white_fly

This is semi-hypothetical at the moment as I don't actually have my engine yet, but I still think it'd be nice to learn more about the Rotrexs. I know that W2W has done a good job making Rotrexs work on LSx engines. It's been loosely said that the Rotrex has a flat boost curve. I hope this is false because a truly flat boost curve would be producing full boost at idle. I suspect that it is a flatter boost curve than a turbo or centrifugal supercharger, but I'd really like to see a dyno'd boost curve or at least hear something from somebody that actually runs a Rotrex. Speaking of somebody that actually runs a Rotrex, how many Rotrexs are running around out there? I don't know of any, other than W2W'S stuff. Thanks.

As a side, errr, umm end note, I've already searched and I know the basic concept of the rotrex and how they work, I just want to know about actual boost curve and who's running them.

DeltaT

iTrader: (5)

They are really too small for the LSx motors. You would have to run duals. That's why you don't see hardly anyone running them. With a single, you might not get more than 5-6psi max.

Jim

70Stang

iTrader: (2)

We were very interested in building a kit for the FBodies using twin Rotrex superchargers.

After talking to W2W at PRI this year, it seemed as if they just didn't have enough CFM to really make big numbers on an FBody, not to mention the difficulty of packaging and twin supercharger setup on one.

We are still interested in the idea and have heard the Rotrex is going to be coming out with a larger supercharger unit for bigger cube motors.


White_Fly - PM me or ask back here if you have any other questions...Hopefully I or the guys at W2W can help out...I know they have a ton of real world info on these blowers .

white_fly

I guess I figured twin Rotrex would be assumed. The Rotrex was conceived in Europe where small displacement rules the day so even the biggest are small compared to us 'Murricans big centrifugal blowers, but I cannot tolerate the boost characteristics and noise of the centrifugal blower or the heat and height of a roots blower, not to mention how difficult it is to intercool. Also, they've got to be doing something right to attract a manufacturer like Koenigsegg to their product. So basically nobody is running Rotrex on the street and so we don't know the boost curve?

andereck

Maps are available on their website. I don't see how their "boost curve" is really any different from other centrifugal blowers, which it is. Their claim to fame is silence.

white_fly

None of the dyno charts on the W2W website that I can find show measured boost. However, the torque curve would seem to indicate a much flatter boost curve than a centrifugal supercharger with close to full boost on the low end, peaking in the middle and falling off a little at high rpms.

DeltaT

iTrader: (5)

It's still a centrifugal blower with its characteristics and limitations. The drive mechanism is different but cannot change the overall performance envelope of a non-positive displacement blower. I believe the early Paxton blowers used the same ball & friction drive.

Jim

white_fly

The drive mechanism can absolutely change the performance envelope. If you think about it, the main difference between a centrifugal supercharger and a turbocharger is the drive mechanism.

The Rotrex is apparently designed to operate at roughly double the impeller rpm of a traditional centrifugal 'charger which allows it to use a much more efficient impeller design similar to that found in modern turbochargers and so at the very least it will operate at higher adiabatic efficiency. However, the only way to know the boost characteristics for sure is to see a real live boost curve measured on a dyno.

DeltaT

iTrader: (5)

OK, so Vortech and Procharger are clueless (I'm inferring here)? If there was a substantive design change they could make, they would. Most of the stuff you are citing is marketing pap.

Jim

white_fly

If you think I'm attacking centrifugal superchargers, you're mistaken. They have their place but I don't want to run one because I want to maximize low end torque.
Now, Bill is comparing centrifugal superchargers to turbos in this quote, but right there is the reason I'd rather not run a centrifugal supercharger.

Also, the Rotrex design is patented which could be a significant reason why Vortech and Procharger don't run it.

DeltaT

iTrader: (5)

My point is a Rotrex does not have a different boost delivery profile than any other centrifugal, no matter what their drive mechanism is. It is still dependent on and linked to engine rpm. Rotrex is not a breakthrough product like a VATN would be in the turbo world. It is simply a small centri.

How about a correctly-sized centri with a small shot of nitrous to add bottom end?

Jim

white_fly

Well, my understanding was that the whole point of the Rotrex design was to make boost faster than a centrifugal, but that's the reason I started this thread. I can find no real boost curve. However, as I stated earlier, the dyno charts I've seen tell me the Rotrex is absolutely making boost low down. Take a look at this dyno chart from active autowerke with a Rotrex on a BMW: http://www.activeautowerke.com/dyno/...99_328i_SC.cfm

Even at 1800rpm, the Rotrex is making significantly more torque than stock. This isn't an exception to the rule either. Poke around the active autowerke or W2W site and you'll see these results are typical. Centrifugal blowers almost always exhibit steadily rising torque curves which is a reflection of boost. I suspect that the flat Rotrex torque curves are also a good reflection of boost. However, I REALLY WANNA SEE PROOF!!

ABeasst

iTrader: (5)

It was my understanding it had a transmission that changed the drive ratio to maintain and create boost lower in the RPM range.

andereck

I think that's an add-on enhancement from another company, Antonov.

andereck

I have to say that the gains in your example are typical of just about any centrifugal in that application and rpm range. I don't see anything from that particular test that are extraordinary. Your run of the mill centrifugal will reproduce that powerband.

I'm still seeing the drive mechanism itself as being its strong suit for 4 and 6 cylinder engines which can make a gear driven blower noisy at low rpm.

white_fly

I don't think so. I'll try to find some evidence to substantiate this, but centrifugally supercharged engines almost always experience torque loss or at least very low gains at low rpms. It seems the Rotrex was making close to peak boost even before 2500rpm. I don't think you'll see that from a regular centrifugal supercharger!

andereck

Well at 2300 its has a 20% gain, at 4300 36% and 5800 52%. The flat torque curve is due to BMW engineers and the M52 design. A 20% gain at 2300 is not peak boost.

427

iTrader: (3)

The Rotrex SC is slightly different than a ATI or Vortech type in that it runs a traction drive with a higher step up ratio(7.5-1 up as high as 12-1). The C38-81 that we run on 6.0 trucks will support 600+hp at a max impeller speed of 90,000RPM (this is a 7.5-1 unit). They come on quicker and have a lower angle boost line than a comparable ATI type unit, and they are quieter by a ton.
I ran a ATI truck kit(P1SC) and our Rotrex truck kit(C38-71) on a 6.0 LS engine to compare. The rotrex had more boost at 2500rpm and the ATI had more boost at 5500rpm, but the boost average over the pulls was the same. At the point the boost crossed on the dyno engine, the Rotrex made 25 more HP with the exact boost on the exact engine on the same day.
There is a two speed drive that is an option, it steps the primary drive up 1.36-1 to give better low speed boost response. This is not the normal drive, but it is very nice on a small engine/big car application. This drive really shines on our 5cyl H3 kit to add some much needed low speed grunt.

Kurt

white_fly

This is what I've been looking for. Would it be possible to see charts for the pulls you are talking about?

427

iTrader: (3)

Our testing was internal, but I can try and find the dyno sheets.

Kurt