MGB & GT Forum

I mentioned several months ago when I first bought me B, that it had a horrible mid range drone sound that at 3000 RPM was so loud forget any conversation. Or hearing the engine or the normal exhaust note. I hated the sound of this car.

The PO sometime in the past had a professional replace the resonator with an enormous box, one bigger than the muffler. Today I cut it off and replaced with a length of straight pipe.

Oh, gawd, the music! It finally sounds like I imagined an MGB would/should sound like with, a deep throaty growl on acceleration, and even a wonderful throb waiting at a light. It sounds like a much bigger engine, like a sports car should.

But what really blew my mind is that car is significantly, noticeably faster. I noticed it instantly I pulled away from the curb, and I know it's not just because it sounds faster! Even in 4th it has decent acceleration. Previously I had thought it was a bit of a slug for power, and now it's like I pulled up the anchor I've been dragging behind me all this time.

I checked the resonator - which clearly was the wrong one - and yes, it's straight through without any baffles. But somehow dumping the exhaust into that large space somehow created a vortex or screwed up the flow and turned it into a train whistle and created serious back pressure. And this is an '80 with the crummy exhaust manifold!

Has anyone every heard of something like this? I know folks play with low back pressure exhausts to squeeze out max HP, but this difference is truly amazing.

Part of the function of the exhaust system, is to create a partial vacuum behind the pulses of gas sent down it. This helps to evacuate the combustion chamber so that a full charge can enter it.
Sticking a big expansion vessel in the middle, or even grossly over-sized pipework, just ruins that vacuum extraction system.
Hence it doesn't run as well as it should.

---

soonerv8
Do it right, do it once!

MGBs can and do sound great with the right set of pipes! One of my favourite things about the car. I don’t even have a radio!!
Enjoy your newfound orchestra!

Which begs the question how it works with extremely high powered blown engines that just have header pipes, but no doubt the entire system is engineered for minimum back pressure.

Your key word is "blown" I assume. i.e., not relying on normal air pressure, which is acting as the CC is emptying.

---

soonerv8
Do it right, do it once!