Crank Journal Size: Mopar Versus Chevy

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YO7_A66

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If you are selecting a crank/rod combo (340), and both the Mopar and the Chevy journal size is available, which do you choose and why?
I understand getting the matched set, but why one over the other?
Weight of the different size journals versus the intended rpm?

Thanks!
 
The smaller diameter journal/rod has less rotating/reciprocating inertia. 65'
 
I would choose the chevy. (My opinion is based on big block mopars however). Much better selection of rod lengths, weights, and quality. Lighter piston pins (dramatically so bbc compared to bbm), more room for stroke In the bottom of the cylinder case (smaller rod big end outer diameter), less grinding on the bottom of the cylinder for rod clearance.
 
33IMP said:
I would choose the chevy. (My opinion is based on big block mopars however). Much better selection of rod lengths, weights, and quality. Lighter piston pins (dramatically so bbc compared to bbm), more room for stroke In the bottom of the cylinder case (smaller rod big end outer diameter), less grinding on the bottom of the cylinder for rod clearance.
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^^All of the above^^ It applies to small blocks too.
 
the crank has to be made wider on rod journals , for chev rods , we built a 273 with eagle chev rods, distance is .100 from mopar to chev. just food for thought!
 
Plymouth 65 said:
The smaller diameter journal/rod has less rotating/reciprocating inertia. 65'
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I think that end is splittin hairs. I think the Chevy decision is more toward the budget end of it.
 
Not worth the hassle unless you are racing. Mopar stuff is fine for most general high performance, and is better than stock Chevy stuff.
 
66fs said:
Not worth the hassle unless you are racing. Mopar stuff is fine for most general high performance, and is better than stock Chevy stuff.
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That's kinda the direction I was goin.
 
It appears both would work fine on my application, as I am only looking at 62-6400rpms max. But if the Chevy journals are in stock, I may sway that direction to keep the rotating mass down on this numbers matching block.



Thank you everyone for the replies.
 
YO7_A66 said:
It appears both would work fine on my application, as I am only looking at 62-6400rpms max. But if the Chevy journals are in stock, I may sway that direction to keep the rotating mass down on this numbers matching block.



Thank you everyone for the replies.
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Are you looking at stroker cranks or stock stroke?
 
66fs said:
I know. Everybody wants to make things harder and more expensive than it needs to be.
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To me, it's a wash. You buy the cheap(er) Chevy rods, but then have to have the journals modded to fit. Where's the savings? The weight and smaller bearing surface thing I just bet is a minuscule advantage, if even measurable. It all came about when one of the magazines did it, published it and it was accepted as gospel. Chrysler engineers knew what they were doing making crank journals and rods the size they did. That's one big reason in my mind why Chrysler engines are more heavy duty than other makes. The .903 lifter, the large by huge connecting rods, the bigger journals on the crankshafts. You start taking all that away and you don't have a Chrysler engine anymore, you have something inferior.
 
If he's buying a stroker kit with Chevy rods, I would certainly expect the crank journals to be the proper width for the Chevy rods.
Where you run into rod side clearance concerns is putting Chevy rods on cut down Mopar cranks. Aftermarket stroker cranks with Chevy journals are Chevy width.
I still stick with my recommendation for the reasons I gave, above.
Sorry, I'll take strong light internals over needlessly heavy stuff, every time.
(Well, maybe not in a diesel, lol)
 
33IMP said:
If he's buying a stroker kit with Chevy rods, I would certainly expect the crank journals to be the proper width for the Chevy rods.
Where you run into rod side clearance concerns is putting Chevy rods on cut down Mopar cranks. Aftermarket stroker cranks with Chevy journals are Chevy width.
I still stick with my recommendation for the reasons I gave, above.
Sorry, I'll take strong light internals over needlessly heavy stuff, every time.
(Well, maybe not in a diesel, lol)
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Well yeah, if it's part of a stroker kit and you're in a position where weight really counts I can see it. But not every street car needs that chit.
 
When I bought my R3 block and assembly the stroker kit consisted of an Eagle Mopar sized crank, rods, and pistons. Five years later I sold my crank and rods and upgraded to Molnar crank and rods. I was stuck again with Mopar sizing because I wanted to reuse my old 4.100 pistons. After a 13 month wait I just got my Mopar sized rods. I could have had a set of Chevy sized rods 13 months ago.
 
I just got off of the Molnar web page:

4.00” stroke w/Chevy 2.100” rod pins

4.00” stroke w/Standard Mopar sb 2.125” rod pins

Both in stock and both at the same price and I will buy the rods as a matched set, and they are in stock too.

This is what started my question as to which one and why.


Thanks again!
 
Yep their rods just came in and were finished. I hear another boatload is off the coast but I wouldn’t drag my feet too long. It takes Molnar three weeks to finish the rods when they get them.
 
YO7_A66 said:
I just got off of the Molnar web page:

4.00” stroke w/Chevy 2.100” rod pins

4.00” stroke w/Standard Mopar sb 2.125” rod pins

Both in stock and both at the same price and I will buy the rods as a matched set, and they are in stock too.

This is what started my question as to which one and why.


Thanks again!
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You buy the Chevy sized stuff because you can buy any bearing you want.

Chrysler used those big assed bearings because of Walter P.’s time at GM. I think he was in charge of Buick and they used those big bearings. Look at a Buick and a Chrysler and you can see they are cousins.

There is no reason to buy Chrysler sized stuff when you are doing what you are doing.

When I do my next engines it’s getting chevy rod throws and any decent crank grinder can widen the journal and not jack it up.

If you go back to the Pro Stock Truck days and Comp Eliminator today (ASScar too) you‘ll see they are using 2.00 chevy sized throws and I think IIRC 302 Ford mains. Most are running a 1.88 rod throw (Honda) because it makes the bearing lighter, the big end of the rod lighter and you can make the crank lighter.

Do the chevy sizes. No reason.
 
RustyRatRod said:
To me, it's a wash. You buy the cheap(er) Chevy rods, but then have to have the journals modded to fit. Where's the savings? The weight and smaller bearing surface thing I just bet is a minuscule advantage, if even measurable. It all came about when one of the magazines did it, published it and it was accepted as gospel. Chrysler engineers knew what they were doing making crank journals and rods the size they did. That's one big reason in my mind why Chrysler engines are more heavy duty than other makes. The .903 lifter, the large by huge connecting rods, the bigger journals on the crankshafts. You start taking all that away and you don't have a Chrysler engine anymore, you have something inferior.
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Nope, the cranks are ground for the Chevy sized rods, diameter and width.
 
justinp61 said:
Nope, the cranks are ground for the Chevy sized rods, diameter and width.
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Yeah, I realize that. That's part of my whole argument. That's a lot of machine work to pay for, unless you go with something off the shelf.
 
RustyRatRod said:
Yeah, I realize that. That's part of my whole argument. That's a lot of machine work to pay for, unless you go with something off the shelf.
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Where have you seen Mopar sized journals cranks cheaper than Chevy sized? When I bought my 4.00” crank they were the same price. I don’t recall the small block 4.125 or 4.250” cranks being available with Mopar sized rod journals.
 
justinp61 said:
Where have you seen Mopar sized journals cranks cheaper than Chevy sized? When I bought my 4.00” crank they were the same price. I don’t recall the small block 4.125 or 4.250” cranks being available with Mopar sized rod journals.
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I have not. That's my argument is that they're not cheaper. Evidently, Chevy rods and bearings are cheaper.
 
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