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Engine Masters 54 did a comparison on a BBC with Rod lengths of 6.135" vs 6.800" with custom Pistons to achieve the same Compression Ratio using the same Cam. Long Rod made slightly more Torque under 5K, but the Short Rod mode more peak HP by almost 11HP.. Not exactly a game changer..

I'd find it hard to compare a Rod length between a 331 and a 347 where the difference is only .150".

View attachment 1062063
99% of 331, 347, 363 all use the same 5.400 rod length
 

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Soooooooo wouldn't this whole schmata more be about bore x stroke ratio than stroke x rod length ratio? I do unnerstand that rod angularity came into it somewhere but I think unless it becomes extreme that was disproven unless it comes into longetivity. Sorta like why all the long haul trucks (well majority of) use an inline 6 engine.. hardly any rod angularity in any inline 6 or inline 4 cyl engine (not that long haul truck use 4 cyl engines any more, just for reference) and they have great lifespans.. Just my $0.02 and thoughts.. Cheers!!
 

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Soooooooo wouldn't this whole schmata more be about bore x stroke ratio than stroke x rod length ratio? I do unnerstand that rod angularity came into it somewhere but I think unless it becomes extreme that was disproven unless it comes into longetivity. Sorta like why all the long haul trucks (well majority of) use an inline 6 engine.. hardly any rod angularity in any inline 6 or inline 4 cyl engine (not that long haul truck use 4 cyl engines any more, just for reference) and they have great lifespans.. Just my $0.02 and thoughts.. Cheers!!
Bore size sets valve sizes. From there, stroke sets how much cylinder volume that the valve sizes (more properly their curtain areas) have to feed and exhaust.

It's all kind of tied together, given that you have to fit half the stroke length plus rod length plus piston compression height plus any piston to deck into the deck height. So when you start with a basic block and an existing combination of stroke, rod length, and piston and increase the stroke, one or both of the others have to give up a little. Or, of course, you start all over with a different block.

Bigger bores also tend to provide more room laterally for crank throws (so you don't end up having to grind the pan rails for rod/rod bolt clearance), so there's probably some preferable range for all these things to fall within, without there necessarily being any specific optimum rod:stroke or bore:stroke ratios.

FWIW, rod angularity is more of a matter involving long-term durability - think piston to cylinder wall loading - and that's where I was going with that. A typical OTR truck engine that might have something like a 6" stroke and 12" long rods tends to support this notion (2:1 rod:stroke, vs less than 1.5:1 for a 400 SBC with 5.565" rods and 3.75" stroke. Though the redline for a 14+ liter diesel being way lower than the 5000 - 5500 for the 400 SBC likely has something to do with it as well.


Norm
 
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Good answer Norm!! I like the way you broke that down and explained it!! That's what I was looking for!! I remember when I used to drive one of the big off road caterpillar trucks with a 3500 series engine it had I think it was a 1200 or 1800 rpm redline and the V8,v12 and v16's even had a 60 deg v to em I'm assuming in those to cut down on the rod angularity..
 

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Soooooooo wouldn't this whole schmata more be about bore x stroke ratio than stroke x rod length ratio? I do unnerstand that rod angularity came into it somewhere but I think unless it becomes extreme that was disproven unless it comes into longetivity. Sorta like why all the long haul trucks (well majority of) use an inline 6 engine.. hardly any rod angularity in any inline 6 or inline 4 cyl engine (not that long haul truck use 4 cyl engines any more, just for reference) and they have great lifespans.. Just my $0.02 and thoughts.. Cheers!!

Why not...one piece of dryer fluff is pretty much the same as the next.....
 

