JoeT
01-17-2004, 03:43 PM
Hi There,
Just thought I'd share some of my thought patterns on why I chose the route I did to get more power. Skipping a few chapters, in summary I love my car, I love the power delivery, it's become a purpose built street / fun car to drive, with lots of personality.
Keep in mind, this is the route I took to get the power I wanted for the sport I like. There are other routes, and other means of getting power, but my requirements are for large low end grunt power out of the hole, accelerated sprint type of activities of Autocross. Not drag racing, nor big track racing.
Phase 1: In search of the Migty HP
In search of the holy HP (or so I thought). Early in the tuning cycle of my car, back in late 2000 early 2001, I searched long and wide for an exhaust system that would deliver the best bang for the buck while keeping as quiet as possible.
After reading all sorts of "Online" publications I fell into the typical psychodramatic pseudo performance cauldron of misinformation that's brewed more by money grabbing than real world applications. The world is obsessed with "Numbers" but not the correct ones IMHO... HP numbers being quoted by pseudo performace guru's on a singular plane.
Lesson Learned: Don't listen to any one or group of people only quoting "Peak" hp. What matters most is the "Area under the curve". A car with low peak HP but a flat torque curve will out accelerate a car with a narrow power band, simply because it's pulling harder sooner and continuously pulling harder until it can't, then you shift and the cycle starts all over again.
Exhaust Choice:
After reading and reading and reading and researching, here's the bottom line, and I'll phrase it as close to english as possible.
1) Decide on the application (autox, drag, street, etc.) before you choose an exhaust system.
2) Decide if you want function over looks, or looks over funtion.
Coming to a decision on those 2 points can save you "Hundreds" of dollars, if not thousands.
Exhaust Theory: Contrary to popular belief, it's not backpressure that results in torque. It's the flow characteristics that will make or break a system.
1) The ideal scenario is to maintain energy in the system and exhaust it out the rear with little or no energy loss. Energy = heat = flow. As exhaust travels out the back to the tail pipe, the steel pipe acts like a heat sink, and the cooler the exhaust gasses get within the system, the slower it gets, causing back pressure.
Exhausts are all about compremise, unless you can vent right out of the headers, but that's slightly illegal. Here's where the application or intended usage is very important. Choosing an exhaust system that's not designed or properly sized for the car = loss of performance, period.
Example: A NA 2.5RS with a stock diamerter of 1 7/8" piping has lots of exhaust velosity at low RPM's but is restrictive at higher RPM's, kinds dies out above 5K rpm. But has lots of bottom end torque. Why? Exhaust volume and temperature are controlled and energy is allowed to be maintained down the system and is expelled with moderate energy loss.
Now Same 2.5RS with a 3" exhaust from the cat back, loses tons of bottom end torque (yes as a result of back pressure) but has more top end kick, and pulls beyond redline.
As the exhaust gasses escape the stock catalytic converter output, it has to expand to fill the greater volume of the 3" exhaust piping. As gasses expand, it looses energy since the energy is dispersed into a larger chamber. Here's where the vicious cycle starts.
As the exhaust cools, it slows down, as it slows down it takes longer to get out the tail pipe, as it takes longer to get out the tail pipe, it's has more time to readiate the heat through the pipe walls, and it loses more energy, which makes it slow down, etc....
Meanwhile, there is more exhaust trying to get out through this wall of "Cool" exhaust gasses. This is why it loses bottom end torque.
Why does it increase the top end? Simple, higher RPM = Hotter exhaust flow => Higher Exhaust Flow => Closer to the ideal operating temperature of the system => Power.
Ever notice that high efficiency exhaust systems like on the WRC cars are ceramic coated and heat wrapped from head to toe...
Bottom line: Decide on what you want to do with the car first, then choose an exhaust system to match the application.
Things to consider: Exhaust pipe material, sharpness of bends, muffler material, perforated core design (Ribbed, smooth, pocketed, etc.).
Exhaust temperature and intended volume all play a part in deciding what's good for the application.
Note: Same applies to Turbo Cars, but consider that the Exhaust gas temperature of turbo cars are hotter than NA cars, simply through increased VE (Volumetric Efficiency).
That was my first step and the decision making process I took to decide on the route to go.
Next Article: In search of more power and torque. Headers and Camshafts.
Hope this helps.
Do people like this type of article, should I continue or am I wasting my breath. Please let me know.
