Small Block 3.750 Crank
December 11th, 2016, 06:27 AM
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Small Block 3.750 Crank
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.
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.
Last edited by cutlassefi; February 15th, 2017 at 06:43 PM.
February 15th, 2017, 05:27 PM
#7
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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!!
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!!
February 16th, 2017, 09:41 AM
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February 16th, 2017, 01:05 PM
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February 16th, 2017, 01:29 PM
#17
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Final machined and core hardened, not nitrided. If someone is going for bigger hp then they can have them further hardened.
February 16th, 2017, 01:32 PM
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February 18th, 2017, 02:03 PM
#20
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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
Last edited by 76olds; February 18th, 2017 at 02:15 PM. Reason: a lot of typing Geez
February 18th, 2017, 02:33 PM
#21
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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.
February 18th, 2017, 03:11 PM
#22
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^^^^^ 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
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
Last edited by 76olds; February 19th, 2017 at 08:17 AM. Reason: 34-38rc
February 18th, 2017, 05:17 PM
#23
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$1600 isn't bad for a stronger, lighter crank with a longer stroke. We know playing with Olds costs more $$$. I think this would be perfect for my 260
, 319 cubic inches or 374 cubic inches with a 307, for people wanting to keep their 80's Hurst/Olds or 442 "original". Good job Mark.
, 319 cubic inches or 374 cubic inches with a 307, for people wanting to keep their 80's Hurst/Olds or 442 "original". Good job Mark.
February 19th, 2017, 08:07 AM
#24
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$1600 isn't bad for a stronger, lighter crank with a longer stroke. We know playing with Olds costs more $$$. 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.
, 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.
February 19th, 2017, 09:24 AM
#25
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. 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.
Last edited by olds 307 and 403; February 19th, 2017 at 09:29 AM.
February 19th, 2017, 09:25 AM
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February 19th, 2017, 09:43 AM
#27
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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.
. 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.
February 19th, 2017, 09:05 PM
#28
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. 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.
February 24th, 2017, 05:45 AM
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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
Last edited by GEARMAN69; February 24th, 2017 at 08:38 AM.
May 2nd, 2017, 03:28 PM
#32
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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!!!
you should be able to build a 550-600hp small block Olds with virtually all off the shelf parts. Cool!!!
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