you feel the need to raise the prop shaft, a shorter than stock drive is the way to go. That way it will be easy to go back...
You may also be better off with a 1:1.5 drive ratio. From what I have read, the lower ratio is only needed when you have a 100+mph boat.
If you really have 750HP, that boat should run over 90mph. The previous owner of my boat hit 85 with a little more than 500HP.
I hope you have full hydraulic steering... :eek:

Re: How much faster
 

What are you guys smokin?

85 in a 24' vee with a non-ventilated hull, with 500hp????

My little 22ZX Donzi tops out at 76.5 with an HP500. Granted, it has not been tweaked, but another 10MPH?? I don't think so... I gained ~14mph by going from a stock 7.4mpi to the HP500...That is HUGE!!

My boat is the stepped hull version, with a high X.

Now, if your talking speedo readings, then OK. Mine buries the 80mph Gaffrig II speedo now. I mean 80 is in the lower right hand corner, but the needle is aiming straight down...

BUT I'M ONLY GOING 76.. ON A REAL GPS (Garmin eTrex)!!!!!!!!!!!!!!!!!!!!

Arrgghh....

Re: How much faster
 

Maybe you should do some homework on hulls before you start doubting people.

Re: How much faster
 

My wore out 454/330HP motor with 600 hours pushed my '87 REGAL Velocity to 63mph on a Garman 60C gps this with a Mirage 23P. We'll see what it does in the spring with a 540ci motor. I guess the hull does play a big part....

Re: How much faster
 

I have not weighed the boat but it is heavy I'd say 4500 to 5500. I do have external steering. I have not dynoed the engine and was told it should be 750. Who has a dyno simm program that can run these specs?
8:1 CR
5.7 rods
400 crank
dart pro 1 alum heads 230cc intake runners 2.08 int valve 1.60 exh. 72cc com. cham
whipple charger 6psi non inter-cooled
holly 1050 dominator bench flowed for this app.
stock merc ignition
I believe ign. at idle 10 degrees
powerflow exhaust with 4" risers
comp cam hyd. roller
gross valve lift intake .510 exhaust .520
valve timing @.050 intake open 4 btdc close 46 abdc
exhaust 53 bbdc close 3 atdc
cam installed @ 111 intake centerline
duration @ .050 intake 230 exhaust 236
lobe lift intake .3400 exhaust .3470
lobe separation 113
I'm thinking comp sold me the wrong cam?
Friend of mine built a similar engine for his 1/4 miler and got 750 hp but had a way different cam. I specifically ordered this cam for the boat.

Thanks for the imputes, Buck

Re: How much faster
 

Hi Buck,
I have desk top dyno at home and I'd be happy to run those numbers for you. It may not be totally accurate without the flow figures for your heads though.
I doubt your boat weights more than 4000lbs.
My 1989 24' Pantera weighed in under 4800 on the trailer with fuel and my Superboat is a couple hundered less than that was.

Mr. Mudball,
I do smoke on occasion, but I also know the difference between Speedo and GPS readings.
My 24' Pantera ran 64mph GPS with a 305HP/7.4 and my 24' Super runs 66mph with a 310HP/7.4MPI. Next year she'll run 75+ with the 415HP/502 I just bought... :D
Like Dave said, maybe you should do a little research. There is a BIG defference between your FAT Donzi 22ZX and a LEAN 24' Superboat.
There is a 30' Super that just came down your way.
AKA Krakmeup here on OSO.
His boat runs 72+mph with a 425HP/496HO; and YES GPS... :p

Re: How much faster
 

WOW, is all I can say!

I am not familiar with Superboat, but am with many other vees.

That must be one heck of a hull on those boats. They don't sound super light, either!

You have 3mph over my 22ZX with the 7.4MPI. I went a best of 63.

OK, given that you gave your speed with a 7.4mpi, I come up with the need of 400hp to go 75 for your boat...Incredible!!

To go 85, you would only need 515 hp!! MORE INCREDIBLE!!

I used the formula from Bob at FTM, which works for most vees:
((desired speed / current speed)squared) * old horsepower.

Those are very good numbers for the 30 footer with a 496. That boat only needs 600 hp to go 85!! Awesome for a boat that size!!

