Looking for some input before the season starts.
Last season at the end I changed out from a 7.4 to a 502. The numbers I have are based on my speedometer not a GPS.

The boat was running 60mph with the 454. After putting in the 502 I tried 3 different props.

Bravo1 24P 5100 RPM 75mph
Mirage 25P 5100 RPM 79mph
Hydomotive 25P 4 blade 5100RPM 71mph.

Tried all sorts of things to find out why all 3 run the same RPMs. My first concern was detonation. I tried Avgas colder plugs and lower thermostat to no avail. I have the revlimiter set at 5500 and it will do that while not under load.

The Hydromotive really made for a scarey ride it was pitching the boat all over and chine walking big time.

The Mirage was slower on acceleration and blew out on turns.

I am very pleased with the Bravo1 handling and acceleration sticks to high speed turns like on a rail. Just wondering if there is room for improvement.

Any input is appreciated.

We need more info. What boat, what drive ratio, and which 502. Get a GPS; Speedos are too flaky even on the same day. The numbers are too far apart to make a reference. Hydro motive has several different props. Three blade, which four blade, high rake and which diameter.

Randy

[ 02-02-2002: Message edited by: BigGrizzly ]

Big
Thanks for the interest. I don't know much about the Hydromotive 4 blade. When I told Phil Bergeron how it reacted he said it must have had to much rake and my hull didn't like it.
The engine is a zz502 shortblock, Crane Hyd. roller .598/.610 230/[email protected] 112* lobe separation. Edlebrocks marine heads 2.25 intakes 1.880 inconel exhausts. Crane gold rockers w/stud girdles, 1.7 ratio. Imco Powerflows thru transom. RPM air gap intake with an Edlebrock marine 750.

Drive is a Bravo1 1.50 gear ratio. Hull is an Ultra 21' open bow weighing in at about 2800 lbs. I believe the bottom is 18* no steps. In looking at the bottom it appears as if it has some hook to it. Fully trimmed it seems to break the water just behind the drivers seat.

Your results are all about right. Your experience with the different props is quite charicteristic for each. If you want a little mare speed and RPM I would have the bravo prop labbed. This is a good reason why no 1 prop is the best for everything. So get a prop holder and carry the extra with you. If you want speed put on the mirage, and best all around use the bravo.

I hate to say it but you may want to repeat the testing after checking the tach with a shop tach and use a gps for the speed measuring chores. Your hull will most likely do better with the round ear props as seen by your previous testing. If the tach is ok than the Bravo1 24 with a lab finish will probably add 100 rpms and a little speed. Powerboat did some prop testing and found the Bravo1 labbed prop hard to beat as an all around great performer I switched to one last spring. The Ironman

I agree with Ironman about checking the tach. Try a Bravo 26. If your tach still says 5100 it's wrong. If your mirage is blowing out a bit then you are just about right for top speed. Before investing in a labbed Bravo prop, try a Mirage Plus, it might hang on a bit better and satisfy you without giving up a lot of speed to the four blade.

Ultrafine, Your motor sounds nice. What kind of power numbers are you getting? Were you able to dyno it? I'm thinking 550-575HP? How much do you have in it cost wise?

Tomcat
I was suspect of the tach myself at first but I have an MSD system and when I put a 5500 chip it shows 5500 on the trailer when I put a 5000 chip it shows that as well.

Marty
It dynoed at 590HP @5700rpm torque was 585ft lbs from 3000-5600 at 5700 it dropped to 579ft lbs. The engine builder said it was the flatest torque curve he has ever seen.

Turbo Vector is what I would use on that rig. Last summer I tested and tried props from different makers. (I work for a marine distributor) That’s over 15 different types of props. I found that on my boat a 22 foot 24 degree bottom with a blown 502, the Turbo lightning the turbo2 (similar to the mirage plus) and turbo Vector and the mirage plus to out perform the bravo1 both labbed and standard ones.

Randy

BigGrizzly, Do those turbo props you are refering too come in 4 blades? Who Carries them? So far I havn't found a 4 blade that out performs my labed bravo 1 32" pitch. But I'll try anything that might be better
More speed is more speed. I don't care who makes it.