Thread: SC confused !
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      11-05-2012, 08:34 PM   #295
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Drives: 08 E90 M3, 99 E36 M3 Turbo
Join Date: Feb 2011
Location: Concord, NH

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Originally Posted by Sal@Evolve View Post
Another test of the Rotrex C38-91 vs Vortech V3Si on the same car
Car - BMW E39 M5

You can see again, it's very close. You can clearly see if it was possible to take the Rotrex up another 0.5 PSi with a custom pulley the power and boost are matched.

Both blowers are about the same percentage through their max rpm's.
Rotrex is at 81000 / 90000
Vortec is 46000 / 52000

That's two major platforms now with evidence. If anyone else has proper evidence like this on the same dyno under controlled conditions (we can show this) comparing Vortech vs Rotrex then please post it up rather than make an assumption.

All of this backs up the comparative compressor maps and shows their theory works quite well but can show a variance depending on the type of engine used.

As you noted above, peak potential CFM on a compressor map does not mean the same power is made on all engines. It may well be that to the 550 rwhp range, the Rotrex and Vortech are pretty similar on the S65, but that does not mean they will necessarily be pretty similar after that. The compressor maps probably are not identical.

AA, for example, gave up on the Rotrex because it could not flow enough on a low compression S65. On the other hand, ESS has run the Vortech to 645 rwhp on a low compression S65.

It may well be that for more efficient stock compression motors making 550 to 600 rwhp, the Rotrex works just as well as the Vortech. We will have to see some dynojet comparisons at some point.

One thing I did not notice from the Rotrex C38-91 dyno comparison to the Vortech is any indication the big Rotrex has any torque advantage over the Vortech. I had been wondering whether the big Rotrex would sacrifice that. But daily drivability cannot be seen on the dyno, which is constant full throttle in one gear. Hopefully, on the road, the Rotrex offers some advantage over the Vortech.