FAQ- B6 B7 Exhaust information build Thread

DIY/TECH/INFORMATIVE
#1

Hey guys,

Az’s loss, our gain. This is were I will be documenting my new exhaust build. Seeing how much other platforms beit from plus sizing exhaust diameter like the rs4’s and then c63’s, gto’s, camaro’s and since i am pushing the same if not more power than alot of those guys and with even MORE power coming once my built motor is done, a true 3" dual cat-back was in order.

I have already ordered some mandrel bend pipes which came in yesterday and will post up pics later. I also did HOURS of research on the perfect mufflers for me. The main focal point on the mufflers is flow and power and i followed this test:

[quote]Muffler Flow Testing

All tests via an independent lab
All tests @ 15” wc

2 “ Straight Pipe 283 CFM
2 ¼ “ Straight Pipe 365 CFM
2 ½ “ Straight Pipe 521 CFM

2 ¼” Typical Bent tailpipe 268 CFM
2 ½” Typical Bent Tailpipe 417 CFM

2 ¼” Inlet/Outlet_ Glass Pack Tips- No Louvers- Smooth 274 CFM
2 ¼” Inlet/Outlet- Glass Pack Tips-Louvered 133 CFM
Same as above set for reverse flow 141 CFM
2 ¼” Cherry Bomb 239 CFM
2 ½” Cherry Bomb 294 CFM

2 ½” Inlet/Outlet Dynomax Super Turbo 278 CFM
2 ½” Inlet/Outlet Ultraflow Bullet 512 CFM
2 ½” Inlet/Outlet Gibson Superflow 267 CFM
2 ½” Inlet/Outlet Flowmaster ( 2 Chamber) 249 CFM
2 ½” Inlet Outlet Flowmaster ( 3 Chamber) 229 CFM
2 ¼” Inlet/Outlet Thrush CVX 260 CFM
2 ½” Inlet/Outlet Maremount Cherry Bomb 298 CFM
2 ½” Inlet/Outlet Hooker Aero Chamber 324 CFM
2 ½” Inlet/Outlet Hooker Max Flow 521 CFM
2 ½” Inlet/Outlet Borla Turbo 373 CFM
2 1/2" Inlet/Outlet Magnaflow 284 CFM

Standard OEM 2 ¼” Inlet/Outlet 138-152 CFM
Standard OEM 2 ½” Inlet/Outlet 161-197 CFM

This test was performed by 5.0 Mustang & Super Fords Magazine, December 2002 issue (page 55) on a '90 Mustang LX coupe with 370hp and 11 second potential. 66 pulls were made for this comparison:

The results in HP order:
1.Flowtech Warlock (open) 374.2 hp/ 333.1 tq
2.Bassani Real Street 373.7 hp/ 333.8 tq
3.Hooker Maxflow 373.5 hp/ 333 tq
4.Borla XS 373.3 hp/ 332.6 tq
5.Magnaflow 372.8 / 332.5 tq
6.MAC 372.3 hp / 331.5 tq
7.Flowtech Afterburner 372.3 hp/ 330.1 tq
8.Hooker Aerochamber 372.1 hp/ 330.4 tq
9.Bassani 372 hp/ 333.5 tq
10.Spintech 371.6 hp/ 332.2 tq
11.Edelbrock Performer RPM 370.9 hp / 331.3 tq
12.Borla XR1 370 hp/ 334 tq
13.Flowtech Terminator 369.5 hp / 331.3 tq
14.Dynomax Ultra Flo 369.4 / 333.2 tq
15.Flowmaster 369.4 hp / 331.8 tq
16.Flowtech Warlock 366.3 hp / 325.3 tq
17.No muffs 365.2 hp / 330.1 tq

