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MG MGB Technical - Air Cleaner Velocity Stacks

With the help of the updated and even more extensive SteveS Manual that Steve Strange has just made available to all of us (hats off to the effort and generosity) I have been pulling the pieces together for a set of Bob Cleaners. Pretty simple concept with good instructions readily available for the basic setup.

I thought I was on the right path until I read Steve's comments on installing velocity stacks on the inlet of each carburetor. The best option appears to be a pair of 1 1/2" deep velocity stacks with a 7 taper and a 0.250" radius (APT Part# RP-HS4). They don't sound like much, but Steve notes that they provide the benefits of "drastically reducing the contraction of the airflow at the mouth of the carburetor.......will help to accelerate the velocity of the fuel/air charge, maintaining fuel suspension in the airflow and enhancing volumetric efficiency at high engine speeds." All pretty good stuff I'm thinking.

Checking out the Advanced Performance Technology website for the velocity stacks, (they are beautiful litte units and it's a shame they will be covered up when installed), it appears that these need to be bolted onto the air cleaner base plates and use the same bolt holes as the Bob Cleaners.

I'm sure I'm missing something, but my question is how do I get the velocity stacks bolted in place and still bolt the covers down if I'm using the same bolt locations?

Thanks all - Joe

Joe Lucas Manitoba

Don't use bolts. Use long studs and nuts.
Steve S.

Stacks also make it easier to use a Unisyn gauge to balance the carbs.

Dan Robinson

Perhaps I should elaborate. In order to minimize disruption of the airflow, the velocity stacks should be mounted with the bolt heads on the inside of the airfilter, while the mounting studs for the airfilter covers should be located as far as possible from the mouth of the carburettor.
Steve S.

Steve S - you sure take care of your followers!

Bolts installed with the heads inside the air filter will really keep things very clean and out of the air stream.

That makes excellent sense but leads me to another question.

The studs holding on the airfilter cover would then have to be run outside of the velocity stacks (closer to the outside circumference of the airfilters) and then be bolted (nutted) through the baseplate - is that the case?

I have to say that the latest edition of your Manual is some pretty heavy reading. It's going to take many enjoyable days to work through the depth of knowledge that you've kindly shared with all of us. I see that you're already up to 113 emails looking for copies so your efforts are certainly going to help a lot of great little cars around the world.

Dan - hadn't thought of the Unisyn situation, another bonus that comes from listening to our experts!

Thanks guys - Joe
Joe Lucas Manitoba

You said it best: "The studs holding on the airfilter cover would then have to be run outside of the velocity stacks (closer to the outside circumference of the airfilters) and then be bolted (nutted) through the baseplate". K&N makes a dandy set of chromed plates for the SU carburetttors already set up with this worthwhile feature, along with the two necessary vent holes for the dashpot.
Steve S.

This thread was discussed on 24/12/2006

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