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Midget and Sprite Technical
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Thread: Cooper Air Filters
Posted 10 August 2017 at 14:16:16 UK time
Nick and Cherry Scoop, Hereford, top left corner

I've been looking at these Cooper air filters which were standard on Frogs. The wide mesh across the 28mm opening to the carburettor amounts to an obstruction of just over a third of the area.

Does this matter?

Posted 10 August 2017 at 16:13:38 UK time
M Wood, Strathclyde, United Kingdom


No, unless you care about airflow and have a non-standard state of tune and spec for your engine.

Keep them if you are into the original spec. Are they original or later possibly lower quality pancake filters of the same external dimensions?


Posted 10 August 2017 at 17:21:21 UK time
Nick and Cherry Scoop, Hereford, top left corner

No, Mike, they aren't original, but modern re-makes. I had ram pipes and no filters for the 10 years I drove her. I'm hoping the carved-out head and mild tune cam will make her a little more urgent, but not too much.

Posted 10 August 2017 at 18:11:39 UK time
1 Paper, Missouri, USA

Mike is correct its about air flow but id add constriction as well

Ideally you want a nice rounded edge for the air to flow into the carbs which the purpose of the ram pipes you had ... id consider goimg back to those if they worked for yoj last time

Carbs without filters or ram pipes the air comes across the venture of the carb (the big air hole) and has to take a 90 degree turn to get sucked into tje carb... that is not a good thing for air to accomplish what a ram pipe does is 2 things it gets rid of the 90 degree turn and smooths out the air flow flow into a gental roll or curve and the length of the pipe speeds up the air flow much faster forcing more air into the carbs aka means you can add more fuel to the mix for more HP

I add whats called constriction to the mix, yoj can make the air move alot faster and compressor it more thur constriction think of a shop vac with a 3 hose, if you put an attachment on the end to reduce the diameter down to 1/2 inch you get alot more sucking force for cleaning out those snack bits that got dropped into and between the seats of the car

Same applies to carbs... what mike refered to as these cheap pancake filters are bad for filtering dust in the air but awsome for promoting constriction, as theh are only 1.5 inches thick so the air comes in from the side and gets tightly compressed do to the limited space and raises the ajr pressure making the air move much faster into the carbs ... ive always thougjt adding a large o ring around the air hole of the carb and securing it from getting sucked into the carb would be a great way to get rid of the 90 degree turn in those cheep pancake air filters and will probably add a tad more contriction

On your ram pipes... you might try using foot socks over the pipes and nyon zip ties to secure them to filter out the dust, may have to try several kinds and thickness to get the best filtering to HP ratio

Posted 11 August 2017 at 21:05:32 UK time
Nick and Cherry Scoop, Hereford, top left corner

Thanks, Prop. The only difference between what you're describing and what I've got is that the whole front of the pancake is open to air - not the sides. So there's plenty of comfortable air available, but it then has to get through a 28mm circular hole, 35% of which is wire mesh.

I'm not looking for a lot of power: a fast road head, a 266 cam and a decent Maniflow exhaust are going to give me what? 47hp? But it would grieve me to knock that back by doing something silly and avoidable. I've already vetoed the HIF38 variation, even though I do have one on the shelf, and I'm sticking with the H1s.

One of the apparent advantages of the Cooper filters is that the front one has a spigot for the vacuum pipe from the rocker cover; in my ownership this car has never had the luxury of negative pressure in the engine, and the bellhousing was very dirty when I took it apart, so I'm hoping the oil might stay in better.

Vizard says I need filters, so I'm going to use them. It's just deciding which.

Posted 13 August 2017 at 08:53:53 UK time
Nick and Cherry Scoop, Hereford, top left corner

Do the Coopers need to be oiled? In my workshop manual it says oil them, but the accompanying picture shows pancakes by 'Burgess', blank front and side air entry.

Posted 14 August 2017 at 14:17:28 UK time
1 Paper, Missouri, USA

I guess it depends on the element your using, the K&N need to be oiled but those are the only ones ive ever come across thst need oil

Thst said, its not any oil laying ariund, its very proprietary oil for the K/N elements


Posted 14 August 2017 at 15:45:11 UK time
O K, Netherlands

Nick my 998 mini modded in a similar way made slighty over 60bhp so you should expect a little more.
Though I did run that with a single hiff38 and a big donut filter.
Drilling holes in the filter case and flowing the elbow it was mounted on made a big improvement.

Are rampipes with filter socks not an option?

Posted 14 August 2017 at 20:18:59 UK time
Nick and Cherry Scoop, Hereford, top left corner

They are, Onno, but I really would like to get some vacuum to the crankcase. There's no spigot for that on the carb body of an H1.

Posted 14 August 2017 at 23:09:36 UK time
1 Paper, Missouri, USA


Can you just drill and tap the carb body before the butterfly to get the vacume take off your needing


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