If motor is turning same RPMs why keep looking there?
The outdrive is spinning the same prop the same amount of times per minute.
The boat should be moving forward same distance per revolution.
If not...there is more slippage either between motor, drive, and prop OR prop to water.
That is IF rpm and speed measurements are accurate.
Same engine speed and same prop and no drive line slippage would send attention to prop and water connection.
More weight, drag, hydrodynamic change, aerodynamic change, center of gravity, balance of boat...somewhere along those lines.

I will double check this on my next high speed run as I maybe trimming the drive up higher than I originally was to try to get to the 72 mph that I had originally. So the RPMs could be lower than they were originally at the same trim setting that I was running when the boat was hitting 72 mph.

So I will say this the stainless prop doesn't have any damage, dings or scratches on it but it is no longer super shiny in appearance since it has been in the water for about a month now. I wouldn't say that it has calcification going on with it as there aren't any white spots or patches but it's duller and it's not as slick when you rub your fingers on it. Would this cause a 4 mph decrease in top speed? I can attach a pic of what it currently looks like if I can figure out how to do that on here.

The way you manage to eliminate every possibility suggested, I'm starting to think outside the square......
Are you running on an uphill section of the lake whereas previously, you ran downhill?

RR





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Hi if that last post is for me I'm sorry that you think that I'm eliminating every possibility that it could be because that's not the case. I'm open to all ideas and suggestions that people have mentioned here. I'm not fully eliminating the engine as a possible cause. I have read some weird stories where spark plugs have caused major speed issues by having a small crack in them or something strange. another thing that I have noticed is if the wind is blowing off of the stern towards the bow when I startup & run the boat in my slip I do smell exhaust gases (like it's running rich) which I never did notice last season. Especially when the exhaust pipes are fully under water while not on plane.

Scantool or Techmate will not show a/f ratio. It will show other functions such as MAP, spark advance, etc.... I have Whipple's Stage 2 tune which keeps stock 43psi pressure. 50psi for just the 203 cam upgrade seems pretty high. Raylar spec's 50psi when you run their H0525 kit. There is no doubt in my mind your running rich. Safe, no detonation but rich. Telltale signs are raw fuel smell at idle, black soot transom.

I also wet slip mine thru summer. Always keep scum line around hull and drive/tabs clean. Never have noticed any speed loss from start to end. Though our water is very clean and any buildup is negligible. Your 4mph loss can easily be chalked up to weather/water conditions.

Spark plug readings and pull exhaust off and look into the exhaust ports is a good way of reading rich as well.

So which fuel injectors for the app are being used and fuel pressure regulator ?

hopefully you got rid of all the 3 / 8 fuel side diameter that are in the fuel system.including the fuel pick up and anti siphon valve ?

Which cool fuel are you using ? Or not ? which fuel pump(s) and fuel filter(s)

U are not going to get AFR's out of any marine scan tool. And many do not know what the spark advance degrees should be at thru out rpms when scanning the engine.

Another good way way to look at rich or lean is with a 5 gas analyzer. It is a really good test for the marine cat engines and the efficiency . I have been using one now for a couple years.

So the only change made on the fuel aspect of the engine is Larry @ Raylar told me that I would need to change to an adjustable fuel pressure regulator and I had Larry purchase it for me as he knew which one to get and he shipped it to me with the BP-203 Cam, everything else for the fuel is stock. The main changes to the engine are the Cam replacement and the Computer Reprogram to the Whipple HO program. Everything else is stock including the heads. On the Raylar stage 1 engine upgrade that puts out around 540 HP with the top end changes, they are running the fuel pressure at 51 PSI at WOT. So yes mine is set very close that and I believe that it's pretty rich as well it's a very safe setting but I'm going to talk to Larry today and see about adjusting it down to 48. Thanks Ryan for your input about the Scan tools as I was hoping that they would show the A/F numbers and if it's running Rich compared to where it should be. So Ryan will the computer do the tuning work to try to optimize the F/A conditions to the air temp and humidity conditions? If I'm running on the very rich side will the computer be able to compensate at all to get the engine to run a little leaner?

If it doesn't have A/F sensors and the capability to read them, it can't adjust A/F ratios.