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MG Midget and Sprite Technical - Couple of HIF44 questions.

What sort of performance difference would I see by fitting a stub stack to my HIF44 carb on my 1133cc mk3 Sprite? Also, I have a conical filter which looks exactly like a K&N, but isn't. I got it brand new off Ebay at about half the price of a K&N and it seems OK, but would I be better off going for the genuine article? ( tried to upload pic but it won't let me, even though it's the right size)
Thanks as always for any input.

b higginson

IIRC fitting a good stub-stack to a carb can improve air-flow into the carb by up to 6%. This is one part of the intake system (filter-stack-carb-manifold-port-valve) and what extra power you can achieve depends on the system as a whole.

You might need a small carb adjustment. You might see 1 or 2 bhp improvement. Small - but it's the sum of many small changes that can add significant grunt, often with better fuel consumption.

I'd go for the genuine K&N for its filtering ability.

Anthony Cutler

Thanks Ant. 2BHP is not bad for a simple bolt on like that and yes, I think I will get the genuine K&N. After all, you do get what you pay for.

b higginson

Just thought I'd add that "stub stack" covers a lot of ground...

airflow bench tests have shown that the classic, sharp edged stub stack can actually reduce airflow. These are the really pretty ones you see on race cars from the '50s and '60s.

the larger a radius you can have on the edge of it, the better. There are some for sale that don't even look like a "stack" at all, are more like a 3/4 ~ 1" thick piece of aluminum that is almost all radius. Not pretty, but are supposed to flow the best (and who cares what they look like, they'll be under the air cleaner anyway!).

Here is what they look like (attached), I downloaded this image from a Kieth Calver (mini) website. Even he admits on his website (articles section) that you don't need to use sock filters like shown here, the stock aircleaner housing flows surprisingly well, and these kind of "stacks" fit right inside.


Norm Kerr

Perhaps the stock Mini air filter housing "flows surprisingly well", but the stock A-Series Spridget housing does not. The snorkels are major restrictors. Also, there are washers spot-welded to the backing plate that will need to be removed so that those stub plates sit flush with the backplate. Just sayin'.

On my 72, I used the K&N elements intended for the original housings, modified the backplates as mentioned above, used all-threads in place of the bolts with nuts to hold the stubs to the backplates as well as to support the cover plate. I then topped it off with an aluminum cover plate cut to fit. Works well, but I like your stub plates better than the ones APT sold me. The other benefit is that it is not that difficult to reach the mixture nuts without removing anything.
David "getting the K&N housing one of these days" Lieb
David Lieb

MED in Leicester supply the stubstacks Norm's referring to.
l snowdon

Norm. Those in the picture are exactly what I was refering to, not the "ram pipes" of old.

b higginson

This thread was discussed between 24/10/2010 and 26/10/2010

MG Midget and Sprite Technical index

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