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more VVT ponderings..

more tests have been done (by a well known reno specialist ) to confirm what I summised earlier..

ap22 standing 1/4

15.9 - vvt enabled.

15.9 - vvt disabled..

me thinks mr reno just wanted to put vvt on the brochures..


well, since you/its thought that it comes on @ 1200rpm....then when would you use below 1200rpm? especially on a standing start....

try a rolling start in 3rd from 1000rpm?

Hi Ben..

the system advances the intake cam by about 5-15 degrees..

What I am saying is that, if you disconenct the system, the cam will not advance... - it is effectively retarded at idle. -

However, the lack of advance makes Sod All difference to performance.

the 1200 rpm is the point it switches normally to advance.

advanced or not advanced makes no difference to drivability or power.


let me word it another way Ben..

vvt is not active at idle.. its purpose is to advance the cam above idle.

disabling the system causes the cam NOT to advance at all.

thats the key.. the lack of advance makes no difference.. so whats the point of even having it ??


ok, got you first time round.

but what i was meaning that you could effectively use the better torque with the cam not advanced (thoeretically) and see if the diffrent timing with the vvt off makes any diff....kinda lost myself there.

anyway, could we use the vvt to our advantage in any way then? with a turbo it might help with the inlet cam advanced mightant it?!!???

I know it sounds strange, and not sure if it would work, but from your stats is there any possibility that the VVT works the other way round. Instead of having the normal timing at idle, and advancing above a certain RPM, does run at standard timing and r****d below that RPM? Therefore disabling the the VVT makes it idle at a more advanced RPM Youd notice no difference in performance, but it would idle differently, possibly warmer and faster? Did you actually check the timing at different RPMs with a strobe?

a stobe would give you ignition timing not that of the cam.

but i dont really understand what your saying?

when the vvt is activated, it actually retards the cam? what possible use could this be, if the cam was advanced (relatively) at idle, then it would be very rough and would warm up slower as cylinder filling is worse......supposing to much time is spent in overlap...but i dont know exhaust cam setting so disregard that.
the whole point (supposedly) of the vvt @ 1200rpm was to cure rough running at idle and very low rpm.

Sorry, read that post and its not too clear. Igot my cam/ignition timing confused too.

The VVT is there obviously so you can have more advance at higher RPMs. If you run that much advance at idle youll not have a vary economical/smooth motor, so the assumption is that the cam timing is set to a low advance, and when it hits 1200rpm the VVT is triggered and the cam advances. Now how about if the cam timing is set more advanced all the time, yet when the revs drop below 1200rpm the VVT kicks in to r****d the timing. Do you see where Im coming from? If you disable the VVT then, the car would stay in its advance state even at idle, hence no difference in acceleration.

Hi Ben n Mc.

MC, we have tested it with indcator lights to show powering of the phase shift actuator so I am convinced this is how it is desgined. , it is not in operation at idle.. the cam is retarded (in relationship to the exhaust cam - not overall note.. ie - there is no vvt at all on the exhaust cam) as you move off idle 12volts is applied to the vvt solenoid plunger, oil pressure is released into the phase shifter and the cam turns to adjust the timing.

Ben n MC both, the plot thickens lol..

due to the vvt causing the advance, and hence overla increase, one would presume an increase in power ??.. but that is not what is being proven with the current tests. It would seem that the cam running advanced produces no discernalbe increase in anything... at the moment it would appear to be an economy thing only.. not a power thing..

I am now going to apply 12 volts to the solenoid at idle and actually force an actuation of the phase shifter.. will let you know..


Didnt manufacturers increase cam overlap to recycle exhaust gasses and therefore reduce emmisions? To get that sort of power from a 2.0l you have to sacrafice a liitle on emmisions. maybe they are trying to bring it back within ranges when its being ragged?

so the exhaust has higer lift @ TDC then the inlet cam?
ok, but i would of though more overlap on the exhaust behalf would have given better results?

could you not try playing with the exhaust timing?

or better, i know you want to add a solenoid and plunger onto the exhaust cam!!! hehe, you kow you want too!!! yes you do!! go on!...please.

"Didnt manufacturers increase cam overlap to recycle exhaust gasses and therefore reduce emmisions"

overlap of which valve?
i have not heard this, but how would you recycle the exhaust gasses, it would be down to cam profile weather the exhaust valve stayes open for "x" period of time to keep the exhuast gasses in the chamber.

but were nowhere near the magic 100bhp/ltr mark, so the engine is not too highly tunned.....but thats just me, a tunned engine is when it reaches 100bhp/ltr or makes 25% more power.

the emissions are taken care by the ecu.

Once again, yep sorry just sounding out ideas, the exhaust cam is fixed in this case. I read in CCC some time ago that in modern lumps, the exhaust valves are left open a fraction longer to draw some of the exhaust mixture back in on the cylinder down stroke to recycle and therefore reduce emissions. They recomended on the engine in question that the exhaust cam was advanced slightly. Its totally unrelated. As you can see Im not a genius on this subject, but I am very interested, and I may ask a few strange questions. I and the guy who built the Nova I drive, quite regularly sit and go over stupid ideas for a while and then go Duh as we realise why or why not certain things work.

no worries, in no genius either, joes the real wizzard.

p.s. march or feb issue of CCC this year...the one with the radicals on the cover. In the letter page, the star letter is mine!!! yay!!

got it?

