Final Exhaust Setup for the mustang

[The01Cav]

So I am looking to start collecting parts to redo the whole exhaust system on my mustang., the headers supposedly are 1.75" runners with a 2.5" outlet vs everyone else's 15/8 with a 2.5" outlet. The brand is supposedly decent and used a lot in the 350z/g35 community as well as e46 community.


Headers
http://adfarm.mediaplex.com/ad/ck/9656-122528-2357-0?src=View%20Item&mpre=http%3A%2F%2Fwww.ebay.com%2Fitm%2F390400054029%3Fredirect%3Dmobile&device=Apple%7CiPhone&no_cj_c=1&upsid=271978026091

Cats
Item Detail


Prochamber
MAC Ford Mustang V6 4.0L 2005*-2010, Pro Chamber to MAC Short Tubes

Catback
MAC Ford Mustang GT & 4.0L V6 2005-2010, Cat-Back Exhaust System

 

[riceeater33]

Im not a v6 expert but why not just get the pacesetter LT headers from AM and base your set up off those?

 

[The01Cav]

I don't care for the sound of long tubes on the 4.0

 

[riceeater33]

I don't care for the sound of long tubes on the 4.0

I see, I havent heard so I didnt know it wasnt that great. so basically just for sound, not so much performance.

 

[The01Cav]

Pretty much. I wanted a decent sound and it should pick up a little performance when mating with a 2.5" downpipe with high flow cats vs the stock 2.25 and stock cats.

 

[RunnerInTheNight]

Shorty headers appear in my book to do nothing to the exhaust except a little noise difference & the weight difference. I was thinking going LTs on mine but I have up & downs about Pace Setter headers.

Just remember you need some back pressure on these motors, don't fully understand it but when I went O/R X I changed mufflers to American Thunders and felt better.

Don't forget the tune!

I am eventually going to go with a bigger pipe on the exhaust also.

 

[The01Cav]

Thats why i'm putting cats on it and not going catless that way there is some back pressure, plus the mac mufflers are chambered so that helps some there as well.

 

[The01Cav]

Here is a shot of the headers, UPS dropped them off wednesday

 

[riceeater33]

They look nice

 

[The01Cav]

Thanks they're not too bad for the price.

 

[JCON]

Hey man, I ran those headers on my 05 v6 and it gave it a great tone and woke up the mid-top a little bit. The gains were more than expected from shorty headers. They were right on point with these JBA's (which they were copied in China from). Be sure to get them coated because they will blue then rust in under a year. I also went and bought new gaskets, the ones in the box didn't seem to be that great.

I have a few clips of my v6 exhaust set ups on http://www.youtube.com/midatlanticmustang.

Also I have a set of SLP high flow cats sitting in a box that I don't need. Never installed. Sell them for $150 if you want them (and I'll just meet up with you, no shipping).

Just to clear things up on back pressure. Back pressure is ALWAYS bad. It is never good. What is good is the scavenging effect of moving gases in a tube. That is the reason for true "tuned-length" headers. They even out exhaust pulses and they also increase the exhaust velocity. Example: take one straw and blow air through it, observe velocity. Put 15 straws in your mouth and blow air through them, observe velocity. You'll understand very quickly. It's the reason some cars lose power when they go to a 3" exhaust.

Last point, when you're ready to install the shorty headers, let me know and I can help. I did them on my car and it wasn't too bad to do.

-Jonathan

 

[ejschmidt]

Back pressure is ALWAYS bad. It is never good. ... blah blah blah... You'll understand very quickly. It's the reason some cars lose power when they go to a 3" exhaust.

-Jonathan

Contrary statements. Can you clarify this?

 

[NUTCASE]

I have heard of cars loosing power when going to an oversized exaust. however the reduced back pressure reduces heat in the cylander so this allows you to increase spark advance netting you more power than you did before.

this does not mean you can just throw on a 4 inch dual setup and call it a day. there is a point of diminishing returns when increasing exhaust size.

look for somebody on here with a modded gt500 and ask them how much power they got going from 2.5 to 3inch. you will hear numbers between zero and 10rwhp. not much on a car already making over 700 imo.

 

[JCON]

Putting back pressure on the cylinder is never a goo thing, it' can cause damage to valves and other important parts of the head. What people think is back pressure is something called scavenging. Basically there is a perfect point at which your exhaust flows just right to have an optimal exhaust velocity. This does not however mean that it is pushing gas back in to the cylinder or putting pressure backwards on the exhaust valves (the term 'back pressure'). What it does mean is that your exhaust flows free enough that the speed at which it exits is at optimum efficiency for evacuating cylinder and exhaust system space. If you go to big the velocity is lower (reread my example) because of physics. The same basic principal applies to headers/exhaust. You want the highest exhaust gas velocity and that doesn't mean the largest exhaust. As was stated, you reach a point of diminishing return and when the exhaust velocity lowers, you start to lose some power because you're not moving exhaust gases out fast enough. With the right diameter exhaust you create the right type and amount of pressure which moves forward through the exhaust system and not backwards.

I am running out of different ways to say it. Essentially, you have x amount of gaseous volume and it can go through a pipe that is too small, just right, or too large.

With the pipe that is too small, velocity may be the highest here but the actual flow rate is not high enough to satisfy the total evacuation of exhaust gas before the next combustion takes place, this forces gas towards the path of least resistance (usually slightly open or opening valves)

With a pipe that is just right, velocity in excellent and at the same time the pipe can handle the volume of exhaust produced. There is little to no measurable back pressure, exhaust gases continue to flow in the direction of least resistance and out the back.

With a pipe that is too large, exhaust velocity is decreased but volume capacity is larger. Even though the capacity is greater, there is less vacuum to empty the cylinders and once in-stream, it exits the tube at a slower rate.

I think I made things worse but the best way to demonstrate the proper effects of exhaust velocity is the straw demo.