Sound Off in Quietest to Loudest (Decibels):
1.Borla XS, 80db at idle, 90db at 2,000 rpm, 110db at WOT.
2.Hooker Maxflow, 80db at idle, 90db at 2,000 rpm, 120db at WOT.
3.Magnaflow, 82db at idle, 91 at 2,000 rpm, 114db at WOT.
4.Flowmaster, 82db at idle, 93 at 2,000 rpm, 115db at WOT.
5.Flowtech Warlock, 83db at idle, 92 at 2,000 rpm, 112db at WOT.
6.Dynomax UltraFlo, 83db at idle, 94 at 2,000 rpm, 113db at WOT.
7.Borla XR1, 83db at idle, 96db at 2,000 rpm, 118db at WOT.
8.Bassani Street, 83db at idle, 96db at 2,000 rpm, 120db at WOT.
9.Edelbrock RPM, 84db at idle, 93db at 2,000 rpm, 118db at WOT.
10.Bassani Real Street, 84db at idle, 96db at 2,000 rpm, MAX. (120+db).
11.Flowtech Afterburner, 86db at idle, 94db at 2,000 rpm, 115db at WOT.
12.Flowtech Terminator, 86db at idle, 94db at 2,000 rpm, 119db at WOT.
13.Hooker Aerochamber, 87db at idle, 94db at 2,000 rpm, 114db at WOT.
14.SpinTech, 87db at idle, 97db at 2,000 rpm, 116db at WOT.
15.MAC, 87db at idle, 98db at 2,000 rpm, 119db at WOT.
16.No Muffler, 91db at idle, 103db at 2,000 rpm, MAX. (120+db).

http://www.qsl.net/st0f/mufflers.jpg

http://www.qsl.net/st0f/muff-db.jpg
[/quote]
Now as you see, the hooker max flow is the best flowing muffler that is still streetable and is actually 2nd quietest at idle. Tose are the mufflers i went with. They flow like a 2.5 inch straight pipe which is just awesome. Super excited for them. Will post up pics once i get them in. Best part is they are 71 bucks each!

As for crossover, its natural that i went with a x-pipe. Which x-pipe was the hardest part and i was set on a Kooks narrow x-pipe but at over 200 dollars i couldnt stomach it. Luckily for me i checked out jegs and foudn their narrow universal x-pipe was everything i was looking for. Narrow to keep the heat in the exhaust, 3 inch with a shallw crossover and CHEAP. less than 80 bucks.

Ill post up pics and updates when the stuff comes in. I will piece this exhaust together slowly and also have each section fabbed individually. Watch this space…

#2

Good stuff.

#3

welcome aboard!

#4

This thread is @#%$&# awesome! Great roundup of info 91.

For us 2.5" guys look at the difference in flow between a 2.25" pipe and a 2.5" pipe. That’s amazing.

Those Hooker MAXflow mufflers you chose looks to be a great option. Relatively quiet at idle and cruising but @WOT 120 decibels! CAN’T WAIT for you to get this done. I’m highly anticipating the numbers and, of coarse, the videos. A 3" exhaust on a S4… I like your brand of crazy sir ;D

#5

thanks Apat! good to have you aboard as well. youll find here to be a lot more informative with some real great minds. Minds that actually have a big part of the mods that you purchase for your car so you hear it from the source rather through watered down jargen on AZ.

glad you noticed the flow from 2.25 to 2.5. it is so much more than just .25". it can make or break a car like justincredible showed us on his thread on AZ. the sad part is that if you showed a brainless person like crabpot that, he would scoff at it because its an american car and he feels his car wont respond the same way because it is more “sophisticated”. give me a break. look at the description of the car they used to test this out. 370 hp mustang that is 11 second capable. if that doesnt sound like us than i dont know what does. in the end hp is hp and flow is flow. there is no such thing as german exhaust gasses lol

#6

don’t tell crapbot and dperm that…they’ll call you an asshole when you can’t respond to kick their teeth in

#7

91, if you recall, Beem did some math proofs walking through the difference, when you’re looking at the area of a dual 2.25" vs dual 2.5" it really is amazing, it’s like going from a 3" single to 4" single, the jump is way more than people realize.

That’s why (and I’m NO expert), is 3" too much? I honestly was shocked on JC’s runs of no headers and how much of a difference it made, made me want to go weld my cutouts back in lol!

#8

3 mph gain by just removing his cat-back! insane! thats why i feel 3inch might be perfect for us MD20/20. we’ll see come spring time how my car fares at the track with the 3". if i get some good gains, and you want want, Ill build you one as well.

