Jim,
That kinda builds on what I was going to say to/ ask Z about.

Yes CFM is confusing. Lets be sure to talk about inlet flow of CFM, not outlet flow to lessen the confusion. It seems that inlet flow is an absolute measure of the # of molecules of air flowing into a supercharger given the ambient temp remains constant. If air were flowing back out as mentioned in the above posts then that would displace air flowing in and the inlet cfm flow would still be as measured.
The Air fuel ratio is actually the # of oxygen units (molecules) in relation to the number of fuel units. Not cfm in relation to fuel, specially not in a SCed engine.

Inlet flow then should be a good measure of the ammount of power made. (but not necessiarily the power the engine outputs because of drive power loss and a few other factors)

However since a centrifugal blower has a higher level of thermal efficency, the same inlet CFM will have a lower density exiting the blower than it would with a roots blower. That means for example if both blowers inlet 1000 CFM then they would produce the same ammount of power.(again not output) But the centrifugal blower will be measured as having lower boost because of the lower density of air molecules than with the roots. So as Z has said boost is not a good measure of ability to make HP. The roots has to work against higher boost levels to make the same power. Making it the roots, sometimes, less efficient. The roots may not make the max power the centrifugal blower will make.
The roots will inlet more CFM at lower rpms than the centrifugal will. This means power comes quicker and is spread over the power band. If we took the power # from 100 points spread evenly on the power curve of each and added them up I think (don't know for sure) that the roots would come up with a higher figure overall.

Power down low is important in cars that have very high gears and are by the large majority automatics. It will make our cars faster and more driveable for the style of driving in the US.
Andy K

 

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by Jim Nowak:
<strong>If both cars were running the same boost, the centrifugal blower at some point would equal or exceed the power of the Eaton. The dyno charts do not reflect the same boost levels. Power and torque are both down by 20 with the centrifugal indicating a difference in boost. I do not think this is a good comparison.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">It would probably help if both charts were from the same kind of dyno, instead of one being from a Dyno Dynamics and the other from a DynoJet. If you've ever seen a chart from a Mustang dyno compared to one of the same car on a DynoJet, you're well aware that there are substantial differences.

In my opinion the Eaton is definitely the way to go on a small displacement, low torque engine like that of a normally aspirated 944. Depending on which of the two dyno charts you go by, with the superchargers installed the maximum torque is between 225ft/lbs and 250ft/lbs. I've never driven a normally aspirated 944, but I'd guess they probably wouldn't be much fun off the line, and can use all the help they can get down there. If you look at Tim's chart with the centrifugal supercharger, at about 2,200 RPM he's already making about the same torque as a Z06 Corvette. At some point you're going to find out that any more low end torque is only going to be good for making even greater amounts of tire smoke.

The only time you'd have that extra low end torque anyway would be at the very bottom of first gear, where all it would be good for is wheelspin. Once you go through first gear, when the car shifts to second the engine RPMs never drop that far down again. The same goes for when shifting to every other higher gear after that. The only way it would be of any benefit in any other gear would be if you were lugging the engine in a gear, instead of downshifting to the proper gear, when accelerating. With an automatic transmission, when you accelerate the car downshifts, so you couldn't even lug the engine like that. Off the line with the automatic transmission the RPMs jump right to the torque converter lockup point, so there's no advantage below that RPM point either. If the engine in that automatic transmission car had the same torque curve as Tim's, the instant you'd floor the gas pedal off the line the RPMs would jump to about 2,200, you'd have at least Z06 torque, and lots of wheelspin.

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva"><strong>However since a centrifugal blower has a higher level of thermal efficency, the same inlet CFM will have a lower density exiting the blower than it would with a roots blower.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Nope. The centrifugal will have a higher density of air exiting the supercharger because of the lower temperature of that air that's exiting.

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva"><strong>That means for example if both blowers inlet 1000 CFM then they would produce the same ammount of power.(again not output).</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">There are other things that could come into play which would change the difference in power out put even if the inlets were both flowing that 1,000 CFM. Depending on the exact application, that could be a considerable factor.

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva"><strong>But the centrifugal blower will be measured as having lower boost because of the lower density of air molecules than with the roots
</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">If the inlet flows were both the same 1,000 CFM, the centrifugal would be showing a lower boost, but would have a higher density of air molecules than with the roots. There would be the same number of air molecules coming out of both superchargers, since the same number were going into both of them, and they can't disappear anywhere. The molecules coming out of the centrifugal will be packed closer together (denser), and cooler, which will show a lower pressure on the boost gauge. With the roots, those same number of molecules will be further away from each other (less dense), hotter, and show a higher boost reading.

I hope you guys know what you're doing. In that dyno chart of the roots supercharged 944, that flat torque curve starts to take a dive at 6,000 RPM. If that's the supercharger running out of capacity at that point on a four cylinder 944 engine, I sure hope the setup that's going on an eight cylinder 928 engine is capable of flowing a lot more.

