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MG MGF Technical - Adapting VVC K&N 57i Kit for MGF 1.8mpi

In the quest for a little more get up and go from my 1.8i I asked a while back on the BBS what could be done. The response was that I should remove the rubber pipe from between the air filter and the engine air intake. This is because the 57i kit was designed for the VVC and so did not deliver enough air to the mpi engine.

On Monday while fitting my new cold air pipe bracket under the car I removed the rubber pipe from the filter. It works, the initial lag at low revs has gone and the performance is now much more even throughout the rev range. The only thing that may be a down side is that the Air filter is much louder now. This is a plus for me as I can hear it again, the intake sound is nolonger drowned out by the noise of my SP :-).

So, if you have a 1.8i and a K&N, throw away the gray pipe that comes with the kit and connect the filter directly. Or just buy the cone filter instead of the kit and save a few quid, cold air pipes available from Halfords at a lower price and a bracket for the cold air pipes can be obtained from someone on this very BBS for 7 quid (I think his name Tom, sorry don't have the info here at work, but someone can point you in the right direction I'm sure).
Tony Smith

The brackets are from Tom Randle- I've hosted some pictures of the bracket on part of my web site:

Nice to hear that someone else has vindicated my observations Tony. Removing that spacer tube really does make a difference to the 'pep' of the engine, and I heartily recommend it to anyone with a 1.8i and standard exhaust.

I now have a Trevor Taylor exhaust on my car- and have reverted to the VVC filter set up. The TT Fxtreme exhaust system really compensates for the relative lack of low end torque that results from the standard 1.8i-57i set up.

Filter power curves are due to be hosted on my web site soon... :o)

In the mean time, have a look at Greg's FAQ

Robert Bell


So do I take it that the TT exhaust comes out top on the exhaust tests?

I know you can not give the information of the test prior to the publication of those results but I like others want to get on and do it.

Ted Newman

I hope I understood everything right.

Find loads of cone- or cylindrical Filterchargers on my datacollection. Different companies are stated.

Loads of German, Swiss and dutch F'ers go already since about 3/4 year for a loudly standard airfilter installation (Hose diamiter 70mm. Some with others without fresh air induction.

No fear on to less air. All Filters where calculated by K&N and other companies datasheets.

PS.. prefering the RU-1470 and RU-3190 and Cone types of K&N (cotton fabric filters)
Dieter Koennecke

I remember reading about the K&N on the BB and someone stated that if you remove rubber pipe from between the air filter and the engine air intake you will get a couple of extra HP between 2000 and 3000 revs but from then on you will not gain as much as you would with the pipe left on. in other words the K&N with the rubber pipe gives more HP, but it starts at a higher rev range. My freind has a MR2 with a K&N 751 and that also has a rubber neck attachement. It seems that this is quite a common setup and must be done for a reason.

Behaps I need to have an experiment by removing the rubber pipe to see what I think of the difference,

The bracket that Tony and Rob are talking about are available from me at price of Ģ7.50 or Ģ10 inc. p&p.

Email me for further information. The complete set includes everything required to fix to the car.

For all those who brought them at Brooklands I assume that they fitted okay.
I hope no one encountered any problems fitting the bracket.
If problems occured please contact me so I can solve the problem.

P305 DPB

Steve, the rubber pipe is good for the VVC as that is the car it was designed for, in the MPI this pipe restricts the air flow and the engine can't get the air in fast enough for that initial press of the accelerator pedal. I don't know the physics but it works.
Tony Smith

The length of the tube can be tuned. Very similar to musical instruments.
This will dictate where within the rpm range you get the extra torque/power that the KnN liberates.

As the VVC gets peak power at a higher rpm, I assume that K'n'N bods tuned the pipe for a higher rpm.
As Rob says, remove the pipe and it will peak at lower revs - more suited for the 1.8i.

If you have lots of ruber tubing you could experiment to see what length is 'best' for the 1.8i.
Now enter the debate about what is 'best'. :-)

Think I might have a go and see what difference it'll make to a VVC - might even be 'better'. ;-)


Sorry for spelling your surname wrong Tom :oO And I suspect that the e-mail link may be out of date now too- is it?

Back to the plot:

The idea for removing the the rubber tube came from studying the power curves we collated following the grand filter test which was published in MG Enthusiast eariler this year. (I believe that Erik has a section of the report on his home page.)
I noticed that the Pipercross had a flatter power curve than the K&N up to about 4000rpm, after which the K&N started to make big gains over the Pipercross filters.
The K&N (and also the Ramair filter) had a dip in the power and torque curves at around 3000rpm. I had noticed that there was a slight lethargy with my 57i equipped car at around this point in the rev range- the standard car has a similar affliction. In this respect, the K&N panel filter felt much better!

