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OK, let's go back to what this guy keeps saying, an engine is an air pump, the faster and easier you can get the air in and out, the faster the engine will go, so an exhaust with as little restriction as possible is the key to this. A twin quiet pack will allow the gases out easier than a single, because each silencer only has to handle half as much exhaust as a single, QED.
You must be aware of how an extractor exhaust works, as there are many on offer that are not extractors. To make an exhaust work to help the engine you will require the four pipes to meet together at the same time, that is the four of them must be the same length. Due to the extra length required to get from cylinders 1 and 3 (nearest the front of the car) you need to make number 2 and 4 longer. Look at most performance exhausts and you will see a great winding of metal, this is to make up the extra length required for the back cylinders. These four pipes must then merge into a collector together, this creates a small vacuum in the collector whenever one pulse passes. To put it another way, when number 1 cylinder exhaust passes through the collector it produces a vacuum in the other three pipes, as number 4 is next it will be pulled down the pipe, so helping the piston. The smoother and straighter the pipes are the better this system works, unfortunately this pushes the collector so far out the back it is just not practical for a road car.  
To continue the process of helping the gases escape, you can use a "Stinger" which tapers out for about 18 inches (45cms) and aids this vacuum effect. Of course, using a stinger on the roads is asking for trouble, not only are they loud, but they stick out the back so damn far.
You may want to exchange your heat exchangers for "J" pipes, these are simply a replacement, they do not really aid the exhaust much, but do make the engine lighter. You will have to make some new brackets for the lower tinware if you use these.
Don't expect the following exhausts to help the engine in any way, other than keeping it quiet: Bugpack Universal Exhaust/ JSC Economy Header & Muffler and GT Exhaust Systems, any dual exhaust (used on buggies/Bajas), Monza Performance Exhaust, Zoom Tubes/Zoomie (these are very 1970s). Use your discretion, if it doesn't have a merged collector, it isn't going to help.



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Last modified: February 11, 2007