supercharger vs turbo

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Turbos are the cover girls of speed, getting nearly all the attention.

There's good reason. Turbo's have gained a reputation for pushing maximum power from 4-stroke snowmobile engines. Gosh, some asphalt drag racers pushing 30 PSI of boost are claiming more than 400 horsepower from their machines!

Traction certainly is an issue with that kind of power if you want to run in the 7-second bracket, as racers have to let off on top-end due to track spin. Normally aspirated big 2-stroke engines are usually more consistent off the line.

Lessons learned on track
But maybe we should more carefully consider superchargers.

Take a look at the top-fuel dragsters and funny cars, they run huge Roots superchargers. Reaction time is critical when you run a ¼-mile in less than 5 seconds. Blowers not only have better reaction times than turbo's, they have better reaction times than a normally aspirated engine because pressure already is built up when the throttle is opened. Also consider that blowers typically create more charge pressure at lower engine speed.

Several top snowmobile drag racers are now experimenting with the Mountain Performance Supercharging kits. Pat Hauck of Hauck Powersports is one, and he claims the throttle response is better than a 2-stroke and puts real fun into a 4-stroke snowmobile. Pat's new favorite project is a Phazer with a Mountain Performance blower kit. For an additional 15 lbs. in weight, the Phazer now puts out 130 hp in an extremely lightweight chassis.

Since superchargers are driven directly by the engine, some of the engine's horsepower is used to power the blower. Turbos, on the other hand, use the energy available in the exhaust to power the blower. If you have an 8,000-horse top-fuel dragster, you don't care if it takes a couple hundred horses to run the blower, because without it you may lose 6,000 hp.

So how much power does a modern centrifugal supercharger for a snowmobile soak up?

Mountain Performance has tested both turbos and blowers, and the tests have shown the blower to absorb 10 more hp than the turbo between outputs of 200 to 300 hp. On a 1000cc Yamaha engine, even turbos lose some power, as the pistons have to pump against boost pressure in the exhaust. So the difference is not as large as it may seem at first.

For those looking for more trail power, the horsepower drain is small enough to be a non-issue, but mid-range torque and throttle response is claimed to be better than on a normally aspirated 2-stroke.

Technically speaking
The superchargers used by Mountain Performance are not Roots blowers but have the same compressor as used on the supply side of a turbocharger. Roots blowers have bigger friction losses from seals as rpm increases, while the small centrifugal blowers do not use seals and are more efficient when spinning at high rpm.

For this small blower to work efficiently, it has to spin at 150,000 rpm. To accomplish this, the blower is coupled to a planetary gear-up ratio with a 12.7:1 gearbox, and the drive from the engine via the cog belt is gearing it up another 1.2:1 from engine speed. The blower gearbox has its own self-contained oiling system with filter and tank.

There also are advantages to the supercharger installation.

First, there aren't any hot exhaust gases to worry about and you can use the stock exhaust if you want. But Mountain Performance also offers a freer flowing system. Heat is transferred from the hot turbo housing to the blower side on a turbocharger, so the charge air is usually hotter with a turbo. Air increases in temperature as it is compressed, and both systems use an intercooler, but turbocharged air generally is 15-20° hotter when it enters the engine than it is with a supercharger system.

With no exhaust heat under the hood, burning up plastic panels is a non-issue, as are the potential fire hazards that go with a hot turbo under the hood. Mountain Performance offers several blower sizes and drive ratios depending on the engine kit and boost requirements.

At the trail performance level, Mountain Performance offers a 130-horse kit for the Phazer, operating with 11 PSI of boost. A Yamaha Vector kit claims an output of 210 hp at 10 PSI of boost, while the output of an Apex at 10 PSI is 240 hp.

Mac Randolph of Mountain Performance says the numbers are probably 10 hp on the conservative side. There also are higher boosts available for racing, but these require special parts, as do the higher horsepower turbo kits. An Apex with 18 PSI boost delivers 350 hp, for instance. With this kit you need to beef up the engine with special Crower rods, a lower compression forged piston and stronger head studs.

Installation
Installing a Mountain Performance Supercharger kit is fairly straightforward. The blower is driven off the engine by a pulley mounted directly to the crankshaft through an already existing hole in the side cover. No extra holes are needed, only 2 rivets for mounting brackets. All brackets are of billet design and use already existing mounting holes on the engine or chassis. The charge air tube is of mandrel bent aluminum and is less than 12 inches long.

All connections are made with silicone hose and stainless steel tee clamps. To make room for the blower drive, a new oil tank is supplied. The tank mounts in exactly the same location and all connections remain stock, including all hoses, dipstick and low-oil warning systems.

With higher horsepower, the fuel injection system has to be modified to deliver more fuel.

Mountain Performance's Randolph has a technical advantage over many in this area since he is an electrical engineer by profession. He worked closely with Mark Dobeck - who has been designing EFI control boxes for years. The internal electrical boards on the EFI tuners are substantially redesigned from the base units to fit the requirements of the supercharger kit. No rewiring is required; all electrical connections are made to plug into or bolt onto the sled's original wiring system.

To deliver the additional fuel, a larger pump from a Ford car is used. It's not necessary to use larger than stock injectors on boost pressure of less than 14 PSI.

Mountain Performance also uses an electronically controlled pressure regulator that can increase rail pressure from 42 to 55 PSI to increase fuel delivery. The kit includes a new Odyssey Gel cell battery that weighs less than the original unit, but offers the same performance with a 2-year warranty.

Mountain Performance's kit is well engineered, and after 2 years of being field-tested, it has shown good reliability. Great throttle response, better low-end torque and no heat-related issues are all advantages that should appeal to snowmobile hot rodders. We will be interested in the feedback as more of these units hit the snow.

Turbo or supercharger?
So which system is better, turbocharged or supercharged?

Turbos may give higher max power, but superchargers could be the answer for all-around flexibility on the trail with improved torque and better throttle response.

For those who want both, someone may eventually combine the systems - this is already being done with large diesel ship engines. With some ship engine diesel systems you will find a turbocharger feeding an intercooler that then feeds a supercharger. From the supercharger, the air goes through another intercooler before it finally enters the engine.

This compound system would give you both low-end torque and top-end power, but it is more likely to show up on a diesel truck than on a snowmobile anytime soon.

More info: MPI, Utah, www.mountainperformance.com, 888-649-4609, within Utah 801-619-1569

Olav Aaen is a long-time contributor to the snowmobile industry. As a mechanical engineer and president of Aaen Performance, Olav has been heavily involved with snowmobile performance since 1968. Aaen Performance is best known for pioneering performance pipes and introducing the roller clutch to the snowmobile market.