To see the graphs, down load the MS Word document that I sent to Greg for inclusion into the FAQ. Sorry for the quality of the images!

The graphs to look at are graphs 3 and 4, and note in particular the shape of the torque curve.

It was an easy step to hypothesise that mounting the K&N filter in the same position as the Pipercross would result in a useful gain in low end torque, and improve drivability.

It works- mounting the filter directly to the throttle body does indeed make the 1.8i easier to drive in traffic, and the initial acceleration response is markedly improved. A very worth while improvement IMO.

There is a downside, however- top end power is lost. Instead of producing a maximum of 8bhp, the maximum gain is likely to be half that. But how often do you stretch the car to that end of the rev range in day to day driving?
Also, the ease at which you can extend the engine to the red line is affected.
It depends on your priorities.
That the induction noise is greater with the filter mounted in this position is louder is an advantage IMO- but not everyone will want the extra 'sporty' racket! ;o)

Tom, for Hill climbs and race circuits with few fast straights, the 'tubless' 57i format may well prove best, but for long straights the 'standard' 57i is the best bet.

Robert Bell

Rob, Funny you should say that, I have noticed a slight dip in power at around 4000 revs since I made the change, so mid range is a little worse than before but around town it's great.

I will decide if I like it or not soon.
Tony Smith

I guess the ideal would be to have a telecoping induction tube! ;o)

Personally I found the trade off worth it, as I live in the city it made more sense.

Robert Bell

>>I guess the ideal would be to have a telecoping induction tube! ;o) <<

why not ?
some engines do have variable length induction manifolds ...
the engineering costs are another issue :(



I learned the the "RAM AIR" Effect is not that big on a MPI


So what length should I cut the tube to that the engine doe not have ab big torgue hole in the mid rev range?

Thomas O.

Thomas, I think we have some confusion here.

The ram air effect is minimal, not because itīs an MPI but because this effect is from the air forced through the cold air induction pipes in front of the filter, so this is minimal as the air filter is not enclosed. With these filters you are really relying on the engine sucking in the air it needs, the cold air pipes are just to try and get colder air into the engine, as cold air is more dense than hot air it contains more oxygen so combustion is more efficient.

The tube I am talking about in this thread is the rubber tube between the filter and the plenium that comes with the 57i kit which was designed for the VVC. Now to find the optimum length for this tube may be bit tricky and can only be done by trial and error, this is also up to personal taste, the difference at the low end without the tube is quite large, wheras the difference mid range is not so great, I would say that on an MPI it is better without the tube.

If you wish to experement with it please let us know your findings.
Tony Smith

There was one other disadvantage as I recall. Placing the filter direct on the throttle body makes a hell of a lot of noise. I had the Pipercross cone stuck straight on the throttle for a few months and at 3000RPM it made a loud droning in the cockpit. The K&N on the end of a tube is miles quieter at constant throttle, but just as loud under acceleration.


(Who's been a bit busy recently so hasn't been on the board much!)
Graeme Bishko

Graeme, the K&N is not too bad without the pipe. But what do I know, when I put my SP on I could not hear the K&N anymore so the extra noise from the air filter allows me to hear it again :-) (nice to see you back)....
Tony Smith

Hi there Graeme- long time no hear mate!

Tony is right, with a standard exhaust, the K&N directly on the throttle body is not too noisey. Pipercross+ very noisey Motobuild exhaust= very unpleasant ear bashing! ;o)

Tony, the kind of Ram air effect that Thomas is refering to (I think) is the effect of air travelling down the inlet tract- there's an overview @

Thomas, you may be right about the MPi inlet manifold and throttle design- it is essentially the same for 1.1 and 1.4 MPi K series engines, so for a 1.8 one may expect some limitations. The VVC inlet is cast alloy (compared with plastic on the MPi), so it may be that inlet ram effect may be dissappated to some degree. Anyone able to perform some airflow tests on these two components?

Robert Bell

Thanks, Rob, saving me from my confusion again :-)
Tony Smith


I changed my K&N fitting to direct to manifold this morning - it certainly seems to have a better low rev pick up this way and I can not say that I noticed any fall-off of performance at higher revs, but it is early days and I have only done about 50 miles since the change.

