318 Connecting Rods and Crankshaft

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Grumpyoldman

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I wondered what was available, OTHER THAN THE STOCK MOPAR RODS, what was available. So I did a little searching, limiting the search to 6.123 c/c rods.
Found:
Molnar, H Beam
K1, H Beam
Howards, H Beam
Eagle, both I Beam and H Beam
Scat, both I Beam and H Beam

Did I miss any? Seems we are kind of limited in our choice for an aftermarket source.

Crankshaft choices seem to be even more limited, especially for a stock stroke crank. The only NEW, not reman, crank I found was made by Eagle.
However, after talking with several professional engine builders and receiving their cautions concerning crankshaft quality, I rejected that avenue.
I did not consider a reman crank for a variety of reasons.

I started this with a bare block, main caps, and a set of rebuilt stock iron heads I had laying around. No crank, rods, or pistons. Wanted to build a mildish 318 for a street driven Willys pickup project.

I have abandoned the search for a NEW 3.31 stroke crank. That leaves strokers and a choice of from 3.58, 3.79, 4.00, and 4.125.
In my personal humble opinion, the rod ratio on the 4.00 and 4.125 are to low and put too much side load on the cylinder walls and pistons. For a strip motor, probably just fine, but not for a daily use street motor I expect to last a long time.
So that leaves the 3.58 and 3.79 strokes. For me, I chose the 3.58 stroke for it's more favorable rod ratio, better bore ratio, and a more favorable pin height. Molnar makes this one. A bit pricey, but I can deal with that for a quality product. Using this crank leaves no choice but to use a custom piston since no one has an off the shelf piston for a 3.940 bore, 3.58 stroke, 6.123 rod. But pistons are a subject for later.

That left me on a search for connecting rods, since I do not have any. For this build an I Beam rod is more than capable. But I have no experience with either Scat or Eagle and they seem to be they only choice for an I Beam rod.

What connecting rods have you personally used or are using that have proven to be reliable and durable?

And before you ask:
Strictly street driven
5000 rpm maximum, 70 mph cruise approx 2500 rpm
either a 727 with a gear vendors OD or a 518 (have both buried around here somewhere)
Rear end is a old frankenstein quick change I saved from a dirt car 30 some years ago after I totaled it
318 block +0.030 (because I had it)
3.58 stroke forged crank
Lunati Voodoo Cam and kit (because I had it)
Very mildly ported iron heads (because I had them)
Weiand intake (because I had it)
Holley Street Demon (had to buy this one)

Appreciate any advice you have.
 
Reconditioned stock rods with new bolts are good to 6000+ and live forever. Your choice.
 
Just curious what's wrong with stock ones? Alot of time and money get spent trying to get the best of the best when the factory ones where just as good!
 
Also curious what are doing to get the 3.58 stoke crankshaft to work in the 318. You realize that they have different journals?
 
dartfreak75 said:
Also curious what are doing to get the 3.58 stoke crankshaft to work in the 318. You realize that they have different journals?
Click to expand...
360 stroke with 318 journals. It will give you a 343 with a standard bore 318 block. A .030 over 318 with a 4" stroke will get you a 390. A much better combination.
 
toolmanmike said:
360 stroke with 318 journals. It will give you a 343 with a standard bore 318 block.
Click to expand...
Can a 360 crank be turned down that far?
I'm gonna have to go do some math with stock rods and see where that puts the piston at I'd say you would have to have very short ch pistons to keep it on the block. But this sounds like a fun project I have a 318 block and a 360 cranks and a extra set of 675 rods. I know this has been been talked about before but I dont think iv ever seen anyone actually do it.
 
toolmanmike said:
They have done it for years.
Click to expand...
A 1.687 ch piston would put it at zero on the deck height.
Keith black makes a 1.658 that's about the closest I can find. The standard is like 1.720 IIRC
 
Last edited:
Grumpyoldman said:
I wondered what was available, OTHER THAN THE STOCK MOPAR RODS, what was available. So I did a little searching, limiting the search to 6.123 c/c rods.
Found:
Molnar, H Beam
K1, H Beam
Howards, H Beam
Eagle, both I Beam and H Beam
Scat, both I Beam and H Beam

Did I miss any? Seems we are kind of limited in our choice for an aftermarket source.

Crankshaft choices seem to be even more limited, especially for a stock stroke crank. The only NEW, not reman, crank I found was made by Eagle.
However, after talking with several professional engine builders and receiving their cautions concerning crankshaft quality, I rejected that avenue.
I did not consider a reman crank for a variety of reasons.

