lol, one last crack at it and then let them believe what they want to.

Less rotating mass = less inertia to move it (in this case spin it up or slow it down). Your engine's rotating mass is a parasitic drag on the motor, stored energy does nothing for you in terms of car acceleration*, the less rotating mass the less parasitic drain on the motor.

*unless you can rev it up and dump the clutch like in a 1/4 mile launch.

Very eloquently stated, however your talking points are loaded with logic and empirically proven concepts. Unfortunately, given what we have read earlier, none of that applies here. :rolleyes:

If I could add one additional new point just to add some flavor to this discussion, not only does the heavier big block crank add more parasitic rotational drag on the motor, but the heavier big block rods and pistons add more parasitic drag on the motor due to greater reciprocating mass. Let the games begin !!!!



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Can someone explain to me what is a BOB weight??????????


Intake and exhaust runner lengths will probably effect accel rates on an engine more than mass of rotating assy.

List and verify your engines acceleration rates and show cam specs and balance card.

Heavier than what? Lighter than what?

What examples are you all pulling from? Is there a small block that you have in mind when you're discussing this, or is there a big block that you have in mind?

What parts are they using?

Do you not understand that in a lot of cases, the reciprocating mass of a big block is not heavier than the reciprocating mass of a small block?

Do you not understand that your "parasitic rotational drag" is a bogus point considering that the main journal diameter of an FE is the same diameter as the main journal in a Dart Windsor block?

Instead of speaking from emotional viewpoints, how about you guys ante up with some examples. Quoting from the Olympics and your physics book does nothing to justify your point.

The word "generalization" fits this thread very well.

Generalization: a statement about a group of people or things that is based on only a few people or things in that group.

On the 2nd page of this thread, Madmaxx said that, "as far as FE and stroked small block, the small block will rev much quicker...."

That in itself is a blanket statement, and unless you qualify each and every variable in both engines, it's incorrect.

If Jerry is going to post some balance sheets of both some big blocks and small blocks, you will find that yes, there are some small block rotating assemblies that are lighter, and yes, there are some big block rotating assemblies that are lighter.

Absolutely, spoken from an engine builder and not a figure skating enthusiast. ;)

There's a lot more to it than reciprocating assembly masses, hence my example of one of Jon Kaase's mountain motors, 4.8" bore, 5.75" stroke, with 7.750" rods that weigh a chunk....but yet respond instantaneously and will pull to 10000 rpm.

It's sad really :LOL:




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I've said it a million times before, the only reason you would not put an FE in to a Cobra is to save a couple of bucks. If you throw enough money at it, you can build an FE that will fly you to the moon.:cool:

Yes it is...

Along with these same generalizations:

*Single plane intakes are only good for high rpms.
*Having pistons with the oil ring intersecting the wrist pin will cause the engine to use oil.
*Long stroke engines can not turn high rpms.
*Solid roller lifters fail with street use.
*High volume oil pumps break oil pump drive shafts.
*FE's are high maintenance.

Each statement has qualifiers, but each is not true as a blanket statement.

However, these statements are continually passed on as gospel by forum members everywhere.

Here's a heavy old FE piston....

http://i170.photobucket.com/albums/u...ps9ec7de71.jpg

And here's a light Windsor piston....

http://i170.photobucket.com/albums/u...ps3ee6c874.jpg

Neither one of those are what I would consider "exotic". They are both custom pistons from Diamond, and the FE piston is for a 4.125" stroke, which makes it taller than the pistons I would use for a 4.250" stroke build.

You will notice that the Windsor piston has a pretty substantial 30cc dish in it, while the FE piston has a small 14cc volume. You can also note that the Windsor piston uses a support rail, which adds to the piston/ring package weight.

The FE piston could have been made extensively lighter.

Just one piece of the puzzle of course, and rod design/weight makes a pretty substantial difference in itself, but it's easy to see that you can cut down big block reciprocating part weight without a lot of effort.

I would also suggest that the non-builders here look into the difference between "rotating weight" and "reciprocating weight", which we use to both balance and to pick lightweight combos for race applications.

Thanks for the input. I have been looking at Superformance for years, I like
factory built roller idea and components but one of the biggest reasons is the
leg room in a Superformance compared to the others.

Herc

I am going to suggest that the original statement should have been two engines with similar power curves will accelerate similarily with identical rotating assemblies. Identical rotating assemblies will have the same stroke, rotating assembly weight, diameter and weight placement relative to the crankshaft centerline.

As AL427SBF and/or Cobra ED have already pointed out if you hang a heavy flywheel on one engine and a light flywheel on another identical engine the one with the heavy flywheel will no longer accelerate as quickly as the one with the light flywheel. The same is true if you exchange one rotating assembly for an identical but heavier rotating assembly.

When you remove the rotating assembly from one engine and replace it with a heavier rotating assembly (that provides the same displacement, compression etc) the engine with the now heavier rotating assembly will accelerate more slowly because additional torque is being consumed to accelerate the heavier rotating assembly. Not surprisingly the dyno will also measure less torque being produced because some has already been siphoned off to rotate the now heavier rotating assembly.

