i have a list of crap that i have read differing opinions about and i want yall's input

1. what makes torque over hp bore or stroke?

2.what determines the rev capabilities of a engine bore, stroke, or the combo of B/S?

3. Balancing a engine : dose it still need a weighted flywheel?

4. dose a balanced engine last much longer then a non-balanced when they are used in the 0-4k range? im figuring it make a lot of diff in the 5-6k+ range)

5. whats rod/stroke ratio and how dose it affect the engine?

well thats some for now i will undoubtedly(sp?) have more Q's about the answers ya have

Thanks all
Joe

 

i have a list of crap that i have read differing opinions about and i want yall's input

1. what makes torque over hp bore or stroke?

More stroke = more Torque. The longer the stroke an engine has, the more "leverage" the rod/piston has to move the crank. Up to a certain point, this will also positively effect HP up to the point where the larger crank creates too much drag to accelerate the engine, but this point depends largely on the stroke/rod ratio. A larger bore will increase both HP and TQ, but not as profoundly.

2.what determines the rev capabilities of a engine bore, stroke, or the combo of B/S?

The rev capabilities of an engine are impacted by many things, here are a few of them (I tried to list them with decreasing pertinence):

-valvespring force. If the valvesprings are too soft (not enough force applied to the valve), then at high engine speeds there will not be enough force to effectively close the valve, leaving it hanging open, and unable to build pressure within the combustion chamber.

-camshaft design. The camshaft is designed to optimize airflow within a certain range of engine speeds. High revving engine cams create more overlap, which is where the intake valve and the exhaust valve are held open simultaneously in transition from the exhaust stoke to the intake stroke, which helps induce airlfow at very high engine speeds. If there is not enough overlap in the valvetrain, the engine will not breath well enough to revv above a certain range, and if there is too much overlap the cylinder will not able to build up very much pressure in the combustion chamber below a certain engine speed, and a subsequent loss of low RPM power will follow, and the idle quality will be poor (but it will have that "lopey" sound like racecars have).

-cylinder head design. Cylinder heads are tuned to acheive maximum airlfow velocity at the speed the engine is designed to run. If the ports on a head are too large, the velocity will be very slow, especially at low RPM. Higher velocity generally increases the TQ output. If the ports are small, the airflow will be fast at low speeds and very fast at high speeds. The reason why small port heads are poor for high engine speeds is that if the airflow is too fast, the flow will become turbulent at high RPM as the airspeed goes supersonic within the port to try to match the air demand for the engine, and the airflow efficiency suffers once the airflow becomes turbulent due to excessive head loss.

-stroke. The shorter the stroke, the less rotational inertia the engine has, thus requiring less force to accelerate the mass. Engines with longer strokes require more combustion pressure to accelerate at the same speed that a shorter stroke engine would. Note that the tradeoff is low RPM torque.

-air/fuel induction. Although rarely is this the limiting factor on a street engine, the fuel injection or carburetor must be able to supply enough fuel and air to match the airflow demand of the engine.

-exhaust flow. Higher engine speeds create more exhaust gasses, which if not expelled properly, can create excessive backpressure. Backpressure forces the engine to "push" spent combustion gasses out of the chamber against an increased pressure gradient, consuming mechanical energy. This phenomina is aptly named "pumping loss", because the engine is required to "pump" exhaust gas out of its combustion chamber.

There are many other factors that have an effect on an engine's available speed range. I have tried to list the most prominent ones first, but others will surely post those that I have overlooked.

3. Balancing a engine : dose it still need a weighted flywheel?

Some machinists have acheived a "0", or "neutral" balance in SB Chevy motors, I'm not sure of the popularity of this in the Ford world. Some factory engines, like Ford's 300 I-6 have a neutral balance, and do not require an "imbalance" wieght on the flywheel or flexplate. A flywheel has weight itself, a weighted flywheel as you describe would have an imbalance weight, meaning that it intentionally creates an off-center mass centroid to correct for an unbalanced rotating assembly. A harmonic balancer is always required to oppose the flywheel/flexplate if not for it's ability to correct for engine balance than to dampen or absorb vibrations that the engine creates.

4. dose a balanced engine last much longer then a non-balanced when they are used in the 0-4k range? im figuring it make a lot of diff in the 5-6k+ range)

The benefit of a well-balanced engine, as you mentioned, is most obvious in at higher engine speeds, but the overall smoothness of the engine is also noticable, and it will have a positive effect on everything from HP/TQ output to fuel milage, to longevity, regardless of the speed that the engine operates.

5. whats rod/stroke ratio and how dose it affect the engine?

The stroke/rod ratio is the length of the crank's stroke divided by the length of the connecting rod. A lower ratio will have a positive effect on the revv potential of the engine. This ratio ultimately describes the relative angle that the rod must travel in reference to the wrist pin on the piston. The larger this angle becomes (stroke/rod increasing), the more the piston is likely to "slap" side to side in it's bore, increasing wear and making egg shaped cylinders. The smaller this ratio becomes the more force can be applied directly to the crank, instead of creating secondary moments about the piston bore (therefore increasing mechanical efficiency).

well thats some for now i will undoubtedly(sp?) have more Q's about the answers ya have

Thanks all
Joe


Hope this helps, post away when you think of the rest! TK

 

That was an excellent answer TQ!

 

WOW thanks for the great answer TQ your detail filled in the other questions i had for now
thanks
Joe