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Increasing Horsepower/Torque/MPG



  • zaken1zaken1 Posts: 556
    The basic thing which determines the horsepower of a given size engine is how much air/fuel mixture can flow into and out of it. This is called volumetric efficiency. It can be changed in many ways; by increasing the compression ratio; by enlarging the size of valves and ports; by enlarging the intake and exhaust system or improving their flow rate, and by increasing the distance the valves open or the length of time they stay open (with a performance camshaft). There is an advantage and a disadvantage for each of those changes.

    Just increasing the compression ratio will improve power; but it also will require the use of higher octane fuel. And many performance engines already require the highest octane fuel that is available. So if you increase the compression ratio on an engine that already requires high octane fuel; the engine will begin pinging and knocking. If it is not retuned by retarding the igntion timing; such an engine will soon self destruct. But if you retard the ignition timing; the power will drop back to less than what it was before the compression ratio was increased. So this is an example of why some types of modifications are just not possible on certain engines. And many owners who build up their motors soon become tired of paying higher prices for premium fuel; just to get an an occasional blast of power.

    Installing a bigger exhaust system, or a bigger intake system, or a bigger cam; or enlarging port sizes will all produce power increases at high engine speeds; but they will also REDUCE power and economy at low and medium engine speeds. And in addition; they will increase pollution. There is no free lunch in the power increasing world; every gain comes with a corresponding trade off. And this is something that all too many enthusiasts don't discover until after they have spent months or years of hard earned money and many hours of labor modifying a previously well balanced motor to make more power; only to discover that it has been transformed into a rough running, noisy, thirsty beast; which needs constant attention, can't be smoothed out, and frequently won't pass smog inspections.

    Car manufacturers use sophisticated computer programs to design engines so that all the systems work together harmoniously. They certainly know how they could make their engines more powerful; but they also know what the downsides would be. And when you're designing an engine for a car that is not going to be raced; and in which smoothness, reliability, and great fuel economy are most important; the best way to achieve those goals is to not tune it radically. Other manufacturers try to build engines which have a little less smoothness and economy, but produce somewhat more power. And yet other companies build the most powerful motors they legally are allowed to sell. That's why engines of the same displacement are made with very different power ratings.

    My brother in law, who was a physicist, decided to buy a new Chevelle in 1966. He had the mistaken idea that the most powerful engines had the best quality. So he ordered his new Chevelle with the most powerful 396 cid big block engine that was available. And he soon came to hate the rough running, thirsty motor. Eventually, he had the motor taken out and replaced with a low output small block 283. And he was much happier with that motor (despite the fact that he had ruined the resale value of his Chevelle SS 396).
  • Hey Zaken1,

    I just bought a 2008 F350 6.4L Diesel/Turbo with 73,000 miles on it for my Landscaping company.... I'm trying to figure out what the smart decision would be to increase my MPG. Everyone keeps telling me there are chips that come with computers that I should buy, but I'm not so sure that I want to mess with them after reading some of these forums. You seemed to be very wise and intelligent with cars and I wanted to ask someone like that about them. Are there some chips and programs I should go with and a lot that I shouldn't or a combination I should do or what? I get 12.3 mpg now but would like it as high as possible....

    I've been told by a number of people it would increase my turbo a lot which will help reduce engine use/help fuel efficiency, but I don't want to ruin the turbo and waste money on another when this one is perfectly fine. Your help would be tremendously appreciated, I'm a rookie with these Super Trucks coming from a 99' Silverado....
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