With regard to noise - it is certainly a 'harsher' noise and less of a drone but on cruise seemed no more than before - I'll wait until the wife is in the car and see if she complains:-)

Ted Newman

Well thx for the comments... I think I understand K&N business now!

Let me summarize:

We bougt a approx 250 DM expensive thing

2 cold air induction tubes
a rubber tube a connectorand a cone filter...

Well I was persuaded to buy the original 57i kit because I thought the guys fron K&N would have tested the stuff on both engines and therefor are "allowed" to ask for more money.

What comes out now is, that if you have an MPi engine .. you better save 3/4 of the money and buy a

RU 1470
RU 3190

well I am quite pissed by this ... is this the way K&N deals with their customers?????

Thomas O.
Thomas O.

here is a link to the stuff... THX to Dieter K.
Thoma sO.

I do not agree with Thomas 'statement' in this way.
IMO everybody should be responsible for his own. The 57i users where the first who had their fun with this filter term. The others (me too) followed with copies, alternatives etc.

Purchasing this or that, beleaving or not what any company promises ...

That all is a large 'play yard'.
Why should a company not use the chance to earn money ?

PS.. hope that nobody bothers my data collections ... Or shall I remove it ?
Dieter Koennecke

Hi Thomas

I have no connection with K&N the company, their sales or their R&D department, but they did give me the opportunity to test a number of different filters on their R&D facility for the article that subsequently appeared in MG Enthusiast.

Unfortunately, I am not privvy to all the development undertaken upon the K&N 57i for the MGF, but I believe that most of the initial rolling road work was carried out on the VVC.

It is the R&D you are paying for on the 57i.

The K&N 57i does, in fact, produce the greatest output in terms of power of any filter you can attach to your MPi. 8 bhp versus 4 if you fit a filter on the throttle body.

The advice I have given is purely based on the observation of torque graphs that I calculated when digitising the data I was given- and the observation of the 'torque drop' @ 3250-3500 rpm. This is not a well known fact- the official Rover power curves show no evidence of this phenomena.

K&N probably made the assumption that the 1.8i and VVC shared all hardware except the cylinder head. This is not the case, but they probably had no reason to question the assumption.

This is probably why they developed the system on one model, and halved their substantial R&D overhead on the product. It works well on the MPi- no one else has complained, nor would have discovered any advantage in alternative installation methods had I not had access to dynometer data.

K&N has worked hard on the product, and deserve to recoup their hard work- work that initiated the 'filter sales boom'. What we may do is ask K&N to revisit the development of the 1.8MPi installation.

Ultimately, I would propose that the 57i kit in standard form represents the best compromise so far in terms of power output and refinement. My alternative solution is compromised by noise, and ultimately by less ultimate power gain. I have presented a choice that K&N would probably find unmarketable. (What would you buy- a filter that gave a 8bhp gain or a filter that gave a 4bhp gain? No contest is there?)

I bought my k&N 57i filter for 100 quid, and have no qualms about it.

And now the MPi owner has a choice in installtion methods- which IMO just adds to the fun.

K&N made a good job of the kit- buying one is not a mistake.

Robert Bell


I hear what you are saying, but I disagree with your statement.

By removing the rubber connector tube on the MPi there is a gain in lower revs but a loss in higher revs and a marked increase in engine 'drone' - noise that is not acceptable to all so it is all about freedom of choice.

The Kinnor K&N kit has been tested and works very well (albeit with a VVC) and it gives a marked improvement with the MPi over the standard Rover setup - so I think you are out of order in saying that there is a 'con' in the K&N marketing, after all they are commercial concern and not a charity and if they do not make a profit they go out of business and that does not help anyone.

Finally the difference in price buying the complete kit to just buying the basic filter was of such a small margin that I frankly feel that if it is so upsetting to a person then that person can not afford to experiment with his/her car and perhaps would be better of with a Smart Car!

Ted Newman

Another point that I did not mention:-

I noticed that if you bolt the filter direct to the throttle body the filter does in fact foul the fuel line, whilst this is a soft material rubbing against the line it will in time cause wear and this something that K&N would not be able to reccomend.

I feel that the filter does need to have an angle adaptor to keep it well clear of the fuel line as without it it represents a potential hazard so I propose to actually reduce the length of the rubber pipe by about 3 inches off the straight section and refit the pipe so as to angle the filter away from the fuel line.

perhaps others who have removed their connector pipe can check to see if they concur - or is just the way my MPi is put together?

Ted Newman


I did NOT want to yell on someone here, but in my oppinion it simply isnīt quite fair to sell a product (not thinking about prices or so) telling the customer that it is specially developed for the K series engine.
Afterwards one finds out that 50% of the possible engines werenīt covered by the researches ....

no more no less........


