the selection is widely open to speculation and there are many facts, opinions, and exceptions. there are two basic kinds of intakes short ram and cool air. 4-1 is the best exhaust arrangement for this effect, but n/a also has 4-2-1 which will open the exhaust further out, but will not do what i described above. the longer the runners, the higher in the band that you will produce power. basically, what you are looking at doing is allowing the motor to exhale more easily and causing exhaust pulses to reach the collector at the same time that another pulse is expelled so that one spent exhaust pulse pulls the next one out at a certain power band. this concept is covered in the n/a post, but i will go ahead and cover the basics of it. you want a header that will open up the exhaust and have equal length runners. Header selection is pretty much the same for either turbo or n/a. i will go further into turbo exhaust mods later. with turbo, the hot-side holds all of the back-pressure that you will need, so you can use the same size exhaust that is coming off of the outlet (i.e., some turbos have a 3" outlet, you can continue that through the entire exhaust). the N/A theory post goes further into naturally aspirated exhaust selection. the exhaust needs a certain amount of restriction to operate since it uses exhaust pulses to pull more exhaust out of the engine, therein reducing the amount of energy the engine uses to expel exhaust. These will be your biggest bolt-on gains whether you are forced induction or naturally aspirated.įor natural aspiration, you will want to get an exhaust that will reduce the back-pressure, but not too much. you also need to remember that the higher you get into hp, the less street driving abilities you will have. that is a really ambitious goal and will cost a lot of money and tuning to do, but is possible. i, personally, have seen 1 car that has put down 400 whp with a gt35. some people have tried gt30's and gt35's, but these are very large for this motor and there are not definite whp numbers. a common upgrade for these is a gt28, which will support the motor over 220 whp. remember, the harder you push a small turbo, the more problems you will have with it. a gt25 will spool quickly, but won't put down a ridiculous amount of power. the mazdaspeed protege uses a gt25, so that is usually a good place to start. a smaller turbo is going to lag less, but run out of steam in high rpm's. a larger turbo is going to lag more, but put down more power. Your turbo selection depends on your power goals and uses for your car. i will go into turbo selection briefly since all of the bolt-ons are basically the same after that. forced induction will be covered to it's full extent here. I have covered natural aspiration in great depth with info from a member from another forum, thread titled "N/A theory" ( ) but i will go over the basics with you here. with natural aspiration, it would easily cost you the value of the car to come anywhere near that and odds are that you would never even reach double the wheel horsepower. you can argue that a turbo kit is expensive, but with most cars, you can double the wheel horse power with just 7-10 psi and the right supporting mods. in all honesty, naturally aspirated is way more expensive power for power, but much more unique. this will be divided into bolt-on, top-end, and bottom-end.įirst things first, you need to choose whether you are going naturally aspirated or forced induction. i will cover the naturally aspirated and forced induction options here and go into the options of internal modifications (pistons, rods, oil systems, ect.). these topics have been covered enough times here to require a post to outline them. This is a frequently asked question post about modifying your protege.
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