XSeries-forum

It is often discussed about X pipes and H pipes but always in reference to the V8’s. Having crawled around under the B3 Alpina for several days I couldn’t help noticing that it has an H pipe fitted to Alpina’s own exhaust. As I assume their engineers know more than most, there must be some benefits, after all they managed to add 87bhp. Wondered why there isn’t more discussion by the 3.0ltr owners?

Interesting, as you say Alpina engineers are no slouches when it comes to finding an extra HP or two. It would be interesting to compare an M3 system never looked at one of those.
I have seen underneath my AMG's though when I ran those V8 with H pipe from memory

If I'm remembering this correctly from when I researched exhaust system design in the early '80s, and it still holds true, then putting an X- or H-pipe into a twin pipe system will effectively shorten the secondary pipes of the manifold. What this will achieve in terms of engine performance is to move the power-band higher up the rev-range. It's all about "scavenging". But it's not just about the exhaust. Cam timing, duration and lift also come into the equation. To an extent, one dictates the other. Alpina's exhaust design will be influenced by their choice of cam profiles.

There wouldn't be much noticeable gain from putting an X or H into the system of an otherwise standard 6-cylinder. With a V-engine running a fully twinned system the X or H smooths the uneven exhaust note, that's the usual reason for doing it.

EDIT:- Since I posted ^^^ that, I found this..... https://www.carid.com/articles/are-x-pi ... stems.html

Well I have a 4.4v8 and I have been contemplating removing the centre silencer and putting in a H pipe. Not an X pipe as I want more torque and volume lower in the rev range. I may also swap the rear mufflers to 4.8 ones as they give a slightly deeper tone
We will see...

Just for your interest I changed my exhaust for no other reason than the back boxes rusted enough to develop holes. I fitted a Magna flow system consisting off an enclosed X pipe and two resonators with NO back boxes. Sounds nice not intrusive in any way inside the vehicle, doesn’t resonate, very good quality hand made by Profusion Exhausts.