Crank pulley mod

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skyshadow07

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We have electric powered steering on all SHO models while maintaining an empty belt drive on the crank pulley. I imagine this was oversight when converting or just penny pinching. It was semi address by Ford on SHO's built after August 7th 2016. On the newer pulley, the grooves for the second drive are removed but the mass is still there. I have attached a pic of the original (right) with the newer (left) for reference.
IMG 20200403 123406

So once COVID craziness goes away and I can step foot back in the machine shop, I am going to lathe the extra mass off. I have done this before and had ok results. But I will say, no pulley I have done this to before had this much extra meat on it to remove.

Inevitable questions and their answers
Does this affect the balance of the pulley?
-No, I am uniformly removing the mass upon the whole circumference.

Does this reduce the dampening effects of the pulley?
-No, I am retaining the rubber insulation that absorbs the engine's harmonic frequencies.

What's the reason for doing this?
-Reduction in rotating mass equals reduction in inertial drag. This would translate into a quicker revving of the engine and less parasitic loss.
 

FiveLeeter918

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good luck man! have you checked the metallurgy? I assume it's already aluminum but if not, could be the secret to 10s...
 

skyshadow07

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It's steel. Not sure if cast or mild carbon steel but it's steel. I would imagine it's cast, that's the cheapest way to make things.
 
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krewat

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After seeing a huge discussion about harmonic balancers on another website, I did some looking around... The "harmonic" Ford is trying to dampen may depend on that extra mass to counteract it.

I'm not saying you should halt your endeavor, just that I'm subscribing to this thread to see how it turns out ;)

I came up with the idea to lighten the flywheel of a Triumph TR7 engine I was building back in the 90's ... and my machinist agreed, so we really cut that biotch ;) That engine was to be a high-revving, 5-speed overdrive, 3.90 rear (yeah, on little tires, too...), huge intake and exhaust, etc. I (we) lightened the flywheel up from 23 lbs to 18 lbs. And holy crap did that wake that thing up - it finally had enough free-revving ability to really "push" the gearing...
 

Zpak

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I was kind of thinking the same thing. It would be easy to dismiss the pulley with the useless drive as, why make another when we could just use this one. But, seeing the newer one with just the ribs removed makes you wonder.

Again, not downing the idea to chop it at all. I like where your head is at. That’s race car builder thinking. And, I look forward to seeing the results.
 

Angrymongoose

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I don't want to derail the topic too much here, but how would you go about figuring out if the harmonic dampening was off because of the shaving?
I'm really interested in the lighter pulley idea, but I'm not super familiar with the science behind it.
 

skyshadow07

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The harmonics are a very common fear when doing this. I have turned down and even completely replaced crank pulleys with Aluminum on many cars. I have never had any side effects.
Some things to consider

The harmonics are greater the harder you 'hit' the piston. Think of harmonic warping as ringing a bell (the crank is the bell). If you let the bell resonate and keep hitting it, the metal will vibrate at a higher and higher frequency. So the more power you make, the more harmonics you create because you're hitting the bell harder. eventually, the warp from the vibration can cause two pieces of metal to touch that would normally never do so. If you attach rubber to the bell, it will absorb and reduce the vibration. High end, 800+ hp applications would be smart to have a dedicated dampener capable of absorbing the massive hits. They would also have a torsional twist of the crank from so much power transferring through it.
I have personally eliminated the dampener completely on a Mini Cooper S running around 16psi and had zero issues.
I don't think the changes I'm making will make or break the engine's harmonics. But this is the risk I accept when doing racecar things.
 

skyshadow07

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I came up with the idea to lighten the flywheel of a Triumph TR7 engine I was building back in the 90's ... and my machinist agreed, so we really cut that biotch ;) That engine was to be a high-revving, 5-speed overdrive, 3.90 rear (yeah, on little tires, too...), huge intake and exhaust, etc. I (we) lightened the flywheel up from 23 lbs to 18 lbs. And holy crap did that wake that thing up - it finally had enough free-revving ability to really "push" the gearing...

The flywheel is the real hidden rev maker on standard trans engines. I've lightened flywheels and made the car feel completely different. It would rev like it was half the weight.
 

skyshadow07

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Auto trans flywheels are pretty much as light as you can get without exotic design or materials. They have no reason to have mass. They are merely a point of contact for the starter and a mount for the torque converter. Ford shows ours at 5.57lbs, lighter than the crank pulley.
 

skyshadow07

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Finally got a chance to turn the pulley down. New weight is 5.01lb. That's over 1.59lb of metal removed or roughly 24% of the original pulley weight.
Fun fact, the pulley came from Ford .030" off-center of the core. I'm guessing this is from the rubber dampener curing slightly off. It might not sound like much but .030 is enough to visibly see wobbling on a lathe.
IMG 20200602 120255 IMG 20200602 120247
 

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