When you introduce the variable of different engine designs, even if they result in similar displacements, the ability to noodle this out in our heads is all but non existent. Let me give you an example;

If I choose an engine with 340 gram wrist pins 970 gram pistons and comparably "heavy rods" most observers would say you are looking a a low speed truck engine. In fact they do measure up weight wise similarly. Performance (engine acceleration) is measurably different however. The engine I just described hits it's peak engine speed in literally microseconds after the hit of the throttle — Jerry I am certain already knows what I am talking about.

The reason for the rapid engine acceleration, even under load with this massive rotating assembly, is that the power produced dwarfs any parasitic drag in the engine. If you used this simple comparison, without seeing the actual engine or knowing its power output, you might be tempted to argue heavy rotating assemblies increase engine acceleration. Of course we all know they do not. BTW the engine with those massive rotating assembly components is a fuel motor.

Comparing big block and small block engine acceleration performance can be equally surprising and misleading. The problem is not just the effect of the increased rotational inertia one internal assembly over the other. Instead it is the differences in the intrinsic power production along with the shape of that power curve — one engine architecture vs the other because now we are looking at two different engine designs and implementations. These differences will consistently mislead you and cloud your ability to noodle out the answer in your head.

One thing however is for certain, all things being equal, two identical engines, one of which has a lighter rotating assembly, the engine with the lighter rotating assembly will always out accelerate the engine with the heavier rotating assembly — it is inescapable.


Ed

Wow, great explanation! You took the time and effort to nail it in great detail. I tend to throw out short descriptions because I just assume that everyone will get it. Unfortunately only "most" people get it. You took a lot of time and with a great deal of patience to explain this very very thoroughly. I wish I had as much patience as you. Good for you . . . you get the gold star!


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Unfortunately, it doesn't help those who only read into it what they want... ;)

I agree, eschaider, that was an excellent post, and your example about the heavy rotating assembly weight of a fuel motor more than adequately proves the point that there's more to it than a light rotating assembly, figure skaters, and physics books. Kudos.

Your point about the two identical engines, is also spot on. However, it's about impossible to get these guys to realize that there are big blocks that have lighter rotating assemblies, and not every small block will "out-rev" (in their terms) a big block.

Not sure why CobraEd and Al made this such a convoluted post, it's really quite simple to understand the underlying point. I think everyone here has got it except for those two.

Actually everyone here got it but you. That is why eschaider wrote this. to explain it to YOU. He is agreeing with us! :cool:




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ROFL, I don't think so Tim.

Dude, here's the recap.

*All small blocks won't out-accelerate all big-blocks. Why you're defending that is certainly beyond me.

*Big block rotating assemblies are not always heavier.

*Even when they are heavier, there are other factors that control acceleration.

That's as plainly as I can put it. I know your head is harder than a one piece fuel pump eccentric, but get rid of the ego and the pride and please try. Maybe there's a miscommunication error and we all agree with each other, but by your replies, I simply don't think so.

Jerry (BTW, he understands my viewpoint as well) and I have got to get back to building race engines. You and Al can get back to watching Brian Boitano.

Guess the tide is high enough, time to stop pissin

... to really sad :D

... to comically hilarious :LOL:

I trust you went to a reputable builder so make that 5 very smart, very experienced FE builders chiming in. So three said it absolutely did and two said it absolutely didn't. I'm also sure you weighed all that was said, and at the end of the day was convinced a shorter stroke makes for a better revving engine or you wouldn't have done it. You do realize in doing so, you are in fact trying to make your BB 427 FE more like a 427 SBF :)

Great post eschaider, glad emphasis was placed here ...
One thing however is for certain, all things being equal, two identical engines, one of which has a lighter rotating assembly, the engine with the lighter rotating assembly will always out accelerate the engine with the heavier rotating assembly — it is inescapable.


... some will never get it, or admit to getting it, too much vested on the wrong side of the coin.

I remember Keith C. was pretty opposed to the shorter stroke idea. IIRC, he went so far as to say it was "dumb" to run the shorter stroke crank (4.125") in an FE so that it would rev faster. That was in response to something that Barry R. had said supporting the notion. Neither one of them built my engine. I think you could line up as many smart FE builders as you want on either side of the issue. One thing I really like about my engine, that has nothing to do with its performance, is that, with it not in gear, I can tap the throttle at idle and, instead of it "revving up," it will just go "blam" and instantly be at four grand without having gone through 2k, 2.5k, 3k, 3.5k -- mucho funno to do.:cool: It doesn't rev, it explodes.

This was a pretty heated discussion with a lot of it pointed between Brent and me. After all is said and done it was not a subject that is normally discussed even among car guys and can be tough to present and tough to grasp. Having said that, I still hold to my compliments to Brent that I posted a few pages back. He has proven himself over and over on this forum to be not only a top notch engine builder, but also a good man of character and integrity. I still have very high respect for him in spite of the verbal dueling.

And a good time was had by all. ;)



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Poor Hercf16. New member with 9 posts with an innocent question about Roush/KC motors. I'm guessing it will be a while before he posts again. ;)