Straight pipe or X-pipe - The Unofficial BMW M5 Messageboard (m5board.com)

AlLmItEeM5 · 23rd August 2006, 09:46

hello all. i have a local muffler shop made a custom magnaflow exhaust for my car. i decided to go with the straight pipes. the high pitch tone sounds really good but didn't notice much on the performance side. lately i notice that my low end torque is gone. can anyone tell me in their opinion or expertise which is better? straight pipes or x pipes is better?

Carrera2RS · 23rd August 2006, 10:31

Quote:

Originally Posted by AlLmItEeM5

hello all. i have a local muffler shop made a custom magnaflow exhaust for my car. i decided to go with the straight pipes. the high pitch tone sounds really good but didn't notice much on the performance side. lately i notice that my low end torque is gone. can anyone tell me in their opinion or expertise which is better? straight pipes or x pipes is better?

The xpipe is there for a reason, this forms part of the pulse tuned exhaust. It would be expected that removing this reduces torque. Given very little else is changed I would put the xpipe back in the same location (ie approx distance from manifold etc)

This xpipe is no different than running a 4-1 and putting individual pipes on each cylinder as an alternative - yuk

Pressure waves from each cylinder assist scavenging from alternative cylinders, the maths of this is well documented (rules of thumb) and can be accurately modelled on sophisticated programs like Ricardo wave, Engine expert, and simpler systems like dynomation etc

In short the xpipe does something worthwhile, the strength of the pulses at the distance past the cats and manifold will reduce the impact over header lengths, but it is there for a worthwhile reason....

I'd go back to the shop and mod your exhaust

BBM5 · 23rd August 2006, 11:35

This might explain why i've been feeling a little short changed by the low end torque on my beast. The previous owner had straight pipes put in, in place of the stock resonator which acts like an x-pipe.

badboypolar · 23rd August 2006, 17:27

the stock resonator is not a x-pipe. the stock configuration has an H pipe right after the cats before going into the stock resonantor.

BBM5 · 23rd August 2006, 18:30

Thanks for clearing that up, whats the difference between X and H? and would removing the H pipe for straight through have any detrimental effect on power/torque?

Absinthe · 23rd August 2006, 18:40

I have a feeling you are have that inclination about your TQ more due to the 2 ton weight of the car.

I had my resonators chopped as well, made no noticable performance difference, frankly made very little volume difference too, just a little angrier at WOT.

badboypolar · 23rd August 2006, 19:23

The X configuration greatly increases scavenging in the exhaust system. Instead of pressure being equalized by a smaller, more restrictive straight piece of pipe, the sides come together in a much more effective design. The X section is larger, and the pipes angle directly into it, meaning the airflow does not have to try and jump from one side to the other to equalize pressure; it is a much smoother transition, leading to better flow numbers than its H-pipe brethren.

From BBK performance website.

AlLmItEeM5 · 24th August 2006, 00:10

thanks carerra 2rs. i kind of figured that.