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MG MGF Technical - Home made air box (extracted from Trophy TTB thread)

Had some minor design problems with the 'home made' air box regarding the 'universal' seal around the various air filters where they enter the box. I need a new filter anyway, so i have taken the plunge and ordered an ITG Maxogen to see how they did it (get some ideas) and fit to Scarlet after. Be interesting to do a direct comparison RR test with each box design (and maybe your heat shield and flower pot mod) at some point in the future. We could also try to get hold of a PiperX (Viper is it?) and Hurracane.



That is a tricky area, I agree. I reckon that the inlet should form an interference fit to the tube connecting the filter to the TB (need to measure the outer diameter of the K&N/ ITG tube and go from there- about 74 mm IIRC). Great idea to go for the Maxogen! Had a bonus recently mate? LOL

Have a look at - this is what I am going to use to prototype our 'home-made' airbox. Dimential correct, but without the inlet throat to accelerate the airflow... All I need is some time, and space to work on it...

Rob Bell



The problem i have been having is the external diameter of the pipe that connects the filter to the TB. The K+N has a fiarly substantial 'quarter' radius pipe, whereas the original ITG has a thinner section 'half; radius pipe (the standard PiperX has no pipe at all!) This means that the home made affair not only needs to be supplied with a 'mounting kit' to suit the type of filter you already have, but also needs to accomodate the different external diameters of the 2 main pipes. A couple of solutions spring to mind, one is to simply supply a replacement pipe with the airbox, the other is to come up with some way of adjusting the diameter of the airbox where it meets this pipe in such a manner as it retains its airtightness. A flexible rubber collar and a jubelee type clip would do this, but then you need to mount the air box firmly at the other end as it will not gain any support from the pipe. This is fine until you realise that the two pipes effectively position the air box in different places within the engine bay (one being a quarter turn and the other being a half turn). Hence the need for a mounting kit. Anyway, i think ITG have gone down the 'supply thier own pipe' route, we i feel should try to use as much of the original air filter kit as possible (to try to keep costs down). So The upshot of this is, i needed ideas AND a replacement filter (hence the Maxogen). I am hoping to be able to get some idea of the mounting kit design shortly (i am toying with the idea of a simple bracket which you screw to the underside of the engine bay (not the inspection cover!) The bracket will be different depending on which air filter you have as the position of the airbox dictates the route of the intake air pipe and thus the angle the intake pipe enters the box.

Phew! I hope this makes sense mate :-)



Hi Andy,

I get what you are saying WRT the sealing of the filter to the airbox.

Here's my solution that would not necessarily require the supply of a tube: the airbox should seal around the filter - the section into which the metal collar inserts, and the jubilee clip fastens. The outer diameter of this section seems to be the same on the Pipercross and K&N filters I have- although I cannot comment on the ITG. I'll have to have a look - are you comming along to the Luton meet next week?

Also, I don't think that the seal needs to be completely air tight, so long as the hot air 'bleed' into the airbox is not significant compared to the cold air supply - this is based on the surprising effectiveness of the heat shield that I use currently.

However, I think you may be right- supplying an 'induction tube' with the airbox may be the best option as this would aleviate the need for different mounting positions with various aftermarket filters (different lengths of alternative TBs notwithstanding! ;o). A VVC specific pipe and a 1.8i specific pipe may be required given that the TB is mounted in a different position depending upon the inlet plenum fitted...

I'll try to remember to bring along the Rover airbox to the Luton meet, as I think this explains some of my current thinking quite well :o)

Rob Bell


Not sure about the Luton meet at the moment, there is a strong posibility that i will be doing surveys in the westcountry Tuesday/Wednesday/Thursday next.

