F4R variable valve timing

Forum Moderator Joined: 18 Feb 2004 Posts: 7432

ok i know what it does, but how is it operated? i take it that it is an electromechanically operating thing as opposed to vacuum etc?

Is it controlled by the ECU (with a 'map'..based on what, just rpm or load etc as well?)

or does it just have a seperate little controller 'box'?

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

its magic neal, controlled by fairies.

Solenoid valve control, comes in just above idle and stays till redline.

Basically its there only for emmisions. Not mapped for anything aside from an emmisions compliant idle.

Forum Moderator Joined: 18 Feb 2004 Posts: 7432

special Renault fairies eh? should be easier to obtain than half the other renault parts.

so the VVT isnt really very 'variable' then, just has 2 settings, and one of those is used only at idle, and just to meet emissions?

So when Thierry says its what "makes the clio so responsive...va va voom etc etc", hes just talking out his arse?

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

yes hes talking out his arse and yes its either on or off so to speak.

It switches over around 1200rpm or so, try looking on clio sport I'm sure they have talked about it.

It uses rockers instead of tappet buckets as well.

Its not like the honda set up. although the honda set up like we have discussed before is a marketting gimmick, the hondas can be switched at idle and they pull just fine on the peakier cams. Apparently the best time for them to switch is under 3krpm.

Its left till later so it gives a punch. I mean what would the common muppet have, a car thats ok up to 5krpm when the tame cams dying then swaps to a perkier one which will gain about 20bhp on crossover or one that switches before the stame cam has ran out so you don't notice the switch.

Everyone wants to feel the bang.

1st mod CLEVER honda peeps do is change the activation rpm.

Forum Moderator Joined: 18 Feb 2004 Posts: 7432

guy on cliosport is saying the VVT gets switched off again after about 4000rpm.

eh?

Forum Moderator Joined: 18 Feb 2004 Posts: 7432

my housemate from last year is a honda nut, the one with the turbo'ed VTEC in a rover coupe. He explained all the VTEC theory stuff to me in great detail. Dont remember most of it, but i do remember him drawing a graph showing 2 torque curves, one for each valve lift. The VTEC point is set where the curves cross iirc

i-VTEC is the combination of phasing and lift variation which makes a smoother transition if i have understood that correctly.

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

honda Vtec isn't exactly hard to grasp neither is the toyote VVTI.

both are very simple.

Ask any serious honda tuner, hell even look at old CCC mags and they all show dyno plots where the vtec is switched on much earlier than standard.

Both these systems have been around for decades, old pre injection racers ran with these systems way before you and me were even thought of never mind walking about.

Anyway VVT, you have an engine speed sensor, solenoid and a moveable cam wheel. basically when a pre-determined rpm is reached the solenoid opens allows (lots more) oil to pass through the front cam journal which then passes through the cam (think main bearings to big ends) this then advances the camwheel. Some setups insteasd of engine speed also look at engine load as a more precise way of controlling thing.

On the newer toyotas the VVT is there from 1500 or so rpm up, its not engaged until 50 degrees coolant temp but its used for starting. ALso they don't need the earlier set ups speed sensor. Yaris use it and its quite pokey for what it is.

The VVTi setup is more precise it allows adjustement within the on off position.

BTW the oil solenoid is at the front of the engine and has a pretty muchdirect channel from the oil pumps output pretty much.

The new gen VVTLi set up is a mixture of the VVT and the Vtec setup. You see fancy toyotas with the badges.

VTEC basically you have a cam that operates on rockers, during normal operation the rockers are against the cam and valves, when VTEC kicks in oil pressure goes to the rockers which have a pair rollers in them which are shoved outwards, these rollers are then put into contact with the wilder cam lobes and this is how you get the extra lift and duration.

VTEC is also purely engine speed controlled, not load/rpm, throttle position liek the VVT set ups can be.

Ask Ben R he can tell you exactly what rpm the VVT kicks in on the clios.

Forum Moderator Joined: 18 Feb 2004 Posts: 7432

not sure about your description of the VTEC workings Chris, i've examined one and there were no rollers i think. there are 3 rockers, the 2 outer ones are in contact with the tame cam, the middle one is in contact with the wild cam and floats with VTEC off. When VTEC comes on, a 3 piece pin is shoved through the 3 rockers locking them all together and the wild cam then takes over.

maybe the newer ones have rollers?

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

yes the pins the rollers, oil pressure shoves them out into contact with the big lobes.

Level 5 User Joined: 18 Jun 2004 Posts: 114

Newer K and F series Honda Engines use roller radius followers, just like the F4R because you can run a wilder cam with a larger dwell over nose, as a hydrodynamic wedge isnt neded to stave off cam lobe wear. Older B and D series hondas use the radius follower pads.

The VVT system on the F4R is basic and pretty useless. Basically at any point above 1450rpm and below 6500rpm where the MAP reads above 800mb, the ECU puts 12v's across the solenoid with a plunger on it in a pressurised oil galley, bleeding oil through the front of the cam into the phaser unit on the inlet pulley. The phaser advances the inlet cam 16 degrees, effectively allowing the engine to 'see' overlap that wasnt there before.

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

see near as 1500rpm as damnit!

Not seen a new honda lump, Ben dunno if you recall but my mate Adrian with the self destructing S2000 made engine go boom boom. Cack motors, I think at the time he was trying to use the in built hairdryer and comb system.

Think it was a bad downshift made rpm's go high and then nothing.

Level 5 User Joined: 18 Jun 2004 Posts: 114

They are good motors, but they were built on the limit. You really need to run the correct type of oil as they have ally pistons AND ally block with no liners, the ceramic coating wont last if you use the wrong oil.

The valve springs are close to the edge, especially the exhaust side. Apart from that, you can abuse them, its normally the diff housing that goes all the time due to the incorrect oil (honda doesnt actually stock or sell the reccomended oil for the rear diff!), with it being off an MX5 and all.

Love me hondas.....oh the shame

Mr Quoter-vator Joined: 16 Feb 2004 Posts: 7405

was reading up on them recently...clever bugger them japanese....

like the 3 stage vtec...running on 1 inlet valve, then 2 mildly, then 2 wildly! very clever...

and now they do a i-VTEC where as well as all the magic of vtec you also have variable cam timing in the equation too. marvelous

Level 5 User Joined: 18 Jun 2004 Posts: 114

I dont think I-VTEC allows phasing yet, just variable triggering.

Mr Quoter-vator Joined: 16 Feb 2004 Posts: 7405

all i know is in one particular article it described it as being able to vary the over lap by mounting the camshaft in a sleeve within the cam sprocket which has a helical gear interface, so by hydraulic means sliding this sleeve to and fro in the sprocket causes the camshaft to rotate in relation to the sprocket, changing the timing. ill see if i can find th article.

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

yes JB thats VVT like the clio has.

Mr Quoter-vator Joined: 16 Feb 2004 Posts: 7405

cool.