the clio has vvt and has twin cams is this correct? is there a noticeable point where it will pull harder? i dont mean if u can kinda feel it i mean similar terms to a civic hitting vtech?
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on cam
- Thread starter royalsgoingup
- Start date
the clio has vvt and has twin cams is this correct? is there a noticeable point where it will pull harder? i dont mean if u can kinda feel it i mean similar terms to a civic hitting vtech?
Was a Clio 1.8 16v
I think u have got the incorrect word there, u were looking for the word: good
My cars "on cam" all the time. I drive like a slug on the road (well I try) and I take it on track about once a month. Nothing happens at 4k that doesnt happen at 3.5 or 4.5. In fact on track, I keep it between 5.5k and 6k where the power/torque peaks.
Before modifying the car, I do remember getting a power surge feeling between 4 and 4.5k, but that no longer exists now. Its just good throughout the rev range.... As I said above, I believe the 4k "surge" has nothing to do with cams, but has everything to do with the airbox second electrovane opening up and admitting considerably more air into the engine. So Im not denying that a normal 172 has that effect, its just got nothing to do with cams, thats all.
TDI tyre shreader
There is such a thing as on cam as that is what happens at 4k... 1k nothing 2k....3k.....4k BAM, ON CAM, this is where the duration of the cams comes into play and the gas speed through the head is increased as the inlet and exhaust valves are just about open at the same time drawing more air into the chamber, happens at certain revs as rpm increase. hope this makes sense as beer has been playing
Variable Valve Timing, alters the cam TIMING (as the name sugests) at a set RPM. inlet cam is advanced so as to give more overlap and so dynamic pressure of exhaust gas leaving cylinder literally sucks in fresh charge--scavenging. at idle however (when butterfly is closed) there is a vacuum in inlet plenum. as gas speed is low at idle, exhaust gas tends to be drawn back in2 chamber (due 2 vacuum in inlet) and cause crap emmisions and idling--exhaust gas dilution.....Jones u were half right!!
Vtec-this system increases valve lift at set rpm. it uses oil pressure to operate a plunger which shifts from one rocker arm to another. the first having a lower ratio and so giving less lift, the second having a higher ratio giving more lift. more lift=better gas flow=more torque/power (and change in exhaust note!)
both systems give an increase in torque when they start to operate, often known as/refered to as on cam----personally i think its a bit of a gay statement!!!
The phenonmenon reffered to as comming on cam refers to the rpm level where inlet charge speeds are high enough to significantly increase the level of VE. So sorry to some, the F4R 7XX series comes on cam at about 4500rpm. its VVT mechanism however advances the cam anywhere above 1500rpm when at full load, dephases it when not on the throttle and on overrun.
The VVT system in the 172/cup advances the inlet cam 16 deg as stated via a pahse shifter on the inlet cam that runs of oil pressure (activated by a plinger solenoid ontop of the head), it does not alter lift or duration, just the timing of the inlet valve opening and closing points relative to the crankshaft position.
VTEC systems (ill limit my talks to the better and more modern 3 stage system as the 2 stage is old and no point talking about it) Use 3 cams per cylinder.
The high cam or big lobe is in the middle of the 3, and there is a less racey middle cam onthe right of it, and a low cam on the left of it. There is 1 finger follower per cam, so 3 per assembly, built onto an oil feed rail, which they pivot off, with 1 oil inlet. At all times each follower is tracing its respective cam lobe. At low rpm each roller is independant and only the low and mid cam is lifting the valve. Thus there is one low lift and one mid lift cam (duration and timing also alter with cam lobes). When rpm incrases the Vtec solenoid ont eh side of the head passes oil pressure through and a pin locks the low cam follower onto the md cam follower so you get 2 mid cams effectively, or its what the valve and cylinders see. At high rpm all followers are locked together via another set of pins in the lower part of the rocker, so the valves are running off the high cam in the middle only and the followers aret actually touching the low and mid cam.
This is the basic 3 stage Vtec, but cars like the S2000 with the F20C and the CTR with he K90 use a slightly different system where the low and mid cams are the same. The finger follower is also slightly different where teh cam is onto rather than below and is less complex.
VTEC is simply activvated by rpm only, not throttle position.
Toyotas VVTL-i uses both phasing and cam changing. The cam can pahse like a 172, and it runs 2 cam lobes per cylinder, and they swap between each other when the ECU decides, dependant on rpm, throttle position.
I have an S2000 head so if the mods/admin want im quite happy to do a full how it works with pics and the lot if there is enough interest. Even though its a Honda head and technology. Its rather facinating, since its all in peices.
Was a Clio 1.8 16v
Id say the airbox/filter will have a lot to do with the feel of when the power comes in.
I.e an original filter element will be more restrictive and give better torque at lower revs where an air filter will make peak higher in the rev range and expand the power band IMO.
And me !! please do a breakdown of the head !! Fascinates me
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