Has anyone ever................

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JBurch

JBurch

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Has anyone ever made a comparison of power loss due to main journal diameter? What were your test engines, and, at what point of development ( how much power were you trying to make )did you discover power loss, what was the power loss, at what rpm level?

I'm asking because in the Small block section a member asked the question; "what block to use?" He had choices between a 360 and a 340 and a respondent made the statement that the 340 had smaller main journals have less friction as a power robber. I read this statement often; is it significant?

I DO NOT DISPUTE THE FRICTION LOSSES DUE TO A LARGER MAIN JOURNAL! That is a given, that is a matter of Physics. WHEN DOES the difference in diameter COUNT?? AT WHAT RPM? WHEN WILL YOU AS A DRIVER FEEL IT?

I'd like to hear/read real applied science and engineering.

Thanks.
 
Too many other variables are present for a simple comparison.

Most mechanical engineering machine design texts have the info you'd need to estimate this.

That said, "seat of the pants" feel is also hard to quantify but would be more noticeable in a lighter car.
 
Actually I think it would be fairly easy to test the hypothesis build 2 engines of equal displacement with the only variable being the difference in main journal diameter. Could be done using a 340 and 360 block as a starting point.
 
JBurch said:
Actually I think it would be fairly easy to test the hypothesis build 2 engines of equal displacement with the only variable being the difference in main journal diameter. Could be done using a 340 and 360 block as a starting point.
Click to expand...

Good thought. Absolutely everything would have to be exactly the same for the test to be accurate.
 
JBurch said:
Has anyone ever made a comparison of power loss due to main journal diameter? What were your test engines, and, at what point of development ( how much power were you trying to make )did you discover power loss, what was the power loss, at what rpm level?

I'm asking because in the Small block section a member asked the question; "what block to use?" He had choices between a 360 and a 340 and a respondent made the statement that the 340 had smaller main journals have less friction as a power robber. I read this statement often; is it significant?

I DO NOT DISPUTE THE FRICTION LOSSES DUE TO A LARGER MAIN JOURNAL! That is a given, that is a matter of Physics. WHEN DOES the difference in diameter COUNT?? AT WHAT RPM? WHEN WILL YOU AS A DRIVER FEEL IT?

I'd like to hear/read real applied science and engineering.

Thanks.
Click to expand...

I agree with jos51700 too many variables.

David Vizard did a rod comparisons of rod lenght in a 383 Chev. 400 vs 5.7 vs 6 and 5.7 had about 3.5 hp increase and the 6 had about 7 hp increase over the 400 rod which ain't huge and we're talking way more friction loss than the bearing size.

I wonder if the extra support of oil per square inch of the 360 has any advantage ?
 
When it matters as related to RPM is strength and journal overlap with OEM crankshafts.

I'm not aware of data regarding bearing speed power gains.
 
I do recall reading about the small/large journal chevy 327's

and ford on the boss 302/351 clevlands and windsor 302/351's in a ford power book published by PETERSEN'S
 
Larger diameter can also support more load.

It may be worth the hit on drag for the extra load capacity and durability....
 
You are talking about a difference so small it doesn't matter in the real world. The crank rides on a film of oil anyway.
 
Put cranks in a 340 and a 360, see how much torque or hp it takes to spin to a specific RPM. Done. Probably not that much of a difference. Call Mythbusters, they can build any rig! lol
 
This would only apply to guys making enough HP to do 5-6 second runs at the slowest. Think John Force injected and blown 700cu in hemi that runs 235 in 1/4. the diff would probably equate to .003 sec in 1/4 times which to those guys is like 2-3 seconds to all of the 11-13 sec guys.

While some can probably tell the difference between an exactly built 340 vs 360, I doubt anybody could tell the difference between a 340 w 360 stroke vs a 360 bored .040 over, even dyno would have a hard time picking it up. I would be shocked if it was more than 1/2 hp on a 450 hp street engine.
 
273 said:
I agree with jos51700 too many variables.

David Vizard did a rod comparisons of rod lenght in a 383 Chev. 400 vs 5.7 vs 6 and 5.7 had about 3.5 hp increase and the 6 had about 7 hp increase over the 400 rod which ain't huge and we're talking way more friction loss than the bearing size.

I wonder if the extra support of oil per square inch of the 360 has any advantage ?
Click to expand...

That would not be relevant as they all have the same rod bearing diameter on GM crap. The engine made more power with a long rod because it has a better angle and thus less side load on cyl walls plus a few other principals of physics I dont care to explain here.

It also explains why a Mopar with a 6.123" rod will make more torque than gm with 5.7 rod ie blow the doors off it.
 
273 said:
I agree with jos51700 too many variables.

David Vizard did a rod comparisons of rod lenght in a 383 Chev. 400 vs 5.7 vs 6 and 5.7 had about 3.5 hp increase and the 6 had about 7 hp increase over the 400 rod which ain't huge and we're talking way more friction loss than the bearing size.

I wonder if the extra support of oil per square inch of the 360 has any advantage ?
Click to expand...


