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MG MGF Technical - Wanted: VVC Manifold/plenum

Has anyone got a cast VVC inlet manifold/plenum for sale?
A Stubley

Why exactly do you want the Cast Aluminium plenum? There is little or no benefit using this item on a non-VVC car. Air speed is important in an engine and a larger plenum will slow air speed and may even rob the engine of a little bit of performance.
tim woolcott

I disagree with Tim here, any K with a ported head will benefit from having a matched VVC plenum and manifold. It's not just the capacity of air flow (which as Tim rightly points out is surplus to requirements on non-VVC engines), it is also to do with flow dynamics, and in this regard the VVC set up is more efficient.

Also, TF 135 uses an updated version of the same casting, this is a non-VVC engine and the VVC spec plenum and manifold is standard fit - at first i thought it was for cost reasons, you now simplifying the product range, but the lower capacity K engines still use the plastic manifold so there must be another reason. Given that this engine has a revised air intake tract, the efficiency reason i have given above and the increased power output of the 135 spec engine, i believe that the plenum and manifold are there to get the most out of the revisions and supply the extra air this engine needs to make the 135PS claimed.

The only other reason i can think of for fitting it turns out to be a bit of a red herring. The famed inlet manifold gasket leak has been attributed to the IMG on the MPi plastic manifold only, this is a reason to swap to the VVC one (HGF prevention). However i have had an IMG leak on my VVC manifold, so if you are thinking of changing it to prevent this happening then i wouldn't be to confident in this regard.

You should be able to pick up a VVC inlet manifold and plenum from Victoria at the MGF Centre, among others.

Scarlet Fever

I asked this very question about the VVC plenum when Dave Andrews flowed my head, it was then that Dave expained to me the flow dynamics involved (OK in very simple terms) and that there was very little to be gained through swapping and to save the cash.

So although the new aluminium casting is used on the TF I would still suggest there is little advantage, and especially if the original 48mm TB is being used and the engine is otherwise un-modified other than say a filter and exhaust.

I would suggest that the aluminium cast is most probably a result of the IMG problem TBH.

tim woolcott

The VVC plenum is a liability, only really useful for the VVC or maybe as a doorstop or perhaps for hand to hand combat. It may give a couple of BHP more at the top end one some engines but it compromises mid range torque on most. You are better off with a stock plenum properly matched to the head and with the internal flashing removed. It's incorrect to say the VVC plenum is 'more efficient', what does this mean? Efficiency can mean many things, with any induction system port velocity and momentum is just as important as overall airflow.

Dave Andrews

> stock plenum properly matched to the head and with the internal flashing removed

Dave is it reasonably straigthforward to remove the internal flashings and how long would it take. Can you remove too much perhaps? Any pics of a standard one and a modified one?
Bob Millar

Bob, From what I understand the flange is inside the plenum where the two plastic castings are mated together. It will be pretty self evident what needs to be removed and there is little risk of removing too much. Only problem is getting the old one off....

tim woolcott

< stock plenum properly matched to the head and with the internal flashing removed >

So your comparing a de-burred plastic manifold with the VVC alloy one? What about a standard plastic manifold (which is what 99% of us have)?



>So your comparing a de-burred plastic manifold with the VVC alloy one? What about a standard plastic manifold (which is what 99% of us have)?<

To summarise:

For an Mpi the standard plastic plenum is OK but not fantastic due to the internal plastic flange left over from the manufacturing process.

With this excess plastic removed the plastic plenum give better air flow into the cylinders increasing performance.

The VVC plenum although larger will not necessarily lead to better performance on an MPi as the larger capacity reduces the speed of air flow.

So if one intends removing the plenum for any reason, it's a cheaper and more beneficial to fettle the plastic item rather than fit the alloy VVC item.

Does that make thing clearer....?


tim woolcott

Much, thankyou.


Try the cast alloy one of the metro gti, simmilar propotions to the plastic one but easier to work with and will match the inlet ports of the 1.8i head better, you can also use the 56mm TB as well and this set up works very well on a 1.8i.

The Metro plenum is OK, but it moves the TB to a different angle which no longer mates with the inlet ducting, it is set up for a stepper motor to control the idle quadrant rather than an IACV , the fuel rail from the later MPIs doesnt fit, and the throttle cable pickup and MAP sensor take off/ servo take off are in different places. Other than that its fine.

