How much HP to spin the Eaton

[04 RedFire]

I've got a question I haven't been able to find the answer to yet. How much HP is used to spin the Eaton on our Cobras to 8, 14-16 PSI, and finaly what effect does porting have on that? I tried the search function but nothing came up.

Thanks,
Rob

 

[04 RedFire]

Anybody know where I might find this information?


Thanks,
Rob

 

[Hank]

I'm not positive, but the 2nd graph down might be power required to drive the Eaton M112. I assume this because power added to the engine from the supercharger is much larger than that power axis dictates.

http://www.automotive.eaton.com/product/engine_controls/superchargers/M112.asp

 

[Black2003Cobra]

Yes, that graph indicates the power required to spin the blower. Make note that drive power depends on boost pressure and rpm, so if you're making more boost than shown in the graph, the amount for your case will be even larger.

 

[magstang1]

Wow. did I just read 60hp @ 12k rpm and 10 psi? That seems like quite a bit more than I expected.

 

[Black2003Cobra]

Yup. You read it correctly. This is why the adiabatic efficiency of the blower is such a big deal. For the stock Eaton, AE is only about 40% at 10 psi and 12 krpm. The 2.3L Whipple has an AE of about 60% at 10 psi while flowing the same volume of air. Since the drive power is inversely proportional to AE, that means the drive power for the Whipple would only be about 40 hp for that case. At higher boost levels where you have to spin the stock Eaton much faster, the AE really goes to hell. (Note how the drive power graphs curve upwards at higher blower speeds. That’s because AE drops lower and lower at higher rpm. That’s where the twin-screws really shine.) Of course the drive power at any given rpm goes up with higher boost, too, even if AE was the same. A higher AE will also result in a lower IAT2 at a given boost level, and this will also increase indicated power some (due to the slightly denser air, and perhaps because the computer will not pull as much timing).

But I don’t think porting is going to affect the AE of the blower. It may improve the efficiency of the intercooler, however, since a larger surface area is exposed with the larger port. This would also have the effect of reducing IAT2 and hence improve power for the reasons given above. My feeling is that porting is improving the volumetric efficiency of the blower at high speeds, and that this is why they make more power…because they can flow more air at high rpm. Unfortunately, there is no AE or VE data available for the ported Eatons, however.