Freeing up power and need some insight!

[hampsterzone]

What exactly do under drive pulleys do for my truck?

[Longshot270]

A friend of mine put some efans on a huge chevy 2500 with more engine than he deserved and he said the fans made a noticable difference. It will lighten the load the engine has to turn.

Underdrive pulleys change the gear ratio of all those pulleys powered by the engine. It makes them turn a little bit less for each revolution of the engine. This means that the engine does not have to pull as hard on those other pulleys to rev up. The easier the engine can rev up the better throttle response and power you will have. It does not add any more horsepower to the engine but it does help more of the total power reach the wheels. If you do a lot of idling you may want to bump up the idle speed a bit to keep the alternator at the charging RPM.

[BLFX4K]

You're making your truck work too hard with 4.10 gears

Go to 4.56's or 4.88's if you plan on 37" tires or for some extra city get up and go.

Electric fans make a huge difference and there are several routes to go. Whatever route you choose, just pick one and do it right the first time over

You will love the electric fans and gears, I would also recommend doing the underdrive pulleys while your fan is out and you have access to the engine bay and custom tunes to tie it all in together

IF you're mileage concerned the fans and pulleys should net you 1-3 mpg average. I saw 2mpg increase on the fans and the gears will help ease the stress on the transmission as well as gain back the hp/tq lost from those 35s

[hampsterzone]

Thanks, I really appreciate it. My mechanic says 4.56's will give me lots of off the line power/torque but my top end power will suffer from being at too high of rpms. What is the best route to go? in all honesty. They will be ordered today, so I kinda need to know what to buy soon. I just want good power and not to affect drivability. Thanks to whoever responds.

[Longshot270]

If you go with the 4.11 gears, you'll have a similar drive ratio of a stock truck with 3.55 gears. I would go one size bigger to give you more low end power that you were used to. That might even improve your mileage compared to the gears you've got now.

[hampsterzone]

One size bigger than 4.11? My truck has 3.73 in it now. So does that mean I should go w/ 4.56? Or 4.11? Thanks.....

[Longshot270]

When you went from stock 30ish inch tires to the 35's, you went to having something similar to an effective 3.11 gear ratio. If you put 4.11 gears in, that is similar to 3.55s.

Pegasus has a little gear ratio tool and the chart on this website Differential Gear Ratio Chart - Tire Size to Gear Ratio
That chart is pretty close to what I see going 70 with O/D off and the TC locked. You should play around with those to get a better idea of what the different gears will result in.