I started this with a bare block, main caps, and a set of rebuilt stock iron heads I had laying around. No crank, rods, or pistons. Wanted to build a mildish 318 for a street driven Willys pickup project.

I have abandoned the search for a NEW 3.31 stroke crank. That leaves strokers and a choice of from 3.58, 3.79, 4.00, and 4.125.
In my personal humble opinion, the rod ratio on the 4.00 and 4.125 are to low and put too much side load on the cylinder walls and pistons. For a strip motor, probably just fine, but not for a daily use street motor I expect to last a long time.
So that leaves the 3.58 and 3.79 strokes. For me, I chose the 3.58 stroke for it's more favorable rod ratio, better bore ratio, and a more favorable pin height. Molnar makes this one. A bit pricey, but I can deal with that for a quality product. Using this crank leaves no choice but to use a custom piston since no one has an off the shelf piston for a 3.940 bore, 3.58 stroke, 6.123 rod. But pistons are a subject for later.

That left me on a search for connecting rods, since I do not have any. For this build an I Beam rod is more than capable. But I have no experience with either Scat or Eagle and they seem to be they only choice for an I Beam rod.

What connecting rods have you personally used or are using that have proven to be reliable and durable?

And before you ask:
Strictly street driven
5000 rpm maximum, 70 mph cruise approx 2500 rpm
either a 727 with a gear vendors OD or a 518 (have both buried around here somewhere)
Rear end is a old frankenstein quick change I saved from a dirt car 30 some years ago after I totaled it
318 block +0.030 (because I had it)
3.58 stroke forged crank
Lunati Voodoo Cam and kit (because I had it)
Very mildly ported iron heads (because I had them)
Weiand intake (because I had it)
Holley Street Demon (had to buy this one)

Appreciate any advice you have.
Click to expand...

Scat Cast Crankshafts 9-340-3580-6123

Scat, molnar, K1, and others make inexpensive 318/340 main size cranks.
 
Grumpyoldman said:
I wondered what was available, OTHER THAN THE STOCK MOPAR RODS, what was available. So I did a little searching, limiting the search to 6.123 c/c rods.
Found:
Molnar, H Beam
K1, H Beam
Howards, H Beam
Eagle, both I Beam and H Beam
Scat, both I Beam and H Beam

Did I miss any? Seems we are kind of limited in our choice for an aftermarket source.

Crankshaft choices seem to be even more limited, especially for a stock stroke crank. The only NEW, not reman, crank I found was made by Eagle.
However, after talking with several professional engine builders and receiving their cautions concerning crankshaft quality, I rejected that avenue.
I did not consider a reman crank for a variety of reasons.

I started this with a bare block, main caps, and a set of rebuilt stock iron heads I had laying around. No crank, rods, or pistons. Wanted to build a mildish 318 for a street driven Willys pickup project.

I have abandoned the search for a NEW 3.31 stroke crank. That leaves strokers and a choice of from 3.58, 3.79, 4.00, and 4.125.
In my personal humble opinion, the rod ratio on the 4.00 and 4.125 are to low and put too much side load on the cylinder walls and pistons. For a strip motor, probably just fine, but not for a daily use street motor I expect to last a long time.
So that leaves the 3.58 and 3.79 strokes. For me, I chose the 3.58 stroke for it's more favorable rod ratio, better bore ratio, and a more favorable pin height. Molnar makes this one. A bit pricey, but I can deal with that for a quality product. Using this crank leaves no choice but to use a custom piston since no one has an off the shelf piston for a 3.940 bore, 3.58 stroke, 6.123 rod. But pistons are a subject for later.

That left me on a search for connecting rods, since I do not have any. For this build an I Beam rod is more than capable. But I have no experience with either Scat or Eagle and they seem to be they only choice for an I Beam rod.

What connecting rods have you personally used or are using that have proven to be reliable and durable?

And before you ask:
Strictly street driven
5000 rpm maximum, 70 mph cruise approx 2500 rpm
either a 727 with a gear vendors OD or a 518 (have both buried around here somewhere)
Rear end is a old frankenstein quick change I saved from a dirt car 30 some years ago after I totaled it
318 block +0.030 (because I had it)
3.58 stroke forged crank
Lunati Voodoo Cam and kit (because I had it)
Very mildly ported iron heads (because I had them)
Weiand intake (because I had it)
Holley Street Demon (had to buy this one)

Appreciate any advice you have.
Click to expand...


Let's talk about connecting rods first...

