Worth going full 3" exhaust?

laesala said:

I am interested in this as well...specifically is a better downpipe only going to be really beneficial if you get a 3" exhaust?

Reason being that I want the Borla ATAK for the sound, but the piping is extremely small at 2.25"...

Click to expand...

If you got a 3" DP, you would want that to feed into a resonator/Y pipe that has a 3" inlet. After that the dual can be 2.25 or 2.5. A dual 2.25" setup has 0.88" more area than a single 3" (7.95" vs 7.07") so dual 2.25" would be fine given the above. (FYI, dual 2.5" area is 9.82").

EB with bolt-ons+tune, stock Y-pipe with Borla would be fine.

Keep MarylandSpeed in mind when you decide how you want to go about your mod. We can get you great deals on your mod needs just ask for Holly or you can check out the link below.

http://marylandspeed.com/getingear-i-24.html

But if you give us a call you can get an even better deal then what we list on our site.

As mentioned previously, it's only "worth it" if you have a decent amount of mods. I have a 3" tru dual exhaust but also have several engine mods.
Really, to fully take advantage of the 3" pipes I would need headers but I live in CA so there's a lot of BS wrapped up in that. Also not that the down
pipes from your EM is only 2.5".

Here's a recent episode showing that exhaust modification and a couple other things.

ELPYBOOST said:

How about a 3" down pipe with high flow cats then y pipe tapers down to 2.5" dual vs a full 3" dual?

Click to expand...

I think that's how the newest exhaust from Cobb is set up.

I have no direct experience with the Mustang Ecoboost engine, however, I have tweeked a 944 Turbo (951) engine, including installing a full 3" exhaust. The larger exhaust on the 951 increased power above 5K rpm, but decreased power/response below 3K rpms. This is somewhat intuitive, in that the reduced back pressure at low rpms increased turbo lag, but the increased exhaust flow capacity prevented overloading the hot side at high rpms, thus allowing it to maintain higher boost levels at higher revs. The Ecoboost engine is much more advanced than the 1986 951 motor, but the laws of physics haven't changed. I would suspect a somewhat similar response for the Ecoboost engine by installing a full 3" exhaust, i.e., better top end, reduced bottom end. It all depends on what your trying to achieve and how you plan to use the car.

SVO MkII said:

I have no direct experience with the Mustang Ecoboost engine, however, I have tweeked a 944 Turbo (951) engine, including installing a full 3" exhaust. The larger exhaust on the 951 increased power above 5K rpm, but decreased power/response below 3K rpms. This is somewhat intuitive, in that the reduced back pressure at low rpms increased turbo lag, but the increased exhaust flow capacity prevented overloading the hot side at high rpms, thus allowing it to maintain higher boost levels at higher revs. The Ecoboost engine is much more advanced than the 1986 951 motor, but the laws of physics haven't changed. I would suspect a somewhat similar response for the Ecoboost engine by installing a full 3" exhaust, i.e., better top end, reduced bottom end. It all depends on what your trying to achieve and how you plan to use the car.

Click to expand...

The engine turbocharged or not, does not need backpressure in the exhaust, the freer the exhaust after the turbo, the faster it will spool

mJolnir said:

The engine turbocharged or not, does not need backpressure in the exhaust, the freer the exhaust after the turbo, the faster it will spool

Click to expand...

Yes, I may have been confusing back pressure with velocity. But in any event, a bigger exhaust system is not always better. It will change the characteristics at different rpm ranges. Here is a bit more info (from PCA Great Britain);

Back pressure:
One of the most misunderstood concepts in exhaust theory is back pressure. People talk about it with no real understanding of what it is and what it's consequences are. I'm sure many of you have heard or read the phrase "Engines need back pressure" when discussing exhaust upgrades.

1. Some basic exhaust theory
Your exhaust system is designed to evacuate gases from the combustion chamber quickly and efficiently. Exhaust gases are not produced in a smooth stream; exhaust gases originate in pulses. A 4 cylinder motor will have 4 distinct pulses per complete engine cycle, a 6 cylinder has 6 pulses and so on. The more pulses that are produced, the more continuous the exhaust flow. Back pressure can be loosely defined as the resistance to positive flow - in this case, the resistance to positive flow of the exhaust stream.

