Re: Gas hop up

Posted by Adam B. on January 31, 2004 at 02:08:42 from (199.35.113.128):

In Reply to: Gas hop up posted by Pumpkin Head on January 30, 2004 at 12:45:11:

I'm in the same situation, trying to think of forced induction solutions for the old tractor I'm working on. Not for competition, or because I need more power, its just part of the fun of tinkering with it.

So, I've been looking at what's available and trying to read up on how they work, what they do and which is better.

The first thing to simplify things is to consider that a turbo is a specialized type of supercharger. There are other types of superchargers, based on their design. Also, most setups for a supercharger or turbo (even mild) will boast at least a 40-50% power boost. You probably already know these devices force more air into the cylinders, providing more fuel/air mix to burn, and more power results. That extra volume of air also means you're effectively raising the compression ratio. So, if you have extra-high compression pistons, you probably shouldn't go this route. In fact, for really high-boost (racing application) superchargers/turbos, the engines are built with special low-compression pistons. If you're stock, you can work with a mild setup and make some power.

A supercharger is a compressor run by a belt drive. A turbo is a compressor coupled to a turbine that captures energy from the engine exhaust (like a windmill). For those reasons, a supercharger is easier to install than a turbo. A turbo will require a special exhaust manifold it can attach to, and will need to be supplied with oil from the engine. The turbo will spin at extremely high speeds and will need the oil to be a fluid bearing. It will get very hot, and can break down the oil, so you should have an oil cooler and maybe an extra oil filter. The tuner articles I've read also indicate a turbo system can be very difficult to tune, because the boost comes in bursts. When idling, the turbine reaches a sort of lazy speed. Crack the throttle, and there's a delay while the turbo catches up. That choppy characteristic makes it more challenging to tune-up your engine. However, once you have it installed and running, there's not much for you to do other than keeping your engine oil changed, air filter clean and allow the engine/turbo to cool a little after you've worked it.

The roots and whipple superchargers get mounted on your engine. These are the kinds you see on street rods and drag cars, sticking up out of the hood with big carbs and a scoop perched on top. They have a similar design, with close-tolerance lobes or screws that spin quickly and push air into the engine. The air gets packed into the cylinders. When you compress a gas, it warms up. When a gas gets warmer, it expands. That heated and expanding air kind of defeats the purpose (hot air isn't as dense, so there's actually less air in the same volume of space compared to cold air). You'll hear about intercoolers and aftercoolers. They're devices used on pressure-charged engines (super and turbo charged) to combat that problem. The roots-type is said to be great at low-end (right off idle) power building, and fall off some at high rpm's. The whipple is a newer design that is supposed to create a bit less heat and have less power dropoff at higher rpms.

The other type is the centrifugal supercharger. These are compared to a turbo with the exhaust-side turbine removed. They mount to your engine like an accessory, same as your car's alternator. The benefit of this type is that all the compression is done right in the housing, then compressed air exits and goes into the engine. As a result, the heat build-up is greatly reduced. This type is described as a good full-range boost, but isn't as powerful on the low-rpm side as the roots/whipple type, and isn't as powerful on the high-rpm side as a turbo.

The cost is about the same for supercharger or turbo units, but the turbo may run more, since you'll have to possibly custom fabricate a manifold. I'm leaning toward a centrifugal supercharger for my tractor, or possibly a turbo. (The other styles aren't likely to be available for a tractor engine.) Specifically, I like the setup of the Powerdyne supercharger units. The Powerdyne system doesn't require an oil supply from the engine, because the compressor is self-lubricated. There are several other brands, but they're the only one I've seen that has that feature, which would greatly simplify the installation. Running an oil line, mounting an oil cooler and maybe adding an intercooler/aftercooler shouldn't be very complex, but just add more plumbing. You also have to consider the output of your oil pump, if you look at a turbo or supercharger that needs oil supplied by the engine.

That should be enough general info for you to think about and take to a shop that can help you pick out parts for a custom system.

For all the more power you're thinking of adding though, you should be able to get there with high compression pistons, some head and manifold work, some carb tweaking and a good, high-flow air filter (K&N style). I would think. I have seen a 50 hp John Deere 'B', that's simply running really high compression (without a stroker crank).

Good luck, I know I'm still kicking ideas around my drawing board here as well.

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