I like to have the oil squirt holes in the rods to help oil the cylinder walls... Many of the aftermarket rods do not have squirt holes... They claim that you don't need them, but I'm not going to be the guinea pig to do their testing for them...

I prefer to use the stock connecting rods and have new bolts installed and re-machine the bores as replacing the rod bolts may cause a mis- match in the crank bore for the rod which can cause excess wear and even lock up the crank from turning if the mis-match is too much.... You can get replacement rod bolts from Mancini Racing....

Second the crank...

You can just get the stock crank reconditioned... 318's had cast cranks and they will be enough for what you are going to do with your engine... However if you want a stronger crank, you can look into a forged crank... A stock 273 crank from 64 - 67 is forged and will bolt into a 318 with no modifications needed and they are balanced for the lighter 273/318 connecting rods... If you want a beefier crank, you can look into a stock 340 crank from 68 - 72, however they are balanced for the heavier/stronger 340/360 connecting rods and you may need to get it re-balanced if you use the stock 318 rods... You can always use the 340 or 360 connecting rods to keep the balance without having a machine shop re-balance it... The stock 340 rods are full floating, where the stock 360 rods are press fit...
 
krazykuda said:
Let's talk about connecting rods first...

I like to have the oil squirt holes in the rods to help oil the cylinder walls... Many of the aftermarket rods do not have squirt holes... They claim that you don't need them, but I'm not going to be the guinea pig to do their testing for them...

I prefer to use the stock connecting rods and have new bolts installed and re-machine the bores as replacing the rod bolts may cause a mis- match in the crank bore for the rod which can cause excess wear and even lock up the crank from turning if the mis-match is too much.... You can get replacement rod bolts from Mancini Racing....

Second the crank...

You can just get the stock crank reconditioned... 318's had cast cranks and they will be enough for what you are going to do with your engine... However if you want a stronger crank, you can look into a forged crank... A stock 273 crank from 64 - 67 is forged and will bolt into a 318 with no modifications needed and they are balanced for the lighter 273/318 connecting rods... If you want a beefier crank, you can look into a stock 340 crank from 68 - 72, however they are balanced for the heavier/stronger 340/360 connecting rods and you may need to get it re-balanced if you use the stock 318 rods... You can always use the 340 or 360 connecting rods to keep the balance without having a machine shop re-balance it... The stock 340 rods are full floating, where the stock 360 rods are press fit...
Click to expand...
I had this exact same conversation with my machinist when we was talking about my rods. He said he wants to see the squirt holes he told me that small block mopar stock rods are some of the best ones for street engines of course. He does not like eagles at all.
 
toolmanmike said:
360 stroke with 318 journals. It will give you a 343 with a standard bore 318 block. A .030 over 318 with a 4" stroke will get you a 390. A much better combination.
Click to expand...
Once again in my humble opinion, the rod ratio with a 4 inch stroke is is too low, 1.53075, for a daily driver. The 4 inch stroker makes a very nice combination for a strip and occasional street motor. I just do not care for the higher cylinder wall and piston skirt side loading with a rod ratio o 1.53.
 
dartfreak75 said:
Can a 360 crank be turned down that far?
I'm gonna have to go do some math with stock rods and see where that puts the piston at I'd say you would have to have very short ch pistons to keep it on the block. But this sounds like a fun project I have a 318 block and a 360 cranks and a extra set of 675 rods. I know this has been been talked about before but I dont think iv ever seen anyone actually do it.
Click to expand...
Not starting with a 360 crank. Crank is a forges Molnar product designed and manufactured for my application. With 6.123 rods, a custom piston is required because no piston manufacturer has a piston "on the shelf". This is not a is a problem, just more expensive than a "on the shelf" piston". Cost is one of the reasons, the 4 inch stroker kits are so popular.
 
dartfreak75 said:
A 1.687 ch piston would put it at zero on the deck height.
Keith black makes a 1.658 that's about the closest I can find. The standard is like 1.720 IIRC
Click to expand...
Yes, a 1.687 pin height is zero deck.
I'll have to check with KB. Obviously, I missed that one when I was going through the catalog. I did call and received a response that they did not have anything that would work and were not interested in making a custom.
 
Grumpyoldman said:
Yes, a 1.687 pin height is zero deck.
I'll have to check with KB. Obviously, I missed that one when I was going through the catalog. I did call and received a response that they did not have anything that would work and were not interested in making a custom.
Click to expand...
I will send you a link! It's a cast kb silvolite flattop piston.
 
Those pistons with a standard blue felpro headgasket and 70cc heads will give you around 9.2 scr. Not shabby for a street car
 
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