We did not do any steady state pulls. We will when the engines go back on. Although it seems all these pulls could have been done better and provided more detailed and accurate info, their purpose was just to see where power was going with each comb and I guess that was accomplished. The engines are going back on again and they will be swept slower and run steady state. As far as sweep rate, I was just curious as to why someone that builds all manner of boat engines would set the rate so fast. Even completely stock black motor rebuilds that come in from the marina get run before they are returned to verify they have no problems and those customers likely don't even know or care that they were run. He runs the piss out of this dyno and should know it like the back of his hand. Might just be bs but he claims about 14k pulls and he knew exactly where each combo would peak before it ran. He doesn't lack experience, that's why some of this just doesn't quite make sense.

IMHO: Set it for the 300rpm/sec rate.

Reason for acceleration rate options on a dyno is to try to match what the engine's acceleration rate is actually in the vehicle. Example: think how fast the rpms climb when you go WOT in a chosen vehicle.

A boat will accelerate less quickly thru it's rpm range then a, say 4000lb car, vs a 2800 tube frame Camaro, vs a rear engine dragster. Again, this is reason why you can choose different acceleration rates on dyno. To better match how engine will accelerate thru rpm's in real life.

I want to add in my post above, any time I see a BSFC (how much fuel is used per horsepower uncorrected) in the .300's to alomost .400, a red flag goes off in my head telling me that the corrected hp is going to be a lot higher than as measured. So, with my above post, if the fuel use is lagging behind because of the huge acceleration rate, this may make the corrected hp % (not actual corrected hp # ) look higher than it is.
Edit in: I slept on it, and saw I was headed in wrong direction. Lagging fuel flow reporting will not change corrected #'s.

Sorry, hard for me to write/type some things down. Hopefully someone will understand what I'm saying here. LOL.

Sometimes I forget what info I've posted and it gets more confusing because I've also been exchanging emails and texts. All the pulls were between 800-1000 rpm/sec. One of them exceeded 1000. I understand why the dyno is capable of different sweep rates, still wondering if there is a reason one would sweep a boat engine that fast. I'll just ask him next time I go. I haven't been there in over a week and sort of lost interest in talking to him due to serious health issues of immediate family, but the show must go on.

I just noticed another parameter titled: Inertia- ft lbs- sec. This was in the same area where he input hi-low sweep limits etc. What would that be?

Just for kicks I went to the go-fast website and plugged in some numbers for different boats and their calculators have the same mindset I do. I plugged in 1600 hp for a heavy v-bottom and then plugged in 1760. There was a 4mph difference. I said sometimes there's only 2-3mph, so I was 1 mph off on my guestimate using their calculator. Then I used a 50 hp gain (25hp each engine) and it netted only whopping 1 mph gain in a heavy v bottom. Lastly, on a fast cat with a 300 constant factor the increase of 160 hp netted 6 mph.

Site disclaimer: "There are so many factors that affect boat speed that it is hard to make accurate estimates of what the real top end will be. Mercury Marine uses the following formula to estimate potential top end, this calculator uses this formula."

To support what I originally posted. Even when using the speed calculator, there's no magic formula to say that X power increase results in X mph increase. case closed. :-)

I think the steady state pulls are really nice because you give the engine a chance for the EGT to level out and it better simulates how the engine will run in the boat. I like seeing steady-state pulls at 4K, peak HP and even peak torque.

I plugged in 840hp (stock 420s)total in a heavy vee weighing 8500lbs like donzi matts boat. Said 71mph. I plugged in 80hp per side more for 1000hp total, said 77mph. I then plugged in 25hp per side more, 50hp total , and got 73mph. Seems like his assumption of a 2mph gain equating to around 20-25hp per side, is a heck of alot closer than 80hp per side than his engine designer claimed. At least in that application.

What about when you swap your cams for custom ones, and lose several mph? Theres quite a few who have experienced that. Lose 3mph, how much HP is lost is their question, rather than gained

It depends a lot on the speed range in question. It is easier to gain 2-3 mph at a max speed in the 60 mph range than the same gain on a boat with a 100 mph top speed. Also there are speed barriers to hull and drive combinations. Once you hit the wall it takes huge horsepower gains to find speed. It is usually easier to do some setup or rigging changes to gain performance.

We're actually speaking the same language here but for some reason there's still a disagreement. You gave one example, I gave another and I still say that it's really hard to tell what speeds a boat will gain by stating who much HP increase etc.

One last example, that is exactly why I asked him what kind of boat it was. But it wasn't made clear to me. You seem to know, but I don't.