Thx for the tip with the fuel-line Iīll check this today.
Maybe Iīll cut teh tube to 6cm...

Thomas O.

>or is just the way my MPi is put together?

I see and thats my serious opinion.
The simple looking modification of adapting this or that filtercharger from this or that company needs RESPONSIBILITY.

If someone is not able (technicals skills are meaned) to valuate for his own wether this or that is good or bad he should take off his fingers from trying out 'self developed' changes at his car.

IMO everybody is responsible for himself if he/she changes anything at his car out of the cars spec. or out of the aftermarket parts suppliers specifications.

These BBS threads seam to be sometimes a little dangerous for 'naiv' people.
Equal its dangerous to take only one term of any data base.

Hope this clears some of the confusions on our so called 'technical discussions'.

FAO Ted,
I fixed my fuel pipe in a way that it does not touch the filter :)

Dieter Koennecke


How did you 'fix' your fuel line?

Mine is 'moulded' plastic and there did not seem to be any anchor points to hold it clear of the filter and I did not want to use a cable tie or such because in my opinion the line needs this flexible length to allow for the movement differential between the rigid filter fixing and the engine.

Ted Newman

What about mailing K&N direct? We could ask them for their views and have a discussion about the 57i kits for the 1.8i and the VVC. If I remember correctly and this was many moons ago,didn't one of the guys at K&N post a message on here when the kits first came out? Many people said at the time that this was very responsible of them and they should pride themselves on good customer service.

I have no doubt Rob is correct, without a Research facility at K&N there would never have been a K&N kit for the MGF and no-one would be getting the extra BHP from it. Admittedly some people would have tried other K&N 'ideas' but what if damage had been done to the engine? I don't think you could go back to K&N and moan.

Just a thought

(with a full 57i kit on my 1.8i F)

Ted, I had no fuel line fouling with the K&N on the throttle body. In fact, no pipes or cables were even close if I recall, but I'll go back and check.

No damage will result just by fitting the filter without its spacer tube. Remember, this is how Pipercross, BMC and Green all fit their filter installations.

Ultimately, this is a question of choice.

Choice 1: good top end power (8bhp gain), but a *minor* limitation in low end torque = standard 57i

Choice 2: more noise (lovely hiss actually! ;o) more low down torque, but less top end breathing/power (4BHP gain) = 'tubless' 57i.

I had the latter for some time, and thought it was great (as has Tony), but have subsequently fitted an alternative performance exhaust and returned to the former standard set up.

This is a thread for the do-it-yourself car tinkerer! ;o)


Robert Bell

Just a thought:

cutting the tube to half lenght would be a compromise between:

yes or no?

>Choice 1: good top end power (8bhp gain), but a *minor* limitation in low end torque = standard 57i

>Choice 2: more noise (lovely hiss actually! ;o) more low down torque, but less top end breathing/power (4BHP gain) = 'tubless' 57i.

(Iīll try ....or Ted did you even do this, your last comment sounded like you would.)

Like Rob I do not have Problems with any kind of Pipes tubes cables or else getting close to the filter even if it is fitted directly to he throttle body.

(with clear indicators now) :-))


I don't know Thomas. I was thinking about trying a number of lengths of tubing and just trying it out to see what happens.

I think that the tube is 70mm diameter. I have been told that this is the same diameter as the filter tubing from a Montego/Maestro/Rover800 etc, so I was going to pick up some tube very cheaply and try it out.

Be my guest to beat me to it! ;o) I am not sure when I'll next have time to experiment.

Good luck


PS Too dark last night to peer into the engine bay- sorry Ted.
Robert Bell

Ted, you are not alone, I also have a problem with the the filter pushing against the fuel line. I was a bit nervous about it, but I love the sound so much I decided to live with it and just check regularly for wear. Like you I also couldn't see anyway of 'fixing' it.

Glad to hear that I am not alone:-)

But I will check it out again this coming weekend - don't have time in the evening

Ted Newman

An idea but never done:
Placing a aluminum coated shielding board between the mushroom(we Taiwanese call the filter like this.) and engine room. And this shielding board should cut a 70mm hole for tube passing.
For What: shielding the engine room heat air. For sure that all the mushroom air is cool.
Logically it should enhance the performance.
I saw that some IMPREZA workshops did it like that.
Now who will be the mouse for hanging a bell on the cat?