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Good answer Norm!! I like the way you broke that down and explained it!! That's what I was looking for!! I remember when I used to drive one of the big off road caterpillar trucks with a 3500 series engine it had I think it was a 1200 or 1800 rpm redline and the V8,v12 and v16's even had a 60 deg v to em I'm assuming in those to cut down on the rod angularity.
Rod angularity goes to piston side thrust and ultimately cylinder bore wear. Inclining the cylinders would add a relatively small gravitational component to that, though that should be negligible by comparison. FWIW, side thrust is not equal on both sides of the piston (sides, as you look along the crankshaft axis), so it'd be no surprise to see an old V8 block with a lot of miles on it where one bank shows higher wear on its valley-side and the other bank shows the higher wear on the side opposite the valley.

That 3500-series 60° bank angle was really only "naturally correct" for the V12. Any other cylinder count would require either uneven cylinder firing or crankshafts with some journals offset from the others. "Naturally correct" for a 4-stroke V-type engine would be 720° divided by the number of cylinders. You can make other bank angles work, but some compromises are required.

Which in addition to those Cat engines, we've seen in automobile engines with GMC's 90° 231/3.8 engines, which used a 90° bank angle rather than the 60° arrangement (it was originally developed from one of the 90° V8 engines of the time). Early engines with the non-offset crank were odd-fire, and the later even-fire version used the offset crank approach. I have no idea which approach Cat took.

I can only guess that Cat hung the whole 3500 series design on 60° in order to be able to run all three engines down the same production line. It's not like they were going to be building millions of each every year, and could justify three sets of tooling. 60° is in the middle of a V8's 90° and a V16's 45° preferred bank angles, which would make sense once you've decided you're only going to run a single set of tooling. Plus, all three engines would be of the same width and height, differing only in length.


Norm
 

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It sounds like a lot of people would bash the Subaru flat fours and sixes, because the cylinders would wear unevenly. Those concepts are insignificant to actual real world wear, immeasurable without 200k miles and 20 years of time with the engines intact the entire time.

There are no examples of that, so as said by someone before, so what? It's a waste of time to discuss the wear differences of a 347 versus a 332.

BTW, has any one bothered to do the math on a 33"1" engine, it is not a 331. It has always been 332 cubic inches. Why do people accept and spread bad information? I accept the 351W and 351C as named, but I learned in the 70's they are 352ci in size, Ford wanted a different name than the 352FE engine. I buy that, but not the 331, that does not make any sense to misname the combination. 332 sound just as good, and it's accurate, while 331 is not.
 

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It sounds like a lot of people would bash the Subaru flat fours and sixes, because the cylinders would wear unevenly. Those concepts are insignificant to actual real world wear, immeasurable without 200k miles and 20 years of time with the engines intact the entire time.
Like I suggested above, the contribution of piston and rod little end weight is a minor contribution compared to piston compression forces acting against rod angularity. Safe to ignore the weight part of it.


BTW, has any one bothered to do the math on a 33"1" engine, it is not a 331. It has always been 332 cubic inches. Why do people accept and spread bad information? I accept the 351W and 351C as named, but I learned in the 70's they are 352ci in size, Ford wanted a different name than the 352FE engine. I buy that, but not the 331, that does not make any sense to misname the combination. 332 sound just as good, and it's accurate, while 331 is not.
Did you know that Ford also had an FE-series engine of 332 CID (4" bore x 3.300" stroke, for 331.75 CID)? So 331 for the 0.030-over x 3.25" Windsor stroker (331.64 CID) should be just as acceptable as the 351W and 351C are vs the "real 352" FE (all three at 351.86). FWIW, the "331" is actually a little bit better on things like bore:stroke and potential valve shrouding than the "real 332". Not as good with respect to rod:stroke. Much better than the FE in terms of overall engine weight.


Norm
 

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Like I suggested above, the contribution of piston and rod little end weight is a minor contribution compared to piston compression forces acting against rod angularity. Safe to ignore the weight part of it.



Did you know that Ford also had an FE-series engine of 332 CID (4" bore x 3.300" stroke, for 331.75 CID)? So 331 for the 0.030-over x 3.25" Windsor stroker (331.64 CID) should be just as acceptable as the 351W and 351C are vs the "real 352" FE. FWIW, the "331" is actually a little bit better on things like bore:stroke and potential valve shrouding than the "real 332".


