3 inch or 2.5 inch exhaust?
08-12-2006, 03:55 AM
#11
6th Gear Member
Join Date: May 2006
Location: Ohio
Posts: 6,448
RE: 3 inch or 2.5 inch exhaust?
ORIGINAL: racer02GTstang
yea, i now what you mean.... we have a 69 super bee with a 383BB and a cam, heads, intakemanifold, and alot of other stuff... we run 2.5 inch exhuast on it to keep the backpressure...
ORIGINAL: oxfordgt
Sorry Black98GT but you are alittle off. You do not need back pressure.
Most of the time bigger is better, but that's not always the case with exhaust. Today's late model cars are designed with several restrictions on the manufacturers. So in order to perform but still stay within the limits of emissions and other regulations, the exhaust is usually the first thing to suffer from the factory. The easy power that is found in changing the original equipment exhaust system, is just one of the many reasons there are so many aftermarket manufacturers capitalizing on this insufficiency. But just opening the exhaust doesn't always make more power, it takes the correct combination of flow capability and velocity. That's why performance exhaust manufacturers spend so much time in search of just the right combination, so that they can ensure peak power to their customers.
In this article we will discuss the effects that exhaust backpressure has on your engine. Backpressure is the restriction of the exhaust gases that are produced by your engine while they are being released through your exhaust system. Exhaust gasses are the burned and unburned gasses that are released out of the exhaust system after engine combustion happens.
The exhaust system should have minimal restriction to the exhaust flow that is being released in order to create the most amount of power from the engine. With restriction present, backpressure is developed, making the engine work much harder to release the exhaust out of the engine cylinders.
The standard for exhaust diameter is to not run too large of exhaust, for the engine needs a certain amount of backpressure. This is correct in the sense of one should not run too large of diameter exhaust tubing, but the statement of the engine needing backpressure is not. You need to have the least amount of backpressure possible to produce maximum power. Too large of diameter exhaust will cause a power loss and loss of low end torque because a larger pipe has less exhaust stream velocity than a smaller pipe. If the exhaust pipe is too large, then the exhaust flow will be slowed with less velocity. There are exceptions, forced induction or high-volume race engines require a larger diameter exhaust due to the flow characteristics of the engine. Supercharged and turbocharged vehicles can have an exhaust gas volume of 1 to 2 times more than an equivalent displacement naturally aspirated engine. In this case, one is able to use a larger diameter of exhaust for greater performance.
This was taken from https://mustangforums.com/m_1789889/tm.htm
This has been a big argument for along time and I'm glad this guy posted it cause I could never find hard evidence before.
Sorry Black98GT but you are alittle off. You do not need back pressure.
Most of the time bigger is better, but that's not always the case with exhaust. Today's late model cars are designed with several restrictions on the manufacturers. So in order to perform but still stay within the limits of emissions and other regulations, the exhaust is usually the first thing to suffer from the factory. The easy power that is found in changing the original equipment exhaust system, is just one of the many reasons there are so many aftermarket manufacturers capitalizing on this insufficiency. But just opening the exhaust doesn't always make more power, it takes the correct combination of flow capability and velocity. That's why performance exhaust manufacturers spend so much time in search of just the right combination, so that they can ensure peak power to their customers.
In this article we will discuss the effects that exhaust backpressure has on your engine. Backpressure is the restriction of the exhaust gases that are produced by your engine while they are being released through your exhaust system. Exhaust gasses are the burned and unburned gasses that are released out of the exhaust system after engine combustion happens.
The exhaust system should have minimal restriction to the exhaust flow that is being released in order to create the most amount of power from the engine. With restriction present, backpressure is developed, making the engine work much harder to release the exhaust out of the engine cylinders.
The standard for exhaust diameter is to not run too large of exhaust, for the engine needs a certain amount of backpressure. This is correct in the sense of one should not run too large of diameter exhaust tubing, but the statement of the engine needing backpressure is not. You need to have the least amount of backpressure possible to produce maximum power. Too large of diameter exhaust will cause a power loss and loss of low end torque because a larger pipe has less exhaust stream velocity than a smaller pipe. If the exhaust pipe is too large, then the exhaust flow will be slowed with less velocity. There are exceptions, forced induction or high-volume race engines require a larger diameter exhaust due to the flow characteristics of the engine. Supercharged and turbocharged vehicles can have an exhaust gas volume of 1 to 2 times more than an equivalent displacement naturally aspirated engine. In this case, one is able to use a larger diameter of exhaust for greater performance.
This was taken from https://mustangforums.com/m_1789889/tm.htm
This has been a big argument for along time and I'm glad this guy posted it cause I could never find hard evidence before.
08-12-2006, 07:12 AM
#12
4th Gear Member
Join Date: Jul 2006
Location: Pittsburg, CA (BAY AREA!)
Posts: 1,399
RE: 3 inch or 2.5 inch exhaust?
Just like albiz066 said, you WILL gain horsepower from a 3' exhaust, but it will only be at higher RPM's. But by adding that high end horsepower, you lose some of your low end torque.
08-12-2006, 09:58 AM
#14
5th Gear Member
Join Date: Jul 2005
Location: Georgia
Posts: 2,387
RE: 3 inch or 2.5 inch exhaust?
Even when faced with the facts, people still do not want to believe them. His car appears stock. Without forced induction of some type, or one hell of a high-cpmpression N/A motor, the 3 inch exhaust is too large. Exhaust velocity will slow and create back pressure, reducing scavaging and making the motor work harder to evacuate exhaust gases from the cylinders.
Backpressure = bad
Hight exhaust gas velocity = good
Think of it another way. If 3 inch was better, why do most of the companies offer 2.5 inch? Because they have done the CFD analysis and concluded the 2.5 is optimum for 95% of our cars.
Backpressure = bad
Hight exhaust gas velocity = good
Think of it another way. If 3 inch was better, why do most of the companies offer 2.5 inch? Because they have done the CFD analysis and concluded the 2.5 is optimum for 95% of our cars.
Go for it dude!
04-08-2008, 01:24 PM
#19
3rd Gear Member
Join Date: Jan 2007
Location: Philly, PA
Posts: 965
RE: 3 inch or 2.5 inch exhaust?
YOU DON'T WANT/NEED BACK PRESSURE. WHY DO THINK PEOPLE AT THE TRACK RACE WITH OPEN HEADS? CUZ IT FLOWS BETTER AND YOU GET MORE POWER. with that said, i know you can get Pacesetters Longtubes that have a 3 collector but on the back end of the mid-pipe it is 2.5 inches because that is how most aftermarket cat backs come. so if you want, do 3" in the tubes and then duck it down to 2.5" for the catback
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