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V.V.T on a 172... the facts..

There has been much talk of feeling the vvt kick in on the 172...

fact.. you dont

I just went out and tested my theory.. hooked up a dvm to the vvt actuator in the head, and heres the results..

VVT *Varaible valve timing* is actuated at 1200 rpm !!!.. it is then on al the way to redline..

the only time it is off is on idle, on *very* light throttle, and on over-run..

the mechanism used by renault is a phase shifting device on the inlet cam only.

A solenoid plunger in the head casting allows oil pressure to be fed to the phase shift unit.. this effectively increases advances the inlet cam timing.
there is NO VARIATION.. it is actuated, or not actuated.. ie.. full on, or full off.

so.. now you know.. what you feel at 5k is PURELY the cam coming on.. nothing more.. you cannot even feel the vvt when it actuates.. it is there for a slight torque increase during acceleration (From 1200 rpm).. and off at idle to make the idle smoother and reduce emmisions.. same on very light throttle and over-un..

another myth dispelled..

  Renault Laguna Coupe

So, Hondas wimpish VVT doesnt come in until 6000rpm, but on a Clio its on as soon as you move off! COOL!


yep.. but I must add.. the wimpish system on the honda is extremely good, bordering on genius.

Mind you, honda systems are a bleeding NIGHTMARE to alter..

the Renault system is rather cool actually...

what we have here is a pretty MAJOR oportunity for some serious tuning mods without suffering a lot of the drawback of previous, non dynamically adjustable timing systems..

you blow a WILD profile onto the cam (Reprofiled).. this would normally hit you hard in the idle and transition phase.. but wait.. theres more lol..

ok, we set the cam up for max go-go.. we forget the idle - set it to 3k for now... get max urge from the dyno... we then time the cam statically to varying degrees r****d.. seeking the best idle and low speed.. and, dont forget, this is a twin cam.. NOT a single cam engine.. what that means in english is that the relationship between the inlet cam lobes and the exhaust lobes can be varied at will.. we find a sweet spot for idle and inlet timing.. we restrict the shift of the phase unit (simple engineering - its a fairly simple device) by limiting the rotation stops.

we now have a streetable cam with long duration and happy days power that doesnt cause the car to idle like a diesel with an injector missing !..

even plainer english for the surf doods ...

Big, silly cams, big silly outputs, idle speed overlap adjustable (Better, in fact probably for the first time, a POSSIBLE idle), lower down torque off cam

bloody excellent. !!!

172 rally and race cams may be available shortly from here (With fitting service) (The terms rally and race are actually quite appropriate for the style of driving you want - but race wont do the shopping, traffic jams, etc.. but it will be a damn site better with the phase shift at idle system) !!! lol..

Cs. Joe..

Joe - "even plainer english for the surf doods"

Can you follow up more of your posts with the "surf dood" English. I like that...I understand


Ive read somewhere that Ferraris have a different way for doing VVT where the cam gets pushed across , each section of cam has different VT, according to the engine speed. That sounds cool. Hondas system changes life as well as VT so seems the best system on paper.


chun mate: "Hondas system changes life" huh?

Joe: did the RR testing yesterday. Once with standard airbox, once with Viper and once with no airbox at all....which happend to be the worst? ill send you a copy to post up or have a look at.

BTW, ambient air temp......37 deg!!!!
its outdoor too!! i was sweating like a hairy man in botswana!

It was supposed to say "Hondas system changes lift as well as VT". Hey it was late and you cant edit these damn posts.