[Zmagnette] Stub stacks

monster at caverock.net.nz monster at caverock.net.nz
Fri Nov 15 13:55:02 MST 2013

On 16.11.2013 08:03, Allen Bachelder wrote:
> The K&Ns are
> slightly noisier than stock MGB air cleaners. I don't think that's
> because they're less efficient. My guess is that they provide less
> acoustic insulation.

I'd agree with this - there is a lot of material in an oil-bath filter 
and a substantial metal container.

> Kelvin - your point is well-taken. Are you saying that even if
> everything else is spot-on, it's still not worthwhile to mess with
> velocity stacks for those of us who spend most of our lives below 
> 3500
> rpm?

Barney Gaylord has a section on stub-stacks at his website:

Interesting commments from one of the MGA crew:

"Just been for a 25 mile drive to road test them, and the throttle 
response, in top gear particularly, is very noticeable over 2000 rpm. It 
makes the 40 to 60 mph acceleration noticeably better and more fun to 

Another had a book with figures for the factory installed stub 
stack/backplate on the MGB - made a 5% improvement and BMC were stingy 
with unnecessary parts!

I would certainly agree that I wouldn't pop a pair of these on until 
you've got the ignition working well and SUs balanced, tappet clearances 
set etc.


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