Hi MC.. please DO ask questions and offer coments m8.. !! Its how I learn too.. You may well come up with something I havent considered.

Ben, m8, yes, the andvance in this case is theoretically a case of the inlet valve opening being further up the cam lobe ramp at tdc (hence inlet opening slightly greater than exhaust), hence an overall increase in advance of the inlet only. not a true advancement as the lobe relationship angle changes. (You been reading Dave Walker again huh ?? if so, bloody good show.. his knpwledge is excellent!)
There is no way to add a phase shifter to the exhaust unfortunately, I already considered that one lol


Fraid not, there has been a long period up until recently where other commitments (wife and house) have prevented such luxuries as magazines! Why do you think Ive got a 1.2!

lol Ben, thanks for the kind words, but I am a mere novice to some of those guys.

Have you got Daves engine management book.. that is soooooo good to read..

  Corsa 1.3 CDTI


Just a thought, the VVT is done on a CAM basis, was there anyone who looked into doing this without a Camshaft using a set of Solonoids to push the Valves open instead ?

This would have the added benefits of being able to control the valves per cylinder so you could get the max power out of each piston individually !

Sounds mad but just a thought !

well, it wouldnt really be possible to control them with accuately at theat speed.

however, renault F1 are working on a electromagnetic valve train system to get rid of excessive friction. but the prob is excessive weight high in the car.

spinning roller valves are another idea....kinda.

lol at Ben... bet it was the engine management.. !!!

Chavvy, indeed, renault ARE working on an electromagnetic valve train, and you are correct, it would make all sorts of things possible..

Now, I have just done the test with the engine at idle, hooked up 12volts to the solenoid.. and.. it idled like a tractor !!!..

So, what we know so far..

VVT off is for stable idle

VVT on (inlet cam advances) is supposedly for best performance and operates from 1200 rpm.

if we do not advance the cam at 1200 rpm, then the feel of the car is no different and the ap22 confirms no difference in 1/4 mile times.

That begs the question, what the hell is it trying to achieve ??..

If the only difference is in fuel consuption, then its a hell of a lot of work for not much.. if there is an increase in power on the rr graph between vvt in and vvt out, then it is not worth the hassle as it does not equate to better feel or actual performance times.

Captn bangs head on table....


Ben M8 !

a stobe would give you ignition timing not that of the cam.

actually ... I INTEND to use a strobe to see cam timing changes..

If you put no. 1 in overlap tdc... paint a line across the cam wheels, then run on the rollers (You would have to drill a hole in the cam cover to see it lol, but I have a bucket full of cam covers ... then, the strobe would show you the phase differnce. even though the ignition is running at cam speed * 2 it would work well.

MCs idea isnt that crazy lol.


Surely with VVT off there should be some kind of performance decrease. Capt you tried this on another 172 yet?.



YES M8!!!

Chun, trust me..

not only have I tried it.. my friend Nick Hill has tried it too. we compared notes.. exactly the same !!.

it dont do jack..

unless.. there is one possiblilty, but we have ruled this out until proven conclusively.. that is, that the oil pressure rise at off idle can somehow overcome the force of the spring in the vvt actuator solenoid...

at this moment in time, I have no reason to believe this is the case.

  Williams 2, STi N12

What about..the fact that renault knew they would be racing these suckers so built the vvt in there for them only, as they would be using wilder cam profiles than the standard road cars?
There has to be a logical explanation for this huge amount of work just for a smoother idle!

Anders, at this moment it time, I have no reason to believe that the vvt is nothing more than an idle stabaliser.

the race ones, if ya mean cup racers, are the same engine design, cams etc...

vvt sells cars m8 !!!

thats it so far doood...

I will attempt to clarify the oil pressure rise activation theory, but until then, its pretty poor... piss poor really..


it DOES have its advantages in later states of tuning as you elude to, but that probably wont be offered by reno to the public...

WOW, go out for a few drinks and all hell lets loose!!

Capt, your twiting of works only gets me into trouble!! haha
OK ok< you can use a strobe, but, not as intended and easy..

Anders: if renault were gonna race them, they would have already...i mean not in the cliocup as its a 1 make series, there would be no need for all out theyd all be the same.
i would love to see a factory LM clio!!
  Williams 2, STi N12

So what oil pressure is it actually triggered? Is there a way of delaying it and then throwing new cams inside?

anders, no, its not triggered at any specific oil pressure, it is triggered by a plunger solenoid that diverts oil pressure to turn the phase shifter..

it is electronically operated, on or off.. ie - non variable over its range -

you could delay it as much as you want with electronic control.. so yes, you could put any profile you want in there.


Anders, re my rise in oil pressure activation theory...

it is * possible * , but unlikely, that the oil pressure at off idle is enough to overcome the phase shift actuator solenoid spring... if so, then the shifter would operate even if disconneted from the 12v supply..

I HOPE that is what is happening.. cos otherwise its probably misrepresentation under the trades description act....



heres the olive branch m8.. we had a good few rounds crossed swords lol.. but aint that what its all about... ??..

a forum.. the Romans had it off to a tee...

Joe.. Nice one !