Last time Joe B and I talked, I remember asking him how he liked the 1000hp roots mills, compared to the 1200HP procharged ones. Being they were in the same boat. Sounded like he was much happier with how the roots engines performed all the way around.

Here's my thoughts, for whatever they are worth. I've dyno'd quite a few, including boatallyinsane's engine. I'm pretty sure the numbers don't lie. What I believe is the biggest problem with a procharger setup is not that they are really weak down low, but they make so much high rpm power. Therefore you end up with a higher pitched prop to accommodate the high end power and not enough low end torque for the setup.. A roots supercharged engine has a much flatter torque curve. For example a 1000 HP roots or screw supercharged engine would have much more low end torque than a 1000 hp procharged engine. So setup becomes much more critical. You can't overprop a PC engine and have it perform correctly. Also, you need to throttle it harder getting on plane to build boost. On a roots engine you've got a much larger window to work with. One last thought, dyno runs are done at wide open throttle. If you are not using WOT to get on plane those dyno numbers are meaningless.

Bob

Thanks for the reply bob. Is your dyno capable of displaying the varying rates of rpm increase ? Meaning, say at 3500rpm, vs 5000rpm, in RPM per seconds?

I saw on another racing forum, where they were able to show the varying rates of acceleration. I dont know what kind of dyno it was however.

you hit the nail on the head,the pro charged 1000 hp engine uses a fairly large prop due to the max power but because the pro charger needs to get spinning fairly fast before it starts to make boost the engine is weak down low until it gets into boost.the 26 cat joe is talking about i believe is the one my buddy owns and i built his engine last year.i went 9.2 to 1 compression in hopes that the engine would make more power in n/a mode before boost and if i had it to do all over i would go to 10 to 1.we got a different impeller for the charger this year that should bring the boost a little sooner,also going to see if joe would write a program for the daytona box i installed on it.

i think a boat with some sort of two speed transmission would really help with the pro charged engines.i think that is why they work so good in car,s and motorcycles.

Thats no problem. Gimme a call tonight, we can put something together

I guess it is not a good idea to run rpm's up to 6k and put drives into gear...

Spot on.

The Checkmate 253 we used to have had an M3SC on it and when propped correctly (or close to it) for top end/RPM it was sluggish to get on plane because it didn't start making boost till about 3700 or so...after that it was game on.

Some call it sluggish, I called it a Bravo saver.

.... And HOPEFULLY I'll know how well it'll pull in the boat shortly.. Plan on installing the blower this weekend. starting with a 34 pitch Bravo I prop..

The software will do it, but using a water brake I don't see how it could be very accurate. You would need a constant load such as a chassis dyno uses.