#9

^Sounds good and looking forward to it. I’m just hoping to make it to the track early spring and set some appropriate times, that would have me happy enough. Too bad we couldn’t get a little K-Sauce X pipe. I got the same X-pipe you bought, but in a 2.5" on my old build.

I still have those 2.5 dumps though, I had thought about placing them right where the cats go on the headers after seeing JC’s times jump like that, I knew the turbo guys have gains like that, but never thought the NA guys would, and that hasn’t even been seen on the s/c guys yet!

#10

if you want a k-sauce x-pipe, ill sell you mine. lmk

yea i was ready the gto forum and there saying is back pressure is the devil. the whole “NA cars need back pressure or you will lose power and torque” is the biggest bunch of bologna. torque is in the nature and make up of the motor. you dont lose torque, it just shifts the powerband up the rev range.

#11

^Yea, but if I’m changing from my 2.5" F.I. (which I’m not really planning on anytime soon), b/c I want to go bigger, I want a bigger X-pipe as well :wink:

Also, I’ve read the same stuff, but what I don’t get is with my e-cutouts open (placed right before the mufflers) on my “frakenstien” 2.5" catback, I def lost some power & response (and I have the logs back to back to prove it). Now that catback was crap I understand, so maybe there was too much shit in the way for it too matter, but that’s just my experience with the cutouts and zero back pressure. You could always buy some cutouts for a couple hundred and weld in like I was talking about to see the results, but I guess you’re a little past that now.

#12

Posting for beem:

“This is an excel program that calculates cross sectional area based on od/gauge/pipe count for different exhaust setups.”

pipe_diameter.xlsm (21.6 KB)

1 Like
#13

^cutouts before the crossover?

for the excel sheet you need to enable macros, its not a virus so relax even though excel is gonna through a hissy fit

#14

i think the length of the exhaust has a alot to do with it. not sure though. maybe count could chime in and tell us his thoughts

#15

Correct about the macros, good point there. (maybe I’ll change the file to a killer virus later for shits & giggles)

I don’t mean as “ideal” I just meant as an easy way since that 1.5’-2’ section of pipe is pretty simple and would be easy to replace rather than cutting into the middle of a catback, or in my case the F.I. that I could sell if I wanted to change. It’d kinda be tough to sell with two big chunks taken out right after the crossover.

Also, I just mean in the sense of mimicking JC’s run, b.c he was running completely open right after the headers was he not?

Yea I’m sure there is a lot to it. Like I mentioned, there was probably more wrong then right with my original setup. You should have seen Count try to take it all in, while at the same time a S/C is being strapped on.

#16

well what I’m thinking is the loss in response/performance could have been due to having the cutouts before the crossover… the stock exhaust manifolds really need some help sucking the gases out (what a good x-pipe will do) whereas the headers flow awesome and may not need the help as much

#17

[quote=“Maddog,post:11,topic:3030”]
Beem, think you got confused what I meant. I had the cutouts literally right before mufflers on old setup. Now I have headers and F.I. obviously. I was just saying in an attempt to re-create no catback as JC did, you could put thin where the cats would go on a header car. I only say this due to the expense of 2 new sections vs patching up a nice catback.

I’m not doing it either way, I’ve got too much other stuff to deal with as is, but was just mentioning to try and confuse people obviously.

LOL:

http://i278.photobucket.com/albums/kk89/mbgt72/My%20Audi%20S4/Exhaust%20and%20skid%20plate/P1010108.jpg

#18

oh thought you had them under the car by the cats, my bad

#19

I am not fond of my Sebring mufflers on my 2.5" FI exhaust… I did not see those on your muffler charts? But I would like to replace with something louder.

-91, I can not wait to hear your car!

#20

@91 thanks for the welcome

@Vdub I’m pretty sure if you go catless you’ll be happy with them. But to each his own…especially when it comes to exhaust volume and note.

Referring back the the information in the original post. They dyno’d the car with no mufflers and actually lost HP compared to the stock exhaust. What would cause that power loss besides lack of back-pressure? Flow most certainly increases with no mufflers but Maddog states he felt as though he lost some power while using cutouts. Could that power loss be tuned away?

Sorry for all the questions but that’s all I have because I sure as hell don’t know the answers…haha.