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MG Midget and Sprite Technical - K&N on a HIF

I've seen quite a few different K&N filters being used on spridget HIF conversions and thought (being me) that I'd try and design the perfect one! Up 'til now i've been running a small offset oval K&N and I wasn't convinced it could cope with the airflow required on full chat. - Now before you all say it, i'm aware that ITG filters are available off the shelf, that fit well and that are race proven, but call me sad I just dont like their foamy look! Give me a nice K&N anyday.

So heres a couple of snaps of what i've been upto today:

I've used a full radius ram from calver special tuning and a blank k&n box which I had to drill the backplate for, I measured up before hand and got as deep as possible without inner wing issues. Might just be me, but it does seem to have made a difference to the car - it seems to idle more smoothly and seems a bit quicker above 4500rpm ( that might be psychological though!).






Nick

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Nick

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Nick

Not bad nick, I like it....you captured the essance of modification "A defined balance of form and funtion"

prop
Prop

Nice but a bit close to the wing maybe, it might hit as the engine moves on it's mountings.
Jeremy Cogman

Luckily i'd thought of that! Theres actually about 1cm clearence, even though that last picture doesn't make it clear. Not saying I wasn't worried when I first got the new k&n out the box though, cos it did look too deep! Quite difficult to measure in 3D isn't it!?
Nick

Nick,
Do you have a head steady? That would take care of any tendency for the engine to move. And easy enough to make for someone with your skills.
Guy Weller

verry nice

the calver st stuff always works perfectly and looks great but.....
one su on a midget it's a bit like one testical isn't it?

i mean it works fine and is easy and all but it looks like sh*t

and for a double su they make a filter with backplate formed like yours with the cover saying midget!
and they have been here for ages..

but still the filter ram combo looks great (put two on there a twin hiff 44 how cool is that!)
o Könemann

No engine steady needed to be honest, the thing runs pretty smoothly as it is. Even when hunting a bit at idle and cold it doesnt shake like i've seen many a-series do before. I put this 50% down to having been balanced properly and 50% down to having the single carb. The only way that it could contact the inner wing as it is is if the engine cant's due to torque

Mr K: Have been thinking about twin HIF44's for ages, and indeed have seen this very motor run on twin HS6's - which to the initial eye looked standard. It went like stink above 4k. I mean really like stink. BUT theres method in my madness for sticking with one carb. I agree, it doesn't look as nice as twins, but for my purposes and with the engine package I have its the right level of carburetion. With twin 44's i'd be heavily overcarbed at the bottom end and would lose a lot of low-end torque. It also wouldn't idle as smoothly.

Does anyone know if twin HIF38's would work!
Nick

Nick,
I was thinking of torque reaction rather than imbalance. Mine has only a single rubber mount under the tail of the type 9 so there is less support at the back end than on a standard rib-case. That is why I added the engine steady at the back of the block.

Guy
Guy Weller

Nick
Very neat, which K&N did you use?? I too have a foam Pipercross which came with the HIF44 carb and I would like to bin it for exactly the same reasons as you.
Just a small point you might want to fill the attachment screw holes with some silicone sealant, if done it can help to smooth the airflow, admittedly by a miniscule amount.. but every little helps and as a bonus it will also help to stop the screws loosening, it can easily be hooked out any time you want to remove the filter backplate.
Ian
Ian Webb '73 GAN5

Cheers Ian, I'd considered that but didn't want the risk of it vibrating out and going 'down the 'ole' However, thinking about that, on the same basis maybe I should have locktited my allen-caps in.

I used a K&N 56-9244, which is basically a blank box with the same filter size that fits inside the standard HI44 small oval (KN 56-9142), but much deeper (83mm). I could have reused the back plate from the small-oval too, but the hole is offest too much to be accomodate the ram so I drilled my own in the blank, was even thinking of buying a 1" 3/4 q-max punch for the perfect hole, but at 27 quid it was getting an expensive extra hp or 2!

Nick

Nick,

That sounds rather expensive for a Q-Max cutter of 1.75" diameter. Seem to be a number of places that sell them for around £12 - £13 + postage.
David Billington

Wish i'd known that last week!
Nick

Nick,

I usually get them as required and add to the selection, I have about 6 in various sizes from about 3/4" to 2". IIRC I choke at the price for 2.5" and above as they seem to start going up exponentially at that point.
David Billington

Nick
Thanks for the info, I will look into it.
By the way your heatshield, is it basically the same size a the std one ? I havnt experienced any fuel evaporation but it should be done anyway, as for sure the float chamber is running fairly warm.
Ian
Ian Webb '73 GAN5

Yeah, its basically as wide as the piece of mirror stainless that I could get my hands on! Which just so happened to be about the same as a normal twin carb one. I've got a big bore maniflow lurking underneath and as i've got no intentions of louvering my bonnet (wolf in sheeps clothing is the ultimate game!) I thought i'd go overkill on the shield front. Seems to work well, i've had no fuel evapouration probelms.
Nick

Nick,
one problem you will encounter with that enlarged filter arrangement, is getting a screwdriver to the mixture screw. On mine it is really awkward - I can only properly access the mixture setting screw by removing the K & N first which is a bit of a pain!
Guy Weller

This thread was discussed between 14/06/2008 and 17/06/2008

MG Midget and Sprite Technical index

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