So, you've decided to do some modifications
that are going to give you some real hp gains. Now, how do you choose which
onese to do? Well, this article is devoted to answering that question.
In it, I'll try to discuss the pros and cons of each type of mod for different
types of vehicles. Detailed discussion of each type will be in their respective
Camshaft and powerband changes are extremely effective at making horsepower. Just look at F1 cars: 3 liters, 900hp, unsupercharged, unturbocharged. That's serious power. However, big power can only be achieved through a complete go through of the intake and exhaust systems. They say a chain is only as strong as the weakest link. You have to flow everywhere, from the filter to the tailpipe. If you have a big intake setup and manifold, long duration camshafts, and a free-flowing exhaust hooked up to a restrictive exhaust manifold, you're not going to get anywhere near the performance potential of the system. Then again, with all elements of the system balanced, decent gains can be realized. Case in point: a VW 2.0l 16v engine puts out 134hp stock. By improving intake system airflow, porting both the intake and the exhaust sides of the head, fitting a EuroSport header, and a SuperSprint exhaust, the engine output is increased to 165hp. However, their is a trade off. The higher in the rev range the powerband occurs, the less drivable the car is. In short, the engine becomes peaky, and is very likely to lose power in the lower range, meaning it has to be revved up higher to take off. Also, because the power band will be narrower, it requires more gearshifting to keep the engine in "on the boil" than it would normally. You can go a long way with powerband changes, but for street driving, particularly with smaller engines, these modifications work better for smaller power increases. If you want larger increases, you can get a lot of money into this type of mod and end up with a engine suited only for the track.
The use of Nitrous Oxide as a power booster began around WWII, when manufacturers were looking for a way to boost the takeoff power of aircraft without signifigantly increasing weight. Hot-rodders picked up on this fact soon after the war, and we've had the use of the stuff ever since. And, properly used in the correct situations, NOS is perfectly safe for your engine and is a good idea for cheap power. If you have an engine that is a pain to install any type of forced induction , and you want a boost once in awhile to beat some asshole off a light, NOS is perfect for you. Alot of late model v6 cars don't have much room for a supercharger, and putting a turbocharger on most of them is out of the question too, so NOS is a good choice for them. It's also cheap to install and it does deliever the goods. However, it does have its drawbacks. If you use it much, or have a higher horsepower boost (>50hp on a v6), you end up having have the bottle refilled a lot. If you happen to live next to a specialty gas supply, then you can by the stuff at wholesale charges and you're all set. But if you don't, and you have to travel 2h to get to a speed shop so they can scalp you on your fill up, NOS can get expensive real fast. The key to having NOS is having the self control not to nail it off of every light.
Forced induction also has roots in aircraft engine design, but it was first utilized, albiet unreliably, in Grand Prix racing soon after the development of the racing automobile. The idea itself is simple: Normally aspirated engines have only atmospheric pressure (1 atm) to force air into the cylinders during the intake stroke. In a forced induction engine, air is shoved into the cylinders by some sort of pressure producing device, such as a mechanical blower, at pressures exceeding 1atm.. This allows more fuel to be burned in the cylinder, yeilding more torque. And, as we all know, more torque across the rev range equals more power. The setup has it's drawbacks though. Higher intake pressures mean higher peak compression pressures, so engines with forced induction are more prone to detonation. Thus, their compression ratios are generally lower. Also, the forced induction system, whether it is a supercharger or a turbocharger, adds mechanical complexity to the engine, and it can sometimes be difficult to find room for the extra components. But, if you want continous power, a lot of it, good drivabilty, and your vehicle is set up in such a way that it can be installed, forced induction is certainly a good way to go, particularly for smaller engines.
Displacement increases are another proven method for increasing torque and thus hoserpower. However, the modification is very dependent on the particular engine you have. Some engines share cranks that can be swapped, or cylinder and piston sets from a bigger engine that can be installed to increase displacement. However, most engines need to be bored and/or have a stroker crank installed. Because of the expertise involving such operations, I'm going to leave this section out of this guide for now, because most DIY tuners won't be performing this mod.
:Big site full of info on T'nT and Blizzard SkiDoo's
Antique Ski-Doo & Vintage Ski-Doo Restoration Resources
Report on Power Valve Maintenance
:Keep those R.A.V.E. valves clean
:An interesting article on the fable of "ram air"
:A tech article about rear cylinder siezures in PWC twins due to crankshaft torsion (very interesting)
:A page that has the skinny on Polaris triples (ie which ones to avoid)
New Hampshire Snowmobile Association
Vintage Arctic Cat Site
Phillips, Stib Inc.
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