283 vs 289!! (longest VS thread?)
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quote:Originally posted by iceracerx
Like a Olds Rocket 88 Doug?
Yup.
Doug0 -
quote:Originally posted by iceracerx
quote:Originally posted by Jim Rau
quote:Originally posted by iceracerxOriginally posted by Jim Rau
Probably not. The 289 (Ford) was a 2.87 inch stroke X 4 inch bore which made for some HIGH reves before you reached critical piston speed. Most of the older V-8's (50's) were much longer stroke and narrower bore. More torque at the low end, but very short in the RPM area.[;)]
Since Torque and HP are equal at 5250 RPM, and torque is higher than HP below 5250, it's very difficult to make HP, which is dependent on RPM, with a standard push rod v8 production engine. The laws of Physics must be obeyed.
And your point is????[?] Critical piston speed has nothing to do with 'push rods' only the 'connecting rods and pistons'.[?]
Isn't piston speed also dependent on RPM? What you seemed to have missed is that "push rod" is used as a classification of engine and there was no mention of any relation between the part, push rod, and piston speed.
It's a rare push rod engine that can turn 9 grand. The point is that anything under 5250 rpm deals with torque and over 5250 starts to deal with HP greater then torque.
Pistons for high RPM engines are vastly different then pistons for low RPM applications, but of course you knew that.
HP = (Torque x rpm) / 5250
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You are talking about two different things here.
Critical piston speed is when the energy in the moving mass (connecting rod, wrist pin, and piston) exceed the strength of the rod cap and bolts to hold the assembly to the crank shaft. The longer the stroke the higher the velocity of the assembly (rod, wrist pin and piston) at the same RPM. Thus the shorter the stroke the higher RPM you can reach before you reach the critical piston speed. The longer stroke lose in two ways.
1. The longer stroke require the assembly to reach a higher velocity at any RPM when compared to the shorter stroke.
2. The longer stroke usually have a heavier assembly.
Therefore it loses in two ways.
One of the other ways any engines RPM is limited is the valve train. The weight of the intake assembly (lifter, push rod, rocker arm, and valve) have this same limiting effect. The heavier the assembly the stronger the valve spring must be to move it. You get 'valve float' when you reach a point where the spring can no longer return the valve to the seat quick enough. In some case this 'float' can cause the piston to strike the valve. High spring pressure coupled with the extreme heat on (exhaust) valves can and do sometimes pull the head off the valve or stretch the stem.0 -
Actually a short Con rod has a faster "speed" from 270 deg to 90 deg (the TDC range) and due to the ACCELERATION of the reciprocating mass requires stronger pin bosses, piston pins and connecting rod than a long rod does. A short rod requires better breathing to make the same peak HP as a long rod engine. Short rods exert more force on the crankshaft from 20 deg ATDC to 70 deg ATDC but also cause greater side loads on the cylinder walls (thrust side).
A long connecting rod is "faster" from 180 deg to 270 deg (the BDC range)
An IC engine is a "push me pull you" and there is no one optimum design or recipe.0 -
Sure there is.
Doug0 -
quote:Originally posted by Colt Super
Sure there is.
Doug
Don't tell me, let me guess. 289 FORD?0 -
I was thinking more of the 392 Chrysler HEMI.
Doug0 -
quote:Originally posted by iceracerx
Actually a short Con rod has a faster "speed" from 270 deg to 90 deg (the TDC range) and due to the ACCELERATION of the reciprocating mass requires stronger pin bosses, piston pins and connecting rod than a long rod does. A short rod requires better breathing to make the same peak HP as a long rod engine. Short rods exert more force on the crankshaft from 20 deg ATDC to 70 deg ATDC but also cause greater side loads on the cylinder walls (thrust side).
A long connecting rod is "faster" from 180 deg to 270 deg (the BDC range)
An IC engine is a "push me pull you" and there is no one optimum design or recipe.
You are over complicating the issue here.
The property of inertia is at play here. The 'assembly' MUST accurate from 0 fps to X fps and then decelerate from X fps to 0 fps twice per each revolution. Here in lies the problem.
