How high can ya rev it?

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Hyperballsmcgee

Hyperballsmcgee

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at some point in time a '73 340 was stuffed in my scamp, before it was put in the car it had an Eddy intake carb put on it, as well as other small things like a hotter coil, and a cam which I (sadly) don't know the specs of. I don't know if they put in the forged crank or anything like that when it was built, so based on stock specs for a 73 340 what would be a good place to consider redline? I ask this cause I plan on putting a tach in the car, in my opinion it's kind of scary to not know your exact rpms. I'm one of those who likes to know what's going on in there
 
An easy way to check for a likely cast crank is to look at the front dampner for a offset weight. 6k on a stock bottom end is no problem.
 
340 ? About 500 before it stops pulling. should be at about 6000. Factory red line is 5500. Depending on where the ring ridge is you wouldn't want to take it higher then its been through its life. Chances of braking a piston ring land is pretty good if you exceed where its been.
 

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Till it blows up :twisted:
5500-6000 Rpms would be the highest I'd take your motor.
 
probably valve springs and hydraulic lifters are going to restrict your rpms...
 
5800-6000 is about all I'd spin a stock bottom end w a cast crank, providing your cam and valve springs allow
 
Power range for the stock 340 cam is idle to 5800.
 
Stock valve springs with hydraulic cams begin to float around 6000. If yours was a '73 340 it came stock with a cast crank. With stock valve train I would limit a motor like this to under 6k or you can start breaking piston skirts and, as was mentioned, rings.
 
rap it until it sounds sick, 500 below that. nothing like the sound of a motor, when its at its limit.
 
My rev limiter is set at 6,500 in my 340 but it pulls hard till it kicks in at 6,500, some say I could go a little higher but I am nervous, even though the engine is not that old and I have it built good with a steel crank :glasses7:
 
A fully blue printed one,with 4:88 's out back/4800 stall. 7800 shift point,stock parts EXTREMELY MASSAGED. Tell us what, you have in mind.... So far,we have no clue.
 
Hyperballsmcgee said:
what would indicate a forged crank?
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Forged cranks are internally balanced and used a standard damper out front. The cast cranks used an externally balanced damper and are marked "FOR USE WITH CAST CRANK ONLY" on the front. Unless somebody installed a forged crank (not likely....$$$$) yours left the factory with a cast crank. Not necessarily a bad thing for a street motor...they will stand up fine to everyday use.
 
Without any porting, the heads usually are good for 5500 rpm. Old school wisdom on hydraulic lifters said they were good for about 6000 rpm. Anything past that I'd say you're on your own.

Of course, if you're a wild and crazy guy, you can rev it till it blows. That will ultimately answer your question, but you won't be able to reproduce it any time soon afterwards.
 
Captainkirk said:
Forged cranks are internally balanced and used a standard damper out front. The cast cranks used an externally balanced damper and are marked "FOR USE WITH CAST CRANK ONLY" on the front. Unless somebody installed a forged crank (not likely....$$$$) yours left the factory with a cast crank. Not necessarily a bad thing for a street motor...they will stand up fine to everyday use.
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Actually, there are several engines that are externally balanced with steel cranks, including the 440 Six Pack. It all depends on how much weight is in the reciprocating assembly. Big block chebbies have steel crank versions that are externally balanced. Most all makes do.
 
RustyRatRod said:
Actually, there are several engines that are externally balanced with steel cranks, including the 440 Six Pack. It all depends on how much weight is in the reciprocating assembly. Big block chebbies have steel crank versions that are externally balanced. Most all makes do.
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You are, as usual, correct. But the OP was talking about a '73 340, which I believe only came factory installed with a cast crank. If somebody shoehorned a forged crank in that motor, they would have needed to change the damper. OP's question was how to ID his crank to tell if it was cast or forged. This is the only way I know of.
 
Actually, the 73 340 crank was cast, but it was also shot peened. Shot peening means that the crank is bombarded with steel shot before the final machine work is done. The process makes the crank stronger, though not as strong or heavy as a forged crank. I'm not aware of any other Mopar crank that was shotpeened.

Generally a small block forged crank has large flash marks running across the top of the counterweights. The cast cranks usually have a narrower flash mark.

The 73 crank is the only 340 that is externally balanced. This crank is designed to be used with the heavy duty rods. Although the 360 is also externally balanced, the dampers and flywheels or torque converters are not interchangeable.
 
2 Darts said:
Generally a small block forged crank has large flash marks running across the top of the counterweights. The cast cranks usually have a narrower flash mark.
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The forged crank I pulled out of my '69 340 motor to use in my build had flash, sharp 'knife edges' and other really bad eyesores all over it. I removed enough metal making it right that I felt I had to have the balance checked

2 Darts said:
Actually, the 73 340 crank was cast, but it was also shot peened. Shot peening means that the crank is bombarded with steel shot before the final machine work is done. The process makes the crank stronger, though not as strong or heavy as a forged crank. I'm not aware of any other Mopar crank that was shotpeened.
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You're correct about the shot-peening. Not sure if any other Mopar cranks were peened.
 
Captainkirk said:
"The 318-3 truck engines were forged as well but are hard to find, so most folks aren't aware of this. I think the "hardened" refers to a cast crank used in later dates that were shot peened."

The mystery deepens...

I have seen references to a "Premium 318-3 Truck crank" that was ostensibly a forging, but other sources claim that the forged cranks were never shot-peened, Those were cast iron cranks that got shot-peened as a part of the hardening process. The forged 318 OEM cranks that were "factory-hardened" may have been subjected to heat treatment under Ammonia for gas-nitriding, a common heat treatment to achieve case-hardening back then. These truck cranks had an 8-bolt flange.
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Want'en to know how high you can rev it is based ALMOST entirely on; what do you have for a cam shaft? You never said. How high do you want to rev it? The bottom end is pretty reliable to 6500 (it's wicked heavy pistons that hurt here), hydraulic lifters with the right springs can be reliable up to 7000 plus. Pick a number that matches your comfort level and then build to it. It isn't rocket science
 
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