Will I need a forged crank??

[allcarfan]

engine is a 347 that should rev to 6800rpm

makes 500 flywheel HP easily NA.

might see a blast or two down the strip, but mainly cruising on the weekends.


Will I need a forged crank?

Shane

 

[rbohm]

for the stated intended purpose a good quality cast crank will do fine. however if you intend on more than that though, pop for the forged crank.

 

[68DARKHORSE]

I agree. I wouldn't put more than 500hp on a cast crank.

I wouldn't spin it to 6800rpm though. Your piston speed would be greater than 7700rpm/stock stroke piston speed. Remember the piston has to travel a greater distance per rotation of the crank.

 

[SandSprite]

500-550 HP out of a 302 is about the limit a stock block will put up with. Have you taken that into consideration? 500HP is an awful lot for a street cruiser-- and I don't think it would be too streetable, just MHO.

 

[foghorn67]

how about a 'nodular iron' crank? still cast and cheaper then forged, but stronger then a regular oem crank.
someone correct me if I am wrong.

 

[D.Hearne]

Nodular cranks are just a step below forged in terms of strength. Back in the late 70's and into the 80's they were running cast Cleveland cranks in Pro-Stock and Nascar. There's nothing wrong running one. I would also side with DarkHorse though in cautioning about the max rpms and piston speed though. A 347 is already pushing the 302 block to it's limits to start with and buzzing it to near 7 grand will stress it with that crank/rod combo.

 

[HookandLadder]

You might consider upgrading the block before your stuff any quality parts in a stocker for that horsepower level.

Or...........

 

[brianj5600]

Those pics are a late model block. They are weak compared to the early stuff. I had a 302 with stock rods that I shifted at 7500, so with good rods, 6800 with a 3.40 crank should not be an issue. You would be suprised what can become boring. 500hp might someday leave you wanting more. If you ever think you might want N2O, go forged crank. Nitrous or not, you need forged pistons for that rpm.

 

[D.Hearne]

Those pics are a late model block. They are weak compared to the early stuff. I had a 302 with stock rods that I shifted at 7500, so with good rods, 6800 with a 3.40 . Nitrous or not, you need forged pistons for that rpm.

Ever hear of the 428CJ? It came with cast pistons and a longer 3.98" stroke, so did many other Hi-po motors, like the 289 Hi-po and some of the 427's.

 

[kslushy]

Those pics are a late model block. They are weak compared to the early stuff.

Not to argue or anything, but I'm one of the ones that believes the later blocks are stronger. Theres no inherent answer which is stronger, but just pointing out that the reason it broke had nothing to do with what year the block was.

 

[D.Hearne]

Not to argue or anything, but I'm one of the ones that believes the later blocks are stronger. Theres no inherent answer which is stronger, but just pointing out that the reason it broke had nothing to do with what year the block was.

I tend to agree with you on that, but I have since began to wonder if it's true. I have had no recent experience with older small blocks, only the newer roller 5.0's of which I've just had my first block failure, a crack developed in the #4 cylinder wall of the 400HP 40 over 5.0 roller motor. I think that overall the casting quality is better in the newer blocks, than the older ones which should lead to a stronger block , but the question of which is better may never be settled.

 

[brianj5600]

The main webs are thinner on a late model block. In the early days engineers did not worry about weight. They have been taking metal out of the main webs and the pan rail since the early 70's. The hp ratings for a hipo were at 6000rpm (2870fps piston speed), that is with a stroke of less than 3 inches. The 428cj some were rated at 5400 (3582fps) others at 5200. I have never owned either of them, but piston speed at these levels is still way lower than 6800 and 3.40 stroke. I would not build a motor with a short rod (5.4) and a 3.40 stroke and rev it to 6800 (3853fps) very often w/o forged pistons, too much side loading on the skirts for cast pistons. Also look at the hieght of the piston from the top to the bottom of the skirt. Another reason for forged.