Dave Andrews


Do you know if the Metro plenum has any (flow) benefits on a VVC-engine?

Arend Groen

Another nail in the VVC plenum argument: I remember a few years back Roger Parker showing me the difference between the MPi and VVC plenums and heads. The VVC head has a much greater mating surface area - especially along its lower edges. When you open out the head's inlet ports to match the VVC plenum (as you must if you want to reap the rewards of fitting a higher flowing plenum), then you end up with an MPi head that has an alarmingly precarious seal with the alloy plenum... Rog's solution, which isn't cheap to replicate, was to build up those mating surfaces, and have them machined...

Given the RR evidence, the VVC plenum is a costly option that has surprisingly little gain - and even, as Tim and Dave have already said, has a penalty in terms of reduced low/mid-range torque.
Rob Bell

Hi Rob,

What I meant is; does the Metro manifold have any advantage over a VVC manifold when connected to a VVC engine. I do have a VVC and I don't intend to swap my manifold for a plastic MPI one but I was just curious what a Metro manifold would do on a VVC.
Making a matching surface plate would not be so difficult or expensive for me as I can do this myself and it would only cost me a piece of aluminium.

Arend Groen

Hi Arend,

I don't know too much about the Metro manifold at the moment (although that may change - I'll explain later). However, from what Dave Andrews has written about it, it seems like a lot of work to make it fit: you'd need a different fuel rail, different throttle cable, some way of controlling idle speed etc etc... which all means that we're not talking a straight swap, and some of the new parts may prove expensive.
So the question then becomes: is it worth the hastle and expense to fit? I suspect that the gains simply won't be there to justify it - and on a VVC, the Metro manifold may rob top end power... :o(
Rob Bell


The last thing I will is loosing top end power. I understand it isn't worth it.
Thank you for explaining.

Arend Groen

No problem Arend :o)

Have you performed any other mods to your car?
Rob Bell

Yes I've done a little bit to my car. I've fitted an airbox from a Rover 220 TurboD to my car. The mounting isn't a problem, the air inlet an outlet needed a bit of work. AFAIK this box has the same dimensions as the box on the TF160/ZR160.
I've "polished" the first part of the intake manifold and grinded away the ends of the tubing that were protruding there.
I've fitted a VW throttle body with 56mm I.D. This needed a bit of turning and milling and yet it looks as good as an alloy OEM one. The latest thing I've done is making a wingshaped throttleplate for this body.
Last year I've made a stainless steel fuel rail with concentric tubing, where the fuel flows between the inner and outer tubes, and the inner tube is connected to the cooling system. So the fuel is preheated to about 70 to 80C (I guess).
At the same time I've fitted a adjustable fuel pressure regulator. I've no idea about the make of this, I've found it at a scrapyard and cost me 1 euro.
I've milled a sort of little manifold for this to make things fit and I've made an extra connection where I can connect a pressure gauge.
Between these mod's I've done a lot of experimenting with different tubing for air intake.
Last week I've ordered a GREEN AIR panel filter for my (diesel)airbox. Sadly it didn't arrive yet.
That's about my car, what about your's?
Arend Groen

A really impressive list of modifications there Arend - certainly not something I can personally compete with: do you have rolling road figures and pictures of what you've done?

My car has been modified with a Rover 820 cylindrical air box, containing a K&N cone filter (flexible hose to the left side engine air intake), and connected to a 52mm alloy "Trophy160" throttle body. The butterfly valve is unfettled; Roger Parker looked at this on a 48mm TB and found little benefit in doing a 'Vizzard' on it (Mr Vizzard is an A-series engine tuning legend in case you've not heard of him). The plastic plenum is standard, although I am thinking of removing any moulding flashings that may be affecting airflow.
Exhaust wise, I'm using Mike Satur's excellent Daytona back-box system with the standard catalyst. The exhaust manifold is currently standard, although a 4-2-1 aftermarket design is planned.
Fuelling all is standard, although the fuel pressure regulator has been calibrated @3.2 bar (top of the standard tolerance range)
This combination is giving me somewhere in the region of 135 bhp and 140 lb.ft torque. I'm happy with these results for the modest outlay in parts! ;o)
Rob Bell

Hi Rob,

Unfortunatly I don't have RR-figures, that would be too expensive for me, everytime I changed something to my car.
I don't have pictures either because I don't have a digital camera (yet). As soon as I've bought one or when I can lend one from a friend, I will take some and send them to you.

