Stock 3.850 crankshaft limitations

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Stock 3.850 crankshaft limitations

Post  Petersonpulling on October 8th 2016, 9:11 am

I am wondering what the max rpm and horsepower limitations of a stock 3.850 crankshaft are.

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Re: Stock 3.850 crankshaft limitations

Post  Paul Kane on October 8th 2016, 12:34 pm

In stock configuration while in application specific engines they've supported in excess of 1000 HP.   In properly prepped form for other application specific engines they've sustained in excess of 10,000 rpm.  Your results may vary, and if you are building such engines you can certainly afford a better suited crankshaft.

(These max effort success stories do not apply to the offshore reproduction crankshafts, only to the factory OEM crankshafts.)
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Re: Stock 3.850 crankshaft limitations

Post  Petersonpulling on October 8th 2016, 2:08 pm

Thank you, I have a 472 that is in need of a freshen job. Currently I only turn the engine 7400 rpms. I'm going with a different top end and want to go up to 8600-9000 rpms. I have Crower rods, forged dome pistons etc. Really didn't want to have to change all that to upgrade the crank.

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Re: Stock 3.850 crankshaft limitations

Post  cool40 on October 9th 2016, 8:52 pm

Are you running the standard 2.5 rod journal? I'm weighing the options on a 429 truck crank vs a billet for mine. The machine work to get one where you need to be gets into some money but not billet kind of money. Laughing
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Re: Stock 3.850 crankshaft limitations

Post  Petersonpulling on October 9th 2016, 9:16 pm

I am running the stock 2.5" journals. I considered going with a 429 truck crank but, by the time I have it offset ground and buy new rods and pistons, I'd be further ahead to just start with a whole new short block rather than pick mine all apart.

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Re: Stock 3.850 crankshaft limitations

Post  Paul Kane on October 9th 2016, 10:01 pm

Petersonpulling wrote:...I only turn the engine 7400 rpms.  I'm going...up to 8600-9000 rpms.  I have Crower rods, forged dome pistons etc.  Really didn't want to have to change all that to upgrade the crank.  
Again, in properly prepped form the crankshaft itself is up to the job.  That being said, there is a very big difference between how a "7400 peak rpm" short block is built and how a "9000 peak rpm" short block is built.

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cool40 wrote:I'm weighing the options on a 429 truck crank vs a billet for mine. The machine work to get one where you need to be gets into some money but not billet kind of money. Laughing
I don't know exactly what your building or at what performance level you compete, but in all but a handful of pulling classes I think the 429 steel truck crankshaft is far more than adequate and a great option for those who have the foresight to begin with a steel crank core and customize it for the specific engine.  That's as close to a custom billet crank as you can get and at a much lower price because of the core you start with. Further, one can get a great price on a finished modified truck crank if he takes the time to shop around with several capable crankshaft grinders...of which there are many.
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Re: Stock 3.850 crankshaft limitations

Post  cool40 on October 9th 2016, 10:56 pm

Not to hijack this thread but my build is 485" with A460 heads and Cast intake with one 4500 carb. Typical rpm for the class is 9000-9500 but I'm going to try staying in the 8800 range. I have the truck crank already and have a good place in mind to work on it. Would the counter weights possibly need cutting down?
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Re: Stock 3.850 crankshaft limitations

Post  Paul Kane on October 10th 2016, 1:19 pm

cool40 wrote:Not to hijack this thread but my build is 485" with A460 heads and Cast intake with one 4500 carb. Typical rpm for the class is 9000-9500 but I'm going to try staying in the 8800 range. I have the truck crank already and have a good place in mind to work on it. Would the counter weights possibly need cutting down?
You can do whatever you want to the counterweights or nothing at all. I'm assuming you will be running lightweight pistons and aluminum rods at 9000 rpm, and that probably gives you room to remove material on the counterweights.  At that rpm I'd at least aero them a bit.
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Re: Stock 3.850 crankshaft limitations

Post  cool40 on October 10th 2016, 1:37 pm

Paul Kane wrote:
cool40 wrote:Not to hijack this thread but my build is 485" with A460 heads and Cast intake with one 4500 carb. Typical rpm for the class is 9000-9500 but I'm going to try staying in the 8800 range. I have the truck crank already and have a good place in mind to work on it. Would the counter weights possibly need cutting down?
You can do whatever you want to the counterweights or nothing at all. I'm assuming you will be running lightweight pistons and aluminum rods at 9000 rpm, and that probably gives you room to remove material on the counterweights.  At that rpm I'd at least aero them a bit.
yes definitely lightweight assembly. Years ago I had a 460 crank stroked to 4.375 and it had a lot of the counterweight cut off. It was ultimately a pia to balance! Thanks Paul. Very Happy
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Re: Stock 3.850 crankshaft limitations

Post  kjett on October 11th 2016, 10:13 am

Not saying I know anything, but I can say I've been running a 3.975 stroke offset ground stock crank for the last 3 years turning the motor to 7600 every pass in my mud truck with no issues. Motor made well over 800hp then I added another 250-300 tune up on the NOS plate. If you only need a stock or short stroke, I wouldn't hesitate to run a factory ford crank again!
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