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MG Midget and Sprite Technical - New airbox and stub-stacks

I'm dead chuffed my new airbox fits reasonably well. I've also fitted the new stub-stacks. Tomorrow I'll disassemble and paint the airbox, cut the fixings to the correct length and cover the box with reflective heat-mat insulation. I'm reasonably confident I'll have a much cooler and more free flowing air intake as a result. I'll need to do a bit of pipe-bending too to re-route the fuel feed to the carbs.

This pic shows the stubstacks screwed to the backplate.


Nick Nakorn

And this one shows the airbox fixed on prior to paint, insulation and finalising the fixings.


Nick Nakorn

Looks good Nick, nice job.


Guess you'll be ducting in a big cold air feed from behind the grille?


Will it clear the expansion tank or will you have to move it?


Which exhaust manifold have you fitted btw?
SR Smith 1

Thanks SR, I think it will work well. I've already moved the expansion tank - you'll see from the pic that I've shifted it up, to the right (looking backwards)and back. I'll find a clearer pic..

The Exhaust manifold was a cheap MGOC item that needed a lot of work: cut, bend and re-weld the downpipe to clear the 'chassis-rail', file to match the ports, file to match the studs then strip off blobby red paint and repaint in high temp satin black. The exhaust system that came with it was the wrong length, had joints that had to be sleeved to fit etc.. etc... But the end result is now as good as a more expensive unit.

Air supply, yes, I've some concertina ducting that goes to the space to the left (looking back) of the radiator where I'll make a housing for the air filter and I'll cut away some of the bonnet slam-panel to make a hatch to access it for cleaning.


Nick Nakorn

Looks good. Be sure to use some threadlock or safety wire on those fasteners for the stub stacks.
Trevor Jessie

Thanks Trevor, indeed - I have a tube of Loctite at the ready!
Nick Nakorn

Gotcha, clearer in that pic.




Won't really piss you off by telling you've I've just bought and fitted the maniflow one, which fits beaufifully!



Hope it goes as well as it looks mate.
SR Smith 1

SR, I looked at the Maniflow item but I'm time rich and cash poor so I save where I can and where it's practical. Still, I had hoped the MGOC system would at least fit.
Nick Nakorn

Nick,

very nice

are the holes at about 2 o'clock on the stub-stacks for the air relief (or whatever the correct term is) holes in the carbs
Nigel Atkins

Nigel, thanks. Yes, I've put two holes in each stub; one at about 10 o'clock and one at 2 o'clock as they were the shortest route to the air holes for the dashpots. btw, has anyone used builder's fire-proof silicone as a glue in engine compartments? I was going to use an automotive heat-proof silicone to glue the heat shielding mat onto the airbox but I note that it's now over £5 for 60 ml whereas the builders version is about the same price for over 300 ml - I'm pretty sure it's the same stuff and useful to know about it. In the old days a lot of people used contact adhesive but it had a habit of catching fire ...
Nick Nakorn

Now with a coat of paint...


Nick Nakorn

...and insulation


Nick Nakorn

I didn't realise you were going to paint it as well !

I hope this car won't be too nice to use :)
Nigel Atkins

I hope it will go as well as it looks :-)! Here it is installed.
Nick Nakorn

weird - pic didn't upload... try again..


Nick Nakorn

Nice job Nick, very smart.
SR Smith 1

Thanks SR - I'm not going to enjoy the wiring though..
Nick Nakorn

Funnily enough Nick that's the bit I like the best!
SR Smith 1

Nick,

Where's the air filter ?

Malc
Malc Gilliver

Hi Malc, it goes in the space beside the radiator under the bonnet slam panel. I'll make up a housing for it so it is separated from the radiator heat and gets a good flow from the front of the car.
Nick Nakorn

I took Malc to mean the actual air filter elements but as always I could be wrong
Nigel Atkins

Nigel, yes - me too; the actual filter goes where I've said :-)on the end of the concertina tube.
Nick Nakorn

oh, right of course, doh!

like the induction kits
Nigel Atkins

Nick,

Yep, that was what I meant !

As you are supplying the air to the front of the plenum, do you think there is a risk of uneven air flow or pressure into the carbs, such that the front carb runs lean and the rear rich ?

Could you feed the plenum from below - so it looks like a 'T' piece ?

Malc
Malc Gilliver

Malc, in practice it makes little difference providing the airbox and inlet are big enough. In effect, the volume of the airbox includes the volume of the concertina tube so the pressure drop will be minimal. Add to that the fact that the filter inlet is about 4 times bigger than it need be and the air supply will be more than enough - almost like leaving the carbs open. Remember too that the carbs work in sequence rather than together and so with a slow revving engine they don't really compete with each other. Many race engines (in F1 for example) suffer because they often have (rules) restricted inlets, operate at very high revs and are multi-cylinder (air has less time to change direction) but even some non-turbo F1 cars have had airboxes fed from one end. In short, for a road car (I'm making a torquey road car rather than a semi-race car) there will be no problem.
Nick Nakorn

Re: Filter element. I think this is not too bad a place for it; perhaps a bit exposed to puddle-splash but the front grill and a perforated guard should keep most of it out - plus it's a climb up to the airbox over concertina tube. The only opening to the housing is at the front and most splash is from the side of the tyre.


Nick Nakorn

... with the filter in place...


Nick Nakorn

...tidied up and painted..


Nick Nakorn

.... with the cover fitted...


Nick Nakorn

This thread was discussed between 21/06/2014 and 03/07/2014

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.