{"id":10981,"date":"2016-02-11T12:06:29","date_gmt":"2016-02-11T20:06:29","guid":{"rendered":"https:\/\/rallyways.com\/?p=10981"},"modified":"2016-02-11T12:10:10","modified_gmt":"2016-02-11T20:10:10","slug":"exhaust-system-advice-beware-straight-pipes-and-diy-exhaust-systems","status":"publish","type":"post","link":"https:\/\/rallyways.com\/10981\/exhaust-system-advice-beware-straight-pipes-and-diy-exhaust-systems\/","title":{"rendered":"Exhaust System Advice \u2013 Beware Straight Pipes and DIY Exhaust Systems"},"content":{"rendered":"

One of the most popular vehicle performance add-ons is an upgraded exhaust system, and with good reason: A correctly designed and tuned exhaust system can add torque and horsepower across a wide RPM range. But, what about an untuned system or a DIY exhaust system? Let’s find out.<\/h3>\n

As stated in the intro, a correctly designed and tuned exhaust system can increase torque and horsepower across a wide range of the power band. While this gain usually isn’t \u201cbig\u201d \u2013 we’re talking about a 2-3% increase \u2013 the modification offers a few benefits:<\/p>\n

    \n
  1. An exhaust upgrade is relatively cheap.<\/strong> If you’ve already done an engine tune and an air intake, an exhaust is your next best ‘bang for the buck’ performance upgrade.<\/li>\n
  2. Exhaust upgrades are essentially risk free.<\/strong> Provided you invest in a quality system, you don’t have to worry about any reliability or performance issues.<\/li>\n
  3. The upgrade is fun to drive.<\/strong> Usually, exhaust systems are pleasing to the ear and make driving that much more enjoyable.<\/li>\n<\/ol>\n

    Unfortunately, there’s quite a bit of misunderstanding about the way an exhaust system works. While a tuned after-market exhaust system will add power, a DIY system or straight pipe will most likely harm performance rather than help it.<\/p>\n

    Scavenging Is The Key To Maximizing Exhaust System Performance<\/h3>\n

    Engine exhaust gases need to maintain a certain minimum and maximum velocity as they travel thru the exhaust system. This is because exhaust gases that are traveling in this speed range facilitate something called scavenging<\/em>.<\/p>\n

    Scavenging occurs in the cylinders of your engine. For a brief moment after the power stroke (but before the intake stroke), both the exhaust and intake valves are open. At this point, scavenging acts like a vacuum pump \u2013 a properly tuned exhaust system will pull<\/em> the exhaust gases out of the cylinder. This ensures that the cylinder is emptied of exhaust and filled with clean air, leading to more efficient (and more powerful) combustion.<\/p>\n

    The problem is, scavenging only occurs when exhaust gases are traveling thru your exhaust system at the right speed. If they’re moving too slowly, there’s no vacuum effect. If they’re traveling too quickly, the timing will be off and scavenging effects will be minimized.<\/p>\n

    \"Factory<\/a><\/p>\n

    Basically, if you want to maximize scavenging \u2013 and engine power \u2013 your exhaust system has to be tuned to your engine.<\/p>\n

    Racing Style Exhausts Are For Race Cars, Not Street Cars<\/h3>\n

    Most people tend to think of an exhaust system as a drain pipe \u2013 the bigger the pipe, the more effective the drain. This is incorrect for two reasons:<\/p>\n

    1. Exhaust is a heated gas.<\/strong> As it travels thru the exhaust manifold, catalytic converter, and muffler, the gas cools. As the gas cools, it becomes more dense. As it becomes more dense, the velocity changes. Therefore, you don’t want the exhaust gases to cool off too quickly OR stay hot for too long.<\/p>\n

    2. Exhaust gas volume changes with RPM.<\/strong> At redline, your engine is producing a lot of hot exhaust gas. At idle, it’s producing very little. As a result, an exhaust system that works well at 5,000RPM is going to be oversized for an engine at idle. Likewise, an exhaust system tuned for 2,000RPM is going to be at least somewhat restrictive at higher RPMs.<\/p>\n

    \"Classic<\/a><\/p>\n

    When a race team gets their hands on a stock vehicle, the first thing they’ll do is replace the factory exhaust with a bigger after-market system that doesn’t have a muffler. They do this because race cars spend most of their time driving around at high RPMs. A large, unrestricted exhaust is a great idea when you’re trying to maximize top end performance. You want an exhaust system that facilitates scavenging when the engine is going as fast as it can.<\/p>\n

    But if you’re driving a vehicle on the street, your average RPM is going to range between 1,500 and 4,500 RPM. Most of the time, your engine is going to be at about 2,000RPM. As a result, your vehicle’s stock exhaust system is sized (and tuned) to facilitate scavenging between 1,500 and 4,500 RPM.<\/p>\n

    …a race car style exhaust system is a bad upgrade for a street vehicle.<\/p><\/blockquote>\n

    Therefore, a race car style exhaust system is a bad upgrade for a street vehicle. Street cars need good performance at stop lights and on highway on-ramps. A straight pipe, for example, can cause exhaust gas velocity to increase. This will likely reduce engine performance below 2,000 or 2,500 RPM, making your vehicle a little slower to launch from a stoplight. Your engine may show more horsepower on a dyno \u2013 and might even finish the quarter mile a little faster \u2013 but it won’t be faster on the street.<\/p>\n

    Street Cars Need Street-Tuned Exhaust Systems (and Mufflers)<\/h3>\n

    To recap:<\/strong><\/p>\n