In rebuilding a plenum I took two apart and noticed some similarities in the flow pattern on the walls left from perhaps 20 years of deposits that I think may be revealing about the plenum design and as a pointer to engine condition.
I had washed the first one before documenting what I saw, so here I have not done anything except some gasket and dust and pollen has dropped in, to be ignored. Next I'll soak the part in kero without scrubbing and let it dry. Next clean and fit a couple of bearings (mr117,mr137) to replace the brittle, broken, decomposed plastic 'bushes' that hold the VICvalves shaft, butterfly valves.
On the whole I think this is a good design. Possibly it might be worth expanding the plenum a bit and have the throats of the long and short rinners extend into the plenum air reserve away from the wall dead spots. I'll stick with the original though and perhaps see about making some changes, while keeping runner lengths, as a separate project at some time.
Here are some snaps of the middle part of the plenum that holds the VICvalve

http://i27.photobucket.com/albums/c168/yanndee/IMG_14p8_zps72bd8da8.jpg

edit add :

sorry, have to work out a way of posting full size image.

The top one here is before rinsing. The two after rinsing shows better the flow patterns. The second and third short runners seem best off and the first and last the worst. This was roughly the same for the other plenum. Possibly the plenum should widen out faster after the tb and then a taper plus a bulge past the last runner to clear intakes from dead air areas while keeping the volume to about three litres.. ?

edit add :

http://i27.photobucket.com/albums/c168/yanndee/IMG_1482_zpsfc20060c.jpg

good effort

this part is copied from 'I have no idea what this is' topic in third gen sub forum, minus pics for now


This is a pic of a 6G74.

Directly above the mileage (km) on the right is the VIC. (refers to pic) The VIC is attached to the passeneger side of the plenum.

3 allen bolts holds a metal body with two black things on its right.

The bottom one is a dc motor that drives a worm gear that turns a rod with its central axis at the white spot on the metal body. On this rod are 6 butterfly valves (held on by very soft little machine screws with spring washers.) The servo starts with the butterfly valves closed to direct airflow along the longer narrower curved channels. At low revs this aids torque. The butterfly valves turn according to demand till at high speed the valves are fully open. (There are issues regarding turbulence, back pulsing and other things re fluid dynamics I don't fully understand but the function of the thing is such.)

The black bit above the servo is the position sensor. If this is the issue don't rush into fixing it. There are tests that I think are dealt with in chapter 15? You may find the contacts a little corroded. If the VIC is not installed correctl;y there's a plastic lug that can break and the plastic worm gears getting damaged as the motor strains at a point when it should'nt and the valves don't work as they should so the sensor sends the wrong signal to the ECU and the ECU sends the wrong signal to the wrongly installed VIC unit.(?) The ohm reading of the servo can go out of specs.. If it's the issue and you find anything about fully testing one I'd be interested to read about that.

If you find you need to remove the assembly be aware that there are four little bumps on the plenum body that line up with one bump on the VIC, as the bolts are loosened the unit can be turned in a little arc. Note where the one bump lines up first. When you take the bolts off: as you ease the unit away from the plenum the worm gear disengages from the worm gear on the valve shaft, a spring will flip the valves to open. When refitting the unit or a replacement take the throttle body (or reach through it. You have best control over it with TB off but if you take the time and use a torch you might be able hold the butterfly valves close(not too closed, not jammed) off and reach in and close the VIC valves as you push the unit in so the worm gear enagages again with the rods worm gear. the VIC holds it now and the TB goes back on (clean the gasket with wax and grease remover and spray it with high temp paint for a few layers and reinstall when dry) Tighten the bolts (I suspect the optimal position of the VIC is at the second bump). At this point I'm as yet unclear about how the fine settings work with the unit in place and whether there is some reading one can take like when setting the TPS.

edit add :

airflow is controlled by the valve, closed at low revs to direct along long path, open : along short path at high rev.

add 2 :

The resistance across the servo connectors(?) should be between 5 and 35 ohm

add 3 :

some further things to consider : There is a fair bit of tolerance in the butterfly valves and the passages and between the shaft (hard rubber) and the holes in the passages the shaft passes through. Also, the rather fiddly and ultimately crappy guides at the ends of the shaft, They're a little brittle, by now, rubber seal at the VIC end, be gentle with it (I'm going to try an o-ring), and a piece formed from the same plastic as the worm-gears. At both ends these have degraded not through wear but through pitting/corroding away of material by the hostile environment created by blowback of fumes(?, from the breather?). On a couple of 20 year old ones it's not all the way, there's still a few milimeters that are ok and with care the rubber seal can be reused. At the other end is an amazing fd up 'planned obsolescence' in the form of very fiddly set of plastic bits locked together by a metal spring clip that holds it in position on the shaft and in the loose hole it rests in and helps to break the bldy thing. Too loose and any closing of the valves wont be true because the shaft is not centered (I imagine with a really loose one because of the airflow it'd vibrate a lot at best of times aand perhaps put undue stress on an otherwise ok servo et.c...), Most likely it's broken but in place. : simple : cut about 12 mils off the end of a rocker cover breather hose and use the metal clip, slightly pressed together for less spring before installing. Clean out and grease the hole and thread everything back, spring, seal, guide, 5 rubber guides, hose, metal clip and align everything and then in turn replace the buttterfly valves, holding the shaft in a closed position with a little g clamp. Youv'e probably buggered up a couple of the screwheads so get some long ones from the nuts and bolts shop, carefully reposition the valves and lightly tighten up the screws (the stamped on 6G7 goes up, they're slightly assymetrical top to bottom, three of the valves are mounted using two of the sets of four holes the others the other three sets of two out of the four. Test fit the VIC with the valves held close. Remember there's a bit of tolerance all around so don't look for an all round snug fit. Just adjust the positioning of the valves even all round and no knock while turning through range. Tighten screws and clip the ends of the screws off which will lock them in place. Should be many years, decades, till this needs attention again. With all that back in place do any fine tuning of the VIC and tighten bolts, rebuild plenum. The amount of blowback(?) deposits can be an indicator of which valves need particular attention. It's a good idea to clean the lot out. A bit of acetone in the metal tubes with a bottle brush works well. Do it outside in the wind, use long gloves and don't smoke. Wash non metal parts (note the inner half of the long path tubes in the curved bit of the plenum are plastic.) in detergent and or kero.