The good news is that my ITG Maxogen arrived today (thanx Mike!) and already have an idea or two around the problem. The ideal AFAIC is to have the airbox mounted in the same position for all model / air filter / TB variants and the only way i can see this happening is to supply a connection pipe from the box to the TB that is specific to each model / TB / filter. By my calculations that breaks down as follows:

MPi + K+N + standard TB = pipe length A
MPi + K+N + Trophy TB = pipe length B
MPi + K+N + GM TB = pipe length C

MPi + ITG + standard TB = pipe length D
MPi + ITG + Trophy TB = pipe length E
MPi + ITG + GM TB = pipe length F

MPi + PiperX + standard TB = pipe length G
MPi + PiperX + Trophy TB = pipe length H
MPi + PiperX + GM TB = pipe length J

VVC + K+N + standard TB = pipe length K
VVC + K+N + Trophy TB = pipe length L
VVC + K+N + GM TB = pipe length M

VVC + ITG + standard TB = pipe length N
VVC + ITG + Trophy TB = pipe length O
VVC + ITG + GM TB = pipe length P

VVC + PiperX + standard TB = pipe length Q
VVC + PiperX + Trophy TB = pipe length R
VVC + PiperX + GM TB = pipe length S

A full 18 pipe variants!!! Admittedly there may be some overlap of dimensions and the K+N and PiperX being similar designs are likely to be the same but this could be a major headache. One solution that presents itself is to have the filter attached to a standard length pipe and the airbox sleeving the pipe. In this way all filter/plenum/TB variants could be accomodated, as the differences would be taken up by the amount the air filter projects inside the airbox. The downside is that it would tend to make the airbox that much bigger, making it more difficult to DIY fit (and it doesn't get round the sealing of the pipe end problem either). A rubber 'skirt' around the end will probably do the trick and if the airbox is mounted at the fuel pump end then there is probably no need to use a jubelee clip. This is the avenue i am currently pursuing and is the one that looks the most promising given all the variants.



Andy, I am sure that this number of variants are unnecessary- luckily!

For starters, the external dimentions of the standard and Trophy TBs are identical.

Secondly, all filters I have come across use the same internal diameter oulet - that being 70 mm. The primary differences in terms of the induction tube are length and the angle of turn. Given that these are specified no more scientifically than 'oh this is what is lying around in the store room,' 'it'd be a jolly good idea to have some kind of bend in the tube to smooth out air flow' and 'right we need to get this mother to fit into the space available' we could settle on a single design of inlet tube, with the four variants being:

1.8i inlet plenum - standard or Trophy TB
VVC inlet plenum - standard or Trophy TB
1.8i inlet plenum - GM TB
VVC inlet plenum - GM TB

One thing though - if the airbox is to be rigidly mounted (and ours would have to be) we'd need to use a flexible inlet. One option would be to re-use the standard fit flexi-tube. Not an ideal solution by any means. An alternative is to use the same flexi-tube that ITG use, but I've no idea where this is purchased from :o(

Rob Bell



OK, i have now finalised the revised design details and have given the drawing to the fabricator (well, his missus anyway!) along with the ITG box - for inspiration.

To get over the above problems i have used a straight length of 70mm dia pipe (hey, it works for ITG and who am i to argue!) and a rubber seal. This means that the box completely encloses the entire filter and the pipe projects out through the rubber seal. This allows the pipe and the box to 'telescope' to suit whatever plenum/filter/TB combination you may have, the seal also compensates for any differntial movement between the box and the engine - clever eh?

I have exported the drawing as a JPEG and can send you a copy Rob (or i could post it on the X-Power forum and link to it from here.)

Downside is that the fabricator has just picked up a large order (for oxygen pipework and 'sockets' for installation in people with emphasymia <sp?>. They can wander around thier home and plug into the system when necessary), so i am not sure when the prototype will finally be available.



Phew! On with the discussion... ;-)
Scarlet Fever

Hi, found the thread

Hoses and similar stuff can be found here
I think there should be local shops with technical rubber parts.
Again the pictur of Hartmut with such a flexy hose.

Is it this material ?
Picture courtesy Hartmut ??? a german Elly enthusiast.
He got such hose at a shop for standard rubber parts. (Not what some may think).
I know one in 'Essen' just behind the main station. ;)

Dieter Koennecke


You've got mail... :-)

Scarlet Fever

Thanx to Dieter (cheers mate), my design drawing is now online for anyone who is interested:

>> <<

Should clarify a few of the design concepts i have been rambling on about. Not sure how clear this is, but on the bottom left hand side are soem notes and a couple of sketches showing how the airbox accomodates different filter/TBs etc (the telescoping idea).

Scarlet Fever

This thread was discussed between 22/03/2002 and 23/03/2002

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