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varible valve timing





I ve just read in a forum where someone was being tore to pieces that the 172s have varible valve timing is this the same as hondas vtec and toyotas vvtis?

If so could the point it kicks in be lowered like in the Hondas with the apex-i vtec controller?
 
  Corsa 1.3 CDTI


The 172s VVT is different. It adjusts the CAM position insted of the CAM profile (Lobe on the end of the CAM)

I think this is right isnt it captain and BenR.
 


The 172 has a one shot cam timing (inlet only) adjustment.

this is a very simple attempt at controlling idle mainly.

it is nowhere near as complex as the honda vtec offering which offers a different lobe shape availability.

I am under the impression until proved wrong, that the vvt on the reno lump only operates at a bout 12-1800 rpm and is mainly used to ensure a stable idle at low gas speed. (so, you wouldnt want to lower it )

Joe.. waht forum is that - I might take a look.
 
  Corsa 1.3 CDTI


Stable idling, is that why the Touring cars when they come into the pit rev the knackers of them to kick them running cause they cant tickover.
 


hondas system (well there are 2) first one is when the actual cam is mechanically switched over to a 3rd (inbetween the 2 normal lobes) lobe which is for high rpm running. It just alot wilder in its profile and is huge compared to the normal lobes.

the second honda system is when it runs as a 2 valve per cylinder engine until rpm and oil pressure reaches an amount high enough to push in a pin which overcomes the spring that stops the other 2 vaves from working. Its now a 16V motor.

the renautl system uses a mechanical system to advance/r****d one of (not sure which, will have to ask capt) the cams so there is more valve overlap and better VE at high rpm.

the toyota system im not familiar with, i fact, i have never even seen the toyota system, but i would suppose its close to the renault system.

all these are just methods to over come the lack of torque you find with cams that are needed for high rpm power.

capt, anything you could add to clear anything up?
 


oops, looks like whist i was typing other beat me to it.

the touring cars have a very strong clutch which is hard ot engage smoothly....so they just dip and let go, dip/letgo till up to speed where the gear can be fully engaged. same as F1 really, i suppose they would idle about 2000rpm. F1 is about 4000rpm.
 


basically the same, but more for fuel economy....then switch to power when you need it.
it probably runs lean all the time
 


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