Stronger Crank? - Stock Forged 3.31” vs. Aftermarket Cast New 4”

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SheSaid

SheSaid

Mopar/Jeep Guy
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So I am doing some more planning on a 69 340 build.

What would be stronger, the stock forged crank or a new cast 4” stroker from Eagle or whomever?

I am planning to bore the block 030 over, so that means new pistons and probably rods too.

With the stock stroke, I was thinking of building around 425 HP with X-heads, big cam, headers, air gap intake ect.

But with a 4” stroke I could probably push that number up to around 500 HP.

The car will be Street/Strip type with very little daily driving. 4 Speed with 3.23 gears right now.

Should I keep the stock forged crank or go with a stroker 4” cast piece? I know in general forged is better than cast, but the forged crank is also 40 years old... The other option is a Forged Stroker crank, but then that is really pushing the costs up.

Thanks for the help FABO!
 
Frankly, at the power levels you are talking about, a cast 4" stroke crank from Scat will hold up just fine. Will it be as strong as a factory forged piece? Probably not.

But does it need to be?

You need to decide what you want to acheive, and how much you're willing to spend to do it.
Power levels do not automatically increase with a stroker, as the heads hold the key to ultimate hp numbers. But you can step up on the cam size and still have a boatload of torque to hand.
 
IMO the cast is stronger because it's designed for performance from the get-go. It has the larger rolled fillets and while it is cast the material is still decent in most of them. But - if you want that power level, it's going to be more cost for the crank, pistons, heads, and carb at minimum. And I'd also add in money for internal balancing and main studs for the stroker. You will not reach 500hp on stock heads, while you can reach 425 on them. Generally I add about 20% over a performance build for a non-factory stroke. If a stick is what you're running, and you race it, I would go with a forged crank. A cast will work, but a forged will work better for longer and some of the initial cost is offset by a savings in the cost of internal balancing it.
 
Forged stroker and aluminum heads. Will get you the 500 hp your are looking for. I think an A727 trans. will be easier on the driveline. JMO
 
A forged crank period is the better way to go either way. Plus I wouldn't trust and eagle cast crank with anything (do a search on here and you'll find eagle cast crank failures) that said they do make great forged cranks though. I have a forged stock stroke eagle crank in my 340.
Oh yeah something else, you'll get more miles out of the block with a stock stroke then a stroke because strokers beat on the cylinder walls bad.
 
I know the 51-58 stock Hemi crankshafts could withstand 1000-1200 HP. Were we talkin about early Hemis, I'd say stick with stock. The factory stuff was usually pretty damned good.
 
SheSaid said:
With the stock stroke, I was thinking of building around 425 HP with X-heads, big cam, headers, air gap intake ect.

But with a 4” stroke I could probably push that number up to around 500 HP.

The car will be Street/Strip type with very little daily driving. 4 Speed with 3.23 gears right now.


Thanks for the help FABO!
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its decision time for you. to use a stock stroke 3.31 even at 425hp level on the street you will have to rpm the motor. witch will move you away from friendly street stuff force bigger gear to take advantage. no big deal if you rarely street run it. were as the 4.00 will achieve this much easier and still be friendly no matter what heads you use.. you wont hurt either pieces at this level. and 500 in not a big deal for the cast crank. the stronger piece i dont have enough experience to say but i have beat the holy living hell out of a stock 340 steel crank and it not be a issue. i have worked with the stock crank and the stroke and both are fun to drive and race. rpms are harder to maintain and inches make you feel like a king. rpms with gear are fun to hook up and listen to at idle or winging it.
 
the wall said:
its decision time for you. to use a stock stroke 3.31 even at 425hp level on the street you will have to rpm the motor. witch will move you away from friendly street stuff force bigger gear to take advantage. no big deal if you rarely street run it. were as the 4.00 will achieve this much easier and still be friendly no matter what heads you use.. you wont hurt either pieces at this level. and 500 in not a big deal for the cast crank. the stronger piece i dont have enough experience to say but i have beat the holy living hell out of a stock 340 steel crank and it not be a issue. i have worked with the stock crank and the stroke and both are fun to drive and race. rpms are harder to maintain and inches make you feel like a king. rpms with gear are fun to hook up and listen to at idle or winging it.
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And this is where O/D comes into play.
 
forged is always stronger than cast.... it's just cheaper to produce cast cranks now days, than a forged peice.
 
New cast steel cranks can handle piston speed close to factory forged but from what I read to balance them put the cost in the range of aftermarket forged which can handle more RPM's and HP than factory forged.
 
The material the SCAT/EAGLE/MP cast cranks (the same chinese casting house, ask any honest vendor) is nodular iron, better than the cast stuff they used back in 68 and they have full radiused fillets. That being said, I would put an aftermarket cast crank squarly between an old cast and a new forged aftermarket piece. Old forged are probably a tick stronger than the new cast pieces but they dont have the stress relieving the new cast ones do. cast Eagles fail (so do others), but look at the HP they are listed for and dont exceed that. The differences I have heard are final machining of the cast blanks. I have an Eagle and it had satin smooth journals, smooth chamferes and dead nuts on everywhere that I could measure with my calipers and mics. Maybe I got a good one.
 
Wow some great responses!

Seems the stock forged would be stronger, assuming when I pull and inspect it there are no issues.

However when it comes to price, seems the cost of turning the mains, polishing, and balancing my old crank would be about as much as a new cast crank and selling the forged unit... Oh hell I dont know.

Then there is the RPM issue. I had planned a stock stroke build with lighter slugs and rods, with a solid lift cam, beehive springs, ignition, ect. I was planning to have the ability of spinning the assembly up to 7k when needed.

What about weight? Isnt the forged stock crank heavier than the cast? How much of a weight savings / performance gain would there be?
 
SheSaid said:
What about weight? Isnt the forged stock crank heavier than the cast? How much of a weight savings / performance gain would there be?
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At this point, make a choice and stick with it. If you start wffling now you'll be doing it through the whole build... And if you post, expect to have dissenting opinions either way...lol.

In terms of bob weights, a lighter is better, but in terms of a street car, longer stroke is more expensive, but it's also King.
 
moper said:
At this point, make a choice and stick with it. If you start wffling now you'll be doing it through the whole build... And if you post, expect to have dissenting opinions either way...lol.

In terms of bob weights, a lighter is better, but in terms of a street car, longer stroke is more expensive, but it's also King.
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Good point. I think I'm going strokin!
 
Save the extra coin and put a forged stroker crank in it. Yeah those cast ones are cheap and you may pay for that later. I've seen them break and it wasn't a boat load of horsepower either, plus it was an automatic car.
 
Guitar Jones said:
Save the extra coin and put a forged stroker crank in it. Yeah those cast ones are cheap and you may pay for that later. I've seen them break and it wasn't a boat load of horsepower either, plus it was an automatic car.
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I am assuming the crank in your 408 is forged since its pulling the wheels off the ground yeah? Ever had any trouble with your crank?

I dont plan on doing wheel stands but I have heard a 4 speed in general is much harder on cranks.
 
SheSaid said:
I am assuming the crank in your 408 is forged since its pulling the wheels off the ground yeah? Ever had any trouble with your crank?

I dont plan on doing wheel stands but I have heard a 4 speed in general is much harder on cranks.
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Yes mine is forged, from Bloomer Performance. I have no problems with the crank. It checked out fine but did require some heavy metal to balance.
 
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