small block differences. someone want to fill me in please?

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rabius75

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ok, so,
318 is 3.91x3.31
340 is 4.04x3.31
360 is 4.00x3.58

could a 360 crank be run in a 318 if the main sizes were turned down? what about the connecting rods if this were possible, would they have to be 360 connecting rods? that would make it a 'stroked' 344 roughly?
3.91 x 3.58? that seems like a very easy budget stroker motor to me..
and if this motor were bored .040 over, it would make roughly 351 cubes? thats not bad for a 318 ;)
depending on the connecting rods, this could be accomplished with a 360 rebuild kit minus the pistons, and a trip to the machine shop.

and what about a 4" stroke crank? what size connecting rods would you use? could you just buy a 416 kit and use 318 pistons or what? 390ci (+.030) would be a nice conversion..
 
Rabius...I've kicked around this idea...and i've heard that you weaken the crank to turn it to a 318 size so...i figured...why couldn't you line bore the so many thousandths and Turn the crank and then you won't be weaking your main caps and y ou won't be weaking the crank...just something i thought of...but i think i'm gonna do it on a magnum 318 and run it in a dakota...
 
Mopar performance sell the 3.58" stroke crank for the 318, 340 bore size. They are aroun $400.

But No one makes an off the shelf piston ffor the 318 /3.58" stroke combo so you'll need custom pistons for around $600

Now the better choice. the mopar 4" stroke crank is cheaper then the 3.58" crank bu around $75 and Diamond sell pistons part # 50001 for flat tops and 50010 for dished. They are only $550ish.

So save your self $100 and gain 40 cubes.
 
rabius - You can put a 360 crank into a 318 (buy turning the mains down as you mentioned). All sb mopars use the same rod length and small and big end sizes, just the weight and strength vary.

The question would be is why? If you are budget minded, build up a 360, You already have a long stroke and a long rod. and would make more power than trying to fit this stuff in a 318 block.
 
Or use your block and go with the 4" stroker crank like I said.
 
With a 4" stroke, you HAVE to clearance the block for the connecting rods. From the pics I saw (can't remember where right now), using stock I-beam rods requires a lot more grinding on the block than the stronger after-market H-beam rods. To make matters worse on a 318 block, you are starting from a smaller bore.
 
Scotty has picture of how much he had to grind his bores down. Thats not realy a big deal though.
 
Okay, I remember this issue I was thinking about. If you look at Scotty's picture, the rod bolt goes up through the cap into the rod.
rodbolt.jpg


On a stock connecting rod the bolt goes the other direction. It is pressed into the rod pointing down, then the cap goes on and a nut holds it all together. So depending on the nut used, and the length of the bolts, you may have to clearance the block more. I still can't find that picture.
 
all 273s
all 318s, 71 and earlier (I think)
and all 340s mid 72 and earlier.
No 360s ever came with them.

A cast crank will live to around 500-550 horse power.
 
It will have a cast enless someone else put a forged in....
 
all 318s, 71 and earlier (I think)
Click to expand...

Wow!! My car might have a forged crank?!? It is a '71 model w/318, but it was actually built in October of '70. I was going to trash this 318 when I get the 360 built, but I guess I better open it up and see what's in there now. :scratch: Maybe I'll hang onto it for a future project.
 
hey man, if you decide to trash it, let me know. i need to check my engine out. im thikning its fixing to fall apart and may not be useable for a small build up.
the 318 from your car is probably a 230hp model, whereas mine is of the '150/170' line :(
 
rabius75 wrote:
the 318 from your car is probably a 230hp model, whereas mine is of the '150/170' line
Click to expand...
The actual hp didn't change. Just the way they measured and reported it changed.
 
Got Dart yes it may have a forged crank. Im not sure when the 318s started getting the cast crank.
I know 340s had forged threw most of 72.

Also all horse power ratings dropped in 72 becuase they lowered the compression.
 
My 72 340 has a cast shot peened crank. I think 71 was the last year for forged. Or early 72.
 
I think it was early or mid 72. My 340 is a 72 and has a forged crank.
 
AdamR said:
Also all horse power ratings dropped in 72 becuase they lowered the compression.
Click to expand...
Thank god i hav a 70 318 in my car i dont know how id live with a 150hp 318 :eye: :drunken:
 
well, i think it has to do a lot with the bullstuff emissions laws they were trying to appease. lowering compression and adding some screwey *** fuel pacer system, me, not having it. i pulled just about all of the crap off of my car yesterday and rearranged some stuff under the hood, moved my wiring harness off of the top of the motor and installed a mechanical 2" oil pressure guage, and you know what? it doesnt like, stutter (for lack of a better term) at higher rpms under acceleration like it was. but that may be because of me sealing the vaccuum ports on the carb instead of leaving the crappy dry rotted lines on it.
 
I was on the "I got a forged crank" train till my engine builder explained that cast is just as good, and, actually the cast being softer has more give as the engine rolls off the high end especially in a gear car.

I bought the MP 3.58 318/340. The builder said it really looks good. That crank in a 318 will net you around 350 cubes. A good size. Match that with a set of good light pistons and your on the road to a 340/360 killer. Not to mention all those blue ovals and bowties. :king:
 
i love the way my 318 just runs up the rpms. the short stroke lets it rev really fast, and i like that. and the stock cam must have some torque on the low end, because even with the 2.45 gears, it jumps from idle.
i guess thats why the 340 is so popular? revs fast but has a bigger bore for more power?
 
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