I'm considering installing a pair of K&N pancake filters on my 164 equipped with a pair of SU HIF6 carbs. Is that a good or bad idea?

I installed the three bolt style (HS6 type) on my HIFs.

I had to make an adapter because the HS6 and HIF do not have the same bolt pattern. I did this because I did not have the factory rectangular box and I sometimes try to be creative. All in all it worked out ok.

If you go this route though, be sure you do not block off the holes that lead to the suction chamber of the carb. The holes are not in the same spot in relation to the carb throat on the HS6 and HIF.

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'60 544, '68 220S, '70 145S, '72 144E, '86 745T

Good for sound, and good for high rpm breathing, but it might not necessarily make much more power unless you provide them with cold air. I'd do it regardless though... For the sound and higher rpm pull, it's nice. Engine'll warm up faster in the cold weather/mornings as well.