Prop Confusion: #'s don't make sense....
 

I am running a 1992 Liberator 221 with a 502. Here are the numbers.

Stock:
5200 rpm with a 14.5x20 Raker prop would see about 62mph giving me about 11% slip. (Engine RPM as measured with Snap on Tool on #1 wire, GPS speed)

Post Engine Build:

5050 RPM (engine built to 5500rpm max) 14 3/8x21 Ballistic 68.5mph (in the conditions/load that day) which give me about 3% slip and I know that is not reasonable.

The prop is acting more like a 22.5" prop. It's an OMC drive so I don't have a ton of options to try.

Ideas? Thoughts? I'd like to bring up the max operating RPM's a bit as the engine made peak power about 5150. Will labbing help a ballistic prop? They are already fairly thin.

Actually you have many options, you can run any Merc prop with the proper hub kit. I am running the same hull with the stock 502 and a raker, I want to try a Tempest and an Enertia on mine this summer.

How heavy were you running that day? Did you buy the prop new or could it have had previous work?

Yeah I know I can go the merc route if needed. The prop was used, but it was a demo prop, it looked perfect. If they told me it was new I would have believed them. I was running full fuel with 3 adults and the normal gear. The more I read about it, it looks like Ballistic props are kind all over the map for pitch.

I've seen a best of 71.5 gps. It likes a good chop on the water to get the last couple out of it, and that was with a quarter tank and just me and the wife. I just wonder if it is worth going any further with this prop, or try something else.

Curious, what do you see stock?

Here is what it looks like now.
https://www.dropbox.com/s/q2fub78lkhblq83/502.jpg?dl=0

https://www.dropbox.com/s/bn55uy5hp7...%20pm.png?dl=0

Did you run it with the prop you had with your stock setup? If so, what were you seeing? How much increase in horsepower post build? I'd PM Brett at BBlades for his thoughts.

I've seen a best of just over 65 with just me and under a 1/2 tank of fuel, I am def getting the most out of it, I also have heard mixed things about the Ballistics, I ran one on my first Libby a long time ago and loved it but it was also one of the "Atwood" Ballistics which had far better consistency

If I keep it I will be doing a cam and exhaust at some point in the future...

Did you try a 22 or a 24 Raker on it?

5050 is fine if peak power was 5150.

I've tuned several boat where best mph was actually a few hundred rpm under the max rpm on dyno.

I guess this can be the difference between WOT under real conditions vs a dyno sweep test.

I did, I could easily blow past 5500, since that was the case I bumped the pitch right away. Dynoed 539 through wet manifolds.

Gen V converted to full roller with Bob's help.
Port Matched (not full porting) on stock Heads
Minor Valve work
SM Manifolds
Marine Kinetics Cam with all of the roller pieces Bob recommended
DUI ignition ilo the stupid OMC spitfire system
Scorpion Rockers
Bump in compression
EB High Rise Intake
850 Holley Mechanical

Some other little thing Bob Suggested.

Maybe if nothing else I could have BBlades check the prop, or recommend something.

I would love to try a Raker 22", if I had one available. I actually had one previously and sold it before...

Duplicate

I don't disagree with that at all, but I would like a better hole-shot, and since I lost VERY little power until 5500 rpm, seems like a waste not to go there.

Wow, that's flying for a stock one!

Well, I have a line on a 14.5x22 Raker to try, hopefully this weekend i can give it a try. If I pick up any RPM I'll know what to do. I would think labbing will help a lot more on that prop than a ballistic, so maybe that is an option. The numbers will tell when I get it on.

If I see 5100-5200 with the stock Raker, how many RPM will I pick up labbing? I know every prop is different, but just in general. I've always heard ~150rpm increase, sound right?

Good luck! It should be enough prop as you are built to rev to 5500 anyway, if not it will be a great baseline

did you get a chance to run the 22?

I did -- the 22" Raker was about right actually. I lost about .8mph but picked up about 200 rpm (just over 5200) over the 21 Ballistic -- yes I know this doesn't make sense, as noted before the Ballistic is acting like a ~22.5" prop. The speed loss does make sense as the ballistic should be the faster of the two props. I ran at the same load, same water conditions (or as close as you can get really). The holeshot was slightly better with the Raker 22" as well.

I talked to Bblades and am going to send in the Ballistic for labbing, and may take a hair of the pitch off to get closer to the 22", the labbing should add 100-150rpm according to them. This should get me more in the 5350 range in this loading condition, lightly loaded I may see a bit more, closer to the self imposed 5500rpm limit . I have a DUI ignition with a 5600 rev limiter in it now, I'll probably swap that out for the 5800 chip just to be sure, that should keep me from hurting things if something goes wrong.

I guess the bonus is, it should get me a "free" couple mph. 1-2mph for $400 is about as free as it gets in the boating world. They are backed up about 3 weeks, so I won't have an update for a bit.

EDIT: As noted earlier in this thread, this makes me wonder if the prop I have isn't actually a 23" Ballistic that has been re-hubbed, worked on etc. who knows...

Update -- I did get the Ballistic Measured here: http://www.wolverinepropeller.com/ -- it measured 22.1" and 14.5" diamter (advertised 14 3/8 x 21). That right there certainly explains bunch of my difference. I have a day/time to run the props back-to-back on Saturday morning. I'll then have the Raker measured. After I have back-to-back rpm and speed data and measured props, then I'll decide which prop to send out to bblades after a discussion. Work got crazy and weather got nice so I've FINALLY been enjoying some time on the water.

Ok -- I stopped on the way home from work and got the Raker measured. While the Ballistic was almost dead on blade to blade @22.1, the Raker was 21.88, 22.08, and 22.2 between the 3-blades for a 22.05 average, and measure 14.5" diameter (advertised 14 1/2 x 22)-- damn near the same as the Ballistic. I am going to make some runs for GPS speed and use my snap-on tach back-to-back. I still turn the Ballistic 150-200rpm less. Hell, if I could get that 150rpm back with labbing the Ballistic without changing the pitch, that would be a home run.

Bblades, what do you think?