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MG MGB Technical - air filters

Hi guys has anyone ever put these big after market air filters on a set of su.I was thinking of putting a 90 on one and tee the other into it and running the intake in front of the radiator to get cooler air.It's got to be better than all the heat under the hood or is this a dumb idea? Go ahead with the bad remarks I can take it.Gust trying to get all the power I can you know.1980b thank you all joe

Hi Joe

Quite a few racers put a cone K&N filter next to the rad and duct cold air into a plenum connecting the carbs. Every 3 degrees C cooler gives 1% increase in bhp. Need cool fuel too so sometimes people duct the cold air onto the floar chambers and air filter area (two K&Ns) instead.

1980 Bs (and all the RBs) seem to run hotter than CB Bs

Warning: cooler air with cooler, damp conditions can lead to icing of the carb, not good if stuck on full throttle or no fuel just when you pull out into traffic.

If you live in a hotter climate the above statement is probably rubbish :)

peter burgess

I am going to be fitting a Sebring style front valence and since I don't have an oil cooler was thinking of running a piece of aluminium ducting from one of those middle vents up to the underside of the carbs. I already have K&N filters installed. Have no idea if it will make any difference but I figure it can't hurt!
Simon Jansen

Rain water?
C Holm

Try Jet-Hot coating your exhaust Manifold and downpipe instead. That will make a big difference in underhood temperatures.
Steve S.

K&N cone filters will assist as will jet hot coating of the manifold. However, in order to get meaningful benefit from theses additions you need to change the carb. needles and rather than jet coating your existing manifold get one of the after market mild steel extractors and jet coat that. Moss has some good ones.

Adding a K&N cone filter will increase airflow and therefore weaken the fuel mixture, hence the reason for changing to a richer needle (for richer read smaller diameter profile). Which needle to use will depend on modifications to the engine, but if your engine is standard you could try a .090 number 6 if you have HS carburetors fitted. If you have the later HIF carburetors the situation becomes more complex because they have a number of 'emission' control modifications. The first issue with the HIF is the throttle butterfly disc which is fitted with an overrun valve which spoils the airflow. If it is not illegal where you live - replace the butterfly with one from a HS SU and then examine the need for a richer needle than the standard AAU or ABD needle. Another complication with the HIF is the bi-metal plate which lowers or raises the jet as the fuel temperature varies. To get things right you need to be sure that you do your mixture analyses at operating temperatures.

Jet Hot is a ceramic coating that in laymans terms moves the heat further down the exhaust. Resulting in cooler under bonnet temperatures and therefore permitting a denser fuel charge. The standard MGB exhaust manifold is heavy cast iron with only moderately good flow characteristics. Converting to a steel extractor will save pounds in weight and improve scavenging, as well as lower under bonnet temperatures

Did not mean to be so long winded, but I hope you find it useful
Aubrey Paverd

Hi Aubrey

The main reason the mix weakens is because there is less pressure drop on the main jet than with a standard filter setup. The most used HIF needle seems to be AAA. Both the No6 and AAA usually suit fully modded engines too.

peter burgess

Would a vacuum gauge ported after the filter and before the throttle plates be used to evaluate the flow characteristics of various air filter arrangements?

C R Huff

Not so much rain water as flood water. Some BMWs and the new Mini I think have the intake low down as the air is supposed to be cooler there which gives a fraction more performance. However drive into a flood and you can fill the cylinders with water which wrecks the engine when it tries to compress it.
Paul Hunt

Hi Charley

Good idea to see what readings you can achieve.

peter burgess

The rain water would need to enter the inlet under the front valence, negotiate a ribbed duct, go around to almost 90 degree bends and then still have to get past the filters into the engine! Anyway, a little water injection never hurt anyone :)

Simon Jansen

Thank you guys think ill get the K$N and get headers and jet-hot coating.

This thread was discussed between 06/09/2008 and 10/09/2008

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