crankshaft help

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bcuda452

bcuda452

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Ok guys, here the deal, i have always ran bigblocks, but now i have a 67 barracuda that im going to equipt with a small block, my good friend (and also my machinist), have given me a 340 block, that has a fresh 030 overbore, and a set of 340 x heads, (fresh rebuild),now heres the question, he states(my machinist-- which by the way is prone to chevys, and fords i think), anyway, he thinks that small block crankshafts ( 318,340 ) where externally balanced, and i told him i didnt think so, now i know from past experance, 360's were externally balanced, however, i believe that the other small blocks were internally balanced, now i have one other question, if im correct (which i may or maynot), 340 had steel cranks until 1972, is this correct? The reason i ask this is because i need a crankshaft, now this motor isnt going to be nuts, thats what my 68 is for, this is a daily driver (more or less), but i am going to be in the 350-400 hp, now do i really need a steel crank, or can i get by with cast? Any opinions will be appreciated, EXCEPT negative ones, keep those to yourself, please,


Thanks in advance guys,
 
You are right: 360's were externally balanced, the others were internally balanced. The 360 has a longer stroke than the 273, 318, 340 and the mains on a 360 are bigger than the others, too. If you want to make a stroker of the 340, you could get the mains on a 360 crank turned down to 340 size and use it. Otherwise, stroke and main size is the same on the other small blocks. The cranks were forged on some of the small blocks early on. 273's and 340's I know were, but not sure of the years. If you're keeping it below 500 HP, a cast crank will be good.
 
I'm not sure wen they went to cast but i know the early273 318&340s ones were internally balanced and the cast externally as far as a cast crank i have twisted them 7000 on dirt with a very expensive balancing and never had a problem with a crank.I'm sure you will here other sides of this but thats what i know about them.
 
BJR has a 349 stroker with a cast crank making close to 600 HP. You'll have nothing to worry about with 350-400.
 
sweet, i knew i came to the right people, now if anybody out there has a good cast crank lets talk, also something else just came to mind, someone told me that truck cranks are the hot ticket (special hardening) is this bs or are they on to something?
 
I THINK, but not sure, that certain year trucks had beafier cranks...beafier as in heavier, not necessarily harder. If so, the extra weight would rob power. Try to find a 273. People practically give them away. Up to '66 and maybe later, they had forged cranks.
 
you know iv herd the same thing with trucks motor homes and industrial use the same with marine .. And the man is right about the 360 crank in a 340 if i remember write comes out to a 372 and believe me its a screamer it take more than a 377 Chevy to run with it.and its not that excessive to build. have fun and MOPAR TO YA!!!!!!!!
 
Funny you should mention 273, i asked a couple of my mopar friends about that, and they say that even though the 273 had a steel crank (in most cases) the throws on the cranks cant take the harmonics and blow apart after piling on the hp, and my machinst said damn near the same thing... now im not saying this stuff, its the people i talk to.......thats why i getting advice from everybody!
 
If i use the 360 crank, can it be internally balanced? Or im i at the externally balanced situation again?
 
360 crank in a 340 (.020 over) is a 371. .030 is a 373.

Never heard that about 273 cranks. A lot of people who build high performance small blocks on a budget use them. I guess if you start throwing 800+ HP at them, they'll come apart.
 
They can be internally balanced. Costs about $85-$100 to get done. Maybe more if they have to add a lot of heavy metal.
 
bcuda452 said:
If i use the 360 crank, can it be internally balanced? Or im i at the externally balanced situation again?
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yes if you plan on turning this you should balance it and yes internally and it can be expensive. i was doing this 20yer ago been away from it a wil i dont know if they have another way of doing it know or not you need to get with i think its BJR racing he makes big power that lasts and knows all the new tricks and i here hes very reasonable with prices.
 
The steel crank 340's were internally balanced, when they went to the cast cranks they became an external balance deal with a special balancer and convertor. So to keep it simple you are probably better off with a steel crank and neutral balance balancer and convertor.
 
