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MG MGB Technical - Air Filters for RB with twin SU conversion

Help, please. A friend has just added twin 1 1/2 SU's to his RB 'B with power brakes. Of course the standard 'B filter cans interfere with the brakes. I know this conversion has been done before. What have you guys used?

Thanks in advance.

TTFN
Derek Nicholson

Derek
A set of K&N conical airfilters are just about the only thing that will fit without getting into major changes. Be aware that these airfilters just barely have enough airflow capacity for stock engines, so performance increases will require major changes to a Rubber Bumper model. You can get a set from Advanced Performance technology (Part # SD-36) at http://www.aptfast.com/
Steve S.

Derek,

The only other solution is one you currently can't purchase from the catalogs. Have a custom air box built. I'm about to install a custom air box that has a 3" deep K&N at one end and is held on to both HIF4s using the standard stub stacks. There's other work that has been performed to enhance breathing, however, the box itself was built with the brake booster in mind (and test fitted on a late RBB). At the moment, my source for this box is not interested in pursuing this business, but rather did it at or near cost as an act of kindness (having examined the conical filters), so I'm not inclined to provide any information, beyond this description. There must, however, be someone who can look at the original twin SU filter arrangement and envision how such a box could be developed that draws air in from the front and supplies more than ample flow to both carbs, without any concern of brake booster fouling.

There are actually mutiple problems with the conical filter solution:

1. They're really not that great a fit to begin with...they clear the booster (in most cases), but have a tendency to not fit flush (without a rather thick cork gasket) on HIF4s (I can't speak to HS4s).

2. There are no radiused stub stacks, nor any room for them. To the extent that any air makes it to the rear carb, it would make it in quite roughly (not good for flow).

3. In fact the backing is a simple, cheap piece of thin aluminum...pretty cheezy to say the least.

So, you get the twin SUs and only realize a portion of the performance such a switch otherwise promises. Now, with that said, even with this restrictive filter setup, either type of twin SU setup will breath better than the STOCK ZS setup (which is hamstrung due to it's air cleaner, stock needle, and intake/exhaust setup) OR the Weber DGV (which doesn't have the greatest manifold, suffers from poor flow through a restrictive filter design [the "square air horns" protrude through much of the filter area], and often suffers from flat acceleration at low rpms when using only the first 2/3 of the throttle). On the other hand, my highly modified, custom ZS setup (the one you can read about in the archives), breathes better than a twin SU setup with the CONICAL filters (but that's another story...not typical by any means). So why am I going with a custom twin SU setup, I wanted to try something different and examine the possibiliites of this carb combination on my engine. The air box and other mods are ensuring it'll be a relevant change.

Anyhow, I hope this helps. Find a shop that'll do some custom work and consider having a box built. OR, go with the conical filters and use good gaskets on the openings to the carbs...otherwise, you'll have a problem with the seal. Moreover, ensure your engine mounts are in good condition. Otherwise, you may experience some fouling with the rear filter anyhow.

FWIW,

Barry
Barry Kindig

FWIW, I know someone who uses the K&N conical filters with the baseplate from the stock filter can for HS-4s. These plates have a radiused inlet, although it is pretty thin, it is a big improvement over the flat plate that comes with the K&Ns. This baseplate also seals much better against the carb body.
Mark B.

Thanks for the input, guys. For the time being, to try to get his car on the road while we seek another solution or $120+ for K&N filters, I've loaned my friend a pair of Vokes pancake filters from my MGA. I haven't heard from him to see if they physically fit. Anyone ever tried them?

TTFN
Derek Nicholson

Check the VB catalog for air filters, longflo.
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This thread was discussed between 30/03/2002 and 31/03/2002

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