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MG MGF Technical - Polishing the intake manifold
|Is it possible (iīve heard of) to polish the intake manifold of the VVC? People have been telling me yes, and they also say that increases bhp in 5-8%. Is this realy good value? Does it have any consequences?|
I'm planning to polish the aluminium intake manifold of my Rover 200Vi (same engine as MGF-vvc) probebly in februari or march. So I can't tell much about it yet.
As far as I know, polishing does really improve the airflow, so it should have an effect on torque.
If this is noticeble I don't know but I think it's worth a try.
I think it would do no more "harm" to your engine than a high flow air filter.
If your engine was a monopoint injection, some negative effect could occur because the gas would then be injected in the plenum, and the roughness of the plenum and runner's would cause a bit of swirl, so the air and gas would be pre-mixed (is better mix) but since the vvc-engine is a multipoint injection the gas is injected (almost) direct in the head. So polishing the plenum and runners should have no negative effect on that, because there's only air flow.
I let you know when I know more about this.
|Polishing theVVc inlet tract would probably be a waste of time(IMO) as the fuel/air mixture likes some turbulance to enable mixing of the gasses, polishing removes this turbulance, a better option is to match the ports together so avoiding any step at the point where head meets inlet and inlet meets plenum. This also applies to the MPI inlet ,although this has (plastic) welding sprue intruding into the inlet tract due to the method of construction which is almost immpossible to remove.|
|Arend Groen says: "vvc-engine is a multipoint injection the gas is injected (almost) direct in the head. So polishing the plenum and runners should have no negative effect on that, because there's only air flow."|
Mikesatur says: "Polishing theVVc inlet tract would probably be a waste of time(IMO) as the fuel/air mixture likes some turbulance to enable mixing of the gasses, polishing removes this turbulance". I donīt have enough technical knowledge to choose wich of them is right. I wonder if anyone can give further explanations... Can anybody also explain what mike means when he says: "a better option is to match the ports together so avoiding any step at the point where head meets inlet and inlet meets plenum." ..maybe somekind of picture of it...
Mmmm. I tend to agree with Mike. I spoke to Peter Burgess last year about this, and his conclusion was the same. i.e. Some turbulance, even with a muti-point injection, is a good thing as the air swirls as it enters the combustion chambers, hence giving a better mix. Could be a waste of time and effort. Porting was a more effective option.
|Polishing is only any good on the outside if you want to have a pretty engine. Inside you are not only wasteing alot of effort, but the process can actually reduce the actual airflow. Grinding casting lumps and clear irregularities, leaving a roughened finish MAY help. |
The problem is very simply that without the benefits of an airflow rig you have now way of being able to confirm whether what you do is actually improving the flow.
In fact flow is not linear through the manifold and you can often have one side of a port runner, in one specific place, carrying all the flow, whilst the other side can actually have flow in the opposite direction! The action of the throttle and the action of valve movement has a significant impact on what is happening to the air mass, all to add considerable complication to the whole issue.
Mike's guidance is spot on as the only clear area where work will not harm power, and may enhance it slightly, is in matching manifold to head and get ports aligned. (This is where the hole of the manifold which is the port, joins the hole of the port in the head. Casting irregularities often mean that these do not match and so you end up with a step that can 'trip up' the airflow. Using the manifold gasket as a guide you can see if there is any mismatch and grind the ports to suit the hole of the gasket.)
Always remember that it is far easier to lose power than gain it, otherwise everyone could do the same as the specialist head and engine tuners like Pete Burgess!!
I agree that polishing the inlet manifold does not not necessarily benefits the airflow, it depends on how the head is constructed. When the constructor had in mind that some swirl should take place in the manifold(runners), then polishing wouldn't do much good. But when he constructed the head with an intake passage that would do all the swirl and/or tumble then, IMO, polishing could improve the filling of the cilinder(s).
And (Mike), matching the port's could improve airflow but it could also remove some turbulance necessary for a good mixture.
I remember the Volkswagen GTI-engine (multipoint injection) from the seventy's/eighty's, where polishing
did much good to the engine.
I would suggest that one of the (Rover)engine tuners does some investigation on this subject.
|Investigation of the K series and the flow potential of the head has been done for some time. There are significant gains to be made with the MPi head, even without valve changes. Then there are other options beyond that spec, which have value under certain circumstances. The comments relating to the effect of polishing are not assumptions! I have much of the information but I am not in a position to publish or broadcast it, however I am already using it!!|
This thread was discussed between 26/01/2000 and 31/01/2000
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