so.....
10-08-01, 12:01 PM
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so.....
So it goes Turbo,pre-cat,cat,cat-back exust? So if i wanted to put in a downpipe and a hi-flow cat , the downpipe would replace the pre-cat, and the hi-flow replace the main cat. Now what does a mid-pipe do (replace the pre cat and the main cat all in one?) If you had a midpipe is there such thing as putting on a 'dummy' cat when going thru emmisions? And the last question whats the best HKS exust thats not expansive? I know of the titanium one but thats 1200$. and thats too much. And i dont want the N1 either.
10-08-01, 01:15 PM
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Downpipe replaces precat..Midpipe replaces main cat....A combination of all three make up total system. Down to mid, mid to catback....Need new ECU map for a mid-pipe..
10-09-01, 07:02 AM
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okay...
there are 3 main sections to the exhaust on a rx-7. pre catalytic converter, main catalytic converter, and cat-back (aka muffler)
the first is like headers on a regular car... stock the car comes with a precat, it's like a mini catalytic converter used to control emissions during start ups. Supposedly because it is smaller and closer to the exhaust outlet/engine, it heats up faster and works before the main cat. however, when once the main cat is warmed up, the precat is useless. The only function it servers after the car is warmed up is providing excessive heat in the engine bay. it also gets clogged from time to time causing damage and is felt as a loss of power. most people replace this with a downpipe, basically a straight pipe from the turbo manifold to the catalytic converter. This helps lower under hood temps, reduces the chance of precat failure, increases exhaust airflow providing better turbo spool and higher horsepower, and reduces weight(stock precat weights a little over 22 lb as opposed to the 11 lb downpipe i installed or so says my bathroom scale). With just a downpipe, there should not be a need for computer of fuel upgrades. Expect about 10-15 hp
the second part of the exhaust system is the main catalytic converter. this, like most other catalytic converters, is used to eliminates harmful pollutants. (hehe) here¡¦s a better description to what it does. http://www.waterloomotors.com/faq.htm#cat%20converter What some people do is change this out with either a high flow cat, which does exactly what the name implies, flow exhaust gasses faster while retaining emission standards; or change the catalytic converter out with a midpipe, which is basically a straight through 3¡¨ pipe with no catalyst material. Both of these, like the downpipe, reduce back pressure allowing the turbos to be more efficient, providing the engine with higher boost and thus more horse power is realized. With either of these, computer/fuel improvements as well as boost control should be taken into account. This is usually not recommended as a first modification. Taken from others, the high flow cat will offer a bigger improvement in power in the midrange rpm, while the midpipe will dramatically improve the top end power. Expect about 10-20 hp
The third and final part of the exhaust system is the muffler section or cat back. This is used to expel exhaust gasses rear of the rear axle, as required by law, as well as reduce exhaust noise to a minimal. The cat-back portion does not offer any reduction of pollutants. The stock cat back system is comprised of a very efficient muffler in terms of noise, but extremely poor in terms of performance as compared to straight through designs. I¡¦m guess the stock muffler is glass packed like many oem mufflers, but i have yet to cut mines open, after all it¡¦s all i¡¦ve got right now. As for aftermarket versions of the muffler, there are basically two designs. The first which is comprised of a series of baffles and chambers which allow exhaust gasses to cool inside the muffler before they are released into the environment, thus quieting the exhaust noise. (after all, that is what exhaust noise is, is the rapid cooling of a hot gas) This type of muffling is less efficient in terms of noise, but better in terms of performance over the stock. The second type is a straight flow through design which provides exhaust gasses the shortest and straightest path to the environment, straight through! The way in which these mufflers quiet exhaust gasses is with the use of ports as are implemented by resonators and such. These work the same way gun silencer do, if that¡¦s a better analogy for you. These offer the best performance, but worst noise reduction. Expect about 15 hp
One word of caution, the old rule of modding rx-7 still implies, 2 mod are usually safe, but more than 2 usually requires computer upgrades. As for the exhaust, I¡¦d get an upgraded computer prior to the second modification. It¡¦s just safer that way. Personally i went with the downpipe because it¡¦s so much more beneficial to the longevity of the engine where as the other 2 are just for fun.