OK, sorry for doubting!! I'll have to look into those boats when I'm ready for a new one!!!! Do they ride and handle well?

Take care,
Kent

Re: How much faster
 

Thanks Patrick, How do I get flow # for these heads? Maybe on Dart's web site?, I'll check and if they are I'll post back,If the cams wrong could you plug some # in and suggest a cam? Thanks, Buck

Re: How much faster
 

Hey Kent,
Have a look...
http://www.superboatonline.com/

Buck,
You may find flow numbers on Darts web page.
Another place to look is High Performance Chevy.

Talk to you later,

Re: How much faster
 

Did World Products completly dump there Dart line, my link dos'ent work anymore and when I went to World Products web page it says nothing about Dart, everything is Merlin and Motown and sportsman

Re: How much faster
 

Hi Buck,
I ran some numbers for a 383 similar to yours...
8:1 compression
high flow heads with large valves
your roller cam
roots blower 6psi max boost
1050 cfm
The numbers are not 750HP, but still quite impressive for a small block.
500+ foot pounds of torque from 3000 to 5000rpm.
Max Horsepower of 510 between 5500 and 6000rpm.
About the same as a NA 500HP big block... :D

I would say that with this engine and the right drive & prop set-up, your boat should run over 80mph...

My suggestion would be to try a 1:1.5 ratio drive and a 26p Bravo I prop.
Good Luck!

Re: How much faster
 

Thanks Pat, I wounder if there's more with a different cam and boost. I checked the prop and it was a 21 pitch quicksilver 48 cleaver. Last year I put most of my cash in the engine and steering. This year I want to tweak it all in. My speed goal is 90.
From my photo it looks like it's running at a good angle, about 1/4 trim, but running to deep to free up some speed. Fast boats I've observed run damn near on the pad.

Re: How much faster
 

Your engine may make more with a bigger cam and more boost. I don't know much about blower motors. Your engine may or may not be making more than 500HP now. I think you will need between 550 and 600HP to hit 90mph though.
I have never had luck with cleaver props. When I first bought my Pantera, I spoke to JO at Pantera. He told me that a 3 blade Mirage plus would be the fastest and a 4 blade Bravo I would be the best over all performer. I have run them both and the 4 blade is not that much slower and a hole lot more stable at high speed.
Good Luck!

Re: How much faster
 

Pat is right on, switch to a 1.5 : 1 drive and try a Mirage plus 23 or 25. A labbed Bravo 1 26 will run within 1 mph and less than 100 rpm's different than a stock Mirage plus 25 but it handles differently. I would guess 5 - 7 gain from the gear change and round ear prop. The gear ratio is very important to multiply the torque applied to the propshaft. Good Luck

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Not to doubt anyone and I WILL be doing what the concences here says but when I bought the drive I was told that the ratio was not that important, it was kind of like a car, that you can change the wheel diameter to change the effect of the rear-end ratio. So on a boat you would change the prop to change the effect on the drive ratio. Also said that the main reason for the 1:36 drive was that high speed boats benefit from a better selection of props,larger selection, lighter and easier to rework and lab. This being told by a OSO drive advertiser.So what is "the rest of the story" ? was I misled?

Re: How much faster
 

Hey Ironman,
Hey you have done a little prop testing on your boat...?
My labbed 26p Bravo pushes my boat 1mph slower than my 25p Mirage+.
How is that Bravo conversion going?

Buck, do a search on drive ratios here in Tech Q&A. The subject has been talked about a lot...
From what I remember reading, with all of the prop available, only boats that crack 100mph benefit from a 1.36 ratio.
I also remember reading that a 25p prop is about the most efficient pitch for the type of props we run. A 26p Bravo I measures 24.5 and a 25p Mirage measures 25...

Re: How much faster
 

Aero, I've personally seen speeds drop by switching to 1.36 gears and smaller props. I would try and see if you can borrow someone's 1.5 ratio drive with a 25p Mirage plus and test it out, you may be surprised.

I've also seen that you need a smaller prop higher RPMs to get the same efficiency as a larger prop at slower rpms.

