Over driving the M90

kenewagner

Registered User
Is there a formula for how much HP it takes to overdrive the M90? We all seem to want more boost, that is given but how much HP does it take to overdrive the M90 15% or 20, or even 25%. There is a lot of talk about the MP111 and how you need to spin it faster to get the real goody out of it. What kind of HP does that take? When I started building my SC 5% or if you were a die hard even 10% seem to be norm. Now I see 15% 20 or more from posts I have read. Dave, from all the dyno testing and tuneing you have done do you have an idea how much HP it take everytime you step up 5 more percentage overdrive? I would just like to know.

Ken
 
I dont think it takes much more horsepower to spin the blower faster. If you add an overdrive pulley, it increases the rotation of the blower, producing more boost and power. The amount of horsepower gained from overdriving your blower will negate any small horsepower loss required to spin it faster. I think the safest bet for overdriving a stock M90 would be 10%, although there may have been others that have done more. Best bet is to get you at least a 94-95 blower to start with for upgrades, umless you can afford one of the Magnum Powers setups. Keep in mind though that opening the exhaust up is a must before any overdriving/porting of the intake side. I might not have answered your question but I hope it helps.
 
Ken,

This chart from Magnuson is the only HP consumption data I've ever seen for an M90.

M90power.gif


As you can see, the boost levels and rpms are well below what many people are currently running. I think it's also important to note that the amount of HP consumed vs. boost/rpm is not linear.

David
 
Stock SC eaton 89-93 takes 60hp to spin. I think i saw a dyno proven 100hp for 10% overdriven. Its been so long i dont know if this is 100% accurate.
 
David Neibert said:
Ken,

This chart from Magnuson is the only HP consumption data I've ever seen for an M90.

M90power.gif


As you can see, the boost levels and rpms are well below what many people are currently running. I think it's also important to note that the amount of HP consumed vs. boost/rpm is not linear.

David

So I am really bad at math and formulas. At 5500 engine RPM what is the blower turning with a stock pully on a 89-93 blower? The curve not being linear, would mean overdriving more means using more HP to turn the blower the faster you spin it? How much less HP would one use underdriving a M112? The M112 moves 22% more air so it should move more air than a M90 overdriven 10% even if it was underdriven say 5 or 10%. Can you speculate on that and tell me if my line of thought holds water.

Ken
 
Ken,

With the MPII and MPIII, I was spinning the blower over 21,000 rpms and getting around 18 pounds of boost. Can't really make an apples to apples comparsion with the M90 Magnuson shows on the chart (doesn't even say what generation it is), but I would assume power consumption is well beyond 100 HP and some have speculated it could be as much as 150 HP.

Personally I have a hard time even imagining how the belts could transmit 25 HP, but everything I've read about Super Coupes says the blower on a stock early model SC consumes 65 HP and the HP chart from Magnuson seems to support that. Assuming that info is true, then I guess it's not unreasonable to conclude that at the speeds I was spinning the blower and resulting boost levels, it likely was consuming roughly twice the HP a stock blower would.

I don't know how to calculate the numbers....perhaps Charles Warner could supply you with that info. I also have no idea how much less or more power it would take with at M112 to move an equal amount of air. I would assume that on cars wanting 18-20 pounds of boost the M112 would be more efficent because of it's larger displacement, but I don't really know that.

David
 
David Neibert said:
Ken,

With the MPII and MPIII, I was spinning the blower over 21,000 rpms and getting around 18 pounds of boost. Can't really make an apples to apples comparsion with the M90 Magnuson shows on the chart (doesn't even say what generation it is), but I would assume power consumption is well beyond 100 HP and some have speculated it could be as much as 150 HP.

Personally I have a hard time even imagining how the belts could transmit 25 HP, but everything I've read about Super Coupes says the blower on a stock early model SC consumes 65 HP and the HP chart from Magnuson seems to support that. Assuming that info is true, then I guess it's not unreasonable to conclude that at the speeds I was spinning the blower and resulting boost levels, it likely was consuming roughly twice the HP a stock blower would.

I don't know how to calculate the numbers....perhaps Charles Warner could supply you with that info. I also have no idea how much less or more power it would take with at M112 to move an equal amount of air. I would assume that on cars wanting 18-20 pounds of boost the M112 would be more efficent because of it's larger displacement, but I don't really know that.

David

Do you know what the RPM range for just a stock M90 on a SC is? I am trying to get a base line for myself on how fast to turn a M112 to get , lets say 18 lbs of boost. My assumption is that a slightly underdriven M112 will produce the same boost as an overdriven M90 and use a lot less HP to boot. From the graph it looks like a M112 consumes 10 more HP at the same 10,000 RPM than a M90 because I assume the rotors have more mass to move. I will check with Charles as you suggest and maybe someone else will jump in as well. Thanks for your input.

Ken
 
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