What will 85 extra HP get me?
 

I have a 2011 checkmate ZT244 with a 502mag 385hp. I'm getting the stage 2 PCM upgrade by whipple. I spin a bravo 1 26 pitch prop to 69mph at 4600rpm. The tune adds 85hp and raises rev limitter to 5400 rpm. How much RPM will I gain with this setup?

Usually takes minimum 20-25 hp per mph so I would guess 3 mph. You might want to reprop because I doubt that extra hp is going to bring the rpms up any significant level if you are trying to spin anywhere near 5400. I would assume that is should be too high on stock 502 because it is past peak hp but whipple is smarter than me and I know there are a lot better people that can give imput over me. Maybe a lower pitch 4 blade will even run it faster based on current setup not even including the added hp. Maybe try a 3 blade m+ 25p. Hope this helps.

Sorry just realized you wanted to know how much rpm not mph. I am guessing less than 400?

I think you'll be close to what livefreeordie says and don't think you'll get to 5400 with that prop......but you have to run it and see. I also don't think your getting 69 at that rpm. Is that speed GPS or dream-o-meter?

Forgot to mention its a raised bravo 1 X outdrive. and the speed is correct. My boat has a GPS speedo and i double checked it many times on my phone and rechecked it with a garmin. I've tried a mirage 25 pitch 3 blade and it sucked, blew out like crazy and had no top end. Seemed to do nothing but slip. I tried a 23 pitch rev 4 which i spun to 4900 rpm at 68mph. Great slip numbers on the rev 4 but the bravo spun less rpm at the same speed.

I actually seen 72mph gps at 4900 with a light load and colder weather running a 26 bravo 1 with some lab work. Like i said tho that was only one time and i was on fumes on a 65 degree day.

With the same prop, my estimate is you will be at about 5200 RPM and plus 3-4 MPH.

Wanting another 85 HP :evilb:

Will my slip increase with more RPM? because at 5200 rpm with a 26 pitch with 9% slip thats 77mph on the speed calculator.

85 off a tune feels like a pipe dream....