Register a free account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members through your own private inbox!
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.
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?
"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.
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.
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
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.
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.
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.
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!
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 power...as theyd all be the same.
i would love to see a factory LM clio!!
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....