Hi Guy , I need some help on my dilemma,
I have a 26' american offshore , it has a 496 HO bravo XR drive with a 2" shorty Imco lower, 28P Bravo one labbed prop. I would run WOT 5100-5200 RPM and trimmed at its sweet spot runs 77-78 MPH.
I wanted to hit the 80+ mark so i decided to get a cam and roller rockers installed hopping that I can jump up a prop size. 30P. Well i got the cam and roller rockers installed and i was told that the ECU was tuned to support the cam . I took my boat out for its first test run and lets just say I was not happy. I ran 71 MPH at WOT at 5100-5200 RPM and trimmed all over the place to just hit 73mph. I had a 27P prop on stand by to see if i had to much prop slip. The 27P bravo ran the same 71MPH speed. This just is not adding up, I was better off with my stock set up. What are some of your thought????????????????????????

Where did you get this cam package?? Who tuned the ECM?????? and how could they tune it unless it was dyno'd or run in the boat with an O2 sensor??
Tuning a PCM555 module is not something your average engine builder can do. Only a few shops in the country can do it.

If you are running the same rpms and trimmed out the same and running the same prop, then speed should be the same.
If you lost speed, then you have more drag for some reason.

Curious about cam/tune also? You were running the same 28p bravo you ran 77-78mph with? If so you didn't gain any power as you can't spin the same prop any faster. We need more details on the setup.

I say tune is not correct. Hopefully the combo is correct for your application and you can find someone to tune it. Good Luck with project. For a good tune, you would need it on a Dyno, with o2 sensors, and you would want to hit all RPM bands. Someone needs to know what they are doing. You don't want to be lean, or fat....you want to be in the sweet safe spot. Also what fuel are you going to run

What are the specs (grind: lift and duration) of your new cam?

even if you gained 50 hp its only net you 3 to 4 mph using the correct prop. Who tuned your PCM 555 and was it on the water you mostly boat in or thru the mail ??.

Tuning by the mail is basic average overall - the tuner does not know water temps - average air temp - climates - gas blends being used / specific gravity / RVP. also Altitude conditions. Nor was the engine ran on a dyno to get all the baselines and so on..

Can you image persay Nascar tuning their Holley fuel set ups using mclaren ecm s thru the mail. They tune per track -- per day.

Forgot the 496 HO Mag revs limits at 5150 so with that said were is your peak HP and tq numbers and was the rev limit raised in your PCM 555 ??

I would definately say your ecu etc is definately not happy with cam change. Did you degree the cam? Like bUP said at 50 hp gain your looking at 3-4 mph at best. Roller rockers are nice but not going to be any gains. What cam did you use? With no other changes on a stock engine with cam change only I honestly wouldn't expect to much. Hopefully you get it figured out otherwise throw the stock cam back in.

I hate to say it but you would have been farther ahead buying a 500EFI or a 525 and selling the 496HO.