That's a good one....

They can be converted to a three helix rotor also and are said to be about 20% more efficient.

Im driving mine at 18% over, with a 10 Rib serpentine belt, with zero issues. I don't think they take nearly the power to turn, guys think they do.

heres some parasitic numbers from a 6-71

nothing surprises me anymore. Might be ok on a NA 330

I've gotta stop looking at these SC build numbers and you know why!!! Wtf.... dish Pistons one week and dome the next. Fken ah.

Im not sure I buy that. B&M did some extensive testing on a 2 lobe, vs 3 lobe GMC 671 blower, when developing the 420 Megablower. There just wasnt much difference. The concept behind the two lobe rotor, is that the rotors take up less space inside the case, which allow for more air to be available per revolution.

I think the 420 is a good blower, but I don't know if I would invest the money to do a bunch of mods to it, aside from a good rebuild, fresh strips, etc. The couplers and main shaft are the weak link . Blower shop does offer a Billet front cover, and option to run their snout on them, as well as replacement shaft and coupler. For a low boost boat application, they work pretty good. I don't think that be the blower I want for a blown alcohol setup though, with high overdrive/boost, and lots of stress on the stock snout, etc.

The one thing I like about the straight 2 lobe rotors, is the fuel distribution is good. You really don't get the big variance from front to rear cylinders with fuel distribution, or bank to bank, like you do with a twisted rotor that pushes the charge to one end.

Mild Valvetrain that lives long time, with some boost, is hard to beat. Mercury marine knows this

Your comments make complete sense. I only brought up the three because I've read about guys doing complete mod overhauls on them "for what".? I would think the heat would contribute also. Good post MT.

Right again but... something to be said about a nasty sounding roller while taking full advantage of dry pipes isn't all bad either. I'm surprised how much blowers have gone up in price over the years. I get what your saying though. If I go SC I might have to consider some saddle tanks!!!

I just need to know the thoughts on what RPM do we want to run the engine at after seeing what a dyno shows. Are we looking for peak HP or peak torque or somewhere in between. I had always thought running at peak torque was stressful on the engine. Please give me your thoughts. Thanks!

Some say prop to peak HP. Personally I prefer to prop 300 + - rpm under peak hp and with previous builds puts me btwn 1,000-1,500 rpm above peak torque. Just keeping it simple. sometimes it takes a day on the water with a handful of props to see what makes your boat happy.