Add :


I'm rebuilding a second plenum using a couple of bearings on the VIC shaft. I got the bearings from apollo bearings at about 2.80 each. I then cut a thin walled bit of brass tubing I have from a hobby shop purchase (in order to build a fuel injector microfilter/basket extractor ( which is coming along ) ) and cut a length off a bit longer than the circumference of the bearing and split it and flattened that out and wrapped it around a bolt and rolled it then inserted that in the hole and pressed the bearing in, sanded off a bit on the shaft so it fits snug into the bearing bore without sticking. So, buried deep in a 20 year old plenum is a really crappy broken up plastic,spring thing in three parts (well, broken into 4+ parts plus all of the plastic corroded) > fixed (minus the hassle of getting the bearings) for about $3.00.


pic1489
http://i27.photobucket.com/albums/c168/yanndee/IMG_1489_zps2ba7e50a.jpg

add: If you look inside the disconnected VICservo,sensor unit you can see that there is a screw that can be moved to tighten up lateral play of the shaft. If you dig out the white spot on the outside you find a small hex head that turns this adjustment screw.

Loving this thread chief - keep it up!

Variable intakes = awesome. Would love to see this work on a third gen, to see if it produced and viable benefit. This and bimodal exhaust...

Variable intakes = awesome.

It is meant to enhance low down torque. Ask any second gen V6 owner if that engine has any low down torque, to judge its worth.

Mine was . . . . 1500 rpm flatten right foot in first . . . . . NOTHING . . . NOTHING . . . 3,000 RPM . . . . oh, shoot!
(Then again, mine may not have been working at all.)

4 valves per cylinder on the 3rd gern and MIVEC on later models has made this system redundant anyway.

It is meant to enhance low down torque. Ask any second gen V6 owner if that engine has any low down torque, to judge its worth.

Mine was . . . . 1500 rpm flatten right foot in first . . . . . NOTHING . . . NOTHING . . . 3,000 RPM . . . . oh, shoot!
(Then again, mine may not have been working at all.)

4 valves per cylinder on the 3rd gern and MIVEC on later models has made this system redundant anyway.

The reading I've done - one one system at least - is that the intake volume is increased at idle (port open), then closed between idle and 4100rpm, then open again at higher RPM. This is on a system that looks not much different to the old vacuum canister I saw on an old Yamaha dirt bike I had once - In that it was just a cavity, not bridged to the remainder of the intake system.

If I dig around I could find a few articles I've kept regarding variable intake systems. If cost and time weren't an issue I'd sit around developing one for my car :P and a variable exhaust to. I mean, how hard could it be? :P

Thanks for the input guys.

The other half: A composite of a couple of photos of the half to illuminate both 'walls'.
http://i27.photobucket.com/albums/c168/yanndee/Untitled_zps68a08c55.jpg

The blue is overspray from when flattening the mating surface. (When taking it apart, the end bolts were unmoveable so I tapped the side of the heads on the far bolts and they came loose and the plenum sprung apart relieving pressure on the bolt at the TB mount end.) So before thinking I had partially obscured, with blue paint, (I put a 320 grade wet'n'dry on a 5mm sheet of glass 6"x14" ($5 from local glass shop with smoothed edges to use as flattener of deformed mating surface with a layer of blue paint to point out low spots,, about 100+ smooth slow cuts to end up with flat. I glued the paper on with water resistant glue. When wet the paper will still curl so I did it dry.)), the flow patterns. I can still see them clearly up close but can't post pics of such magnitude. Anyway just to introduce the other half and also to see how the long runners are formed. IMO the half trumpet could do better extending into the air tank which could be bigger and taper towards the end with a bulbous end to distance all intakes from the wsll where air moves slower. I posit that the increasing amount of deposit past #3 is because the air is moving slower by then. and or there is less air available to flow. or?

http://i27.photobucket.com/albums/c168/yanndee/IMG_1495_zpsbc2bde76.jpg
in grayscale so the blue doesn't show.

http://i27.photobucket.com/albums/c168/yanndee/IMG_1503_zps706f3415.jpg

after all that a finished one. A couple of the allen screw holes were corroded (the two middle ones on the underside) and I replaced the screws with longer ones as the holes had been threaded all the way. Even so, if necessary, there would be no problem about putting even longer ones in with a nut. One would merely have to file the other side down for a seat for the nut. The water pipes were corroded on the outside (quite badly one of them) so I got rid of the rust and rustproofed them so they should be ok now.

add :

If you look at the top left corner on the bench you can see the broken plastic bits replaced by the bearing.

http://i27.photobucket.com/albums/c168/yanndee/IMG_1506_zpsf6450e34.jpg

The end of the shaft, the metal spring clip that locks a tag into the hole and the two bits of plastic broken by the hostile environment, fumes, heat, vibration and not least the spring that likely splits the plastic when degraded sufficiently.


edit add : these are two sets of broken guides from two plenums. See from beginning of topic for more detail and suggested fix. A short bit of stiff hose works fine, or a snug ballbearing. See hobby shops for bearing. Often used on model helicopter shafts. Also in some well stocked bearing shops.