Superchargers: Centrifugal Vs Positive Displacement Question

[mpeach1976]

Why do some prefer a centrifugal supercharger vs. a positive displacement supercharger? Positive displacement delivers immediate power...where as centrifugal while it is constantly creating boost all the same it will lag if you jump on it. How is one advantageous over the other? I'm leaning toward boosting my car and I'm starting research here.

 

[84Ttop]

where as centrifugal while it is constantly creating boost all the same it will lag if you jump on it..

I tend to disagree with this part of your statement... Proper tuning and pulley ratios play a huge role in having a centrifugal perform properly. I would bet comparable PD blower to comparable Centrifugal blower would yield similar results. Where you start to gain an advantage with the centrifugal is in the effeciancy. Centrifugal compressors are notoriously more efficient at moving air than a positive displacement blower. This means then can move a similar amount of air with out heating that air to the same point as a comparable PD blower. The centrifugal blowers will still make plenty of torque down low and have very linear hp curves, I personally prefer Vortech when it comes to blowers and have used their products without incident for a countless number of years on just about every car I own/ have owned.

Here is the dyno graph from my S550 with a JT trim. Car makes 11lbs of boost and has no other mods with the exception of ID1000 fuel injectors, Boost a Pump and Magnaflow Catback exhaust. The car makes a ton of torque right of the hit and makes power all the way to 7200 rpms. Our first trip out to the track in this car at over 4,000lbs yielded results of 10.98@131 with more on tap for next year.

Compare this to the stock dyno graph:

FWIW, if you look at small tire racing these days you will find nearly every car out there running Nitrous, Turbo or a Centrifugal blower. You don't start to see the screw blowers and Helix blowers until car are making in excess of 3,000 hp where the compressors on a centrifugal simply can't keep up with a screw at the 50+ lbs of boost level. There is something in the works as far as a Promod Centrifugal but that is likely a year or two away to support over 3,000 hp.

 

[SpartaPerformance]

Because most people believe there is a significant difference is power ranges. In actual testing there isn't. On The S-197, S-550 cars I prefer positive displacement because the appearance is much cleaner.

 

[85rkyboby]

Most likely with a PD blower you'll be icing your engine down at the track, unless you run alky/meth, E85, etc. Efficiency is key.

 

[a91what]

I have to disagree. Altho my setup is far from the norm... 8psi pd thru an intercooler I only see 120* Temps at the end of the track And that's over spinning the tiny blower by 40%... Now I use an Eaton m90 for mine because they are cheap and easy to find but are highly inefficient. 40-60% abiadic efficiency. That's heat vs boost created.
Now centrifugal have 80-90% abiadic efficiency.
Newer twin screw designs (pd) make crazy amounts of boost and run in the 70-90% range depending on how hard you spin them. You can easily see 10psi with a R1900 twin screw on a 5.0, that will be under its map range (under spinning) the blower.
Just my .02

 

[85rkyboby]

Sorry should have been more specific. I was referring to my old Weiand 174. If you can run an intercooler then by all means.

 

[mpeach1976]

I spoke to GAS (Galpin Auto Sport) and the best blower for my application ('14 mustang GT) is a PD supercharger adding 140 BHP and with 15% loss at the flywheel would yield about 475-500 to the wheels which I think is still a huge gain. Unfortunately I can only do it within the constraints of California emissions laws and available pump fuel (91 octane). All that said; they recommended whipple, as they are the least to maintain with no maintenance for the first 100k miles... Here's where need help from the community. Which other PD blower would be as low maintenance and be a better performing unit for a coyote mustang?

 

[a91what]

What I'm about to post was pulled off of the Corral. I have been following a build by one of there members for a long time. This info is based off of a lot of effort by one of there members.
This first graph is efficiency at 12psi.

This next graph is the same info but based off of HP potential, this info will change based on CID and other factors it's just nice to see it put plainly.

Of course there are many others to choose from, some twin screw blowers have even better efficiency than these. However the one depicted here are the most common.