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MG Midget and Sprite Technical - Cooper Air Filters

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?
Nick and Cherry Scoop

Nick

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?

Mike
M Wood

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.
Nick and Cherry Scoop

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
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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.
Nick and Cherry Scoop

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.
Nick and Cherry Scoop

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

Prop
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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?
O K

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.
Nick and Cherry Scoop

Nick

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

Prop
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Sorry to bring it back, but this didn't really get answered and is niggling me. I do care about airflow, and while the mesh on the outer face and the steel wool inside don't worry me, being of such large area, the 35% obstruction of flow in the 1 1/8" entry to the carburettor can't be overlooked. Unless somebody is going to tell me that sucked air doesn't act like that, or that at my low hp it won't make enough of a difference to matter.

Nobody else seems to do a filter for H1s.

Nick and Cherry Scoop

I may as well go on discussing it.

It occurs to me that the butterfly obstructs the airflow by approx 25% at full throttle.

Nick and Cherry Scoop

I recall from my younger days that the Vizard book had a chapter on optimising airflow through SUs, and that he filed off the screws and reprofiled the spindle.

He also did flowbench tests on some commonly available filter setups. Stub stacks were recommended, mesh wasn't.

Check this before acting, I read this some 25+ years ago and have probably misremembered.
AdrianR

Thanks Adrian. I did look in Vizard, but the real problem is that the minimum size for good filters seems to be 1 1/4" SUs.

I shall look again at the chapter on optimising SUs, but what I really need is for someone with experience and knowledge to come in and say, 'it's a tiny engine; you've got the cam, you've got the cylinder head; it will get enough air.'
Nick and Cherry Scoop

I've been thinking similar thoughts about my 1275 - it currebtly has oversize ram pipes and foam socks which I bodged when I converted from Weber sidedraft back to SUs many years ago in the interests of tractability.

In your position I'd probably buy a pair of deep K&N type pancakes and then get someone with a lathe to machine up stub stacks from 1/2" thick aluminium plate to go inside them, matching the internal diameter to fit your carbs.



AdrianR

Oh what the hell Okay ill say it ! BUt that does not make it true

"" it's a tiny engine; you've got the cam, you've got the cylinder head; it will get enough air ""

Did that make you feel better?

on one side of tje coin your going to get some seriois sucking going on there thats the good news, the bad news is

it's a tiny engine; you've got the cam, you've got the cylinder head; it will ((( NOT )))get enough air

HAHA. I would focus on getting a fromt HS2 CARB, unless your overly conserned about orginality, just a plain ol HS2 thats rebuilt is the way to go... it wont need modifications you can run it stock as i would think it will suck in morethen enough air to do what you want and it looks very close to an hs1..finding tje right needle might be a bit tricky but i agree ... it looks way to conjested and will prevent ro much air entering to be a good thing

Plus hs 2 are more common then you havd a wider range of filters to chose from

Adrian is corroct vizard did a noce job detailing how to hot rod the carbs but i think the 2nd best option is just the next bigger size carb and no or little modification work is the way to go

Prop
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Nick

Looks like someone makes a housing for 1 1/8 inch SU H1 carbs:
http://www.hi-flow.com/hp007aaf.html

Ram pipes: https://www.scparts.co.uk/sc_en/warehouse/tuning-internal-and-external-fixtures/carburettor-and-air-filter/air-filters-ram-pipes-and-cold-air-feed-kits/ram-pipes-for-su-carburettors.html

https://www.limora.com/en/warehouse/tuning-internal-and-external-fixtures/carburettor-and-air-filter/air-filters-ram-pipes-and-cold-air-feed-kits/ram-pipes-for-su-carburettors.html?___from_store=nl

Cheers
Mike
M Wood

Mike, those are very pretty indeed. Long way from Oz, but they are very pretty. Thank you.
Nick and Cherry Scoop

This was the kind I meant - http://www.mgocspares.co.uk/acatalog/MGOC_SPARES_K_N_773.html, scroll down to pancake.

