Underdrive pullys
03-30-2011, 05:02 PM
#21
4th Gear Member
Join Date: Nov 2006
Location:
Posts: 1,229
A piggyback crank pulley has a smaller crank pulley that goes on the crankshaft, but which also has no harmonic balancer--to over come this (as the balancer is necessary) the original crank pulley is bolted to the front of the new crank pulley, I.e. "piggybacked", resulting in a real cluster-f**k.
The major design flaw is that this moves the balancer further outward from the main bearing (it was engineered to be located where it was) which seriously affects it's ability to dampen/control torsional forces in the crank. The secondary CF is that the surface of the OEM crank pulley used to center it on the new UDP was never designed to be used as a centering boss. Combine all of the above with the 3 crummy bolts that fasten it all together and you've got a real mess.
They also look like a jury-rig...
OTH the crank pulley in the auction that started all this, and Steeda's and others that do it right, is a complete assembly consisting of a new pulley bonded to a new harmonic balancer--all designed and precision balanced to do it's job properly.
Here's my Steeda pulley:
The major design flaw is that this moves the balancer further outward from the main bearing (it was engineered to be located where it was) which seriously affects it's ability to dampen/control torsional forces in the crank. The secondary CF is that the surface of the OEM crank pulley used to center it on the new UDP was never designed to be used as a centering boss. Combine all of the above with the 3 crummy bolts that fasten it all together and you've got a real mess.
They also look like a jury-rig...
OTH the crank pulley in the auction that started all this, and Steeda's and others that do it right, is a complete assembly consisting of a new pulley bonded to a new harmonic balancer--all designed and precision balanced to do it's job properly.
Here's my Steeda pulley:
04-01-2011, 02:45 PM
#22
Join Date: May 2006
Posts: 30
Mercury racing (marine) uses them all the way up to their 1350 engine. Yes, that is 1350 Horsepower. MSRP with outdrive is over 200 grand, so a high ticket item.
I have used aluminum pulleys on a Mercury Racing HP500 with no problems. Also Chevy LT1.
Stock pulleys are stamped steel, not machined, which makes them far cheaper to produce.
04-01-2011, 05:33 PM
#23
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
I don't get this statement. At all. Aluminum pulleys are more expensive to manufacture, which is why they aren't used.
Mercury racing (marine) uses them all the way up to their 1350 engine. Yes, that is 1350 Horsepower. MSRP with outdrive is over 200 grand, so a high ticket item.
I have used aluminum pulleys on a Mercury Racing HP500 with no problems. Also Chevy LT1.
Stock pulleys are stamped steel, not machined, which makes them far cheaper to produce.
Mercury racing (marine) uses them all the way up to their 1350 engine. Yes, that is 1350 Horsepower. MSRP with outdrive is over 200 grand, so a high ticket item.
I have used aluminum pulleys on a Mercury Racing HP500 with no problems. Also Chevy LT1.
Stock pulleys are stamped steel, not machined, which makes them far cheaper to produce.
Additionally engineering considerations in racing environments are far and full away from the everyday world. Top fuel eliminator teams think nothing about blowing engines in one run; the big concern is whether the pit crew can install a new engine before the next run--and they damned well better!
Though some stock pulleys are stamped many are not. For example crank pulleys are rarely if ever stamped (I've never seen one; nor are they aluminum).
On my '03 GT the OEM crank pulley and the AC drive pulley are machined parts. The generator and power steering pulleys appear to either sintered metal or sintered metal/stamped composite parts--finished machine of course. I took a peak at my wife's '03 Highlander as well; the crank, generator, and AC pulleys are all machined.
As to production costs, in large volume the difference between using aluminum alloy or steel disappear as the increased tool life (and recycle value of the swarf), and speed of production tend to cancel out the base material cost. Having been a professional engineer for over 40 years now I have made those calculations more than once.
In very high volume production just the downtime to change tooling, can add up very quickly and again make material costs an insignificant part of the mix.
Then there is that, for the reasons I stated in my previous post, aluminum is a crummy material from which to make V-belt pulleys. The after market doesn't have to warranty things for 36k, 60k or 100k miles, nor do they have to bear the cost of replacing them when they do fail--including the cost of pissing off a customer.
In the last, why is that no maker of UDPs of which I am aware makes an aluminum crank pulley (excluding the piggy back crap), and why do you suppose that the aluminum sets are all cheaper than the steel sets?
Hint: It's because even in small volume the overall production costs of machined aluminum are less than producing the same items in steel.
I know it seems popular on these forums to view automotive engineers as idiots, they are not--in fact I know several, one a close friend (a former SVT member. They are all some of the sharpest most knowledgeable people I have known. Their art revolves around balancing production and warranty costs, and material selection is a big chunk of that.
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