I agree with everything JCL has said, but just be careful when putting a too large of an exhaust. The car (if an automatic) still needs back-pressure for the torque converter. This *could* be the reason why TowX had to tow in lower gears because there wasn't enough back-pressure for the torque converter.

I wouldn't consider putting a larger diameter exhaust on, unless I was doing something like a forced induction system and had more exhaust gas flow to deal with.

I do agree that reducing the back pressure can reduce low-end torque. I don't see the connection to the transmission torque converter, but it can reduce engine torque. The torque converter is downstream. And once you are moving you should be getting it into lockup mode and removing the torque converter from the equation in any case.

I added the 4.6is exhaust on my 03 4.4i, it appears that the 4.6is has 2.5" tubing vs 2.25" from resonator to the mufflers, Side by side, visually it appears to be a larger pipe leading up to the mufflers. At any rate, it does seem to make my car purr a little bit nicer when i step on it going down the highway, not sure if there are any hp gains, but the sounds makes me feel like it does!

I see your point, but ultimately, the connection is that there may not be enough low-end torque to lock-up the torque converter. I'm talking in the worst case scenario where the engine would simply stall. The torque converter is downstream from the engine, but still coupled to the motor via the flywheel.

It's almost like taking off in 6th gear on an MT car. But I think I digress and you and I agree that backpressure is somewhat needed for low-end torque.

Great this thread has just thrown another bone in the mix... I have a 4.6is replaced resonator with straight pipe, not happy at all with the sound or feel. The sound is not smooth and I feel a loss of torque with a lot of back pressure on deacel.

So I ordered the X pipe and it will be here today, but based on what Tow is saying should I have gone with a simple H?

Don't use me as an example. I seem to be the only one who lost torque when I did the x-pipe. Perhaps if I'd moved it 2" forward or 3" back it might have worked, but based on where I had it mounted I was extremely disappointed. As I've said in other posts, I lost so much power/ torque at 2500-3500 rpm that I had to tow in one gear lower than stock. If I had to guess, I lost 20-30 lb-ft in that rev range. Sounded great at 5500, but I don't drive that way.

TowX, can you tell me if there is a difference in sound between the x-pipe and the h-pipe.
I'm leaning on the side of a h-pipe because I need all the torque available to tow my racecar, and also, it is simpler and less expensive to install.
I just want to know if there is no burble or pop pop from the exhaust on deceleration.
Thanks.


EDIT:
I just found this video on YouTube where the guy tests a x vs h-pipe back to back on a Mustang. The h-pipe seems to have a lower tone compared to the x-pipe. Did you experiences the same TowX?
YouTube - Mustang Exhaust - H VS X Pipe

The H is a bit deeper, maybe a bit raspier, than with the X. But I only had the X on for a week and pulled it off. The only time the exhaust pops or burbles on decel is first thing in the morning when the exhaust is cold. Once warmed up, no popping at all. Though on some cars I like the burble, stainless steel mufflers on a 911 or 930 burble on decel and I think it sounds good. But my 4.4 doesn't. Frankly from inside the car there's just a bit deeper rumble, and from outside a nice sound that isn't loud at all. And towing my trailer for hours at a time is comfortable, no resonance or loud exhaust that can get tiring on long tows.

What are you towing?

Thanks for the reply.
I'm towing a E30 (the one in my sig).Right now I use an Econoline, and my E46 is my daily driver. In April, I will sell both of these vehicle and replace them by a 4.4 X5, and of course some mods including a sportier exhaust note. :D

Very nice. I tow my track car, and try to avoid driving offroad as best I can. :rofl:

My '04 4.4 tows extremely well. When I was pulling my 911 on my open aluminum trailer it was no big deal to set the cruise at 75 and go for hours at a time comfortably.

Unfortunately my new enclosed trailer has max'd out the tow rating of the X5. By the time I load the car (2450 lbs) into the trailer (2900) and throw in 8 spare wheels and tires (350), tool chest (250) and spare parts (250), I'm at the tow rating. Sure, the engine has the power, but I can't come close to being able to see around the trailer. I've tried the aftermarket mirror extensions but at highway speeds they vibrate so much that anything along side is just a blurr. Too bad because the 4.4 pulls so well, and being able to leave the Steptronic trans in 5th at highway speeds is the perfect powertrain setup. I can pull at 70 pretty easily, just can't see. So sadly I'm now looking at changing vehicles- Yukon Denali or Infiniti QX56. Might just sell my 528 and keep the X5 as my daily driver though.