Out of interest: Valve Timing

[Hybrid]

Hey guys just wanted to point out something I found the other day using an engine dyno simulator.

When I entered the valve timing stated in my Gregorys engine manual the simulator told me there was an imbalance in engine components or wrong valve timing. This is the valve timing it stated under engine specs

Opens Closes Duration
Inlet 31 BTDC 122 ABDC 333

Exhaust 73 BBDC 80 ATDC 333

Q1. How can there be no point were both valves are closed? Wouldnt both have to be closed at combustion?

Q2. Whats is the difference between advertised valve timing and .050" valve timing?

So either I cant get my head around valve timing or Gregorys farked up. Either way the specs I got with the new cam though working in the simulator and completely different to above seem to me to allow no point where both valves are closed.

Heres a gay paintbrush of the new cams timing and how I understand it to look. You can see why I think there is no point where they are both closed



Cheers

John

[-Scott-]

I don't know about your engine simulator, but the good old Otto Cycle is called a FOUR stroke cycle. Suck - Squeeze - Bang - Blow (if that helps.)

The inlet valve timing figures involve Blow - Suck - Squeeze (in that order) while exhaust valve figures involve Bang - Blow - Suck. They are both closed for some of the Squeeze cycle and some of the Bang cycle.

Cheers,

Scott

[Hybrid]

Thanks mate thats the kind of answer I was looking for. Didnt even think about that. Im a little slow. Think its cause I spent 6 months in Canada aye. Guess the sim just didnt think the timimg from gregorys was usable. If anyones interested I got the program off kazaa and its called Desktop Dyno 2000. Anyone know if those Gregory's stats are right? Its for a series 2 V6 commo.

[HEY CHARGER]

I reckon your cam specs are wrong for valve timing i'll try and explain .
Lets imagine a wall clock to make things easier ,
* INTAKE STROKE *
Piston traveling downwards , intake valve opening at the same time from top dead centre which is 12 o'clock and completing intake stroke at 6 o'clock bottom dead centre.

* COMPRESSION STROKE *
Piston travelling upwards , intake valve closing at the same time from bottom dead centre which is 6 o'clock and completing compression stroke back at 12 o'clock top dead centre.

* POWER STROKE *
Piston travelling back down from top dead centre 12 o'clock to bottom dead centre 6 o'clock with both intake and exhaust valves closed.

* EXHAUST STROKE *
Piston travelling upwards , exhaust valve opening at the same time from bottom dead centre 6 o'clock to top dead centre 12 o'clock .

4 strokes every 2 turns of the crank to produce 1 pulse of power.
2 stroke every turn of the crank produces 1 pulse of power.

Your quoted cam specs are like this intake valve opens 31 degrees before top dead centre or 11 o'clock ,
and it stays open till you are 122 degrees past bottom dead centre which is back at 10 o'clock .
That motor cannot run because you have only 58 degrees left of compression stroke and you have forced most of the air fuel mix back in the intake manifold.
and the same goes for the exhaust open far too long , i reckon there might be a miss print in the gregorys manuel.

I better stop havi'n these beers cause im starting to confuse the shit out of myself , anyway hope this can shed some light !!!!!

and quickly the advertised duration is
333 degrees that is the total amount of degrees out of a possible 360 that the valve spends its time of the valve seat .

duration at 0.050" is where you set up most cams from and all that means is that your no 1 intake lifter has started to lift on the face of the lobe and with a dial indicator on it turn you cam over till its up 0.050" and stop turning, that is your zero point now.
So from there you duration will be a smaller number cause youve already used X amount of degrees to get your lifter up 0.050" .

Sorry ive rambled to long now !! and im going ....
Cheers
Hey Charger !!

[Hybrid]

Thanks charger, yeah I wondered if the rgegorys was wrong. Wonder what other specs are wrong. Would be nice doing a rebuild from it with this reliability.