Bore, Stroke, and block strength

[Tom Walker]

x2 on what Madbill said. Same amount of torque equals same amount of stress on mains.

[Circlotron]

x2 on what Madbill said. Same amount of torque equals same amount of stress on mains.

I disagree.
Say you have 100 lb applied vertically at the end of a 1 foot crank throw. You have 100 lb/ft of torque and 100 lbs of vertical force on the main bearings. Now you change it to a crank with a 2 foot throw and 50 lbs of force applied vertically at the end. You still have the same 100 lb/ft but now only 50 lbs on the main bearing.

[strokersix]

I think both answers are correct. How about this:

From a practical perspective with typical nearly square engines main bearing life tracks more closely to torque produced at the crank or power production and bore/stroke is minor effect at most.

From a technical perspective the main and crankpin bearing loads are directly related to bore/stroke,all else being equal (which it never is in real life).

[peejay]

Yes it is.
Also crank has quite large journals.

Yes the cranks are very strong, but the blocks are known to crack at the water pump area. That is on the smaller bore engines that don't have the cylinder wall splitting problem.

All the same it is interesting, to me, that when they went for 300hp/300ft-lb they upped the stroke from 90 to 93.something. And the next series of engines at that power level kept the long stroke but reverted the bore to 81mm and these blocks don't crack. If mine ever cracks, it will get one of those 81mm bore blocks, but given that the engine has done nearly the equivalent of driving to the Moon, it's probably not going to.

[peejay]

x2 on what Madbill said. Same amount of torque equals same amount of stress on mains.

That is the opposite of what I thought he said...

[Kevin Johnson]

.

[Stan Weiss]

Two 400 ci engines everything the same but bore, stroke and rod length. Look at the difference in pressure by the piston ATDC.

Stan

ab-pp-400.gif

[Stan Weiss]

While the bore, stroke, and rod length are different the two combinations do have the same rod stroke ratio. This graph shows the turn force.

Stan

ab-tf-400.gif

[MadBill]

.

Ah, the usual incisive commentary from KJ...

[MadBill]

x2 on what Madbill said. Same amount of torque equals same amount of stress on mains.

That is the opposite of what I thought he said...

Tom is correctly interpreting my words.

Let's try this: Torque results from a force applied to one end of a moment arm (in this case the crank throw) but that force must be balanced by an equal reaction torque at the other end, in this case the force being provided by the main journal and bolts.

Example: imagine trying to torque a bolt with a swivel socket and extension on your ratchet. Can you do this properly without supporting the ratchet head with your other hand? (Hint: NO.) Does the requires support vary with the applied torque? (Yes) Does it diminish if the torque remains the same, but the ratchet handle is lengthened? (If it does, do you no longer need to support the ratchet head at all if the handle is infinitely long?)

[Schurkey]

What stress does piston speed/inertia place on the block and crank?

[Kevin Johnson]

.

Ah, the usual incisive commentary from KJ...

I spent hours over multiple days looking at Volvo engine specs: Redblock, Modular and Porsche engineering examples. Patents on modular engines, etc. This was to determine the "engineering rationale."

In a nutshell, Volvo engineered (or had engineered) the basic modular unit or cylinder/bay to use a 90mm stroke. That modular unit was destroked for particular later engines. Near the end of the engine design series life the stroke was incrementally increased to 93.2mm. If you examine the peak rpm hp ratings of numerous modular engines, there isn't a hard and fast relationship between operating rpm and stroke. Concurrent with the life of the engine was a dramatic increase in computer simulation expertise.

The Windsor V8 dates back to the early 1960s and started with an even shorter stroke than 3". It was not an over-engineered system that was de-tuned, so-to-speak.

Anyway, it's just indicating that the thesis that Volvo increased the stroke appears to be incorrect. Yes, if you compare it to the Redblock engine series that preceded it, you could say that. That doesn't mean that there are not interesting relationships in the various possible engine combinations and that is where the thread was/is heading.

[tt 383]

.

Ah, the usual incisive commentary from KJ...

I spent hours over multiple days looking at Volvo engine specs: Redblock, Modular and Porsche engineering examples. Patents on modular engines, etc. This was to determine the "engineering rationale."

In a nutshell, Volvo engineered (or had engineered) the basic modular unit or cylinder/bay to use a 90mm stroke. That modular unit was destroked for particular later engines. Near the end of the engine design series life the stroke was incrementally increased to 93.2mm. If you examine the peak rpm hp ratings of numerous modular engines, there isn't a hard and fast relationship between operating rpm and stroke. Concurrent with the life of the engine was a dramatic increase in computer simulation expertise.

The Windsor V8 dates back to the early 1960s and started with an even shorter stroke than 3". It was not an over-engineered system that was de-tuned, so-to-speak.

Anyway, it's just indicating that the thesis that Volvo increased the stroke appears to be incorrect. Yes, if you compare it to the Redblock engine series that preceded it, you could say that. That doesn't mean that there are not interesting relationships in the various possible engine combinations and that is where the thread was/is heading.

I would assume they (Volvo) had to change rod length and or piston height with some of those changes?

[Kevin Johnson]

Ah, the usual incisive commentary from KJ...

I spent hours over multiple days looking at Volvo engine specs: Redblock, Modular and Porsche engineering examples. Patents on modular engines, etc. This was to determine the "engineering rationale."

In a nutshell, Volvo engineered (or had engineered) the basic modular unit or cylinder/bay to use a 90mm stroke. That modular unit was destroked for particular later engines. Near the end of the engine design series life the stroke was incrementally increased to 93.2mm. If you examine the peak rpm hp ratings of numerous modular engines, there isn't a hard and fast relationship between operating rpm and stroke. Concurrent with the life of the engine was a dramatic increase in computer simulation expertise.

The Windsor V8 dates back to the early 1960s and started with an even shorter stroke than 3". It was not an over-engineered system that was de-tuned, so-to-speak.

Anyway, it's just indicating that the thesis that Volvo increased the stroke appears to be incorrect. Yes, if you compare it to the Redblock engine series that preceded it, you could say that. That doesn't mean that there are not interesting relationships in the various possible engine combinations and that is where the thread was/is heading.

I would assume they (Volvo) had to change rod length and or piston height with some of those changes?

I do not have access to AERA data but I am sure they would. That is supported (to my thinking) via wikipedia entries where some engines have rod length info added by enthusiasts who are mixing-matching-brewing. The 1.6mm incremental increase in approach to the head/combustion-chamber in the later engines is probably a by-product of the increased simulation power, i.e. what can we get away with without spending a lot of money on an old platform.

[tt 383]

With a 5.0l I personally think their is some merit to running long rods for less side loading and if possible getting that huge weight off the end of the crank, the main girdle may help bolster cap loads. Cant say I have ever heard of one being filled maybe that would add some integrity/strength?