V8 exhaust balance pipe

[kabaman]

I thought someone might find this useful.

I got my 289 running last weekend with a view to breaking in the cam. The system is my own 4:2:1 manifolds, 2 1/4" system and one dual box where box banks share it under the transmission tunnel, all stainless. I assumed that a balance pipe wouldn't be needed as the box bleeds between both cylinder banks. When I started it up though it was bloody deafening!

So, in desperation I fitted a 2" balance pipe between the banks just after the end of the manifolds. I had no idea whether this would make any difference but I didn't know what else to try.

The good news is that at low RPM including idle it's much better - much deeper burble, much less crackly and quieter.

So for anyone wondering if a balance pipe might offer an advantage on a co-joined exhaust system - it does.

My theory on this which might be wrong is that with each cyclinder firing you get a pulse of spent gas effectively a tube of gas headinh through the system, but susperimposed upon this is a sound wave travelling much faster. I believe that a proportion of the sound wave goes down the balance pipe and is cancelled somewhere by the next pulse rom the other bank (two waves hitting and cancelling). I'm not sure how much scavenging and flow you get across the balance but it's the sound wave cancellation that matters. Compare this to when the sound waves meet in the box - at this point it's not a clean sound pulse but a multitude of waved coming through the peforated tube and it's all but impossible to expect any part of that to cancel (well any more than you'd expect them to add).

Anyway - that's my guess - and it certainly works.

Cheers,

Neil

[Slow M]

Do yourself a huge favor and read the article!
http://www.popularhotrodding.com/enginemasters/art...
It's stated so straightforwardly, that even I can understand it.

Right click it now, and send it to your hard drive. This is worth always having access to.

Also, may I suggest you get PipeMax software to analyse your system? From my engine design slave's[1] feedback, the results are VERY repeatable in real life.

Best,
B.

[1] AKA my elder brother and favorite engine builder.

[kabaman]

It's a good article - and not one I'd found before, thanks. With a SWB chassis and ground clearance requirements options are limited. I guess I'll find out when I dyno it as to whether I f*cked up the design.

N