To keep things as close to 'stock' as possible, 4.10s for 33's, 4.56 for 35's.

 

For towing I'd stick with 4.88s. Really you're only looking at a 200 or so rpm difference between the 2 at highway speeds and you get extra low end to get that 5k rolling. I'm going 4.88's in a couple weeks just tryin to get money together.

 

So, then is the consensus that if i were to go with the Hughes Air Gap that gearing would correct the low end issue? And if i were to go with the gearing to fix the low end issue how would my MPH be effected. I know usually with gearing when you go numerically higher in ratio you lose overall speed (mph wise) but pick up bottom end acceleration. I know i will have more power in the mid-top end thanks to the Hughes Air Gap but if the gearing makes up for the bottom how much do i lose out on the top i guess what my concern would be is i dont want my max speed being 70-75mph because i went with to much gear (if i were to go with the 4.88) im just assuming bigger tire with a gear ratio equivalent to stock would allow me to get my stock acceleration and speed.

 

been watching this thread, but haven't posted..

I have the FI, and 4.56:1 gears on 35" tires..

I noticed a gain over stock, coming from 3.92:1 w/ 265/60 tires, and going to 35x12.5 tires and 4.56:1.. I can pull as easily as I did on stock, and maybe even more so.

The 4.56's, in 1st, 2nd, and third keep the truck in a sweet spot for the documented curve on the FI.. I didn't lose any low end at all.. In fact, I may have gained just a touch.. I blame the gears though, as they keep the rpms a little higher as has been discussed.

I have no clue how much it's helped top end.. I rarely see top end.. I can say this though- passing on the highway is much easier. it is in the bottom part of the curve at cruise, so hitting the meat of it is quick and efficient.

 

It isn't going to make that big of difference unless you really get crazy with tire size like 38 and up. I put 4.10 with 33X12.5X15 BFG on my truck and I get to 90MPH a whole lot faster than I could with 3.55 and 265/75R/16 which is almost a 31. The thing gears will do for you is allow the engine to stay in gear longer which is really good in the lower gears. The downside is it keeps you in gear longer in those higher gears as well where if you could drop a gear you would speed up faster. A little more throttle fixes that easily. I maybe wrong, but I don't think it is possible to gear our stock axles, biggest usable gear is 4.88, so low you won't be able to do at least 85MPH.

 

Decide what tire size you want to go with first, THEN pick your gears accordingly.

 

for what it's worth- my truck doesn't hide out in 1st, 2nd, or even third longer.. It is pretty quick to find fourth and stay there- which is the logic behind lower gears while not pulling a load.. I'm out of first in likely under two seconds w/o load and average throttle.. out of second in less than 10..

If I'm not crazy, the theory behind lowering gears is to multiply torque to the ground by allowing more RPM's per individual turn of the wheels..

'holding gear longer' is an impossibility in the context of acceleration.. it flies in the face of gearing and transmission theory.. Holding, in context of 'not searching/excessive shifting' is accurate..

gears simply reduce load on an engine/transmission by allowing the drivetrain mechanisms to pick up the stress.

that being said, bigger tires lower the overall gearing ratio.

unlike the mysteries inside an engine, and the really minute alterations that can mysteriously effect performance that is so damn complicated and inter-related- gearing from the tranny back isn't. It's the opposite.. It is a precise thing that is easily determinable.

So- what Hey You said is the bestest truth here.. find a chart, and stick with it.. eff wit it if you want, but the chart will tell you the best set-up for what you want to achieve.

the only whacky thing about gears, and in relation to engine performance- is getting gears that keep you in the most productive RPM range for your rig.. It's for that reason that 4.56 or 4.88's will be more fun to drive. 4.10's on 35's will reduce acceleration but increase mileage once you get 'em rolling.. 4.88's will explode off the line, but cost you big time in mileage..

I only routinely pull around 2.5k# behind me.. I love the 4.56's, but I would really like to see a 4.30:1 or thereabouts.. but hell, that's splitting hairs at this point..

 

Thanks for the input mine intention is to run 35's with 4.56's 97TN4x4 had said 4.88's and i thought that to be overkill on 35's for a daily driver. For the most part it is just a pavement pounder as i have a built Wrangler with a 383 that allows me to get my high horsepower offroading fun out of. As for the truck id just like to get it to where i see more power than stock without losing the option to tow, or take advantage of the pulling the power if i need to pull, such as stuff out of the ground (bushes, trees whatever might be the case, i dont do it that often but if friends or something need i love pulling the stuff out with ease with this truck) i guess i just say that cuz its just fun to rip stuff up haha and not really make it a race truck that drinks a ton of gas and make it a poor choice of a daily driver.

Drewactual- So, you don't have a problem getting the trailer going from a stop with your 4.56 and AirGap set up then?

 

none..

and once at speed, I have to force myself not to turn o/d back on.. it's been said that 4.56's will give you about the same w/ 35's as stock with, well stocks.. but I think it is a touch lower, but it isn't something I can prove..

if you're pulling something heavy, the gears will land you in the manifold's sweet spot almost instantly, which eliminates the argument in my opinion of 'low end loss'.. maybe there is a low end loss for guys running 3.55's- especially on oversized tires, but there was zero for me.. I can't accurately gauge it, but my levi's dyno tells me I picked up a little bit.

 

That's the difference between an engine dyno, and real world though. In reality, the engine IS making less power at the lower end of the RPM range, BUT, the gears move the RPM/MilePerHour range UP just a hair, putting the engine into, as Drew so eloquently puts it, the "sweet spot", so, PERCEIVED power actually goes UP.

This is the main reason to look at your drivetrain as a WHOLE, instead of just individual parts.