Another x-pipe exhaust question, but need technical details

[Professor]

Still looking forward to hearing it.

[TiAgX5]

Same here.

[Papa13]

Sorry for the delay. I just got my car back yesterday. This is cold. I will get a warmed up video soon. Hope you all like it.

BMW X5 e53 4.8is Res delete w/ stright pipes (cold) - YouTube

[TiAgX5]

Will sound less raspy when warmed up, sound tolerable cold. Will be doing mine soon.

[Papa13]

I think it sounds great when warmed up. Not raspy at all. Hope this helped. I will still get a video posted of the truck warmed up.

[jbfrancis3]

A couple thoughts having completing this myself on a 4.8is two months ago:

- $150 is too cheap. I suspect the shop might be using an aluminized x-pipe or 308 stainless. Neither would be acceptable as they'll both rust. The stock system is 304 stainless and Magnaflow is a known manuf. of 304 x-pipes. I'd stick to their product and 2.25" inlet/outlet is the closest match to the stock system's metric tubing. Make sure the shop also uses a mig wire (they sure aren't going to tig for anywhere near that price) that is meant for 304 and won't rust/corrode.

- You will not end up with a CEL unless the 4 sensors are handled or stored improperly, or contaminated with metal filings. To be safe, request that the shop they mark each sensor's location, completely remove then, and cover the inlets with masking tape. This won't entirely prevent sensor failure as sometimes removing them will kill a sensor on its last legs.

- Raspiness will only be heard when revving in park/neutral. Otherwise, under load, you won't get a raspy note. Nor will you end up with a very load exhaust note, its simply more pronounced. You do hear it more in cabin through, you guessed it, resonance. Its not obnoxious or in any way over-bearing.

Hope that helps. And this is highly recommended, you won't be disappointed!

[TiAgX5]

Originally Posted by jbfrancis3

A couple thoughts having completing this myself on a 4.8is two months ago:...... And this is highly recommended, you won't be disappointed!

ANYONE, including myself, who has been at a dyno test where unequal length exhaust tubing was in place upstream of an X, H, or Y pipe, would NOT recommend it! This condition actually DECREASES performance at several areas thru the RPM range.
ANY knowledgeable "custom" exhaust shop owner/employee will tell you this if they're being honest with you and not just interested in seperating you from your money. EQUAL LENGTH TUBING UPSTREAM OF X-PIPES ONLY!!!!!

Food for thought below......

X Pipe Exhaust??????????????? - SRT8 Forums and Owners Club - 300C - Charger - Magnum - Cherokee

[jbfrancis3]

Originally Posted by TiAgX5

ANYONE, including myself, who has been at a dyno test where unequal length exhaust tubing was in place upstream of an X, H, or Y pipe, would NOT recommend it! This condition actually DECREASES performance at several areas thru the RPM range.
ANY knowledgeable "custom" exhaust shop owner/employee will tell you this if they're being honest with you and not just interested in seperating you from your money. EQUAL LENGTH TUBING UPSTREAM OF X-PIPES ONLY!!!!!

Food for thought below......

X Pipe Exhaust??????????????? - SRT8 Forums and Owners Club - 300C - Charger - Magnum - Cherokee

^Forum theory at it's best...

You're assuming quite a lot to make that blanket statement, the biggest being that the exhaust manifold is comprised of equal-length runners...which we know the N62 does not employ.

And let's not lose sight of performance gains/reductions, as a percentage of overall performance. Numbers will always change, but is significant enough to debate? Also, for performance, do you mean horsepower or torque?

Finally, until we measure how flow (again, if we were to assume better flow translates to better performance, another blanket assumption) is affected through a various exhaust configurations, we are speculating at best.

Let's stop being BMW weenies and not lose sight of the big picture! (my $.02).

[TiAgX5]

Originally Posted by jbfrancis3

^Forum theory at it's best...

You're assuming quite a lot to make that blanket statement, the biggest being that the exhaust manifold is comprised of equal-length runners...which we know the N62 does not employ.

And let's not lose sight of performance gains/reductions, as a percentage of overall performance. Numbers will always change, but is significant enough to debate? Also, for performance, do you mean horsepower or torque?

