VVT, cams and ECUs

[viceroy]

As some of you know (or maybe not) the Clio engine has the most basic form of Valve Timing.

Basically the engine runs one cam profile for smooth idling and at 1,500rpm the profile switches to the other profile.

Ive been thinking, would it not be possible to change the low rpm cam profile to give better power to say 4,500rpm, and then switch to a more advanced profile from 4,500 to about 7,500.

Would this be possible with the SMT6?, ie change the cams, then program the piggyback chip to switch profiles at 4,500rpm instead of 1,500rpm.

Would getting this right be a very complicated affair since the VVT on the Clio only works on the inlet cam, while the exhaust cam uses the same profile throughout the rev range...

Might make the car more drivable at low rpm if it had cams designed for low rpm power.

Okay, Ill stop thinking now...my head is starting to hurt a little...I need some coffee

 

[McBunny]

lol who said smooth idle lol its lumpier than a badgers nipple

so you got the smt6 working yet mate as im interested in it ??

 

[viceroy]

Havent ordered it yet...

wheres that swedish bloke gone who said he was having it fitted...he was supposed to come back with details.

Ha ha ha, yeah smooth is a laugh...Where are the techy geniuses...would my idea work? I mean take the "non functioning" Renault VVT and give it purpose

 

[Rich-D]

Quote: Originally posted by viceroy on 30 October 2003


As some of you know (or maybe not) the Clio engine has the most basic form of Valve Timing.

Basically the engine runs one cam profile for smooth idling and at 1,500rpm the profile switches to the other profile.

Yup, its simply a way of using a high lift cam for peak power, but still allowing a smooth idle with low emissions, as normally they give a "lumpy" tickover.

Quote: Originally posted by viceroy on 30 October 2003


Ive been thinking, would it not be possible to change the low rpm cam profile to give better power to say 4,500rpm, and then switch to a more advanced profile from 4,500 to about 7,500.

Would this be possible with the SMT6?, ie change the cams, then program the piggyback chip to switch profiles at 4,500rpm instead of 1,500rpm.

Would getting this right be a very complicated affair since the VVT on the Clio only works on the inlet cam, while the exhaust cam uses the same profile throughout the rev range...

Might make the car more drivable at low rpm if it had cams designed for low rpm power.

Okay, Ill stop thinking now...my head is starting to hurt a little...I need some coffee

Yeah, in theory that "should" all work ok and if you could set the trigger point for the VVT advance to kick in higher and use a wilder cam, then yes you would have a very peaky high revving car, without sacrificing too much low end driveability.

Its how it should be...

 

[viceroy]

Quote: Originally posted by Rich-D on 30 October 2003

Its how it should be...

Also does anyone know what the 172s std cam profile is? 265 degrees?

 

[Rich-D]

Quote: Originally posted by viceroy on 30 October 2003


Also does anyone know what the 172s std cam profile is? 265 degrees?

Do a search through the old posts as I bet Slarty knew...

 

[telford_mike]

wots an SMT6??

 

[McBunny]

a different ecu

http://www.perfectpower.comhttp://www.perfectpower.com

 

[viceroy]

Well I didnt find out much from searching on cams but according to BenR, to get any decent gains you have to rework the entire head, and basically create a racing engine, and that as we know is expensive for minor gains.

 

[Tom]

Quote: Originally posted by Rich-D on 30 October 2003

Quote: Originally posted by viceroy on 30 October 2003


Also does anyone know what the 172s std cam profile is? 265 degrees?

Do a search through the old posts as I bet Slarty knew...







Actually the good captain said it was useless, and couldnt be tweaked. i dont agree

 

[BenR]

I posted details on the cam values ages ago....full specs

The VVT system on the 172 is actually a phasing system not a cam changing system with different profile lobes. It runs a single inlet and exhaust cam and the VVT system advances the inlet cam as soon as you run over 1500rpm. It retards it again when your off throttle. Its there to sort idle problems, fuel economy and emissons ONLY. Each lobe for the inlet and exhaust valves are slightly different profiles. Still, its only phases the inlet cam.

the VVT does very little on the 172.

 

[Mitchy]

Not like the K-series VVC used on the MG range, Low profile is used up to around 3500-4000revs and then switches over to high profile. Its the same with the Honda Vtec and Toyota VVTi, the vtec being a bit later.

However tunability of these engines is very poor, normally a +30bhp rise and then the variable valve needs to be binned in order for some solid race cams.

I never knew renault used this system also, doesnt seem to be as good as the ones ive mentioned though

 

[McBunny]

not as good or just not needed you see all those engines tend to suffer from worse low down torque (iirc) and if the variable valves need to be binned wouldnt they be replaced with solid lifters to get rid of the hydraulic lifters ??

 

[StevieB]

VVT seems to be just there to get modern cars through tough EURO emissions tests without sacrificing "on paper" power (peak power figures sell cars afterall!). The K-series is going to be killed off soon because the continously VVT system means its emissions are worse than stuff like VTECs (with their hydraulic pin switch over mechanism) at approx 4K rpm - which is used in the EURO test drive-cycle.

 

[BenR]

VTEC switches later than that.

And most of the EURO compliance is programmed into the part throttle running and test sites.

Mitchy, if you read my post youll see that they DONT run a variable cam design like VTEC, VVTL-i or any other profile changing system. And teh Ren system isnt good no.

Doggy, the engines suffer from poor low down torque due to the nature of high output per litre engine, the conservative low rpm cam profiles is an attempt to claw back some torque by increasing cylinder filling.