Not at all a good comparison; not to take anything away from Visard, a smart talented man but the engines are not EQUAL.
 
jazak5 said:
I do recall reading about the small/large journal chevy 327's

and ford on the boss 302/351 clevlands and windsor 302/351's in a ford power book published by PETERSEN'S
Click to expand...

Large and small journal 327's would be a very good test of the hypothesis but they are Chevies and we're talking Mopars.

The Fords don't make it as 302 and 351 deck heights make the tests impractical.
 
I guess I got to get better in text something always seems to get loss in translation lol

I know rod length isn't a direct comparison.
My point is the greatest friction loss is bore and ring.
And we know short rods add greatly to it and if there a minimum gain going from short to long rod I'm sure the bearing gain would be a small in comparison.
 
fratzog lover said:
Put cranks in a 340 and a 360, see how much torque or hp it takes to spin to a specific RPM. Done. Probably not that much of a difference. Call Mythbusters, they can build any rig! lol
Click to expand...

An interesting notion...........maybe get "Hot Rod" tv to do it, Dulitch is a Mopar guy.
 
273 said:
I guess I got to get better in text something always seems to get loss in translation lol

I know rod length isn't a direct comparison.
My point is the greatest friction loss is bore and ring.
And we know short rods add greatly to it and if there a minimum gain going from short to long rod I'm sure the bearing gain would be a small in comparison.
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We are not talking rod length,we are not talking piston, ring effects, we are talking main journal diameter.
 
You'll never feel it. It is an amount the dyno can show and show a small amount it will. For me, the amount is nothing. For racing, for the money, in a serious way, all out as in ALL OUT, it's worth the consideration.
 
JBurch said:
We are not talking rod length,we are not talking piston, ring effects, we are talking main journal diameter.
Click to expand...


I know we're talking about bearing friction and rod and bores have nothing to do with it.

But I also know ring to bore is the greatest point of friction for an engine and if the things we do there have minimum hp return I have a hard time seeing bearings offering anything near those gains. That's that point I'm trying to make .

As for why people bring it up cause when your comparing 340 vs 360 there's only two positives bearings and bore size and there miniscule and minor respectively pluses.
 
It would come down to "difference in friction". There's an "App" for that, well...not an app but a formula!!

The engineering of a bearing’s Babbitt lining is usually completed during the design of the machine. In selecting the proper type of Babbitt for a particular job there are a number of factors to take into consideration, the most important of which are as follows:
1.Surface speed of the shaft
2.Load that the bearing is required to carry

There is no doubt that if a bearing is to be highly loaded in relation to its size, a high tin alloy is desirable; whereas for much slower speed work and less heavily loaded bearings, a lead-Based Babbitt may be employed, and is far more economical.

1. Surface speed of the shaft: (The number of feet traveled per minute by the shaft circumferentially.)

Formula: (Pi x D x RPM) / 12 = S
Example: Determine the surface of a 2 inch diameter shaft going 1,400 revolutions per minute (RPM)
(Pi x D x RPM) / 12 = (3.1416 x 2 x 1,400) / 12 = 733.04 Ft/min

Where: Pi = 3.1416, D = Diameter of shaft, S = Surface speed of the shaft

2. Load bearing is required to carry: (the weight which is being exerted through the combined weights of the shaft and any other direct weights on the shaft and measured in pounds per square inch.)

Formula: W / (I.D x L.O.B.) = L
Example: Determine the load on a bearing of a 2 inch I.D bearing, 5 inches long and carrying a weight of 3,100 lbs
W / (I.D x L.O.B.) = 3,100 / (2 x 5) = 310 Lbs/sq.in

Where: W = Total weight carried by bearing, I.D = Inside diameter of bearing, L.O.B = Length of Bearing, L = Load bearing required to carry

You can actually calculate the amount of friction gained or lost simply by knowing the speed of the shaft, weight carried by the bearing,ID of the bearing, etc, etc.

I doubt you could measure it on a Dyno because threre are too many variables, it's like building two engines exactly alike, and I mean exactly!! The chances of them both having exactly the same horsepower is next to none, even though they were built the same!!

Treblig
 
rumblefish360 said:
You'll never feel it. It is an amount the dyno can show and show a small amount it will. For me, the amount is nothing. For racing, for the money, in a serious way, all out as in ALL OUT, it's worth the consideration.
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To be honest, I tend to agree with you.......it's a mute point in 99.9% of the time, yet it is a point that is brought up on occasion, and delivered as critical information to people who know little or nothing about their cars, as they seek information, advice, about what should they do as they work on their car.

Thing is though, still don't have any real numbers...........
 
JBurch said:
To be honest, I tend to agree with you.......it's a mute point in 99.9% of the time, yet it is a point that is brought up on occasion, and delivered as critical information to people who know little or nothing about their cars, as they seek information, advice, about what should they do as they work on their car.

Thing is though, still don't have any real numbers...........
Click to expand...

Its mostly brought up in my opinion because it falls into the old wifes tells category. And another thing to consider, is that a "narrow" rear main bearing can be installed in the 360, reducing a SMALL amount of bearing surface area. Its in the engine bible. ALSO, where the 360 has larger main journals, it has a SHORTER and LIGHTER piston than the 340, so that probally nullifies ANY bearing friction difference anyway.
 
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