273 crank in 318 bennifts??

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Youngthrill

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so i have came across a few threads were people say they put a 273 crank into a 318.....but never really specified why...shorter stroke ???gain rpm or do you gain torque is my real question...:colors:
 
i believe ( and could be wrong wouldnt be the first or last time ) the early 273 cranks are forged. that would be the only reason i could think of. same stroke as the 318
 
The 273 crank is a forged crank and is a bolt in on a 318. These are a very good place to start on a 318 build and a high rpm Engine.
 
The 273 cranks are forged, but the main reason is weight. They are a good bit lighter than the 318 cranks. Much like the 273 rods.
 
The '64-7 273's have forged cranks.....the '68-9 273's used cast cranks. They will all swap into a 318 (or 340 for that matter) block but remember that the early 273 crank has a small register for the small snout converter those years so if you're running an automatic, you need to have a converter built or conversion parts to change to the later converter. A 318 could have either forged or cast cranks. I usually find the forged ones in trucks and manual transmission vehicles but that's not 100%. If they ran out of one or the other on the assembly line, any engine could have any crank. You should rebalance any time you swap a crank.
 
so one of the 273's i bought had a forged crank....next step im going to use that for my 318 build....is this converter thing going to be a big issue?? im useing the 904 i currently have..well im going to rebuild it..what sort of converter should i be looking for....or should i use the original 318 crank??
 
A cast crank can hold a lot of power without worry. Do you plan on going north of 500+ HP with the cast crank? Then go forged if so. Not that going forged to start is a bad thing.

The only thing I can think of with the 273 crank is IF there is a difference in the bolt holes at the rear of the crank. 6 evenly spread or off set holes? 4spd usage would have the need to look at the pilot hole for bushing use and depth for the manual tranny's input shaft.
 
StrokerScamp said:
The 273 cranks are forged, but the main reason is weight. They are a good bit lighter than the 318 cranks. Much like the 273 rods.
Click to expand...
Actually the 273 rod is a little bit heaver than the same bushed 340 rod...
I was surprised when I was balancing up Vic's 273 as to the weight of the big and small ends.

273rod.jpg
:coffee2:
 
Depending on the year of your 318,
The deference could be the pilot hole in the center of the crank for the converter. I an not sure of the year but the early small blocks have a much small pilot hole, than the later ones. I think all 273's are the smaller hole. Really narrows down converter selection. But I to have been thinking about using a foraged 273 crank on my next engine. I would think any machine shop could open the pilot hole up to the later size. At least that is my hope!
 
That is odd? I have quite a few sets of rods around hear. And the beams on the early rods are way smaller than the 340 rods. I have always been afraid to use them. Just look way to small to me. I just set them in the corner. LOL


Nice work on the rods. They are perdyyyyyyy


slickchick said:
Actually the 273 rod is a little bit heaver than the same bushed 340 rod...
I was surprised when I was balancing up Vic's 273 as to the weight of the big and small ends.

273rod.jpg
:coffee2:
Click to expand...
 
Part of the 340s success is its lighter rotating assembly. A forged steel crank can be used in a 318 or 340 if properly balanced.
As a general rule of thumb all engines painted Chry' industrial red have forged steel cranks. This isn't carved in stone though. Some orange and blue engines has forged steel cranks too.
As far as I know , every 273 ever built and all 1968 model 318s had forged steel cranks.
The only sure fire way of knowing which you have is go in and look.
A similar mystery exists in the bowtie world too. Does their 350 have 2 bolt main caps or 4 bolt main caps ? Only visual inspection will answer that question.
 
Youngthrill said:
so one of the 273's i bought had a forged crank....next step im going to use that for my 318 build....is this converter thing going to be a big issue?? im useing the 904 i currently have..well im going to rebuild it..what sort of converter should i be looking for....or should i use the original 318 crank??
Click to expand...
Check your 318 crank and see if it's a forged one. If it is, use it. If you're not running over 400HP I wouldn't worry about a cast crank. The converter might be an issue if you need a particular high stall one for racing as it will have to be made. Having the crank drilled might be a better option so you have many more converters to choose from. If you're running a manual trans, the only issue is the pilot bearing. You would have to have a bushing made for the crank if it's the automatic version and not finished. Every one I've seen is drilled deep enough but some just didn't get the final machining for the bushing. The crank bolt pattern is the same for all V8's (except hemi) as far as I can remember.
 
604 said:
Depending on the year of your 318,
The deference could be the pilot hole in the center of the crank for the converter. I an not sure of the year but the early small blocks have a much small pilot hole, than the later ones. I think all 273's are the smaller hole. Really narrows down converter selection. But I to have been thinking about using a foraged 273 crank on my next engine. I would think any machine shop could open the pilot hole up to the later size. At least that is my hope!
Click to expand...
Just the 273 and slant 6 had a small converter hole and only up through '67.
 
For the record forged cranks are HEAVIER than cast, that is why the cast crank 340's needed an external counterweight. The 340 also had the heaviest rotating mass of any small block, that's why cast crank 318's were neutral balanced. The weight difference was mostly in the pistons. 340 pistons were the largest diameter, and had the tallest compression height of any small block pistons, and also the heaviest.
 
I'm surprised none of the guru's here have touched on the key reason why one would use a 273 crankshaft over a 340 or 318 crank. The 273 crankshaft's are quite a bit lighter. The only downside is that they also have a smaller pilot hole for the converter's snout. Still, it's worth it to use a 273 crank as it's not a real problem to have a converter snout turned down to fit the 273 cranks pilot hole or... get the right converter the first time.

I remember the first time I used a 273 crank in a 340. The motor was assembled and on the running stand and had been broke in and I was ready to rock and roll! Race day was almost upon us and all's we were waiting on was the converter to arrive so we could mate the transmission to the motor and stab her in the car... to my dismay the converter's snout was too big! Luckily I give my machinist BJs every so often (not really), so he went ahead and turned the converter's snout down to fit the 273 pilot hole before the night was over.

Edit: Oops apparently RustyRatRod already touched on the weight difference.
 
318's had forged cranks until 72. No benefit to using one really. Sorry, I misspoke. I was thinking of 340 cranks.
 
Gotta agree with Mike. Unless your turning serious RPM's & racing.
But then again, there's no harm in its use. If ya got it, use it.
 
toolmanmike said:
318's had forged cranks until 72. No benefit to using one really.
Click to expand...
The '68-71 318's were mostly cast cranks too. Some truck and other industrial engines still used forged ones, even after '72, but not all. I mainly found them in manual trans applications. All the '67 and earlier small blocks had forged cranks. In swapping around small block internally balanced cranks between engine years and sizes, always check the converter hole diameter, pilot bushing hole if it's a manual trans application, and rebalance the recipricatiing assy as the bob weights are all different. Use the balancer that matches the year of your pulleys.
 
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