Norm
Yeah I know about the 332FE engine also. I simply don't like inaccuracies, especially for political reasons. Nobody would ever confuse the 332 stroked 302 with a 332FE engine, except possibly idiots, and I don't make decisions to attempt to satisfy idiots.
 

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Why not...one piece of dryer fluff is pretty much the same as the next.....
You're building the most you can get out of a given block, probably because a couple, maybe a few tenths difference in the quarter mile means that much to you. And that's fine. Just that I'd always build an engine with fewer compromises - or at least different ones - because ET's aren't all that important to me.


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Yeah I know about the 332FE engine also. I simply don't like inaccuracies, especially for political reasons. Nobody would ever confuse the 332 stroked 302 with a 332FE engine, except possibly idiots, and I don't make decisions to attempt to satisfy idiots.
Afraid I'm not following how the 351's being about 0.8 CID understated for clarity against one FE engine can be OK but the 331 being 0.64 CID understated for the same reason against another FE engine is not.


Norm
 

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It sounds like a lot of people would bash the Subaru flat fours and sixes, because the cylinders would wear unevenly.
Naw, I bash the flat four and flat six because they sound like ass......
 
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Naw, I bash the flat four and flat six because they sound like ass......
In a Subaru that's the muffler I think, I've only heard stock cars. I worked at a dealer from 85-88, I heard a few without the exhaust connected. Those sounded like ass for sure, nothing like an open header Cleveland.

I watched them build those little 1.6's on a steel work bench lots of times. They did an engine job in one day, about nine hours, and got paid 24 for it. They used a hoist to R&R the engine, but they'd lift one from one bench to another if they needed to, usually two guys. With the head off they moved them around easily, those were small engines.
 

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Norm,
I've seen a 3508 apart and I believe that it had a splayed crankshaft if I remember right, been years ago, which blew my mind on an engine of this size. The 3516 is essentially a 3508 with 2x the number of cylinders and the whole danm beast stands over 6 feet tall when built, oil pan to rocker box covers. One of the reasons they went with a 60 deg v other than the 3512 was the more popular of the series and used for standby generators and remote powerplants was it had to fit between the rails of the heavy equipment they were selling. As huge as these beasties are at a 90 deg V they wouldn't fit. (I did have to look this part up cause I forgot) These things have a bore of about 6.7 in and a stroke of about 7.5 inches. So you get what kind of dimensions I'm talking about.. Anyhoooo.... This is all moot and just "laundry fluff" as it was part of an example I haphazardly threw out about something else not germaine to the discussion at hand... /me goes off to sit on the bench and let's the adults talk now...
 

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... One of the reasons they went with a 60 deg v other than the 3512 was the more popular of the series and used for standby generators and remote powerplants was it had to fit between the rails of the heavy equipment they were selling. As huge as these beasties are at a 90 deg V they wouldn't fit. (I did have to look this part up cause I forgot) These things have a bore of about 6.7 in and a stroke of about 7.5 inches. So you get what kind of dimensions I'm talking about..
I get it, and it was worth it for the tangential information. FWIW, my son just had the Cummins engine in his Kenworth replaced a couple of years ago. The original engine went over a million miles, a bit more than half of it his.


Norm
 
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You're building the most you can get out of a given block, probably because a couple, maybe a few tenths difference in the quarter mile means that much to you. And that's fine. Just that I'd always build an engine with fewer compromises - or at least different ones - because ET's aren't all that important to me.


Norm
Norm...you don't have much of an idea what you're doing, try not to speak for me.

Your choices are just fine, it's your "facts" that are in error.
 

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...i think i would just go with what Mark said, i mean, come on, he's been at this game since Wizard of Oz came out in black & white on the Pik-to-Tron console TV so, ya...
 

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Late to the party but ....

Rod ratio is so 1950...

When Mark was in his prime. ;)
 
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