I'm putting together a custom exhaust setup and so far the plan is just two tubes flowing straight off each cat. what exactly is the function of the x-pipe? I read places that it INCREASES horsepower but it seems to me like it would just add backpressure and thus DECREASE it, so I'm confused. other than performance, does it do anything for sound? thanks

 

i heard that it'll rob a little top end but add some low-mid range power by exhaust scavaging, also for sound i think it is supposed to make it sound more like the z does stock. I'm actually thinking about getting the magnaflow x pipe muffler to replace my 2 resonaters on the injen i have like another member here did.

 

The objective of the “X” and “H” pipe is to equalize the pressure on the left and right sides of the exhaust. Some custom and aftermarket tuners prefer this method to get the horsepower and toque numbers that they are looking for.

A manufacturer such as Injen negates either method. I believe that combining exhaust gases at any point changes the “sound” of the system. The difference in sound between a “X,” “Y,” “H,” and straight-back system is neither better or worse, its simply different.

 

In the Sport Z exhaust shootout the Stillen made more torque than others and was the only design utilizing the X.

 

An x-pipe adds back pressure, but it creates another phenomenon known as scavenging. To understand scavenging you have to realize that exhaust gases are not flowing out consistantly, they are flowing out in pulses. The pulses correspond to the alternating power and exhaust strokes of your typical combustion engine.

In the Z, we have 6 pistons... when pistons 1,3, and 5 are producing power (power stroke), pistons 2, 4, and 6 are sucking in air and pushing out exhaust gases (intake/exhaust stroke). The header/cat arrangement in the VQ is arranged in such that the exhausts gases from 1, 3, and 5 are isolated from 2, 4 and 6 until the Y-pipe. At which point they mix. In a true dual setup, the exhaust pulses never mix.

The advantage of mixing the pulses with a y, h, or x pipe are that when pistons 2, 4 and 6 are expelling exhaust gases, there is actually a vacuum (harmonic and physical) effect caused by the fast moving pulses. With a y/h/x, this vacuum effect travels up the header through to the exhaust ports of pistons 1, 3 and 5 and help to expel MORE exhaust gases from each of those pistons during their exhaust strokes. When it's 1,3 and 5 turn for power, 2,4 and 6 benefit from the vacuum. It's a repeating effect, that actually yields a non-trivial amount of torque on some engines (proven by NASCAR).

The key to the effectiveness of the h/y/x crossover is its position. There is an optimal location downstream from the headers that a cross-over is most effective, allowing the vacuum effect of the exhaust pulses from one bank of cyclinders to travel up the other bank at the exact moment the exhaust ports are opening. Old-school technique is to spray a light layer of paint on the headers, past the cats, all the way to the resonators (or middle of the length of exhaust tubing). The location where the paint burns off after about 15 minutes of driving, is roughly the best location for your crossover. This varies from exhaust system to exhaust system so the only way to find out for certain is to do the test yourself. Not very scientific, but this has been a proven technique for over 20 years (on hotrods).

The other effect of the crossover is to balance exhaust harmonics (i.e. sound). The sound is subjective, however in general, the exhaust note should be smoother, and also slightly higher pitched (although some have noticed a decrease in pitch - it depends on a lot of factors). IT SHOULD be higher pitched in theory however because the sound wave eminating from one of your two exhaust pipes has now changed from a high magnitude, low-frequency wave to a low magnitude, high-frequency wave.

This all sounds great, however there is a negative side-effect... the potential for slightly lower high-end hp. At high rpms, the frequency of exhaust pulses is high that the scavenging effects are nearly negated, and all that's left behind is an obstruction in your exhaust stream (namely, your crossover pipe).

Hope this helps.

btw, I'm the one that put an x-pipe in my injen SES... seat of the pants, my butt-dyno sucks so I can't tell you for certain the impact it's had. What I did notice was a significant change in sound. IMO, the "stock" injen had a loopy, uneven idle, as well as a raspy tone in the higher rpms. Adding the x-pipe has nearly eliminated the raspiness, and the idle is now smooth as stock. It has also returned some of the stock sound that makes the VQ so unique, but retained the deep aggressiveness and sweet looks of the injen ses. Anyway, that's just my opinion though... to some the injen sounds just fine. It's all relative.

 

Strife - Excellent Write-Up. I have the Invidia G200 which is also a separate dual system. I noticed the same lopy uneven idle. The sound at the pipes also sounded like two 3 cylinder engines. I had an "H" pipe welded in, and as you note, the lope went away, and the idle smoothed right out, as did the sound exiting the tips. IMO, the system should have come that way from Invidia. I believe that Injen is coming out with a second version of their exhaust with an "H".

Lou

 

Injen is just following my lead: J/K

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