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Engine Performance 101: What works, what doesn't, and why






    I hear this all the time: "Well, my car is about 160hp stock, but I've got a K&N airfilter, cold air intake, and a cat-back exhaust, so my car is putting out way more than that. The filter and the intake are good for 20hp each, and the exhaust gives me 35hp, so I figure I've got about 235hp now." Wrong.......so wrong. Usually people like the above mentioned get a rude awakening if they ever have their car run on a dyno. The simple fact is this: Modifications like this usually don't do a whole lot, and the reason is this: The factory that built you car put millions of dollars into the development of it. In most cases, they did a pretty good job (their are exceptions). If they could have changed a couple of little things and gotten an extra 75hp, you can bet your ass they would have. That said, these type of mods have a place in engine performance, but their place is in concert with other, more effective mods, or in situations where just a small amount of gain is desired. From the above modifications alone, with quality parts on a typical engine, an output of say 170hp in the upper range of the engine might be achieved. For those who want signifigantly more than that, other modifications are in order. These include but are not limited to displacement increase, camshaft and powerband changes, NOS, and forced induction. While a detailed discussion of each of these is in the articles following this one, an introduction to them will be given here.
    The thing to remember about horsepower is that it follows a specific curve, defined by this equation: (Torque*RPM)/5252 = HP. From this is is relatively easy to see that increasing the torque for a given RPM will yield higher horsepower, as will increasing the RPM that an engine produces a specific torque. Case in point: A 95' v6 Camero produces 160hp, and 200 lbft of torque. In contrast, a current Formula 1 car only produces 250 lbft of torque, but puts out 900hp. The difference is caused by the fact that the Camero produces maximum torque at 4200rpm, whereas the F1 car produes 250lbft at 19,000rpm. So, performance modifications generally fall into 2 catagories: Those that increase torque and those that increase the RPM that torque occurs at. As far as increasing both RPM and torque, I'll talk about that in a bit. Displacement increase, NOS, and forced induction increase torque by getting more mixture into the cylinders to gain power, whereas camshaft and powerband changes increase the RPM that torque occurs at.  Now with that out of the way, we can move on to the next article, how to choose which is right for you.
 
 



 


Links:

    Bob's Snowmobile Page
        :Big site full of info on T'nT and Blizzard SkiDoo's

    Antique Ski-Doo & Vintage Ski-Doo Restoration Resources

    Tech Report on Power Valve Maintenance
        :Keep those R.A.V.E. valves clean

    Ram Air Article
        :An interesting article on the fable of "ram air"

    Rear Cylinder Siezures
        :A tech article about rear cylinder siezures in PWC twins due to crankshaft torsion (very interesting)

    Polaris Triple FAQ
        :A page that has the skinny on Polaris triples (ie which ones to avoid)

    New Hampshire Snowmobile Association

     Don's Vintage Arctic Cat Site
 
 

©2003 Stephen Phillips, Stib Inc.
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