Why do the valvers have that 'kick' at about 4krpm

[Matty86]

Bit of a noob question, but I can't seem to find a definitive answer

So, why is there a noticable kick at 4000rpm and why is it fairly gutless in comparison below 4k?

someone clue me in :D

Oh, and why is the kick so much earlier on the williams

[FincH]

Summat to do with the power curve of the engine.

Max torque is at 4.5k or summat so it's just where the powerband of the engine lies really (4.5k Max torque then engine pulls upto 6.5k to Max Bhp)

On a Williams the engine has it's power band lower in the rev range, hence the 2.5k pull (from what I hear) and hence the lower rev limit.

No doubt some guru will come and own me but that's the way I look at it.

[Matty86]

yeh, i was just wondering why the powerband was like that. My old RT was completely different, with no kick etc...

[BRUN]

i thought my kick @ 4k was because of my cams, i guess not lol

[nyk]

my cams kick in at 3.5K

Used to be 4.5 before the cams.

[Zollo]

As no one else has had a decent go at answering this, I thought I'd give it a go even though BenR, Stan and most other people on here could give a much more accurate and detailed explaination! But here goes...

The kick in power is all to do with what goes on inside the engine. Could be the profile of the cams, flow characteristics of the head, mapping of the engine, bore-stroke dimensions. Anything and everything has an effect, but I don't know nearly enough about engines to say for sure what it is

One of the reasons there's a difference between the Valver and the Williams is that the crank's stroke is different. The Valver has a shorter stroke than the Williams (pistons go up n down less), so revs easier and faster, but doesn't produce much torque because it doesn't have as much capacity. The Williams has what's known as an undersquare engine (which means more up and down of the piston comparitive to the size of the cylinders), so it can't move up and down as quickly but has plenty of torque.


Some (or all!) of this could be wrong, though

[stan]

alot of factual stuff there mate.

"square-ness" refers to bore versus stroke dimensios...both being equal=square.

The kick is mainly to do with flow of the head, and how this interacts with engine speed...there is always goin to be a sweet spot. gas inertia, VE, etc all affected by parameters such as cam spec and valve timing....and engine speed.

Its not that there isnt similar happening with an F7R, its just it has more torque lower down, so when you come accross the sweet spot it isnt as noticable. similar meaning for one, peak piston speed is greater on the F7R and so gas speed through the head is also greater=diiferent flow rates at different speed events blah blah.


Theres LOADS you can go into on this topic....far more than worth on an internet forum!

[VIPERONE]

a map can adjust the kick... for instance mine doesnt have a kick.. it pulls from 0-limiter