what do I look for in used root blowers - Turbo / Supercharger

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Cobra100+

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Following the same theroy, the larger blower driven slower would be a little easier on drives in the lower rpm ranges much like a centrifigal supercharger is. Just thinking out loud.

Planing and low speed, it does feel like I may have lost a little bit of torque down low. But, I definitely picked up a ton of power up top. Boat gained a solid 5-6mph running less boost, and still not totally dialed in.

Which brings me to my next area of thoughts.

Lets compare two setups, I'll use mine for a example.

I ran 7lbs of boost with a 250, highly overdriven. No detonation, pump gas 93.

Now, most generically would say, 7lbs would be the practical limit for pump gas without a intercooler. But how do we really know that? 7psi is just a number, and there are lots of variables. 7lbs from a 177 driven at 100% over, isn't the same as a 10-71 at 10% under, from a power and detonation standpoint. So from what I see, boost pressures aren't always equal. Kind of why with a procharger you can get away with much more boost on the pump. Its simply a cooler charge.

My thought process is, by switching to a larger blower, I reduced a lot of heat in the intake charge. So, If I ran 7lbs with lots of heat, 7lbs with less heat shoudnt be a issue. Maybe even 8lbs.

Most guys wouldn't hesitate to run 8lbs or more because they have a superchiller. Without any actual temp numbers, we're all just guessing at whats acceptable.

In the book I have here, they did a test, with various GMC 8-71 blowers vs the 420 Megablower (2 lobe). While they said the tighter clearanced blowers made a tad more heat, there wasn't much difference between them all temp wise. They all got about 60* hotter going from 8% under to 15% over. Simply proving the faster you spin a roots the hotter things get. Of course compressing air in itself raises the temperatures, but seems that heat generated by the compressor itself is the big factor in the equation. As you "beat up" the air by spinning the rotors faster, the boost PSI on the gauge will read higher, as the air gets heated. But, the air has become less dense, therefore not making any more power. So, putting a smaller pulley on to raise the boost psi say 2psi on a 177 highly overdriven, wont net nearly as much power gain as doing the same with a larger underdriven setup.

I went from a 250 B&M overdriven at 85%. Ran 7lbs of boost. Then went to a 420, running 6lbs of boost, underdriven at 7%.Planing and low speed, it does feel like I may have lost a little bit of torque down low. But, I definitely picked up a ton of power up top. Boat gained a solid 5-6mph running less boost, and still not totally dialed in.Which brings me to my next area of thoughts.Lets compare two setups, I'll use mine for a example.I ran 7lbs of boost with a 250, highly overdriven. No detonation, pump gas 93.Now, most generically would say, 7lbs would be the practical limit for pump gas without a intercooler. But how do we really know that? 7psi is just a number, and there are lots of variables. 7lbs from a 177 driven at 100% over, isn't the same as a 10-71 at 10% under, from a power and detonation standpoint. So from what I see, boost pressures aren't always equal. Kind of why with a procharger you can get away with much more boost on the pump. Its simply a cooler charge.My thought process is, by switching to a larger blower, I reduced a lot of heat in the intake charge. So, If I ran 7lbs with lots of heat, 7lbs with less heat shoudnt be a issue. Maybe even 8lbs.Most guys wouldn't hesitate to run 8lbs or more because they have a superchiller. Without any actual temp numbers, we're all just guessing at whats acceptable.In the book I have here, they did a test, with various GMC 8-71 blowers vs the 420 Megablower (2 lobe). While they said the tighter clearanced blowers made a tad more heat, there wasn't much difference between them all temp wise. They all got about 60* hotter going from 8% under to 15% over. Simply proving the faster you spin a roots the hotter things get. Of course compressing air in itself raises the temperatures, but seems that heat generated by the compressor itself is the big factor in the equation. As you "beat up" the air by spinning the rotors faster, the boost PSI on the gauge will read higher, as the air gets heated. But, the air has become less dense, therefore not making any more power. So, putting a smaller pulley on to raise the boost psi say 2psi on a 177 highly overdriven, wont net nearly as much power gain as doing the same with a larger underdriven setup.

what do I look for in used root blowers - Turbo / Supercharger

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