64physhy said:
360 crank in a 340 (.020 over) is a 371. .030 is a 373.

Never heard that about 273 cranks. A lot of people who build high performance small blocks on a budget use them. I guess if you start throwing 800+ HP at them, they'll come apart.
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ya i no your write about thos numbers the reson i call them 372s is we got pumped one night at hagerstown speedway here in md. and they called it a 372 and that just stuck so for sum reson i have always called it a 372 it just sounds better LOL... my mistake thanks
 
I'd just buy a used forged 340 crank. The cast crank 340s were externally balanced. That started in '72 but that year was mixed cast and forged. I always internally balance and the forged crank will do that cheaply. The cast crank you may be spending more if you want to internally balance it... depending on your piston choice. Any 273/318/340 forged crank will work fine, but the counterweights on the 273/318 are smaller than the 340 but if they are forged I think there's enough meat to get them balanced without adding Mallory. 350/400 hp is a stock lower end, performance valve job, and a camshaft in a 340. No need to get exotic.
 
Brian at Indio Motor has a cast crank 360 making around 565hp, car runs 10.50's with that engine.

Balancing a 360 crank internally will cost a bit more than a regular balance. By the time you're done, you would probably be better off just buying a fresh forged crank.

If you are looking for is less than 500 hp, no need to go crazy spending money on what I think is useless machine work. Run it externally balanced.

I agree with Moper, get a 340 forged crank and build it to that size. If you want more, spend $300 on a cast stroker crank.
 
nothing wrong with cast cranks. unless you plan on making over 600hp or spinning it past 7000rpm. bearing material is crutial with
a cast crank though. plus another built in benifit is that the cast crank is alot lighter then a forged one.
 
I'm with moper, just get a crank for a 340. From what I have heard and read on here and other places the small A's are the same main size and stroke but 273's and 318's used a lighter rod then a 340 and I've read that balancing the 273/318 cranks for the heavier duty 340 rods is a pain and expensive due to the metal that needs to be added. This is what I have read several places and is not based on personal experience, to me it seems like it's good in theory not in practice.
 
other then TA rods.. every 340 i've seen has the same rod #'s as 318 rods.

on a side note..
bcuda452, thats a wicked looking cuda you have. i'd dump mide ride in a heartbeat for a shot at one of those.
 
360Z28 said:
other then TA rods.. every 340 i've seen has the same rod #'s as 318 rods.

on a side note..
bcuda452, thats a wicked looking cuda you have. i'd dump mide ride in a heartbeat for a shot at one of those.
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t/a engines have standard 340 rods and crank...
 
When I broke my cast crank (prev. owner had installed a neutral balanced converter) I put a 318 truck crank in it. They are hardened and nitrated.
 
in my 340 that broke it used to be an old 340 steel crank.. ull identify it with smaller/narrower notch from the casting.. along the counter weights.. problem i had was that it had a small pilot hole for the converter.. i had to machine down the tap on the converter. next time i rebuilt the engine i replaced the crank with a std 318.. (didnt replace rods, damper) i was told that only the 360 was external balance.. its not true, only the old pre 72 340 was all internaly balanced. they had slightly heavyer rods.. this made my engine vibrate. had to reedo all the worke.. if u use a 318 crank, be sure to change damper and rods to :) .. later 1 rod broke and ihad to weld back the nr 2 skirt on the block... after that a valve broke off and mostly all of the old 340 block is broken.. but the cast 318 crank is still perfectly fine..

the 273 forged steel crank was replaced with a standard nodular cast iron crankshaft to save money. 1969.

here are some info on the subject http://www.allpar.com/mopar/318.html :cheers:
 
Thanks 360 z 28, The machinst that i speak of did the motor, to the tune of 630hp, 642ftlbs torque, all on pump gas, i did all the body work (3yrs), and as we speak, the finishing touches, its quite the pavement pounder......
 
I think i'll look for a truck crank, sounds like the hot ticket,,by the way anybody out there ever have the cranks cyro'd before, i hear that the cats meow, dont know how bout it guys whata think?
 
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