Thank You
Just thought I'd share some of my thought patterns on why I chose the route I did to get more power. Skipping a few chapters, in summary I love my car, I love the power delivery, it's become a purpose built street / fun car to drive, with lots of personality.
Keep in mind, this is the route I took to get the power I wanted for the sport I like. There are other routes, and other means of getting power, but my requirements are for large low end grunt power out of the hole, accelerated sprint type of activities of Autocross. Not drag racing, nor big track racing.
Phase 1: In search of the Migty HP
In search of the holy HP (or so I thought). Early in the tuning cycle of my car, back in late 2000 early 2001, I searched long and wide for an exhaust system that would deliver the best bang for the buck while keeping as quiet as possible.
After reading all sorts of "Online" publications I fell into the typical psychodramatic pseudo performance cauldron of misinformation that's brewed more by money grabbing than real world applications. The world is obsessed with "Numbers" but not the correct ones IMHO... HP numbers being quoted by pseudo performace guru's on a singular plane.
Lesson Learned: Don't listen to any one or group of people only quoting "Peak" hp. What matters most is the "Area under the curve". A car with low peak HP but a flat torque curve will out accelerate a car with a narrow power band, simply because it's pulling harder sooner and continuously pulling harder until it can't, then you shift and the cycle starts all over again.
Exhaust Choice:
After reading and reading and reading and researching, here's the bottom line, and I'll phrase it as close to english as possible.
1) Decide on the application (autox, drag, street, etc.) before you choose an exhaust system.
2) Decide if you want function over looks, or looks over funtion.
Coming to a decision on those 2 points can save you "Hundreds" of dollars, if not thousands.
Exhaust Theory: Contrary to popular belief, it's not backpressure that results in torque. It's the flow characteristics that will make or break a system.
1) The ideal scenario is to maintain energy in the system and exhaust it out the rear with little or no energy loss. Energy = heat = flow. As exhaust travels out the back to the tail pipe, the steel pipe acts like a heat sink, and the cooler the exhaust gasses get within the system, the slower it gets, causing back pressure.
Exhausts are all about compremise, unless you can vent right out of the headers, but that's slightly illegal. Here's where the application or intended usage is very important. Choosing an exhaust system that's not designed or properly sized for the car = loss of performance, period.
Example: A NA 2.5RS with a stock diamerter of 1 7/8" piping has lots of exhaust velosity at low RPM's but is restrictive at higher RPM's, kinds dies out above 5K rpm. But has lots of bottom end torque. Why? Exhaust volume and temperature are controlled and energy is allowed to be maintained down the system and is expelled with moderate energy loss.
Now Same 2.5RS with a 3" exhaust from the cat back, loses tons of bottom end torque (yes as a result of back pressure) but has more top end kick, and pulls beyond redline.
As the exhaust gasses escape the stock catalytic converter output, it has to expand to fill the greater volume of the 3" exhaust piping. As gasses expand, it looses energy since the energy is dispersed into a larger chamber. Here's where the vicious cycle starts.
As the exhaust cools, it slows down, as it slows down it takes longer to get out the tail pipe, as it takes longer to get out the tail pipe, it's has more time to readiate the heat through the pipe walls, and it loses more energy, which makes it slow down, etc....
Meanwhile, there is more exhaust trying to get out through this wall of "Cool" exhaust gasses. This is why it loses bottom end torque.
Why does it increase the top end? Simple, higher RPM = Hotter exhaust flow => Higher Exhaust Flow => Closer to the ideal operating temperature of the system => Power.
Ever notice that high efficiency exhaust systems like on the WRC cars are ceramic coated and heat wrapped from head to toe...
Bottom line: Decide on what you want to do with the car first, then choose an exhaust system to match the application.
Things to consider: Exhaust pipe material, sharpness of bends, muffler material, perforated core design (Ribbed, smooth, pocketed, etc.).
Exhaust temperature and intended volume all play a part in deciding what's good for the application.
Note: Same applies to Turbo Cars, but consider that the Exhaust gas temperature of turbo cars are hotter than NA cars, simply through increased VE (Volumetric Efficiency).
That was my first step and the decision making process I took to decide on the route to go.
Next Article: In search of more power and torque. Headers and Camshafts.
Hope this helps.
Do people like this type of article, should I continue or am I wasting my breath. Please let me know.
Thank You