Ok im looking to buy a 2006 Sierra HD. I have searched some posts regarding fuel economy and performance of the 6.0L engine but there are a couple things I ...

Ok im looking to buy a 2006 Sierra HD. I have searched some posts regarding fuel economy and performance of the 6.0L engine but there are a couple things I can't seem to find reference to.

1: Underdrive pullys, I have used them on vehicles in the past and loved the gains in mpg as well as the extra power they freed up. I found places that make them for the 6.0 so I know they are available.

2: Clutch fan removal and instaling a 12v fan instead. this is a minor mod but does make a difference when you add all the mods together, and my vehicles dont sound like a jet engine on take off.

Has anybody tried these two mods?

I know on my Crown Vic Police interceptor I gained 9% in the fuel economy dept and the tires broke loose alot easier too after I did these mods at the same time.

i dont think i would go with the underdrive pulleys if you plan on keeping the truck for long. everybody on here thats reported back on the 12v fans has loved them(spend the extra money and get the good ones with temp sensor and manual override).

not to sound stupid but i like to think i know a fair amount about cars...but ive never heard of an underdrive pulley? what is it what dose it do?

Underdrive pulleys replace the stock crank pulley and sometimes the alternator and water pump pulleys too. They reduce the parasitic HP loss that all your belt driven accessories use by as much as 25% slower. The result is more of you engines available HP can be used to drive the wheels and the engine does not have to work as hard to maintain speed so you also get a gain in fuel economy also. There are no adverse affects on the accessories in fact they can last longer too. However if your alternator is already at its load limit due to allot of added electrical load like a loud stereo or more lights you will need to increase your RPMs to maintain battery charge. If your cooling system is not in top condition you may experience over heating while idling for long periods in the hot sun because your water pump is only turning at 75% of it stock speed.

I have used pulleys on most every vehicle I have owned with no adverse affects on the vehicle, and every time I get gains in fuel economy and that freed up HP is noticeable too buy shorter 1/4 mile times. I gained .28 seconds with my Police Interceptor.

They also sell lightweight pulleys that reduce rotating mass and allows your engine to rev faster. I don't think I have ever seen either underdrive or lightweight pulleys for our trucks tho(not that I have really looked either).

I would imagine the gains are small with different pulleys. That would be why people opt for things with bigger gains for the same money. Things such as a CAI, tuner and exhaust produce more power and are relatively cheap.

Sent from my Evo

$200 - $400 depending on the finish you want. most if not all vehicles I used them on gained 1 - 1.5mpg not a huge gain but when you put over 30000 miles on annually it will pay for itself very fast. I check my mileage at every fill up so I can get a good overall average fuel economy and watch for drops so I can know when to give my vehicle a check up.

hmm ill be darned..learn something new everyday