Finally, until we measure how flow (again, if we were to assume better flow translates to better performance, another blanket assumption) is affected through a various exhaust configurations, we are speculating at best.

Let's stop being BMW weenies and not lose sight of the big picture! (my $.02).

The link I posted and my statements are referring to unequal length tubing when comparing left cylinders to right cylinders, not unequal length headers. Unequal lenth headers have identical tubing length when comparing left bank tubes to right bank tubes (cyl 1 & 5, 2 & 7, 3 & 6, and 4 & 8 all have common tube lengths). The firing order being 1,5,4,8,6,3,7,2, this keep the pulses out of phase in the left and right exhaust systems. The ONLY way to gain the scavanging effect of an X-pipe is to KEEP these pulses out of phase. The V8 X5s have an additional roughly 20" of tube length connecting the left cyl bank to the resonator (where the X-pipe is mounted) when compared to the length of the tubing connecting the right bank. When you have this unequal tube length left to right, you have an in phase exhaust pulse condition at the X-pipe at MANY RPM/load/throttle,valvetronic/ positions. When in phase exhaust pulses reach the merge point of the X-pipe you have a pressure spike and flow restriction resulting in both hp AND torque loss.

This is hardly forum theory, many have seen it personally on chassis dyno tests of exhaust systems. You will NEVER see a system designed for an application that has unequal left/right tubes upstream include an X-pipe from any reputable manufacturer, Corsa, Heartthrob, Magnaflow, Henessey, the list goes on. Take a look....prove me wrong......you can't! Find just one system from a top tier manufacturer for an asymmeritical left/right tube length application and I will bow to your superior knowledge. The big picture you need to see here is that an x-pipe in this application robs both hp and torque.

[jbfrancis3]

Originally Posted by TiAgX5

The link I posted and my statements are referring to unequal length tubing when comparing left cylinders to right cylinders, not unequal length headers. Unequal lenth headers have identical tubing length when comparing left bank tubes to right bank tubes (cyl 1 & 5, 2 & 7, 3 & 6, and 4 & 8 all have common tube lengths). The firing order being 1,5,4,8,6,3,7,2, this keep the pulses out of phase in the left and right exhaust systems. The ONLY way to gain the scavanging effect of an X-pipe is to KEEP these pulses out of phase. The V8 X5s have an additional roughly 20" of tube length connecting the left cyl bank to the resonator (where the X-pipe is mounted) when compared to the length of the tubing connecting the right bank. When you have this unequal tube length left to right, you have an in phase exhaust pulse condition at the X-pipe at MANY RPM/load/throttle,valvetronic/ positions. When in phase exhaust pulses reach the merge point of the X-pipe you have a pressure spike and flow restriction resulting in both hp AND torque loss.

This is hardly forum theory, many have seen it personally on chassis dyno tests of exhaust systems. You will NEVER see a system designed for an application that has unequal left/right tubes upstream include an X-pipe from any reputable manufacturer, Corsa, Heartthrob, Magnaflow, Henessey, the list goes on. Take a look....prove me wrong......you can't! Find just one system from a top tier manufacturer for an asymmeritical left/right tube length application and I will bow to your superior knowledge. The big picture you need to see here is that an x-pipe in this application robs both hp and torque.

Here's the Magnaflow system for an e46 323i:



You'll probably pick up on this but for others, this e46 has an inline-6 with two exhaust manifolds, one for cylinders 1-3 and one for 4-6. Of course, the foremost manifold must have additional tubing versus the aft manifold to mate up to pictured cat-back system. And no, the mid-section bend does not make up this difference.

The point is, you can throw out all the theories (and often proven) but they must be taken in the proper context. Translation: the scavenging/pulsations/phasing simply doesn't matter this far downstream. Which is why I originally made the comment about equal length headers, that does tend to matter in a given system and the effects do tend to warrant discussion. In our example here, they don't.

I'm not trying to be obnoxious for the sake of being obnoxious - I was triggered by your posting suggesting that would be an egregious error and degradation of performance to install an X-pipe in the resonator's location for an N62. It's not.