Some of you know, I had proposed a 4.00" stroke 4340 small block crank be made. Unfortunately this is not going to happen, at least in the foreseeable future.
However I have gotten some real good feedback on the possibly of getting a 3.750" stroke cast crank done instead. It would be internally balanced and support approx. 500-550hp. I'll keep you all posted. Should know more in the upcoming weeks.

 

Thats some great news!
Eagerly waiting for more information.

 

Thank you.

 

That is good news. That at least allows 400+ ci easily.

 

Dang, I was hoping for the 4.00" stroke, but this is good also. Thanks for getting them to think Olds. I hope it happens.

Kino

 

Bump update.

 

Ok boys and girls, there is hope.
I've kept at this project and have found someone who will do this for me. He'll do 2 to start with for my observation. Those will be a 4.00" stroke 5140 material with SBC LJ rods, be internally balanced for 1900gr bobweight and have late model flywheel bolt pattern. Selling price on this crank would be in the $1600.00 range. THESE WILL BE FORGED, NOT CAST.
He can do 4340's but of course at a higher cost. The good thing is I only have to order them in batches of 5 each. However that's also why they're more expensive as well. Cast is out, forged is actually cheaper in start up costs.
I've considered doing a 3.875" 5140 style, and/or a 4.00" 4340 to satisfy the masses. But the 3.875 actually has better off the shelf rod/piston combos so.........
I'm aware of billet costs etc., but I also think that a billet in anything but a NASCAR or Diesel block is overkill for what the gas blocks will handle, and for the hp most guys are shooting for. This still represents a decent savings over a billet but gives us all more choices. To me it's' a win-win. Let me know what you think gentlemen. Thanks!!

 

Way to go Mark.

 

Bravo Mark

 

Mark this is great news! Can you explain the difference between 5140 and 4340? Will either alloy support ~600?

 

Sweet !

 

Absolutely! Not only because of the alloy but because it'll be forged not cast. 600 is no problem with the right parts.

 

A 428 out of a 68-70 350 sounds awesome 4.125x4.0 flat top with BB O iron 83 cc 9.6:1 ish !

 

A couple more questions if you will - is the forging going to be final machined and nitrided at the $1600 cost or will that be on us after purchase?

 

Would it not be any 68-76 350 not just a 68-70 models?

 

Dave you are 100% correct.

 

Final machined and core hardened, not nitrided. If someone is going for bigger hp then they can have them further hardened.

 

I am not saying against the other years or castings 350 rather just thinking of my own early 558 casting 68 and 70 blocks I have. Move along

 

What alloy are the old 330/425 cranks and how would that compare to this 5140 alloy? I'm thinking diesel stroker here with this new 5140 4.00" SB crank vs the usual turned down 425 crank.

 

Here is a little about each material that may help some guys with tensile strengths etc, that aren't up on Alloy steels.

I hope this helps.

Eric



SAE 5140
Chemical composition: C=0.40%, Mn=0.8%, Cr=0.8%
Property Value in metric unit Value in US unit
Density 7.872 *10³ kg/m³ 491.4 lb/ft³
Modulus of elasticity 205 GPa 29700 ksi
Thermal expansion (20 ºC) 12.6*10-6 ºCˉ¹ 7.00*10-6 in/(in* ºF)
Specific heat capacity 452 J/(kg*K) 0.108 BTU/(lb*ºF)
Thermal conductivity 44.7 W/(m*K) 310 BTU*in/(hr*ft²*ºF)
Electric resistivity 2.28*10-7 Ohm*m 2.28*10-5 Ohm*cm
Tensile strength (annealed) 572 MPa 83000 psi
Yield strength (annealed) 293 MPa 42500 psi
Elongation (annealed) 29 % 29 %
Yield strength (normalized) 472 MPa 68500 psi
Elongation (normalized) 23 % 23 %
Hardness (normalized) 98 RB 98 RB
Hardness (annealed) 85 RB 85 RB
Tensile strength (normalized) 793 MPa 115000 psi


