PQ290Enticer

This question may be on here already. I just couldn't find it. I have however found a few 290 owners on here with some decent power and wonder what prop's they are running. My engines should be approx. 500hp and torque to match. Old setup was 7.4 gen V's. Old setup is WOT 60mph 4400 rpm which is about 10% prop slip. Cruise at 3600 is 50mph which is about 8% prop slip. These are GPS numbers. If I add approx. 200hp per engine, would you keep the current 24 pitch bravo 1 props and just spin them faster? Providing they don't go over the new redline which I believe is going to be 6k. I think I read somewhere that you would go faster turning the smaller prop pitch faster? Is running the Bravo 1 outdrive at that engine rpm okay for an extended period of time? My 290 is very stable and in part due to the switch from 3 blade Mirage to the 4 blade Bravo's. I am wondering if going to a 5 blade would also keep it settled with the increase in speed? I assume there would be an increase in load on the outdrive with the 5 blade props? Maybe not a good idea for the drives with the new hp? Just not sure what others have done to go a little faster and keep the boat settled. Currently running Bravo 1 outdrives with a 1.5 ratio. Thanks in advance for your help.

Rookie

Just run your 24's to get a base line and go from there. If you increase your horsepower your will need to increase your target RPM. What are your HP/TQ peaks from the dyno or engine builder? Also, don't take this the wrong way, but something is off on your numbers. 8% slip is catamaran slip numbers and your hull is not that efficient. I know I asked this in another thread and saw pics, but the tach can be off a little and the speedo can be off a little to skew the slip #'s.

PQ290Enticer

Hey Rookie, Thanks for your comments. I had "upgraded" to the GPS speedo and tach's from Gaffrig because the original ones were giving me some problems. There could still be something wrong. I did have "fluctuations" in the tach readings at WOT. I thought the rev limiters were engaging then someone pointed out that my setup doesn't have rev limiters. Live and learn. Maybe the distributors are the problem? The new engines have MSD distributors. I got the slip number from Mercury's calculator punching in what I thought I knew. The site just mentioned that the slip number is usually between 5 - 20% so I didn't think anything of it. Do you have any idea what the slip number should be for my boat? Hope to dyno test and tune the first engine next week. Do you have any thoughts on running a 5 blade with my setup? Meaning, would a 5 blade increase the stability and reduce or eliminate the chine walk the boat is known for? Thanks again.

liberator221

I thought slip numbers typically went down as speed increased, yours is opposite, seems strange. I always heard the Bravo 1 props were overstated on pitch by about 1 inch. Makes the slip calculation a little fuzzy.

liberator221

We’ll forget that thought, if you go with smaller pitch number it makes your very good slip numbers really good.

PQ290Enticer

So I posted a pic showing the speed and rpm in another post. I am pretty sure at that time I was running the Mirage 25 pitch 3-blade props. Moves the slip percentage for cruise up to 12%. Is this more a likely number? I haven't had the boat in the water for the last 2 seasons and my memory isn't what it used to be. I remember running the 4-blade Bravo's and the speed and rpm were pretty close to the 3-blade's at cruise. I just assumed that the 4-blade props were more efficient at cruise?

Knot 4 Me

Have a buddy with a '97 290 with the 300 HP 7.4L's. Only changes from stock are Edelbrock RPM Air Gap intakes and Holley 4150's with the choke towers milled off (not sure on CFM). He runs 25" Mirage Plus props worked by BBlades. Boat has GPS'd right at 69 MPH I believe at 4,600 RPM. Has 700 hours on it. I would not run 5 blades on your boat.