As for the hks hyper exhaust, it¡¦s basically a straight through muffler combine with a midpipe, that bolts up to either your downpipe or precat, using a full 4¡¨ mandrel bent tube. This runs about 1200$, and used for racing purposes due to it¡¦s elimination of the catalytic converter. Personally i would get an apexi gt muffler and a midpipe which would run about 850. The midpipe would cost around 200$ and be 3¡¨ in diameter. The apexi gt muffler bolts up to the 3¡¨ midpipe and flares out to 3.75¡¨ with either of these straight flow options, boost, fuel, and the law are definitely issues of concern. Not to mention the flames that will ensue. ƒº
Peace out,
Hawaii rx-7
the first is like headers on a regular car... stock the car comes with a precat, it's like a mini catalytic converter used to control emissions during start ups. Supposedly because it is smaller and closer to the exhaust outlet/engine, it heats up faster and works before the main cat. however, when once the main cat is warmed up, the precat is useless. The only function it servers after the car is warmed up is providing excessive heat in the engine bay. it also gets clogged from time to time causing damage and is felt as a loss of power. most people replace this with a downpipe, basically a straight pipe from the turbo manifold to the catalytic converter. This helps lower under hood temps, reduces the chance of precat failure, increases exhaust airflow providing better turbo spool and higher horsepower, and reduces weight(stock precat weights a little over 22 lb as opposed to the 11 lb downpipe i installed or so says my bathroom scale). With just a downpipe, there should not be a need for computer of fuel upgrades. Expect about 10-15 hp
the second part of the exhaust system is the main catalytic converter. this, like most other catalytic converters, is used to eliminates harmful pollutants. (hehe) here¡¦s a better description to what it does. http://www.waterloomotors.com/faq.htm#cat%20converter What some people do is change this out with either a high flow cat, which does exactly what the name implies, flow exhaust gasses faster while retaining emission standards; or change the catalytic converter out with a midpipe, which is basically a straight through 3¡¨ pipe with no catalyst material. Both of these, like the downpipe, reduce back pressure allowing the turbos to be more efficient, providing the engine with higher boost and thus more horse power is realized. With either of these, computer/fuel improvements as well as boost control should be taken into account. This is usually not recommended as a first modification. Taken from others, the high flow cat will offer a bigger improvement in power in the midrange rpm, while the midpipe will dramatically improve the top end power. Expect about 10-20 hp
The third and final part of the exhaust system is the muffler section or cat back. This is used to expel exhaust gasses rear of the rear axle, as required by law, as well as reduce exhaust noise to a minimal. The cat-back portion does not offer any reduction of pollutants. The stock cat back system is comprised of a very efficient muffler in terms of noise, but extremely poor in terms of performance as compared to straight through designs. I¡¦m guess the stock muffler is glass packed like many oem mufflers, but i have yet to cut mines open, after all it¡¦s all i¡¦ve got right now. As for aftermarket versions of the muffler, there are basically two designs. The first which is comprised of a series of baffles and chambers which allow exhaust gasses to cool inside the muffler before they are released into the environment, thus quieting the exhaust noise. (after all, that is what exhaust noise is, is the rapid cooling of a hot gas) This type of muffling is less efficient in terms of noise, but better in terms of performance over the stock. The second type is a straight flow through design which provides exhaust gasses the shortest and straightest path to the environment, straight through! The way in which these mufflers quiet exhaust gasses is with the use of ports as are implemented by resonators and such. These work the same way gun silencer do, if that¡¦s a better analogy for you. These offer the best performance, but worst noise reduction. Expect about 15 hp
One word of caution, the old rule of modding rx-7 still implies, 2 mod are usually safe, but more than 2 usually requires computer upgrades. As for the exhaust, I¡¦d get an upgraded computer prior to the second modification. It¡¦s just safer that way. Personally i went with the downpipe because it¡¦s so much more beneficial to the longevity of the engine where as the other 2 are just for fun.
As for the hks hyper exhaust, it¡¦s basically a straight through muffler combine with a midpipe, that bolts up to either your downpipe or precat, using a full 4¡¨ mandrel bent tube. This runs about 1200$, and used for racing purposes due to it¡¦s elimination of the catalytic converter. Personally i would get an apexi gt muffler and a midpipe which would run about 850. The midpipe would cost around 200$ and be 3¡¨ in diameter. The apexi gt muffler bolts up to the 3¡¨ midpipe and flares out to 3.75¡¨ with either of these straight flow options, boost, fuel, and the law are definitely issues of concern. Not to mention the flames that will ensue. ƒº
Peace out,
Hawaii rx-7
10-10-01, 06:25 PM
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thanx
ok thanx for sum info but i still need to know is there a way to get the midpipe thru emmisions? and what is the best HKS exust not including the 1200$ Hyper. And can all HKS exust make it thru emmisions? I DO NOT WANT THE N1 EXUST EITHER.
10-11-01, 09:33 PM
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no midpipe will ever pass emissions, well maybe if u slip the checker a Benjamin. The visual might if u have some sort of heat shield covering the straight pipe, but as for the sniff test, it will never pass. with a midpipe, the car sounds totally different and will definitely smell really gassy. they will surly know u don't have a cat. as for hks, get the hyper cat back. it runs about 500 ish for the carbon fiber one and 350 for the ss. i think for most states, all cat-backs are legal, as long as it isn't extremely loud, and that u still have the main cat in place. if i were u i'd just get a midpipe and swap in the cat whenever you go down for safety check or emissions testing. do a search on this site about cat-back's. personally i think u should go with the apexi gt. it's one huge motha, and sounds like a monster.
https://www.rx7club.com/vforums/show...threadid=19149
^^ check that thread out. ^^
https://www.rx7club.com/vforums/show...threadid=19149
^^ check that thread out. ^^
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