# Thread: Engine Question for the GURUS !!!!

1. ## Engine Question for the GURUS !!!!

I got a Bonus question for class and I'm having trouble finding concrete examples backing up my theory's and i know someone here knows the answer.

The question is: How does Stroking a motor effect Volumetric efficiency and Engine Vacuum?

Think of everything in 2 motors being equal except the rotating assembly (Crank, rods, pistons, ect) One Stroked 5.0 vs a non stroked 5.0. Same Heads, valves, manifolds, tb, tb opening, ect.

As of right now I'm almost positive VE is worse in a Stroked motor. Engine vacuum I'm at a loss but am leaning twords higher engine vacuum.

Any input is appreaciated, thanks.

Matthew K

2. Originally Posted by ReDevilRXP
I got a Bonus question for class and I'm having trouble finding concrete examples backing up my theory's and i know someone here knows the answer.

The question is: How does Stroking a motor effect Volumetric efficiency and Engine Vacuum?

Think of everything in 2 motors being equal except the rotating assembly (Crank, rods, pistons, ect) One Stroked 5.0 vs a non stroked 5.0. Same Heads, valves, manifolds, tb, tb opening, ect.

As of right now I'm almost positive VE is worse in a Stroked motor. Engine vacuum I'm at a loss but am leaning twords higher engine vacuum.

Any input is appreaciated, thanks.

Matthew K
I would agree with you summation because the engine is simply moving more air(you know what I mean). More air movement would increase vacuum in the same system, and since the ports are the same too the stroked engine's desire to move more air through them would hurt VE

3. I just got back from class and i was right.

You are correct Darth. Even though its really a open ended question because everything depends on the heads valves intake and so on. I explained my paper like i said above 2 of the same motors except crank rods and pistons in the stroked motor. So in that aspect we are correct.

Chances are though if you do a stroked motor your gona throw huge intake manifold, heads, valves, and tons of other stuff to let that baby breath. Which in this case VE would improve and vacuum would decrease.

I could get into why its worse but i would probably be speaking a different language to most people so ill save my time.

4. Are we talking about stroked, but nothing else done? I would imagine VE would improve, even without huge intake tracts, etc. If the intake tract is too big, you could lose VE. And I am WAY too tired to contribute any further tonight!!

5. Your VE may decrease compared to the stock motor but the stroked motor should still move more air.

6. Originally Posted by OBXJeepGuy
Are we talking about stroked, but nothing else done? I would imagine VE would improve, even without huge intake tracts, etc. If the intake tract is too big, you could lose VE. And I am WAY too tired to contribute any further tonight!!
What exactly are you referring to when you say intake tract, are you referring to intake port? If so i think you are incorrect.

Piston Speed in increased when you stroke a motor. One of the biggest things that affect VE Is TIME. The more time that air has for it to gain speed and inertia and get inside the cylinder is cut down since piston speed is increased. Now when i say piston speed is increased its not entirely true. Piston TOP SPEED is increased BUT piston top speed duration is decreased. The length of time that the air has for it to enter the cylinder is decreased in a stroker motor. How do you help it get in there faster? Bigger heads, bigger valves and so on. To help get as much air inside the cylinder as fast as possible.

If you think that Bigger intake tracts would make you lose VE, think of it this way.

Try to fill your lungs with air as fast possible sucking through a straw. Then Open your mouth real wide and fill your lungs as fast as possible. Let me know which method takes longer.