well i suppose i gotta learn..

Yer gonna have to leave it with us for a couple of days love............

we'll take the engine out n see what the problem is, I suspect the double overhead sump.

mean mean people :)

Check your RPM if you've got a rev counter in the Corsa B (is it a Sport/SRi/Other?)

Basically on my Corsa it revs slowly (relatively) up to about 3,000 RPM and then goes through the rev range faster after this.

This is more noticalbe in 16v cars than 8v's.

Always remember my old 8v 1.6 Fiesta S came onto the power a lot earlier than the Corsa 1.6 16v.

Is your corsa 8 or 16v?

LL

Yea, it obviously needs a new long weight. Just hang on a minute whilst i go get my left handed screw driver to sort it with...

very cruel but very funny..

cars do seem to pick up over certain rev ranges not sure if corsas do... And good on you for wanting to know more. Learn to do stuff yourself as it saves loads of time and money..

Lynda

--------------- Do it in Style, do it topless!

This is generally refered to coming onto cam. The cam's the thing that controls when the valves open and close, and how much they open. As I understand it, some cam profiles operate noticeably more efficiently at high revs than low revs, and what you notice is the engine reaching the level of revs where the cam lets the engine start pull in lots of air. Race engines idle like s**te because they've got very extreme cam setups to generate loads of power at very high revs, at the expense of low speed torque. No idea about the corsa, but some cars have variable length inlet manifolds too, which you might notice. Generally that's a feature on an engine someone's bothered to think about, rather than a Vauxhall engine ;).And V-tecs have two cams, one that's kicked in at a certain rev point (somewhere like 6000), which is basically a fast road cam to give more power at high revs.

If you do a google for Autozine and find their Technical School section they've got explanation of a lot of different engine technologies.

co-signed.

Not quite right. You're right that they have 2 cams but they both work just like a normal engine until the Vtec trigger point is reached, the second cam doesn't kick in at higher revs. The Vtec cams have one lobe per valve like a normal engine but they also have a 3rd larger lobe per cylinder between the other 2 lobes. The two normal lobes push on the rocker arms to open the valves but when the Vtec trigger point is reached these 2 rockers are locked to a 3rd rocker which the 3rd larger cam lobe pushes on. This basically makes one large rocker which only the large 3rd cam lobe pushes on to operate both valves.

I still don't understand them. I've read umpteen articles on how they work, triggered by higher oil pressure at high revs isn't it? It's probably fairly simple when you've got one in front of you to look at, but a pain in the arse when you're reading a description of how it works and you're not fully familiar with engine internals.

She only wanted to know why her car seems to gain acceleration after 1/2 a second or so of pushing on the pedal. Probably the delay between the increase of gas flow and the engine management noticing it.

But then my bmw also has a 1/2 second delay when i boot it and it gently blends in a lower gear via its autobox. Of course, if it was our works escort van, the inertia of the throttle cable means movement at one end takes 1/2 hour to reach the other end!!!

Any other excuses apart from the usual "coming on cam".

My little 12 valve vauxhall has 2 inlet profiles which gives a wee but noticeable boost at about 4000rpm.

I drove 250 miles in it today, at an average 56mph, but it still only got

30mpg. Heh.

Douglas

You wanna drive at 80, you do. You'll get 35mpg.

Peter

Don't think they are actually triggered by the oil pressure but the correct oil pressure is one of the things that the ecu checks before the Vtec cam lobe is engaged.

It's more about the type of journey I think. Hint - there wasn't any motorway and only 80 miles of Gatso/Plod infested Dual carrigeway. And lots of towns/villages/tractors/tourists.

56 was only an average.

I thought the 30mpg part was pretty impressive actually, especially given what the consumption-o-meter reads when you overtake things, or even just when you accelerate gently away from junctions.

MOT runs out tomorrow )c:

Douglas

Cough, splutter and all things down the pan. A recent holiday around scotland, 2032 miles in total, returned

29.1mpg on my cars trip computer. Compared to your car, i don't think thats too bad for something with a three litre engine weighing 1600kg's.

Isn't your corsa about 1050kgs ..... the same weight as the early eighties three series???

The engine has power output which varies with revs. As the engine speeds up, the power it develops rises. This is why you have gears.

The power isn't a straight line with engine (or vehicle) speed, it has little power at low speed, and rises quickly after that. Hence, the car will accelerate more quickly once the engine (and therefore the car) has reached a certain speed in any particular gear.

You'll see this dramatically in top gear at low speeds, put the car into fifth at 25 mph, and it won't accelerate much whatever you do with the throttle pedal. But persevere for ages and ages, and eventually the car will reach a speed at which it can accelerate reasonably even in fifth.

The shape of the power curve against rpm depends on all sorts of details about the engine and it's not unusual to find a sharp rise in power at some engine speed. The shape will affect how the engine responds to revs and in various gears, this means you learn which gear to be in for a given car.

I thought it was primarily based on the oil pressure? ie the oil pressure gets high enough and the VTEC rocker is locked to the other rockers.

Nope. You can change the VTec point to anything you like, with a bit of jiggery-pokery. It must be triggered by something else, cos jiggery-pokery can't adjust your oil pressure at-will :)