what if we used 3 inch...

[Canty]

I deal with turbo cars a lot. I have 2 of them. and I know that with a 3 inch exhaust you really open up the power level. I was curious how our NA Cobras would do with 3 inch headers back exhaust? My buddy here says they wont run, I am just kinda curious as to what you guys think.
Matt

 

[CobraKalas]

unless your making a disgusting amount of NA power, the 3" exhaust will be overkill. It will sound sweet but your going to lose some torque due to the lack of backpressure. It's just not economical.

 

[SlowSVT]

A 3" exhaust will lower the exhaust velocity and won't scavenge the cylinder as well. I would not go over 2 1/2" on our little 4.6 in an NA or PD blown car.

If it was a turbo car then "yes" a 3" would be a good choice.

 

[Canty]

OK thanks guys...I never put it together. Larger pipe means less velocity equalling less scavenging.

 

[2001asp]

I disagree.....The theory is right......But, I made a bunch of power with my 3 inch exhaust. Mostly torque, I don't have cams either. My exhaust sounds great, is all aluminum, and tucks up well.

 

[olgreydog7]

I disagree.....The theory is right......But, I made a bunch of power with my 3 inch exhaust. Mostly torque, I don't have cams either. My exhaust sounds great, is all aluminum, and tucks up well.

Do you have before and after dynos or just sotp dyno?

 

[SlowSVT]

I disagree.....The theory is right......But, I made a bunch of power with my 3 inch exhaust. Mostly torque, I don't have cams either. My exhaust sounds great, is all aluminum, and tucks up well.

I'm not sure what a "bunch" equates to. I might help if you're running a radical bumpstick and run the engine north of 7 grand all day. Form idle for low end grunt all the way 6 grand a 2 1/2" system is the way to go. There were quite a few Terminator guys who swapped out the 3" and went back to 2 1/2" exhaust and stated the engine responds better where the bigger pipe didn't come on till close to redline. Having two 3" pipes connected to only 4.6 liters is too much cross section.

 

[Canty]

2001asp do you have a dyno sheet on that? I am kinda curious to see what gains you made and where they were.

 

[K2AHollywood]

seriously I dont buy that for a second its way to large of an exhaust for these torqueless wonders

 

[2001asp]

Here is a pic of my dyno sheet. Imageshack - dbz3kd8.jpg There is a stray line at the top,,But those are my three pulls. The highest pull was with the o2 sensors turned off. I had 7-11 gas that day not knowing they have crappy gas. I use BP now. Do you see anything different about my dyno graph? Please let me know if you really think I am losing any power w/ a 3 inch exhaust?oke:

 

[SlowSVT]

Here is a pic of my dyno sheet. Imageshack - dbz3kd8.jpg There is a stray line at the top,,But those are my three pulls. The highest pull was with the o2 sensors turned off. I had 7-11 gas that day not knowing they have crappy gas. I use BP now. Do you see anything different about my dyno graph? Please let me know if you really think I am losing any power w/ a 3 inch exhaust?oke:

You are a bit sketchy on the details here. I see you are making more power even at low end where those pipes will hurt you. Long Tube headers on a Terminator are only worth about 10 hp over the stock logs yet you seem to be making twice that.

Exactly what changes were made to the car (including the tune ) between both runs? Please provide details.

 

[2001asp]

I wish I could provide you with more details other then it was tuned by DTP Performance here in chesapeake VA. by Brent at DTP. He is a former owner of a Mach1 and tunes Dohc4.6 daily. He is the go to guy for in the area and his tunes are supposed to be sick as hell. I wish I new what he adjusted. As for my mods, they are in my signature in the above post. Before I ordered the exhaust, I spoke to JBA a few different times to try to speak to different sales people. They all said the same thing....3 inch for the N/A cobra and 2.5 for GT. I let him know that my cobra was N/A. Still they said the R&D on this muffler system was dead nuts perfect. I was considering the Magnaflow, but ended up with this. One other thought was that they said the most important thing was to make sure I did NOT step up to a 3inch mid pipe. Also to stay catted.

 

[Canty]

well, I guess a picture is worth a thousand words...thanks 2001asp

 

[SlowSVT]

I wish I could provide you with more details other then it was tuned by DTP Performance here in chesapeake VA. by Brent at DTP. He is a former owner of a Mach1 and tunes Dohc4.6 daily. He is the go to guy for in the area and his tunes are supposed to be sick as hell. I wish I new what he adjusted. As for my mods, they are in my signature in the above post. Before I ordered the exhaust, I spoke to JBA a few different times to try to speak to different sales people. They all said the same thing....3 inch for the N/A cobra and 2.5 for GT. I let him know that my cobra was N/A. Still they said the R&D on this muffler system was dead nuts perfect. I was considering the Magnaflow, but ended up with this. One other thought was that they said the most important thing was to make sure I did NOT step up to a 3inch mid pipe. Also to stay catted.

Something told me there was more to this then meets the eye.....there always is.

What you’re saying is that you’re really running a 2 1/2" system connected to a 3" catback. That is not a 3" system. JBA may have done some testing on a few configurations and that's has been their observation but Bassani or Borla may have a different take on all this. I wonder what JBA recommens for a blown Cobra? Maybe a 3 1/2" systems :dw: You see where I'm going with this? There are so many variables involved here and they don't have the resources to test them all. I wish JBA would pay more attention to the quality of the headers they sold me which the flanges were so warped I has to get them planed and the overlapping metal blocking the rear runners which required grinding.

Put a 3" mid-pipe on your Cobra and run it on the dyno and see what it does to the torque curve? That is a more critical part of the exhaust. I could be wrong but my money is on the loss of some power and an engine that stumbles a bit. Before and after dyno runs, did you swap out the stock catback? That could have been responsible for some of the gain but I bet the tune by DTP Performance was responsible for the majority of it. All he had to do was push the timing and suddenly you got 10 - 20 more hp on tap.

You need to be very careful making simple statements without considering all the variables that other people who are looking for a simple answer will buy into. All it took was Canty to look at your dyno chart and now he is sold on a 3" system when in reality he doesn't realize where the gain actually came from. Who knows, maybe he will have better luck with a 3” system then the guys with blown Cobra's did.

:beer: