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ECU and VVT
- Thread starter Rick_172
- Start date
Tom
ClioSport Club Member
EV (s)
Nah mate the vvt dont do much on the 172.
its to help it idle and not much more
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Tom
ClioSport Club Member
EV (s)
Did you?
http://forum.cliosport.net/display_topic_threads.asp?ForumID=6&TopicID=46332&SearchPagePosition=1&search=valve+timing&searchMode=allwords&searchIn=Topic&forum=6&searchSort=dateDESC&ReturnPage=Searchhttp://forum.cliosport.net/display_topic_threads.asp?ForumID=6&TopicID=46332&SearchPagePosition=1&search=valve+timing&searchMode=allwords&searchIn=Topic&forum=6&searchSort=dateDESC&ReturnPage=Search
Like Tom said, I think the VVT on the 172 is only to help the car idle because the cams are wild for a road car. The kick you feel at 4k is just due to the profile of the cam mate... A long time ago a user called Captain Slarty looked into this and that was what he found. I think the Honda VTEC system is a lot smarter. Sorry
.Matt
vvt is not to improve idle. it works from 1500rpm to 4750rpm when the engine temp is above 80c and on full throttle only.there is a two position camshaft dephaser on the inlet cam controlled by oil pressure directed down channels by a computer controlled solenoid.the oil pressure is directed to either side of some vanes inside the dephaser to switch it from one position to the other.when vvt is active it gives 16 degrees of advance on the inlet cam and the reason for this is to give valve overlap.there has been a lot of posts about this before,do a search.
as with all cam timing the simple basis is increasing the duration that any one valve is open during its component stroke the more air your can get in (forget fuel as its not a primary function you need to worry about) and the more air means more VE, the larger the VE the larger the torque result from the pressure rise and thus more power. The reason why pwoer tails off is because VE tails off.
Overlap is the situation you get where the inelt valves and exhasut valves are open together for a the few degrees of crankshaft rotation the cam specs specify. This is on the exhaust/intake stroke only and you can make use of relative negative pressure zones in teh exhaust port and inertia ramming on teh inlet to provide an earlier filling of the cylidner, despite the fact that the piston is moving up, not down.
Jay, (what the hells going on with my font colours, i aint touched it!) it does help idle......try pahsing ti at idle and the 16deg ad that would be there all the time, if it were not for teh simple depahse, makes the car idle horribly.
its purpose is not to help idle but if you did phase it at idle it would idle crap but thats commen sense.its purpose is to increase torque when needed(at full throttle) but still allow the engine to pass current emissions laws.all new 16v engines have no or very little valve overlap due to the affect on emissions. of course it would idle crap if you activated vvt at idle due to that amount of cam advance is only benficial at the conditions i stated in my previous post.apart from full throttle vvt is unactive so has no purpose when at idle or normal driving.
but at full throttle it already kicks in very early.
Jay, the point i was making, coupled with yours, is that if it was there primarily to increase torque (its not sophisticated to help anything power wise) then why would it kick in so early at low rpm on full throttle....thus negating any of the benefits of no overlap and more timid timing at low rpm and port velocities.
VVT alloys the inlet and exhaust valves to be open at the same time (overlap) when you increase the revs. If this overlap was there during idle your car would idle very bad. The reason that it is ok during higher revs is that the valves open and shut faster the higher you rev so the actual time the valves over lap is not that long during high revs but woudl be open far to long at low revs.
The VVT comes in at exactly the time you want it to as if it was any earlier the car would not run right
The reason it idles poor is because a low VE is acheived with lots of overlap as the fresh charge shoots straight out the exhaust.
At high rpm the need to open the inlet earlier and use severap pulse tuning phenomenons, inertia ramming and exhaust pressure differences actually help supercharge the cyinder.
vvt only works between 1300 and about 4500 rpm.why between this two revs i dont know but it does.valve overlap increases engine power but increases emissions as well.this is why it only works on full throttle when you need the extra power and engine emissions arent checked under full throttle conditions so the engine passes current emission laws.
Im not doubting its there to increase torque, but im argueing its not its primary function.
And the rpm operating zones kinda show this. @ WOT from 1300rpm it would be making more torque in an unphased state, port velocities arent high enough to make use the overlap.
And are you saying it dephases after 4500 again?
got me confused.
Its also a fairly big marketing ploy (just like Hondas VTEC), saying you have VVT is far better than not. It really doest do that much and if i were building a high output version of the engine i would junk the VVT.
definatly works between those revs but i dont know the reason why.did a complete section on this system when i did the rte course.the principle of the system would appear to mean that it would phase at high revs but the renault system does phase at the revs previously stated(between 1300 and 4250rpm).i do admit the principle and the revs it actually operates at dont really match up but im sure renault has a reason for it.
unphased @idle>1300rpm
phased @1300rpm>4250rpm
unphased @4250rpm>max revs
phased only also occurs at full throttle(inlet manifold pressure above 850mbars) and at a coolant temp of above 80c
no idea why the phased is at those revs but i do know for sure that it is.
i see this kicked off a major debate!!! Good stuff.
One further question. Is the "phasing" of the VVT mechanically activated or activated by the ECU? If it is the latter, then surely it can be modified by reprogramming the ECU???
(P.S. dont give me a bollocking cos of my ignorance
)UPDATE:
Since writing the post above, I have heard from Dastek UK in Dalgety Bay in Fife. Stuart has provided me with a list of variables which can be altered by a Unichip. This includes "control variable valve timing", amongst an exhaustive list of others.
Price is: "The Unichip costs £245 + Mapping (the mapping charge varies from dealer to dealer - due to varying overheads, rolling road rates etc, as well as the different time to map each individual car, & any extras you may want added, such as Water injection, N20, Boost control etc..)"
Please PM if you would like the full list of alterations that can be made.
I was gonna go for a Group N, but this looks much better, for not much difference in price...
the vvt timing is controlled by the ecu.the ecu controls a solenoid in the cylinder head which directs oil down oil channels.there are two oil channels and each channel is linked to one side of the vanes in the dephasor.i suppose a chip could change the operating ranges of vvt if it wanted to.