I don't know Mr. Vizzard but as you've heard allready a butterfly valve modification won't give you much. In my case the biggest advantage was, because of the round shape of the valve where the air meets the valve, driving away from stand still with low revs is much easier and with no negative effect on top end power.

I think a little attention to your intake manifold would not be so bad. As I've noticed in the past; removing every little (sharp) obstruction in the intake path shows a more or less feelable torque increase.

About my exhaust: I forgot to tell you that I have an almost standard system, the only thing I've done is removing the welding sh*t inside the manifold. (sorry for the word, but I couldn't think of another decent word immediatly)

A 4-2-1 aftermarket manifold is far more better than the OEM I think, but I think too expensive for me.

I've adjusted my fuel pressure regulator to 3.4-3.5 bar, and I think that if you've "done" a little bit to your car 3.2 bar is a minimum.

As I've mentioned I don't have torque or bhp numbers but my car does "feel" rather fast. So I guess it would be in the region of a 160bhp and about the same torque (or maybe a little bit more) than your's.
Arend Groen

Sounds good Arend. Interesting to see that you've set your fuel pressure relatively high. I know that Thierry performed some RR sessions with a range of fuel pressure settings, and found that 3.2 bar was about optimal, whilst at higher (3.6bar?) he started to loose power. This was on a Trophy 160 engine (VVC)
Rob Bell

It doesn't surprise me that on different engines (different specs) there is a difference in what is optimal.
I think that, for example, all the engines which had the original 48 mm plastic throttle body replaced by an alloy TB 48 or 52mm or even larger tend to run a bit lean, especially the first part of the throttle angle. The flow curve is different because of the larger bore and/or because the throttle plate is flat instead of the plastic special shaped one.
I guess that the later engines that have the alloy TB from new, do also have a different mapping.

Another point is, how precise is the measuring device that is used. I think a misreading of 0,1 or maybe 0,2 bar isn't uncommon.
Arend Groen

>> I think that, for example, all the engines which had the original 48 mm plastic throttle body replaced by an alloy TB 48 or 52mm or even larger tend to run a bit lean, especially the first part of the throttle angle. The flow curve is different because of the larger bore and/or because the throttle plate is flat instead of the plastic special shaped one. <<

Interesting that you say that Arend - because that tallys exactly with my experience too. :o) Completely agree with what you say with respect to the flow curve with throttle angle as well.

I don't know if Thierry is reading this thread or not - but his car, being a Trophy 160, was equipped with the 52mm TB as standard. His results seem to indicate a strong 'Bell-shaped' curve, with the optimal fuel pressure being 3.2bar. Your engine may be different, but his observations may be worth bearing in mind...
Rob Bell

Thinking about removing the flashings from the plastic plenum. Can this be removed from the inlet manifold wihout having to remove the manifold from the head i.e. can I just remove the plenum. Dont fancy removing the whole manifold as it looks like a pig to access and I took it to a dealer to have the inlet gasket replaced as I didnt fancy tackling it myself.

If the plenum can be removed seperately then I'd certainly do it.

Anyone know?
Bob Millar

I suspect that you'd need to remove the whole lot to get adequate access to the plenum Bob. :o(
Rob Bell

Bob Millar


my engine is a 143 bhp vvc. This had the 48 mm plastic TB as standard.
I have no idea what you mean with "Bell shaped" Rob, I've never seen a picture of you. :o)


If you don't remove the plenum from the head, you won't find it easy to remove the flashings. Even if you would be able to do so there's the danger of pieces "falling" in the engine.
Arend Groen

ROFL - thanks Arend ;o)

The 'bell' describes a shape of a curve - rather like a normal distribution curve like the one here:

Basically it is a way of describing how one setting is optimal (peak of the curve), whereas settings either side result in less.
Rob Bell

This thread was discussed between 06/11/2003 and 26/11/2003

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