Xoutpost.com - View Single Post - Absurd exhaust system proposal for e53 X5 3.0i M54 // headers back for under $1,250?

workingonit · #6 08-31-2021, 12:52 AM

It seems that the M54B30 engine was made for a balance of torque and horsepower, using higher compression to offset the undersquare design (stroke greater than the bore). I've seldom had a "stroker" engine before, and my favored engine type is "oversquare" (piston diameter greater than the length of stroke), so I'm just saying that just adding headers is an expensive exercise on a semi-stock engine with tight exhaust parameters.

My Chevy race engines were high compression, large bore, short stroke (except for using longer rods on some), and high-lift cammed. My penultimate 427 engine, barely streetable, used 2" headers (3/4 length tubes), and a collector with swing-away exhaust pipes, where I could easily substitute collector extensions in a few minutes (even better if I had a place to detach and leave my pipes and mufflers behind). That engine was good for sub-12 second 1/4 miles, and lasted for quite awhile. Then it blew when the #4 con rod vaporized.

When I replaced it with another 427, it became too race-specific for the street, and it was a real challenge to work on...especially due to the 2.5" header primary tubes. I had to index my plugs, so I had to struggle to get past the large tubes (finally resorting to partially removing them), rerouting oil cooler lines and filter for clearance, and using fire-proof matting under my seat (and over the flexplate blanket) to be able to survive the high heat given off by the large full-length headers/collectors/extensions just under me. Sure, the massive exhaust was warranted, and it made more power than the earlier exhaust system, but it was a pure race motor, after all. I'd never had changed it, if it was just for a small % gain.

I plugged some numbers I found into an exhaust sizing calculator, and found out exactly how restrictive the M54B30 exhaust is...designed for balanced torque/power. Looks to me like it's comparable to using "peanut port" cylinder heads on my race engine (I used massive "square port" Brodix heads, opened even more by Reher-Morrison CNC-machining); I would've retained most of the torque, but lost most of the top-end horsepower that wins races.

If it's power you want, get bigger cam(s), valves, ports enlarged on the head, or if you just want the sound of power, then use by-passes, remove the central muffler (replace with an X-pipe, too), and forget the expensive header. Too much money spent & too many problems often accompany such a change, IMHO.

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