Tom Wilson
December 14, 2009

Examining the data, the supercharger dyno runs that most closely match, 2.8 and 3.6, are compared below:

BlowerPulleyRPMBoostPowerTorqueTemp
2.87.1 x 3.1215,92913.1859692116
3.67.1 x 4.0012,42513.3904721122
Difference-3,504+0.2+45+29+6
2.87.1 x 2.7518,07216.6932787125
3.67.1 x 3.5014,14017.1989822131
Difference-3,872+0.5+57+35+6

Remember the ignition timing was locked at 19 degrees and the air/fuel ratio was manually adjusted to 11.5:1 to reduce the spark and fuel variables. Clearly the larger 3.6 blower didn't have to turn as fast to make the same boost, plus its efficiencies from the straight-cut gears and other tweaks delivered greater boost at less supercharger rpm. And by the way, 18,000 rpm is about as fast as Kenne Bell wants to turn its superchargers, and that's about 6,000 rpm more than suggested by the twin-screw patent-holder, Lysholm in Sweden. But all good hot-rodders dabble in the high-teen blower rpm range for sprint applications such as drag racing.

To put a round number on it, the 3.6-liter blower gets an extra 45 to 55 hp to the flywheel compared to the 2.8 version. Jim Bell's rule of thumb is the 3.6 makes the same power as the 2.8 at 2 pounds less boost. He also says his data on his in-house supercharger dyno and Dynojet chassis dyno indicates the 3.6-liter requires about 75 hp less to drive it than the 2.8 blower at 23 pounds of boost. Such exact numbers are tough to determine, but in any case the 3.6-liter is clearly the better choice for bigger boost levels.

Looking a little closer at the 3.6 supercharger tests we have the following data:
BlowerPulleyRpmBoostPowerTorqueTempDiff
3.67.1 x 4.0012,42513.3904721122--
3.67.1 x 3.5014,14017.1989822131+9
3.67.1 x 3.2515,26019.51,035883137 +6
3.67.1 x 3.0016,52021.51,086952146 +9
3.68.0 x 3.0018,62025.01,1241,032175+29

Here we see an evenly spaced progression as boost increases, until we get to well into the 20-plus-psi boost range where the charge air temperature (the figures listed are obtained at the exit of the charge cooler) starts running away. A partial culprit, Jim Bell figures, is the throttle body. It becomes a restriction over 1,100 hp, proven by 1.7 inches of vacuum at high rpm on the 1,124hp run. Earlier runs showed negligible vacuum at redline. That makes sense, in addition to the blower simply running out of its range when spun over 18,000 rpm.

And what's this 4.2 blower? It's another, larger-yet version of the 3.6 supercharger architecture for '07-'10 Shelbys, '03-'04 Cobras, and '05-'10 Mustang GTs. Longer by 0.61 inches than the 3.6, the 4.2 is otherwise identical with the latest rotor profiles, water-cooling, and seal pressure equalization. Fans with a serious power streak should look for the 4.2 a bit after the 3.6 hits the market.

Belts And Pulleys Maybe one of the more amazing facts about the 3.6-liter supercharger and the big power it supports is just how much Kenne Bell gets out of an 8-rib pulley and belt combination. They made over 1,000 hp with an 8-rib during the test we attended, and in fact, the 10-rib hardware only came out for the final 20-psi pulls.

This is helpful as 8-rib belt selection is plentiful, but 10-rib belts are limited in the variety of available lengths and can be difficult to correctly size to an engine.

In fact, Kenne Bell says its 6-, 8-, or 10-rib drives can be used according to the following boost schedule:
RIBS BOOST
6 8-15 pounds
8 8-26 pounds
10 8-32 pounds
The Price Of Power With its new internals and larger size the new 3.6-liter supercharger and the forthcoming 4.2-liter simply cost more than their 2.8-liter little brothers:
KIT BLACK POLISHED
2.8 $5,999 $6,649
3.6 n/a $6,899
4.2 n/a $7,099

All 3.6 kits are polished, so there is no "standard" black finish available as there is with the 2.8 blowers. Kenne Bell says the company will begin shipping 3.6 kits January 2010.