aero-offshore

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

Pat McPherson

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...

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!

aero-offshore

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.

Pat McPherson

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!

IRONMAN

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

aero-offshore

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?

Pat McPherson

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...

Panther

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.

aero-offshore

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

Pat McPherson

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...