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mg_zs
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Discussion Starter #1 (Edited by Moderator)
Just a quick note to the admin - I did try to post this in the how-to section but it wouldn't let me. Feel free to move it if you wish.

Although opinions will be split on whether this is the way to go when it comes to a noisy inlet manifold, I thought this guide would be helpful for anyone who wishes to follow in my steps.
I removed the internals from my manifold over 1000 miles ago and have experienced no problems since doing so. Although a small amount of torque is lost in theory, when it comes to day-to-day driving, this isn't noticeable and MPG has also remained unchanged. I did a lot of research before performing the mod and decided to remove my internals for two reasons:
1: A new inlet manifold with VIS is in excess of £500
2: Some people who have replaced them with new items, experienced the same problems again.

SORRY NOT ALL THE PICURES ARE GREAT QUALITY, I TOOK THEM ON MY IPHONW

I have a 2002 51 plate MG ZS 180 with 63.5K (62K ish when the problems started) on the clock.



After just a few weeks of ownership, it started to sound less like a V6 and more like a MK3 Fiesta in need of the tappets doing. It was also down on power. I read if you disconnected the VIS motors and you still have the problem the manifold is faulty. Another way to test this is to remove the front VIS motor, exposing the rod that opens and closes the butterfly valves, if this has any play it, chances are this is causing the rattling.

Firstly the tools I used (plus a star bit and phillips to take out VIS and undo manifold cover - not shown). I also applied some heat to the manifold to stop the plastic from cracking.



I removed the 10 screws from the cover.

Next I heated up my scraper and started from the corner, tapping it with a hammer until the seal broke. You have to hit it quite hard to break through the lip but once through the hard part is pretty much done.



By tucking one scraper behind the other and using a hammer, you can tap along the top seal to break it.





From here you can break the seal down each side about 1/2 inch as then the manifold curves and you have to start from the other side and repeat the process. Take your time with this as if you crack the cover it's game over! The manifold has to be air tight again once sealed.



Here is a picture of picture of the manifold without the cover on. You can see the rod attached to the 6 butterfly valves. This is what causes the problem. These valves are attached by a ball joint that wears out, as will be seen a few pics down.



You can remove these valves in two ways
1: Drill through the butterfly valve and remove just the valve, shown here:



2. Crack the valves where they join the manifold

I went for the easier option 2 this time, as I've done one of each, fitted both to my car and didn't notice a difference.

If you line the scraper up on the join (which can easily be seen but I couldn't get a clear picture of) one quick knock with the hammer will split it away.



Here is a close up of the ball joint



As you can see the ball joints have had it! The pic shows that only two of the four valves were connected on this one!



You then have to sand the lip down. A dremel is great for this, just to take the edge off and make it smooth ready for gluing. Picture shows pre sanding.



Once sanded, I cannot stress how important it is to thoroughly clean the manifold out, there will be bits of plastic all over the place and you do not want them getting sucked into the engine! I washed mine out with petrol and a brush, left to dry, then followed blowing it through with an air gun, double check every corner for shards of plastic.

Next put the cover back on with glue around the seal and tighten the ten screws. Depending on how cleanly the cover comes off, sometimes I melt excess plastic around the outside to seal any gaps - it's not pretty but it works. This cover came off fairly easily and didn't need extra plastic.



Glue wise I use Unibond plastic repair as it is heat resistant to 150C.



If anyone doesn't fancy trying to do this mod themselves send me a PM.

Hope this helps
Stew
 

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Whilst I disagree with you that the lack of torque from the VIS system wouldn't be noticeable - mine being almost turbo like when it kicks in - I do think this is an important alternative, and a useful guide, for two reasons;

1. As you mentioned, the plenum isn't exactly cheap, and finding £500 can be difficult, more so given that when it breaks for a fault that can be lived with for an extended amount of time. This is therefore a viable alternative to buying a new plenum, albeit meaning you now have a ZS 160...

2. This is a good guide for cracking open and resealing the plenum, whilst keeping the whole unit air tight. I think in collaboration with Sheddist's upgraded butterfly arm, this could turn out to be a new, important Stew1/Sheddist upgrade akin to the sheddist clutch kit. Perhaps a combined guide might be a good idea?

Thanks for your time putting this guide together, I for one will be calling back here should my plenum break up and I need to know how to get in to put the sheddist arm in.
 

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mg_zs
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Discussion Starter #3 (Edited)
Whilst I disagree with you that the lack of torque from the VIS system wouldn't be noticeable - mine being almost turbo like when it kicks in - I do think this is an important alternative, and a useful guide, for two reasons;

1. As you mentioned, the plenum isn't exactly cheap, and finding £500 can be difficult, more so given that when it breaks for a fault that can be lived with for an extended amount of time. This is therefore a viable alternative to buying a new plenum, albeit meaning you now have a ZS 160...

2. This is a good guide for cracking open and resealing the plenum, whilst keeping the whole unit air tight. I think in collaboration with Sheddist's upgraded butterfly arm, this could turn out to be a new, important Stew1/Sheddist upgrade akin to the sheddist clutch kit. Perhaps a combined guide might be a good idea?

Thanks for your time putting this guide together, I for one will be calling back here should my plenum break up and I need to know how to get in to put the sheddist arm in.
Thanks, a combo would be a good idea, maybe I'll get hold of a sheddist kit and try one. Anyone want to donate a manifold to try this?