 

Z,
Oops, sorry to make you go though that reply when we were basically making the same point. I did mean to say higher density when I said lower density. I was thinking lower exit volume and lower boost though so that is where the lower came from.

I really only got into cars about a year ago. I don't profess to know much. I'll have to argue with you on the automatic transmission though. The scenario that you describe with the automatic seems sound but only durring something like a 1/4 mile run. If you are driving at speeds varrying from say 40 to 90 mph (normal driving) things change. My S4 is my second 928, previously I had an 86.5. Both were autos. Both had the kickdown by-bass. Neither shift down as quickly as you describe on their own. This is especially true from 2nd to 1st. Even with the manual kickdown by-pass neither car would shift into first unless the car is below about 20mph. So the low rpm range in second gear could really use that extra power. Not being able to get into first and not having the power in second at that point is the only thing about my car that I really hate. I would have to say that the low end power is extermely important for the automatics.
Andy K

 

I have seen 2 references to information off of the Eaton website. All the information there is on the old 3rd generation blowers. If any one would like up to date info on current products they should look on the <a href="http://www.magnusonproducts.com/" target="_blank">Magnuson Products site.</a> Magnuson markets and distributes Eaton blowers in the us.
Andy K

 

I think the whole point with the two blowers is this:

Roots blower: fatter torque curve means you can shift (pretty much) anywhere and have power. The thing dies off at high RPM, but that doesn't matter, since you can shift and have power.

Centrifical blower: more power on top, but power is "peaky", so you have to know when to shift and when to not shift to optimize the power you get out of it.

I'm not a supercharger guy by anymeans, but this is the knowledge I think I have pretty squared away.

So, I would summarize that the more novice driver or street driver would want a roots blower. A track guy with experience would want a centrifical blower.

 

The HR Stage II 944 S2 kit runs 5-6 PSI of boost max. The Speedforce kit did indeed run 5 PSI. The reason your numbers don't work is that much of the top end power with our kit came from the intake manifold and EFI work.

 

With the bowden cable adjusted the way it is, my automatic S4 will readily downshift a gear if the throttle is quickly moved to anything above about half way. As you stated, the shift from second to first doesn't occur above 20 mph though. My thinking is that Porsche did that purposly for safety reasons, because of traction loss from a downshift to first while in a turn. Flooring it with the shifter in "D" when at just above 20 mph would be a worst case situation as far as power goes. Any time that you're at full throttle, the RPMs will shoot to at least the point of torque converter lockup, which is around 2,000 RPM. As I said above, at about that point Tim's car is already making the torque of a Z06 Corvette. That's the worst case situation with the automatic. If you can keep the tires from spinning there anyway, the roots might have an advantage there. If someone could figure out how to get the automatics to downshift to first above 20 mph, there would be no advantage by the roots there either.

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by Huntley Racing:
<strong>The HR Stage II 944 S2 kit runs 5-6 PSI of boost max. The Speedforce kit did indeed run 5 PSI. The reason your numbers don't work is that much of the top end power with our kit came from the intake manifold and EFI work.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">So even if the two charts were done on comprable dynos, it would be a comparison of a stock 944 with a centrifugal to a 944 with a roots, a different intake manifold, and EFI work to get more top end out of it?

 

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva"> The HR Stage II 944 S2 kit runs 5-6 PSI of boost max. The Speedforce kit did indeed run 5 PSI. The reason your numbers don't work is that much of the top end power with our kit came from the intake manifold and EFI work. </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Oh, the formula works perfectly; however, it is dependent on equal factors. No offense, but you did not let us know you had made changes to the manifold and the EFI system. You post basically made it sound as if you bolt-up an Eaton it will make more power than a centrifugal at the same boost levels.

I like the Eaton blowers and I feel they are the way to go for the vast majority of street applications but your previous post was misleading IMHO.

 

Sorry for any confusion but this thread is 'Huntley High Flow Intake???' so I thought everyone here was aware that ALL of our SC kits have custom made intakes. What I should have made more clear was that all of our SC kits also come with powerful electronics which remap the entire fuel and ignition curves and convert the cars from Air Flow Meters and Mass Air Flow sensors to Manifold Absolute Pressure sensors which have zero induction restriction. The intakes and the EFI are why our kits don't fall off the power as the RPMs go up with the Eaton. Sorry for the mix up.

P.S. Here is a link to what our production 944 SC intakes look like.

<a href="http://www.huntleyracing.com/superchargerkitpics/images/hr_sc5/4.jpg" target="_blank">http://www.huntleyracing.com/superchargerkitpics/images/hr_sc5/4.jpg</a>

 

Z,
I agree </font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">If someone could figure out how to get the automatics to downshift to first above 20 mph, there would be no advantage by the roots there either.
</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">. I may not even be looking into making more power if there were a fix for this.

Andy K.

 

and no-one ever heard from "dr wolfgang" ever again .... Interesting read.

 

Jiminy Christmas, it must be Lag.

 

The Dr is not another Rennlister under a false name.

 

It was too Lag-like not to make the comment.

 

Hmmm. And why are we so sure... ?