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MG MGF Technical - egine bay coooling

I had thought that the F side vents were for decoration only - ie they didnt actually duct air into the engine bay BUT I have subsequently read somewhere that they do in fact aid engine bay cooling. What is correct? Need to know as I have blanked off one of my intakes!
marc hanson


From what I understand they do assist with cooling but not much. Most engine bay cooling is achieved by air from under the car.
Why have you blanked off a vent?

Off-side vent (RHD) has the engine bay fan fitted to it
David Clelland

i have a cold air induction pipe in the passenger side vent and blanked off the area round it so that any air coming into the vent was directed to the mouth of the induction pipe. Sounds silly I know, especially as its the suck of the filter thats important.... Does this mean Im blocking the engine bay fan? Didnt even know there was one.
marc hanson


As DC says the engine bay fan is on the drivers side so you're OK. If you have a pipe fitted in the passenger side air intake this is fine. There's not exactly much room in there and I suspect blocking off what little surrounding area there is will make no difference at all! If the pipe just goes to the engine bay in the proximity of an open filter e.g. a K&N - it will do very little good. Best to enclose your filter and have it suck from that pipe.
Dave Livingstone

Thats exactly what I am planning to do to mine over Christmas, I am ducting air to the K&N enclosed in a Rover 820 air box.

OK, this is how i understand it...

The air vents on an F are pretty stagnant when the car is in motion, Rob Bell and i tested this using streamers placed around the vent and a video camera from another car. The playback revealed some streamers going in, and some coming out! We concluded then that airflow through the vents is pretty negligable.

However, there is an engine bay cooling fan situated behind the drivers' side vent, this draws air in when the temperature sensor in the engine bay tells it to - this is additional cooling and only when the heat build up becomes excessive (say in a traffic jam for instance).

The passenger side air intake is partially blocked off by the petrol tank, and thus can be considered primarily cosmetic.

So how is the engine bay cooled?

Air is drawn up from underneath the car and then expelled through the top vents in the bootlid - this is the primary route of engine cooling. The vents themselves are actually an afterthought. We know that originally air was supposed to vent out through a plenum in the underside of the bootlid and exit where the high level brake light is situated. When the car was wind tunnel tested at MIRA though it was discovered that this wasn't very effective and so at the last minute the plenum was blocked off (almost entirely - i have managed to dismantle a bootlid recently - there is no real route through here any more) and the familiar bootlid vents were installed.


Scarlet Fever

Eeek! Does the cooling fan draw air in through the vent??? Because when my fan comes on, it is defiantly pushing hot air out the side vent like a hair dryer!!!

My cold air induction pipe goes to a fully enclosed motobuild "rice cooker" box housing a piper cross filter. Sounds like I dont have to worry about anything. Thanks guys.
marc hanson

Sounds like you'll be ok with that setup Marc. But it does spark a related question from me.

I have been thinking about getting some fibre glass or Carbon fibre under the car to smooth the passage of air under there (coz if you hava a look it's pretty messy). But in doing so it would block off the air into the engine bay. Would leaving a opening in an airscoop sort of arrangement be suitable or would it be better to smooth out the front end leaving the engine bay open?

Any thoughts guys?


Phil Brindley

Maybe have a look to see how Lotus manage airflow under the Elise for some inspiration Phil. Perhaps a tray to the sump and then have a scoop behind the engine to aid the natural air flow around the engine bay would be best?
Rob Bell

SELOC boys have come through as always. The Elise is basically flat with 2 small air intakes and a whole for the flexipipe, then difuser at the rear.
Phil Brindley

Any pix Phil?
Rob Bell


There you go. Not sure it would be possible to replicate exactly but we should be able to do something that would help with our cars.

Phil Brindley


We can't view your pics because we aren't members.

I remember years ago Roger Parker was experimenting with a tea tray air deflector under the car. Never saw any results. What happened to R.P.?

Roger now works for the MGOC.

Ted Newman

>> We can't view your pics because we aren't members.