Re: How much faster
 

Thanks Guys, I'll do a search on drive ratios, it does make sense what your saying about smaller and bigger props.
So far I've got
1. 2 or 3" shortie
2. switch to 1:50 ratio
3. start with 25p Mirage plus

Re: How much faster
 

Hey Buck,
Be careful changing too many things at once.
Personally I don't think you need to raise your prop shaft up. Your boat is set up virtually the same as Dave M's Superboat and the fellow that had the 90+mph Pantera. My prop shaft may seem a little higher than the other two, but my boat does not have a pad. You will loose bow lift by raising the prop shaft up. These narrow deep V boats need bow lift to run fast...
I have not done it my self, but I don't believe that it should be that big of a deal to change the 1.36 gears to 1.5 gears in the drive you have.
Good Luck! and happy Turkey Day...

Re: How much faster
 

RLW, the 93+ mph Pantera was a 1999 24' 7' beam 3800+/- lb boat with (I dont remenber exactly, been a couple of year since I owned it) 625-640hp 460ci procharged intercooled engine built by Proroc. Would spin a tweaked 29p Mirage (not mirage plus) at about 5600 rpm to a best speed of 93.4 on GPS. Boat would consistently run in the 89-91 range. Most fun I ever had with a boat. Tricky driving at those speeds in that boat. Unfortunately for the gentleman that bought it from me, I dont believe his experience was as pleasant.

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ok THATS TOO SHORT for a long story, whats up Scarabman, somebody get seasick?

Re: How much faster
 

What happened, Scarabman????

Is it similar to this story?
A fellow I met a few years ago at Shades restaurant on this lake had just bought a Donzi 22 classic with a 502 mag, with a Blackhawk surface drive. It went into the 80's, apparently. He was white when I first met him at the restaurant, and he could not sit down.

He had been hotrodding around, and happened to hit one of those stealth cruiser wakes. He said he was maybe 15 feet in the air before he could blink, and was looking down at the water when the boat was about 90 degrees to the water! It landed hard on it's side, but did not flip. He said he was selling the boat right then. He was bruised up, but not that bad...
If only I had a check with me then....

I hope your story was not that bad...

Kent

Re: How much faster
 

I read somewhere that a 38' awesome gained speed and cracked the century mark with stock Hp power by using 1.5 bravos and 34 or 36 bravo props instead of the 1.36 they started with. I did some testing many years back with a 19' boat with 1.32 vs 1.5 ratio alphas and the 1.5 with a bigger prop was 4 mph faster at the same rpms. Torque is what boating is about, a 600 hp na 454 will usually not beat a 500 hp na 540 in a boat.

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Pat I have found on the Pantera and Donzi classics the plain Mirage, Hydromotive 3 blades, and cleavers to measure or act like true pitch. The Mirage plus seems to be about 1" bigger than listed and the Bravo1 4 bl seems about .5" smaller than listed. On one test day the Labbed Bravo1 26 ran .5 mph slower than the stock Mirage+25 and the stock Mirage+ 27 was .4 faster than the 25 but handling, acceleration, and rpms were lost. It wasa poor test day though 93 deg and dead flat water. I think that on rough water with a more neutral prop(like a 3 blade) and neutral trim the Mirage will be closer to 1mph faster like you observed. Oh yea the transom assembly is on at 17.625 X and I found the Bravo to be more than 2 inches shorter than the TRS so I actually Lowered my X slightly to keep the bow carrying abiliy of the drive. Jo said that over 18 I would probably be looking for a spacer to go back down so I settled on this. Chris

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Although it is really the Member's who bought the boat from me story to tell, he developed engine gremlins very shortly after purchasing the boat from me. He went through a couple of re-builds before successfully defeating said gremlins. Once that was all said and done, he never really, to my knowledge, got the hang of driving that boat with that kind of hp. I dont know the exact details, but I know his wife was washing underwear with skid marks on a regular basis. After awhile it seems he just got discouraged and kind of gave up. To his credit, he asked all the right questions, and as far as I know tried all the right things, I just dont believe it was the right boat for him. Not a boat power combination meant for very many people.

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Rolling cruiser wakes are killers, Scarabman, that boat must have been some wave jumper :D Thanks for the story.