more VVT ponderings..

[Bryan]

talk about bringing a topic back from the brink of death

1 year and 1 month on

 

[Matbrown]

For a minute i thought Joe was back, he was a star.



Mat.

 

[Bryan]

sadly he moved on before i had a chance to get to know him

 

[jonnyboy]

didnt see this originally and I dont know if its already been covered but if the 172s vvt does nothing, what the hells happening at 4.5 k revs?

 

[rt172]

I think at 4500 revs the car comes "on cam". The VVT is meant to turn on at revs above idling.

 

[Rich-D]

Quote: Originally posted by Rhys on 20 September 2003

I think at 4500 revs the car comes "on cam". The VVT is meant to turn on at revs above idling.

Correct...

In my 106 GTi there was a kick at 5000rpm and in my 306 Rallye there was a kick at 4500rpm, yet there is no VVT on either car.

Thats just the way it is.



p.s Nice topic ressurection!

 

[jonnyboy]

ahhhh is that the cams working at their optimum level or whatever then? As you can probably tell Im not a mechanic

 

[spirez]

is this the same as the toyota vvt-i system? nothing can touch a VTEC tho!

 

[Paul_P1]

AH...the forums worse off without these characters!!

Anyway, does anyone actually have an answer to Neils query?

 

[Eddd]

Where is the Captain hiding these days?

I miss him.

Ed

 

[anthonyj207]

Quote: Originally posted by Rich-D on 20 September 2003

Quote: Originally posted by Rhys on 20 September 2003

I think at 4500 revs the car comes "on cam". The VVT is meant to turn on at revs above idling.

Correct...

In my 106 GTi there was a kick at 5000rpm and in my 306 Rallye there was a kick at 4500rpm, yet there is no VVT on either car.

Thats just the way it is.



p.s Nice topic ressurection!

Im confused here, my valver had no VVT and youre right, at 4000ish RPM it came on cam and you had that lovely push and all hell broke loose. However, below 4000 it had very little go or torque.

If the VVT does nothing, how come the 172 seems to have both the advantage of low down torque and high end ability but the power feels progressive throughout the rev range and there is no discernable push at higher revs? Is that just better engine design, I thought there was always a trade off between low rev torque and higher end performance?

Ant.

 

[Matbrown]

Just cos the 172 has more torque, same if you compare the willy to the 16v.



Mat.

 

[anthonyj207]

Yes, but I thought that was a matter of a trade off between torque and better top end performance? My mate has had a set of racing cams fitted to his Rover and at low revs it is hard work to get going, but come 4500 it takes off like a rocket (due to the high lift cam profile).

I dont know owt about engines (perhaps obvious from my question and reply)!

Ant.

 

[telford_mike]

Those who have owned motorbikes, particularly 2-strokes, will know about something called a powerband. As the engine picks up you get a rush of power somewhere between halfway and maximum revs. Its just something that petrol engines do. Nothing to do with VVT (2-strokes dont have valves lol).

 

[anthonyj207]

I understand about the engines powerband but I always thought that the purpose of VVT was to provide a smooth transition, or best of both worlds between an engine that pulls well at low revs and a high revvin screamer.

Ant.

 

[Rich-D]

Quote: Originally posted by anthonyj207 on 21 September 2003


I understand about the engines powerband but I always thought that the purpose of VVT was to provide a smooth transition, or best of both worlds between an engine that pulls well at low revs and a high revvin screamer.

In some cases this is true...

Not in this case though!

 

[anthonyj207]

Quote: Originally posted by Rich-D on 21 September 2003

Quote: Originally posted by anthonyj207 on 21 September 2003


I understand about the engines powerband but I always thought that the purpose of VVT was to provide a smooth transition, or best of both worlds between an engine that pulls well at low revs and a high revvin screamer.

In some cases this is true...

Not in this case though!

OK

Ant.

 

[papa?]

Quote: Originally posted by ChavyBoy on 20 August 2002

Guys, Just a thought, the VVT is done on a CAM basis, was there anyone who looked into doing this without a Camshaft using a set of Solonoids to push the Valves open instead ? This would have the added benefits of being able to control the valves per cylinder so you could get the max power out of each piston individually ! Sounds mad but just a thought !

Lotus have been working on a Cam less car for a few years now. They believe that using their system economy can be increased by about 25% and you would see more advantages than just VVT...