exhaust question..
#1
07-22-2004, 11:59 AM
exhaust question..
hey everybody.. i was curious as to what the difference is between say a catback exhaust and just welding a damn plate to the end of your pipe with a hole and making a homemade restrictor. i realize the catback looks a hellva lot better and sounds better, but what's the performance differences? thanks for the time.
peace
nate
peace
nate
#2
07-22-2004, 03:11 PM
RE: exhaust question..
the exhaust system is made to create back pressure (hard to explain, but you need some), damper the sound, and clean some of the harmful gases that come out of you engine. A plate with a hole in it won't, plus its ricey and illegal.
#3
07-22-2004, 04:57 PM
RE: exhaust question..
You dont need ANY backpressure. backpressure slows gases as they are coming out of the head, hurting your power production. the reason this myth came about is because people would take off the stock exhaust and bolt in a custom made 4 inch sewer pipe exhaust and it would kill the power, as does gutting a catalytic convertor. so everyone assumes that it is from too little backpressure, when really it is from too little exhaust velocity , the faster the exhaust moves away from the head, the more suction it creates behind it. think of a plastic bag, caught in the bed of a truck. it keeps getting sucked back in behind it because of the vacuum the truck is creating. if you put a certain amount of moving substance(in this case, exhaust gas) into a smaller area it will speed up, making more suction behind it and this scavenging effect helps remove more of the exhaust gases from the cylinder, leaving more room for fresh, unburnt air and fuel. if you are thinking of gutting your cat, dont. this larger diameter pipe in the exhaust system will create a stalled area of exhaust flow, slowing it down and hurting your power. if you must run without a cat, get a race pipe that is roughly the same size as the rest of the exhaust system. BTW, disregard everything I just said if it is on a turbo application. With turbo you want the most freely flowing exhaust you can get. so all you turbo'd people, go for that 4 inch sewer pipe!
#4
07-22-2004, 09:48 PM
RE: exhaust question..
ORIGINAL: sacicons
You dont need ANY backpressure. backpressure slows gases as they are coming out of the head, hurting your power production. the reason this myth came about is because people would take off the stock exhaust and bolt in a custom made 4 inch sewer pipe exhaust and it would kill the power, as does gutting a catalytic convertor. so everyone assumes that it is from too little backpressure, when really it is from too little exhaust velocity , the faster the exhaust moves away from the head, the more suction it creates behind it. think of a plastic bag, caught in the bed of a truck. it keeps getting sucked back in behind it because of the vacuum the truck is creating. if you put a certain amount of moving substance(in this case, exhaust gas) into a smaller area it will speed up, making more suction behind it and this scavenging effect helps remove more of the exhaust gases from the cylinder, leaving more room for fresh, unburnt air and fuel. if you are thinking of gutting your cat, dont. this larger diameter pipe in the exhaust system will create a stalled area of exhaust flow, slowing it down and hurting your power. if you must run without a cat, get a race pipe that is roughly the same size as the rest of the exhaust system. BTW, disregard everything I just said if it is on a turbo application. With turbo you want the most freely flowing exhaust you can get. so all you turbo'd people, go for that 4 inch sewer pipe!
You dont need ANY backpressure. backpressure slows gases as they are coming out of the head, hurting your power production. the reason this myth came about is because people would take off the stock exhaust and bolt in a custom made 4 inch sewer pipe exhaust and it would kill the power, as does gutting a catalytic convertor. so everyone assumes that it is from too little backpressure, when really it is from too little exhaust velocity , the faster the exhaust moves away from the head, the more suction it creates behind it. think of a plastic bag, caught in the bed of a truck. it keeps getting sucked back in behind it because of the vacuum the truck is creating. if you put a certain amount of moving substance(in this case, exhaust gas) into a smaller area it will speed up, making more suction behind it and this scavenging effect helps remove more of the exhaust gases from the cylinder, leaving more room for fresh, unburnt air and fuel. if you are thinking of gutting your cat, dont. this larger diameter pipe in the exhaust system will create a stalled area of exhaust flow, slowing it down and hurting your power. if you must run without a cat, get a race pipe that is roughly the same size as the rest of the exhaust system. BTW, disregard everything I just said if it is on a turbo application. With turbo you want the most freely flowing exhaust you can get. so all you turbo'd people, go for that 4 inch sewer pipe!
#6
07-23-2004, 06:20 PM
RE: exhaust question..
the torque loss is from loss of velocity. that is the same reason that a longer stroke will give you more low end power, the piston has to move faster to make the revolution in the same amount of time at X rpm, speeding up the exiting gases, read exhaust velocity. the higher horsepower shows that the uncorked motor makes more power when it is allowed to breath. a properly designed exhaust system will give you similar gains in the top end W/O the torque loss. i believe you, but for my own records, can you post the dynos? im interested to see them.
If anyone says you need backpressure, ask them why. then ask them why top fuel racers only use headers. no backpressure there.
If anyone says you need backpressure, ask them why. then ask them why top fuel racers only use headers. no backpressure there.
#7
07-23-2004, 09:01 PM
RE: exhaust question..
ORIGINAL: sacicons
the torque loss is from loss of velocity. that is the same reason that a longer stroke will give you more low end power, the piston has to move faster to make the revolution in the same amount of time at X rpm, speeding up the exiting gases, read exhaust velocity. the higher horsepower shows that the uncorked motor makes more power when it is allowed to breath. a properly designed exhaust system will give you similar gains in the top end W/O the torque loss. i believe you, but for my own records, can you post the dynos? im interested to see them.
If anyone says you need backpressure, ask them why. then ask them why top fuel racers only use headers. no backpressure there.
the torque loss is from loss of velocity. that is the same reason that a longer stroke will give you more low end power, the piston has to move faster to make the revolution in the same amount of time at X rpm, speeding up the exiting gases, read exhaust velocity. the higher horsepower shows that the uncorked motor makes more power when it is allowed to breath. a properly designed exhaust system will give you similar gains in the top end W/O the torque loss. i believe you, but for my own records, can you post the dynos? im interested to see them.
If anyone says you need backpressure, ask them why. then ask them why top fuel racers only use headers. no backpressure there.
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