Rat's I'll post them into the FPOWER gallery this evening as you don't need to be a member to view them there.

Phil Brindley

Wow! Someone's gone to a lot of trouble with that under tray haven't they? Comes complete with two NASCAR ducts to get some air into the engine compartment. Personally, I don't think that that would be enough for the F - the Elise has much more efficient engine air intakes on the flanks than does the F... also the heat build up around the exhaust must be significant?

Good basis for a project idea though Phil :o)

Andrew, Roger's is well - and still posts here from time to time. Not got an F any more though - but many other interesting MGs have passed through his hands since that time.

Roger's scoop idea was based on a simple pressed steel tray as used on the MR2 Mk2 - and fitted very neatly too. The intention was to get more air into the area around the exhaust manifold. Unfortuntely, preliminary testing of the idea didn't show particularly promising results - and plans to repeat the tests just didn't come about unfortunately.
Rob Bell

Here are the pics so you can see what we're talking about.

Thanks to Ben from SELOC for the pics, hope you don't mind me re-posting, if you do just say and I'll remove them.

I agree Rob, I don't think those little scoops would be much good for the F. I was thinking about constructing a tray from the back of my Trophy splitter back to the start or the engine compartment then some form of defuser to cover the exhaust back box to the rear bumper. Thus leaving the bulk of the engine bay exposed to the elements. do you think this would do much good or would the turbulances created around the engine bay negate any benefits from the front end?
Phil Brindley

Phil, I guess the primary objective to the plan is to smooth underbody air flow and cut lift? If so then there is one very significant spoiler to your plan - and perhaps isn't immediately obvious: the front coolant radiator - and particularly where the hot air exiting the radiator ends up.

On the Elise, the air, very obviously, is ducted upward, over the top of the bonnet. On the MGF, the opposite happens - all that air is ducted downward, towards the road. This hot air that enters through the front grille is what is largely responsible for front end lift on both the F and TF - and it is no coincidence that the TF 200HPD has a different arrangement to manage the radiator air flow - see

Therefore unless the airflow from the radiator is managed properly, all that hard work giving your F a flat underside is going to go largely to waste (although I am sure there will be some improvement, it just won't equal the effort invested in it).

Been giving the radiator 'problem' some thought - I like you would be interested in solutions that will further improve aerodynamic efficiency :o)
Rob Bell

Like this you mean?

Please forgive the rubbish picture.
Phil Brindley

If so, then could the warm air not be helped out into the airflow in a more rearward direction like so.

I might be looking too simply here (not unusual for me to be a bit simple) but it doesn't look like it would be too difficult to overcome the problem. Or are we saying that even in this configuration the extra air would create lift no matter what direction it is flowing?
Phil Brindley

airflow1.jpg is exactly how the standard set up works. This excess of warm air is what causes the lift problems over the front axles. Unfortunately, airflow2.jpg doesn't really solve the problem - and may, depending on the aperature for the exit of radiator air, impede radiator cooling :o(

I think that the easiest option is to vent through the bonnet, as per 200HPD/ Lotus Elise
Rob Bell

Old thread but you might be intersted in this one...


>> I think that the easiest option is to vent through the bonnet, as per 200HPD/ Lotus Elise <<

Been thinking about this for a while now Rob (since before the rebuild actually), got some sketches drawn up and everything.

It would mean ditching the spare wheel and having a scoop made up for inside the under bonnet area - i reckon a hole cut in the spare wheel well wall and then some simple vents in the bonnet would be sufficient along with a blanking plate shaped into a scoop to ensure the air is directed upwards through the hole in the wheel well wall rather than downwards out the underside.

Might even look into getting hold of a spare bonnet and constructing some XP500 look alike bonnet vents...

Scarlet Fever

Exactly my thoughts too Andy :o)

Personally I'd go for something that is as subtle and 'standard' looking as possible (which means 200HPD) - but for SF, the XPower 500 would look awsome! :o)
Rob Bell

This thread was discussed between 23/12/2004 and 14/01/2005

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