Here a sadish story about what happens to a 4-speed BTR auto 221 hp factory 1999 XR6 Falcon Ute. It recieved mods that whould have boosted the flywheel power to well over the level of the latest 321 hp BA XR6 Turbo.
This story was in the Aussie Street Machine April 2000, page 118, by BobKotmel, an old racer from way back!
"Called in on a mate, Peter Arthurs, and found him studying the instructions on how to fit an AUS$7000 CAPA centrifugal blower kit to his Falcon XR6 Ute. I reckoned it would be good to get some before and after times and power readings. So the stock XR6 ute rocked up to the track and laid down consistant 15.9's @ 86 mph.
Then it was off to the Muffler Shop in Mackay for a new exhast and a dyno session. Extractors, trick cat and free-flowing mufflers were fitted. On the chasis dyno the plain-Jane sleeper cranked out 120 hp ath the rear whells. The following Friday night it ran a best of 15.6@89 mph. The exhast mods picked up three-tenths and 3 mph.
A couple of months later, lifted the bonnet and checked out the neat blower job. Installer David Hall happened to turn the blower over before it went on and noticed a broken shaft right out of the box. CAPA replaced it with a new one. Good to see some distributors back up their products. With that out oof the way, the time to install the kit was minimal.
At this point the supercharged Falcon was fresh out of the box, untired, and had to be run-in for 100 miles. Unfortunately, it wouldn't idle properly or run right. The EFI board was checked. Three legs on the chip were dirty. Once cleaned the car ran better, but by no means perfectly. During the week the Falcon was lined up for a dyno session at GP's Auto Tech, a local chassis dyno centre that specialises in EFI, turbos and blowers. In the meantime, CAPA was cntacted and immediately sent up another engine management chip. With the new chip the Falcon spun the rollers up to 220 hp at the back wheels, a 100 hp increase.
Next Firday night it was off to the darg strip again. The blown ute avoided the water, howled the street tyres a few times then staged. The light went green, the supercharged Ford took off and stopped the clock at 15.0@95 mph. The driver didn't lift on the first pass, the 95 mph terminal speed was falt out! With a perfect hook up, gearing, convertor, etc, 95 mph theoretically equates to a 13.6 by the Moroso Power Speed Calculator. Next pass the ute ran a slower 15.2@93 mph. Local Ford mechanic, Stuey Fenner, said the under bonnet heat was hurting power."Getting more cold air," he stated, "is one of the best performance mods for any EFI engine." In fact, any engine.
How could a dyno-verified 100 hp increase at the rear wheels produce less than a one second gain at the track?
Centrifugal blowers are like belt driven turbos. The more revs, the greater the boost. At low revs there isn't much more power than stock. But once the engine's up around 5000 rpm there's 9 psi boost and an extra 100 neddies. The centrifugal blower comes on strong right on the top end. Discussing the conundrum with a colleague, he hit the nail on the head when he stated "by the time they wind up, the race is half over".
To get the maximum benefit from a centrfugal blower on an auto, a high stall convertor should be fitted to let the engine get up into the high-boost rev range ASAP. The results should be even more impressive than fitting a high-stall convertor to a naturally aspirated car. By keeping the engine on the fat part of the power curve, you get max boost and max torque. For street, reckon a 2500- 3500 convertor would work best and a 4000-4500 stall convertor for the race track.
Pete recently took the ute on a 370 mile trip. Fuel used was 29 miles per [imperial] gallon [36 US mpg!]. hE'S RAPT IN THE WAY THE falcon goes and doesn't really care if it's not a drag strip terror. He knows the car could run better times with a convertor change but doesn't want to lose functionality. Another postive is the low-stall convertor doesn;t shock the driveline.
A centrifugal blower kit is an easy bolt-on that definitely produces horsepower. To get the best performance from an auto, consider a high-stall convertor from someone like Dominator of TCE. Finally, keep in mind big horspower numbers might win dyno shootouts but don't always maen the fastest car on the track!
:mrgreen: 
