forged crankshaft

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Confusedcuda

Confusedcuda

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anyone know what the weights are for 318 273 340 cranks cast and forged. Thanks
 
And that very same post we compared, 340 to a 318 both forged
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Okay Thanks guys, thank you mike. Got another question for you. Can you use a 273 forged crank in building a 340 motor? If you use the 273 rods, and use the KB Hypere pistons which are quite a bit lighter than stock 340 pistons. I understand that it will all need to be balanced, but mainly want to avoid adding metal to crank for balance, seems removing metal way cheaper thanks.
 
Confusedcuda said:
Okay Thanks guys, thank you mike. Got another question for you. Can you use a 273 forged crank in building a 340 motor? If you use the 273 rods, and use the KB Hypere pistons which are quite a bit lighter than stock 340 pistons. I understand that it will all need to be balanced, but mainly want to avoid adding metal to crank for balance, seems removing metal way cheaper thanks.
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Should be able to. The 273/318 rods are the same dimension just not as beefy. The 273 crank probably has a smaller converter register if you are running a automatic. Check with your machine shop to be sure. Taking weight away is pretty easy. Adding weight is quite expensive.
 
If I go this route, I'm going to use my 904 that's all ready in my 68 vert cuda. I did this before in my 67 that's in my avatar to the left. I t had a 273 and the crank hookes right up. I had to get a new converter, because the car at idle wanted to pull me through the stop lights. Thanks, again any other info is appreciated.
 
You should be able to achieve what you want with a bit of margin. What piston oversize do you plan?

We used a 273 cast crank in my son's 340. Added SCAT rods and KB's. Bobweight was 1893 grams for .020" oversize pistons, compared to the nominal stock 340 bobweight of around 2308 grams. Took 81-28 grams off of each end's large counterweight to balance the 273 crank.

With the light SBM rods you ought to end up a bit over 2100 grams of bobweight, depending on piston oversize. Nominal bobweight on 273's is right around 2117 grams, so you ought to end up just under that. It won't take much metal removal to make that balance out.

If you used the heavy SBM rods, you would end up about 45 grams heavy on the bobweight for the 273 crank.
 
Thanks nm9, I have a 67 273 that has just under 11000 miles on it that ran great. I was thinking of using it's forged crank and even the 273 rods in a 340 block. Not building a fire breathing dragon, but a nice running zippy 340. probably using the KB's .30 over think there the kb 167 thanks for info.
 
KB243 for the 340 IIRC. (The KB167 is for the 318.)

.030 over KB243's and the ligher SBM rods are gonna be REAL close to the standard 273 bobweight. It'll all depend on the exact parts and how they weigh in; the KB's can be a bit lighter than published, and the rods can be lighter or heavier. And the crank itself can be under or over target bobweight.

If you end up with the pistons/rods being a bit heavy and the crank a bit light (where weight added to the crank would be one solution), other solutions to consider are:
  • Taking weight off the rods, pistons or pins
  • Drilling holes in the ends of the 1-2 and 7-8 journals like the 340 were done
  • Putting in a set of lighter piston pins
So if it comes to it, those are some options to explore with the local machinist.
 
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