So this means the cams could be 180* off and it would not effect the engine one bit?

 

Wouldn't this also mean if you had a dyno set up for a 4-stroke you would show 1/2 the HP (or twice the RPM) than you actually had?

I've seen more than one DS Dyno curve that the HP and Torque curves didn't cross at 5252RPM.

 

If you see a torque and horsepower graph, and they dont cross at 5250, then its wrong.Horsepower is just a computation of torque and rpm, they have to cross at 5250.
Some motors, fire at every top dead center, they usually have the spark tigger on the crank. The more advanced types have the spark tigged by the cam, which only fires on the top of the compression stroke. It doesnt hurt anything to fire at the top of the exhaust stroke.
If you havent gone to www.howthingswork.com, yet....its a good place to learn some engine basics.
how things work

 

So this means the cams could be 180* off and it would not effect the engine one bit?

With the plugs firing every TDC, it would seem it would be a very inefficient system. If it were to fire on only the combustion stroke, it could store twice the amount of power.

 

If your Cams were 180 degree's out, then the wrong valves(exhaust) would be open on the INTAKE stroke, because of the direction the motor turns.


bigger.

 

Yeh Hondabuster. What I meant to say is I've seen incorrect dyno curves (because the HP and Torque crossed at an RPM other than 5250). Correct, HP is a calculation of Torque and RPM.

Bigger - Maybe Sandaholic and I aren't explaining it correctly i.e. 180 degrees apart. What we are meaning is is you take your cams off when they are in the exhaust stroke TDC and THEN you re-install them facing out (at the same TDC - without rotating the engine) the engine will fire without a problem when you put everything back together. The spark system fires every TDC regardless of weather the cams are open or shut.

 

Yes the spark plug will fire, But because the cams turn clock-wise(if looking at the sprockets), The exhaust vavles will now be opening when the piston is on its way down, therefore you will be drawing air through the exhaust into the combustion chamber instead of fuel and air.

What I trying to say is, the notch in your crank is thier so you will be sure to get the cams in the right position(face outwards fom eachother). that way, the intake valves will be opening ,when the piston starts to drop. Remember the cams turn half as fast as the piston(2 rotations of the crank ,to one rotation on the cams). So on its upstroke the valves will be closed again and the spark plug will fire at TDC(again) igniting the comressed fuel. If the cams were 180 out, that could not happen.


Bigger.

 

Yeh Bigger. I think we're on the same page.

Not really talking specifically about cam position as much as Engine Position i.e. compression stroke vs. exhaust stroke. Should have used those terms instead of referring to the cams.

 

OK, cool.

I though Sandaholic was thinking that the engine would run just fine with the cams 180 out. he he he




bigger.

 

I am just trying to get a better understanding of this.... So the crank is at TDC with the cams facing out, then rotate the crank 1 full turn. Now the crank is again at TDC but with the cams are facing towards each other (cams turned 1/2 of the crank). This is normal engine operation...

Isn't this exactly what you described above, Crank at TDC, cams facing towards each other = drawing air through the exhaust into the combustion chamber instead of fuel and air.