SAE 4340
Chemical composition: C=0.40%, Mn=0.7%, Mo=0.25%, Cr=0.8%, Ni-1.8%
Property Value in metric unit Value in US unit
Density 7.872 *10³ kg/m³ 491.4 lb/ft³
Modulus of elasticity 205 GPa 29700 ksi
Thermal expansion (20 ºC) 12.6*10-6 ºCˉ¹ 7.00*10-6 in/(in* ºF)
Specific heat capacity 477 J/(kg*K) 0.114 BTU/(lb*ºF)
Thermal conductivity 44.6 W/(m*K) 309 BTU*in/(hr*ft²*ºF)
Electric resistivity 2.48*10-7 Ohm*m 2.48*10-5 Ohm*cm
Tensile strength (annealed) 745 MPa 108000 psi
Yield strength (annealed) 472 MPa 68500 psi
Yield strength (normalized) 862 MPa 125000 psi
Elongation (normalized) 20 % 12 %Elongation (annealed) 28 % 22 %
Hardness (annealed) 96 RB 96 RB
Hardness (normalized) 40 (112) RC (RB) 40 (112) RC (RB)
Tensile strength (normalized) 1279 MPa 195500 psi

 

5140 is a stronger alloy than the stock stuff by about 20%, and it won't be 50 years old.
I sincerely believe that when used in a gas block that the block will give way before the crank does. Plus this crank will be about 15 pounds lighter than a reworked 425 crank.

 

^^^^^ Dam, does Mark knows his stuff or what?? ^^^^^ I guess, I'm not surprised LOL.

I wonder if the stock cranks are close to PH4140?? I'll mention Pre hard 4140 is about 34-38rc, not bad to machine, drilling is a bit of a PITA, need lower speed to drill this material some will know what I mean by drilling this material, unless using carbide drills then no problem.

Eric

 

$1600 isn't bad for a stronger, lighter crank with a longer stroke. We know playing with Olds costs more $$$. I think this would be perfect for my 260, 319 cubic inches or 374 cubic inches with a 307, for people wanting to keep their 80's Hurst/Olds or 442 "original". Good job Mark.

 

If anyone puts a $1600 crank in their 260 or 307, they need to get their head checked. Haha!

 

Well it will make the 260 worth $1600. I still think a 307 stroker would be interesting for a 80's performance car with max effort 5A heads, ported A4 with custom pistons, SBC rods and this crank would be good for an orignal look in a Hurst/Olds. Don't know how much can be done on the exhaust side and still look original. Maybe a gutted cat, bigger crossover pipe and extrude honed/ported manifolds.

 

And guys bemoan the under square G block 400. That crank in a 260 DEFINES under square....lol.

 

I could turn, and grind 2 out of PH4140 for $1600. haha, you think they would hold up in a 260-307 LOL.

 

With those massive port 10 or 2A heads and that big dual jet carb, it would be wheels up all the way down the 1/4 mile. A solid main 260 with major boost might be fun but still too expensive to build, needing custom pistons and still have a tiny bore and terribly under square, even at max overbore.

 

I know it is slightly ridiculous but this crank in SB main size in 3.75 or 4.0 sure makes me wish there was a aftermarket 403 block with the those big bores a really big SBO could be done for the F.A.S.T. racing , flat tops and lots of compression. 4.351 x 4.0 476 cid zero deck, flat top , max ported big valve and milled #5 , #6 heads down to say 60 cc nearly 15:1 , intake mods and ported exhaust manifolds, dual pattern crazy custom cam in a F.A.S.T. rules W31 post coupe automatic

 

Here is what well built F.A.S.T. car can do on stock tires and no headers or visual mods.

 

I am tempted to run it with my custom stroker pistons with a short 5.7 rod for 484 ci but not good for a long life.

 

Well this project is moving forward. Just ordered 2 each of a 4340 and 5140. Should have them in 5-6 weeks. I'll let you know how they look, 3 are already spoken for. Along with some other parts the will be available you should be able to build a 550-600hp small block Olds with virtually all off the shelf parts. Cool!!!

 

Great news, let us quality, price and all the details of the other parts as well.

 

That's really awesome, good job Mark!

 

Very cool indeed!

 

Awesome!