With regards to power, with out a rolling road it's hard to tell but I doubt you'd lose 20bhp through this, certainly doesn't feel 20bhp down. You still get the nice cam kick at 3500rpm (this is when the VIS motors would open the valves, my valves are not there so already open, hence same power top end) just a little less torque below 3500rpm. As I said without a rolling road will we'll never know, but day to day and when you put your foot down, it feels great.
 

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I believe the 'turbo' thing comes because all all the valves open and you suddenly have extra power.

Thanks for this Stew, there will always be uncertainty with this until one of us does a rolling road test but at least there is a £500 cheaper option and now a guide.

Cheers!
 

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Thread moved to How Do I? section.

Stew - please check that you can still add posts to this thread now moved and let me know if there is a problem.
 

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Discussion Starter #7
Thanks for moving this John, it will let me post in this section, but for some reason I couldn't create a new thread.

No worries Nathan, yep that's your old manifold, no wonder you were down on power!
 

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Interestingly the ball and socket setup used on this system looks to be the plastic version of what Landrover used on the throttle linkage for the series 11, they were steel though, with a slide over steel spring clip to stop them from jumping apart under vibrations or force.

Not saying rush off and start stripping every series 11 you can find, but might be worth a look if someone is near one.
 

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photo.jpg

This is a picture of the first manifold I split. I washed it this weekend ready for resealing. Slightly different to the one Stew has done as I removed the butterflies rather than the whole part.
 

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Nice work and I may well be PM'ing in the future ;)

However, the valve settings are not simply open/closed. They have other arrangements. I think above 4000 rpm they effectively turn the KV6 into two 3 cylinder engines and you are missing that.
 

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Nice work and I may well be PM'ing in the future ;)

However, the valve settings are not simply open/closed. They have other arrangements. I think above 4000 rpm they effectively turn the KV6 into two 3 cylinder engines and you are missing that.
I have to disagree. Another thread shows a chart with both valves open at peak power/torque ranges. The differences are in the lower rev range.
 

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I have to disagree. Another thread shows a chart with both valves open at peak power/torque ranges. The differences are in the lower rev range.
I'd be interested to see it, because it's wrong. The valves do activate again at higher rpm.

From over on XPF;

 

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Yes, those are the figures I posted. Not sure why the other link didn't work, though, as it works for me?. Perhaps you need to be a member.

At any rate, those two figures actually show what I'm talking about - the power valves are closed at peak torque ([email protected]), as you are in situation B - balance valve open (which is still happening with this 'mod') whilst the power valves are closed - or rather should be, as removing the butterfly valves prevent these from closing at this rpm, thus not producing peak torque.

The 'reactivation' I was referring to is the closing and then reopening the balance and power valves at various rpms.

Figures;



 

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Interesting information and supports why you don't notice the difference most of the time. The most common conditions of part speed/part throttle and high speed/wide throttle are both optimised with everything open.
 

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Interesting information and supports why you don't notice the difference most of the time. The most common conditions of part speed/part throttle and high speed/wide throttle are both optimised with everything open.
I think the reason you don't usually notice the difference is a mixture of not driving very often with throttle openings greater than ~31 degrees (what with current petrol prices!) and the comparisons of a broken power VIS system with an absent one. I also don't know the relative proportional effects (or even synergistic effects) of the balance valves vs the power valves, the reports of still feeling a kick at ~3k rpm despite gutting the power VIS system suggests that the balance valve plays a large role in the feeling of that kick when you 'floor it'. This makes sense, as you would expect the power valves to play more of a role at higher engine speeds where shorter inlet tracts leads to an increase in torque.

Also important to note is that torque trend line is decreasing above 4000rpm, and so leads to a knock on effect of decreasing the peak BHP of the engine at higher engine speeds.

Turns out, the boffins at MG Rover really knew what they were doing when they designed this system, who knew, eh?
 

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Very interesting, I think that a rolling road result will show exactly what you're saying. It would be nice if the sheddist mod was available but we would still have VIS issues.

What would be even better is if we had a 'boffin' tell us exactly why they did it:)
 

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Yes, a carefully controlled rolling road analysis would settle the debate one way or another.

As to why they used a variable intake system, they're actually surprisingly common, and come in two general forms - variable intake tract length and resonance systems.

From I've been able to decipher about the KV6 VIS setup, it appears as though it is actually using BOTH of these effects to increase torque, which is something I've not come across on my travels through google, including bits where people refer to the KV6 as a resonance only system.

There's plenty of information available online about both mechanisms;

variations in inlet tract length, which is what the power VIS is controlling, is explained (amongst many, many other pages) here and on wikipedia. The following graph compares inlet tract length to torque and engine speed, and you can see why the shorter inlet path (read: power VIS) 'opens' at higher engine speed;



Opening the power VIS reduces the inlet tract length from 500mm to 350mm, and so it appears the third, otherwise sealed plenum chamber acts as an air 'reservoir', in effect. This was my reasoning in the other post as to why the balance valve is more important in the initial ~3k rpm 'kick'. The reasoning behind why different tract lengths have peak torque at different rpms is explained in the aformentioned references.

The balance motor seems to be linked to the resonance of the inlet manifold; where waves of positive pressure are created due to the opening and closing of the head intake valves. If you can time the waves created by the valves closing on one bank of 3 cylinders to the intake step of the 3 cylinders on the opposite side of the engine, you in effect create yourself a low pressure supercharger - and as the timing of the valve opening and closing is dependent on the engine speed/rpm, you can see why being able to change this through the rev range would give advantages.

If you want to go in to more detail about how these positive pressure waves interact with the power VIS setup, and the actual calculations of plenum volume vs engine speed then be my guest! Fluid dynamics never was my strong point.
 
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