I suppose the mounting centres on your H1s might be different but you could elongate or otherwise enlarge the holes in the fitler backplate and then clamp up with the stub stacks.

Or even make some really thick custom backplates, with an internally radiused edge on the inlet to satisfy both fit and flow criteria.


AdrianR

You can get KN airfilters with blank baseplates that allow you to make your own holes. I used a pair to solve an issue of bonnet fouling on my Sebring rep.

Alan
Alan Anstead

Yes I modified the butterflys, it gave more power and the K & N filters did fit perfectly. I did not have to modify the needles as Peter Burgess concluded.

Flip

Flip Brühl

Sorry not to respond, Adrian and Alan: had a fraught week and forgot about this thread. I had not realised how expensive KN filters are, even at MGOC, which ought to be cheap. Good news from you, though, Alan.

So, Flip, did you use the 'make your own holes' KN that Alan was talking about? And did you have to make your own connection for the vacuum pipe, or was there a spigot on the baseplate?
Nick and Cherry Scoop

The vacuum pipe terminal was delivered with the set so I had to drill a hole. All further holes where in.
Flip Brühl

Nick

The KN are expensive...but, the filter elements are good for 1 million miles, so actually very economimical if you keep the car for a million miles

Haha... perception is reality


Prop
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Finally got an answer on price from Hi-flow in Australia, Mike. The filters to fit H1s are 'clearance items' or similar, and would be about £80 each incl. p+p. Too much for me, I think - especially as I've already got the Coopers. Maybe Peter Burgess would be prepared to test with them on and off - if I ever get there - so that I know if they're as bad as Prop says they will be.
Nick and Cherry Scoop

Maybe Peter Burgess would be prepared to test with them on and off - if I ever get there - so that I know if they're as bad as Prop says they will be.

Hey Nick,

Im going to go out on a limb and assume we are not talking about my thoughts and theories conserning toe nail fungus ...haha

Can you you help me out and fill me in on what i had said that was apperantly pretty bad... im not saying i didnt say something negitive, its just that whole dementia thing of old age that has me a bit lost

Thanks

Prop
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Ha ha - just a little further up this thread, mate:-

"on one side of tje coin your going to get some seriois sucking going on there thats the good news, the bad news is it's a tiny engine; you've got the cam, you've got the cylinder head; it will ((( NOT )))get enough air".

You might be right. I don't know squat about airflow, except around buildings and across ceilings.
Nick and Cherry Scoop

Oh what the hell Okay ill say it ! BUt that does not make it true

"" it's a tiny engine; you've got the cam, you've got the cylinder head; it will get enough air ""

Did that make you feel better?

on one side of tje coin your going to get some seriois sucking going on there thats the good news, the bad news is

it's a tiny engine; you've got the cam, you've got the cylinder head; it will ((( NOT )))get enough air


Now i understand.... yes i did say that while being comical to your comical request of please say this

What i meant was by UP GRADING from the HS1 to the HS2 carbs you may not need to do any modificstion to the HS2 Carbs as the amkount of air flow would be (probably) as much or greater the what a vizard modified H1 would prduce

The 2nd point was about the pan cake air filters ... we have a cheap pancake air filter thst causes a lot of Construction in the air flow which is a good thing cus constriction make the air flow faster with more density (compacted /compressed air) which means means more fuel can be compressed with the compacted air and the fuel charge is more atomized for a more explosive harder detonation making more power

Thank of Construction as a Shop-Vac with a 3 inch diameter hose then add an addapter to reduce the 3inch dia hose to one inch... and the sucktion become 3x more powerful on the shop vac

The opposjte is true if you went to large a carb say an hs6 there would be less constriction on the air flow and air would move much slower and not nearly as compacted or compressed and would loose power even tho you capable of obtaining more air and the fuel charge wohld lose its compessedness and not be near as explosive


Did that help any ?

Prop

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This thread was discussed between 10/08/2017 and 05/09/2017

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