Had a few discussions with friends the past two weeks about procharged engines. My question, is more relative to the dyno than anything. But anyways, in 3 different scenerios, all 3 guys had one common issue. Lack of power getting the boat on plane. One of them was a 42 Fountain with 1200hp M4 blow thru engines. The other a 26FT single engine Cat with a procharged blow thru 565ci. The third, a 42 Fountain, with EFI procharged 950s'.

All these engines make great power on the dyno, and seem to make some big torque numbers as well, even at lower rpm's. In one case, the torque readout on the dyno was much higher with the prochargers, than after the switch to the 1071 roots. However, in the boat, the 10-71 combo, was not a turd getting on plane, or accelerating.

My little roots 468's, even when I had big ssm 5 blades on that didnt slip at all getting on plane, required barely 1/2 throttle in my 38 fountain, icdedppl's heavy old roots blown cig is same way, doesnt need to be pegged to the dash just to get it to lay over.. My buddys that had 42's with prochargers, need nearly full throttle to get the boat up and to lay over.
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My question is, is there something the dyno cannot measure, or doesnt tell you, about how well the engine can actually pull the load? If that makes any sense. I remember watching one of brian tooley's videos, where they talk about the different style of chassis dynos, and how one design, can really show the effects of a engine that cannot accelerate well. How that works, I really dont know.

in the case of the cat with the 565 it is in vacuum until 2800 rpm,on the dyno we don,t start the pull that low,usually 3500+rpm.i can tell you that as soon as it gets into boost in the boat it accelerates like a monster.joe,s 42 was similar when pro charged.

Having never been , how would you compare your whippled 1200's, to joe's procharged 1200's, in the overall acceleration department? I remember his layed down some big torque numbers. I been in your boat, acceleration and response, is NOT an issue lol

I might be wrong but don't the roots type blowers create boost at all RPM's? So at idle if you stab the throttle you have instant boost. With the Procharger you don't create boost untill the Procharger spools up. It is not a positive displacement type compressor. Until the Procharger comes up in RPM it doesn't produce boost. The roots type can't NOT create boost because it is a positive displacement pump.It is sitting there pumping against closed throttle bores. When those bores open the pump goes into action.

I get the whole thing about how they work. But my question is, if a procharged engine is showing its making say, 850 plus ftlbs from 3000-4000rpm on a dyno sweep, why in the boat, at 3000rpm, are they so sluggish, compared to a roots or screw making the same torque?

Mike brings great info, and because the dyno's don't get pulled down to planing rpm, that info is just not in the sheets.

Yes Tinkerer. Roots stay at a fixed gear ratio until you physically change pulley size. Underdriven or overdriven, they stay relatively close to 1:1. Boost is just a throttle push down away no matter hat rpm you are at,

The centrifugals have a step up gear ratio. As engine rpms rise, the impeller speed basically maybe at a 7:1 ratio or close to , as it needs to as at top engine rpm you'll be spinning an im[pellar at 50,000 -60,000 rpm vs a roots lobes at say 6.000 rpm.

If you go to 22:00 in the video, they talk about load bearing vs non load bearing chassis dynos, and how on a load bearing dyno, it might take a very long time to do a pull, vs a non load bearing dyno. And how the tunes, can be completely different . Not sure how this would relate to an engine dyno?

100% correct,very good explination.

oso member boatally insanes procharged 555ci. Even at 3000rpm, it is making 736ftlbs with only 1lb of boost. Thats still good torque down there. Are they that dead between 2000 and 3000, where they have very little power?

not saying this to pizz anyone off but i am not a fan of pro chargers in boats,espically heavy ones.imo the whipple is hands down the better choice.a pro charged drag car is a different story,i love them.