The crankshaft will handle the 'flex' in both direction with out a problem. The 'weak link' is the rod cap and bolts which hold the assembly to the crankshaft.
At the top of the stroke the entire load is on the rod cap (weakest link), at the bottom of the stroke the load is on the connecting rod shaft (strongest point). Stroke is determined by the crankshaft. The distance from the center-line of the crank shaft to the center-line of the rod journal. The greater the distance (radius) the greater the velocity attained and the greater the rate of acceleration.
If my memory is correct critical piston speed for (strong) stock rods is around 4000 fps.0 -
quote:Originally posted by Jim Rau
You are over complicating the issue here.
The property of inertia is at play here. The 'assembly' MUST accurate from 0 fps to X fps and then decelerate from X fps to 0 fps twice per each revolution. Here in lies the problem.
The crankshaft will handle the 'flex' in both direction with out a problem. The 'weak link' is the rod cap and bolts which hold the assembly to the crankshaft.
At the top of the stroke the entire load is on the rod cap (weakest link), at the bottom of the stroke the load is on the connecting rod shaft (strongest point). Stroke is determined by the crankshaft. The distance from the center-line of the crank shaft to the center-line of the rod journal. The greater the distance (radius) the greater the velocity attained and the greater the rate of acceleration.
If my memory is correct critical piston speed for (strong) stock rods is around 4000 fps.
Sorry Jim, but Physics is "complicating" the issue here and there is plenty at play.
You are incorrect about the "Big End" or rod cap and bolts having the entire load on on them. Ever heard of "small end failure"? How about a Con-rod breaking between the two ends? Cranks can and do fail. This is all the nature of the beast that is a IC engine.
On a typical 4 stroke/cycle engine the load is on the rod, crank-pin, pin boss and Piston Pin on the compression and power strokes. The Rod-cap is under load at the top of the Exhaust stroke and during the entire intake stroke (downward).
I've designed Con-rod for over 18 different applications, how about you?
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quote:Originally posted by iceracerx
quote:Originally posted by Jim Rau
You are over complicating the issue here.
The property of inertia is at play here. The 'assembly' MUST accurate from 0 fps to X fps and then decelerate from X fps to 0 fps twice per each revolution. Here in lies the problem.
The crankshaft will handle the 'flex' in both direction with out a problem. The 'weak link' is the rod cap and bolts which hold the assembly to the crankshaft.
At the top of the stroke the entire load is on the rod cap (weakest link), at the bottom of the stroke the load is on the connecting rod shaft (strongest point). Stroke is determined by the crankshaft. The distance from the center-line of the crank shaft to the center-line of the rod journal. The greater the distance (radius) the greater the velocity attained and the greater the rate of acceleration.
If my memory is correct critical piston speed for (strong) stock rods is around 4000 fps.
Sorry Jim, but Physics is "complicating" the issue here and there is plenty at play.
You are incorrect about the "Big End" or rod cap and bolts having the entire load on on them. Ever heard of "small end failure"? How about a Con-rod breaking between the two ends? Cranks can and do fail. This is all the nature of the beast that is a IC engine.
On a typical 4 stroke/cycle engine the load is on the rod, crank-pin, pin boss and Piston Pin on the compression and power strokes. The Rod-cap is under load at the top of the Exhaust stroke and during the entire intake stroke (downward).
I've designed Con-rod for over 18 different applications, how about you?
Sorry, I guess everyone else in the industry is wrong and you are right!!![;)]0 -
Not sure what "everyone" in what "industry" you are referring too. Perhaps they're just mistaken.
I know many people in my "industry" (production engines) and few disagree with me on this topic.
There is a bit of science behind what "we" do and it is complicated.
Next time you order a part from Summit or some such outfit, you can thank someone like me.
And, you're welcome.[:D]0 -
Kin ya make me a purty red one with a shiny silver cap ??
I'm gonna build a nex-gen "COLOR Me Gone".
IBTL.
Doug0
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