Don Liang

Rob, Ted, Let us all know the results of your experements, without the pipe the drop in power at 4000 revs is only minimal compared with the extra low end grunt. I would still like to see the optimum length of the tube though.
Tony Smith

FAO Gary

Glad to hear you got the filter fitted. Did you recieve the bracket okay.



Hi Tom

Thanks for the bracket. Havn't had time to fit it yet, will do it tonight. I will let you know how I get on. Love the filter!




Just a thought:
*The length of the tube is designed for the biggest power gain, when it is installed on a VVC
*The VVC MGF reaches its max. power at a higher rpm than his brother the MPi.

So if I want all the power that is possible (max. power of the standard engine + add. power of the 57i), I need to cut a few centimeters of the tube.

Is this to logical... or have I messed up the things?


well Iīve cut the tube in two halfs!

Results ... well as I could feel it things came out nearly the same! It is a bit quieter inside.
Thatīs my part in this "everlasting" experiment here.
Iīll leave the 1/2 long pipe as it is, a good soluton for all the ones with the fuel line problems like mentioned by ted

Just one thought: (to have a more "lively discussion")

I was reading a technical sheet of Opel yesterday and found out that they do have a 2 way ram air system in some of their cars....
Here comes what I found prodigious:

* the long ram air pipe ist for the lower revs
* the short ram air pipe is for the higher revs

Confusion is at max revs .....

Thomas O.

Well done Thomas - I think I will do the same.

Now the big question:-

Can someone explain to me (in laymans terms) why the length of the tube should make such a difference - I can understand a short tube allows the air in quicker but a longer tube giving better performance at high revs I dont understand - is it something to do with turbulence?

Ted Newman

Ted, I think it has everything to with turbulence, and much to do with the timing of the negative and positive 'shock' waves that resonate in the induction systems as a result of the reciprical air pump nature of a four stroke engine.

What we have found is paradoxical- a very short induction inlet path (by eliminating the spacer tube) appears to benefit low range torque, but maybe that is more to do with the 'tuning' of the inlet tract....

Have a look at

-tried to explain things as best I can there.

Robert Bell

Ah Yes the shock wave principal - one of the bike firms (Suzuki I think) have been experimenting with an auto adjustable shock wave balancer and I seem to remember that it was linked to the ECM so that as the revs increased/decreased the inlet path was altered - now it all comes flooding back - you have to give us BOFs a little time for the brain to get auto-adjusted.

Ted Newman

Inlet tract length laters the frequency of the energy pulses that are contained with in the mass of moving air. These reflect back and forth within the whole inlet system and can have positive and negative effects.

A negative effect is when the pulse is out of phase with the opening of the valves and the movement of the air. This actively reduces the weight of air entering the cylinders. The opposite is true for positive effects where the pulses and aiur movement is in phase with each other and the result is that the pulse actively increases the weight of air entering the cylinders. (Fuel is included in this if it is in suspension with the air.)

The effects of pulse tuning is very narrow and applies at certain rpms only. However the general rule is that shorter tract lengths induce more improvements at higher rpms with longer tracts peaking at lower rpms. Of course many other factors may influence the simplistic assumptions of high and low rpms to short and long tract lengths, not least of which is the airflow capability of the components used.

I once again draw attention to the fact that the advantages from this discussion relate to weight of air that is able to be drawn into the cylinders to produce work. Air temperature reduction is a way of achieving more weight of air into the cylinders AND having this effect applicable to ALL engine rpms.

Roger Parker


FYI the Maestro/Montego air filter box has a 60mm bore cold air inlet hose whilst the Rover 820 has a 70mm bore cold air inlet. The 820 also uses plastic moulding and plain pipe lengths rather than hose. Of note is that there is a 10mm increase on both these sizes for the air to pass through on the engine side of each filter.

Roger Parker

Well today I 'circumcised' the K&N air filter by removing 3 inches of the straight section of the replacement induction tube.


Retaining the 'kinked' section of tube allows me to get the filter further forward and well clear of the petrol line. It also takes it closer to the 'cold air' pipes - but of course these can be repositioned.

Performance does not seem to be any different than without the pipe at low revs and it certainly hits the rev limiter without trouble.

Noise - back to what it was before the removal of the tube, masses of throaty roar when on full throttle and subdued when just crusing.

Conclusion - without the use of sophisticated equipment it is all a matter of feel and I feel that it is about right - so I will keep it as it is.

Ted Newman

This thread was discussed between 13/10/1999 and 23/10/1999

MG MGF Technical index

This thread is from the archive. The Live MG MGF Technical BBS is active now.