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Old 02-24-2004, 10:10 PM
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IS THE 575 SET UP TO HANDLE MORE BOOST IN TERMS OF COMPRESSION? IF SO HOW MUCH AND WILL THE HP EXCEED THE HANDLING CAPABILITIES OF THE XR DRIVE
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Old 02-25-2004, 08:47 AM
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A friend is running 7.5 pounds, a chiller, and ECM reprogram on a pair. Supposed to be around 700hp.

XR's never lasted more than 15 hours on a 12,000# 42 MTI. A lighter boat may make a huge difference in the drive issue, but that's a lot of motor for an XR so you can't ignore that.
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Old 02-26-2004, 01:46 AM
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Roots type blowers make boost by basically rubbing (rolling) two pieces of metal together, that is called friction and it makes heat, which heats the intake charge. Also when you compress air you heat the air , that also heats the air charge. All this heat is pushed into the cylinder and heats the piston, rings, and valves even hotter than they were designed to run on a N/A motor. Thats why intercoolers are cool, they cool the air charge, help it pack in the cylinder more densely and make more power as well as make the parts run cooler and last longer. Just make sure you don't over cool at idle and low speeds, use a intercooler temperature sensitive flow valve to match the cooling level to the need.
Freshening an engine is expensive, make 'em last longer ,save your money for beer!
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Old 02-26-2004, 09:20 PM
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Well, sorta...

The lobes don't actually touch. Except for the ones that sound like you are killing families of cats when you spin them. Blower rebuilders love to hear them make that sound cause in ten minutes they are gonna get to rebuild it (and reset the lobe clearances).

But it is correct that Roots blowers are the LEAST efficient and transfer the MOST heat into the intake charge when compared to screwchargers or centrifugal blowers.

The reason for this is not from metal touching, it is from the "whipping" motion of the lobes both on the intake side and the discharge side. Just like any mechanical motion, the whipping causes heat.

All compressors raise the temp of the charge as they compress it cause that is due to the pure physics of compression. Same reason why a diesel lights off without a spark. Compression causes heat. A mechanical supercharger (of any type) will ALSO add MECHANICAL heat from the METHOD of compression.

And a Roots adds more heat than the others we are familiar with.
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Old 02-26-2004, 09:27 PM
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But the roots looks awsome.
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Old 02-26-2004, 11:42 PM
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The Roots Blower is more efficient than you think in a low boost environment...say 5 or 6lbs. Above 10lbs is where the other types of Forced Induction work well.
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Old 02-27-2004, 10:37 AM
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As far as plumbing an intercooler, we used a thruhull pickup on my cat that was plumbed straight to a strainer then to the intercooler so that at idle the intercooler was not in play at all. Once you get on plane it will start flowing water.

I was told the same thing that mcollinstn was talking about by my engine builder. you don't want the intercooler working at idle
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Old 02-27-2004, 11:20 AM
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Let me make it clear that I am NOT knocking roots blowers in any way whatsoever.

I am just telling you (like it is) that of the three common mechanical supercharger styles, Roots is the LEAST efficient. Are they efficient enough - of course they are. And the look is unparallelled - nowhere else can you get that stack of power "look". Screwchargers pull from one end and out the other. Centrifs are like hair dryers and have to be mounted off one side.

Roots are fine, affordable, and provide instant boost and good service. But they ARE the LEAST efficient. And they DO make more heat than the other styles at a given boost level.

It's all in the "whipping". They present a larger surface area of blade or lobe or whatever you want to call it to the intake and outlet air charge than any other style. And this matters.

ESPECIALLY at cruise. That is where the Roots is even MORE inefficient (heat wise) than the others.

At cruise, the charge is not allowed to pass thru the blower at a high rate. The internal pressure differential maxes out and the incoming charge gets beat over and over again by those long lobes. This builds a lot of heat.

a centrif will go into cavitation, where the same piece of air goes round and round in the blower volute and builds heat but not to the degree of the roots cause the surface area is dramatically less.

The screwcharger has a smallish inlet and a such doesnt present the same surface area of mechanical beating that the roots does.

This is why the roots makes more heat. It isnt a criticism it is just the physics of it.

Unit for unit and size for size, the roots is the least expensive, the centrifugal next, and the screwcharger most.
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