2. Back pressure and velocity
Many people mistakenly believe that wider pipes are more effective at clearing the combustion chamber than narrower pipes. It's not hard to see how this idea would be appealing - as wider pipes have the capability to flow more than narrower pipes. However, this omits the concept of exhaust VELOCITY. Here is an analogy...a garden hose without a spray nozzle on it. If you let the water just run unrestricted out of the hose it flows out limply at a rather slow rate. However, if you take your finger and cover part of the opening, the water will spray out at a much much faster rate.
The astute exhaust designer knows that you must balance flow capacity with velocity. You want the exhaust gases to exit the chamber and speed along at the highest velocity possible - you want a FAST exhaust stream. If you have two exhaust pulses of equal volume, one in a 2" pipe and one in a 3" pipe, the pulse in the 2" pipe will be travelling considerably FASTER than the pulse in the 3" pipe. While it is true that the narrower the pipe, the higher the velocity of the exiting gases, you also want make sure the pipe is wide enough so that there is as little back pressure as possible while maintaining suitable exhaust gas velocity.

Back pressure at it's most extreme form can lead to reversion of the exhaust stream - that is to say the exhaust will flow backwards, which is...er... is not good. The trick is to have a pipe that that is as narrow as possible while having as close to zero back pressure as possible at the RPM range you want your power band to be located at. Exhaust pipe diameters are best suited to a particular RPM range (remember the pulses!). A smaller pipe diameter will produce higher exhaust velocities at a lower RPM but create unacceptably high amounts of back pressure at high rpm. Thus if your power band is located 2000-3000 RPM you'd want a narrower pipe than if your power band is located at 8000-9000 RPM.

SVO MkII said:

Yes, I may have been confusing back pressure with velocity. But in any event, a bigger exhaust system is not always better. It will change the characteristics at different rpm ranges. Here is a bit more info (from PCA Great Britain);

Back pressure:
One of the most misunderstood concepts in exhaust theory is back pressure. People talk about it with no real understanding of what it is and what it's consequences are. I'm sure many of you have heard or read the phrase "Engines need back pressure" when discussing exhaust upgrades.

1. Some basic exhaust theory
Your exhaust system is designed to evacuate gases from the combustion chamber quickly and efficiently. Exhaust gases are not produced in a smooth stream; exhaust gases originate in pulses. A 4 cylinder motor will have 4 distinct pulses per complete engine cycle, a 6 cylinder has 6 pulses and so on. The more pulses that are produced, the more continuous the exhaust flow. Back pressure can be loosely defined as the resistance to positive flow - in this case, the resistance to positive flow of the exhaust stream.

2. Back pressure and velocity
Many people mistakenly believe that wider pipes are more effective at clearing the combustion chamber than narrower pipes. It's not hard to see how this idea would be appealing - as wider pipes have the capability to flow more than narrower pipes. However, this omits the concept of exhaust VELOCITY. Here is an analogy...a garden hose without a spray nozzle on it. If you let the water just run unrestricted out of the hose it flows out limply at a rather slow rate. However, if you take your finger and cover part of the opening, the water will spray out at a much much faster rate.
The astute exhaust designer knows that you must balance flow capacity with velocity. You want the exhaust gases to exit the chamber and speed along at the highest velocity possible - you want a FAST exhaust stream. If you have two exhaust pulses of equal volume, one in a 2" pipe and one in a 3" pipe, the pulse in the 2" pipe will be travelling considerably FASTER than the pulse in the 3" pipe. While it is true that the narrower the pipe, the higher the velocity of the exiting gases, you also want make sure the pipe is wide enough so that there is as little back pressure as possible while maintaining suitable exhaust gas velocity.

Back pressure at it's most extreme form can lead to reversion of the exhaust stream - that is to say the exhaust will flow backwards, which is...er... is not good. The trick is to have a pipe that that is as narrow as possible while having as close to zero back pressure as possible at the RPM range you want your power band to be located at. Exhaust pipe diameters are best suited to a particular RPM range (remember the pulses!). A smaller pipe diameter will produce higher exhaust velocities at a lower RPM but create unacceptably high amounts of back pressure at high rpm. Thus if your power band is located 2000-3000 RPM you'd want a narrower pipe than if your power band is located at 8000-9000 RPM.

Click to expand...

Ok, hes got the pulses part right, header design take that into account and creates what is called the scavenging effect, i have seen a couple of videos in youtube where they blow air in one of the primaries and that makes a vacuum in the other, that helps the gasses come out at faster speeds.

Now on to the garden hose example you have to remember that flow is a volume of whatever substance you have in a measure of time (gallons per hour, liter per minutes.....), if we open the faucet we have a constant flow (x gallons per minute), since that flow is calculated in area of the hose multiplied by speed in order to keep the same flow with a smaller area you need higher speed, so water is going out of the hose at a faster speed but flow is the same.

My best result to date in 1/4 mile racing and dyno horsepower on ecoboost mustangs come from cars that have no exhaust after the downpipe, IMO after the headers the rest of the exhaust is there for noise and pollution reasons only.