4l80e, 3.42 or 3.73 gears?

[STOCKISH]

I have heard that if running a 4l80 over a 4l60 that you can run 3,73 gears instead of 3.42 gears and wind up about the same cruising rpm's on the highway. I have also heard that the 3.42 gears are too tall for the 4l80 and will cause the trans to continually downshift in town to try to find it's happy spot. Can anyone with actual experience elabprate on this. All help is again, greatly appreciated. --Josh

[munger]

this would be better in the drivetrain section but the 4l80 has a overdrive of.75 the 4l60 it .67 so lower gears would be better for cruising

[pcmcobra]

i run 3.73 on my 4l80e rpm is fine

[dan76]

http://www.grimmjeeper.com/gears.html


Use this chart to compare the two axle ratios with your trans. Consider how you'll use the truck (cruise night, freeway cruising, towing) and match the ratio to your engine's torque curve.

[Pyrotechnic]

4L60E - 3.06 1.62 1.00 0.70

4L80E - 2.48 1.48 1.00 0.75

When concerning gas mileage, the overdrive gear in a 4L80E won't drop as much RPM as a 4L60E, so a numerically lower gear would be better for a 4L80E...if cruising RPM's and gas mileage are your main concern.

When concerning acceleration or pulling ability in first gear, a numerically higher gear would be better for the 4L80E because of it's higher first gear.

The biggest thing to prevent constant downshifting is to consider the terrain and payload against the power your engine produces at lower RPM's.

For example if you never intend to tow and you live in a mostly flat area, you can get by with cruising at a low RPM. If you intend to really load the truck down or you live in an area with a lot of hills, then you will want the engine to run at a higher RPM in overdrive.

Also consider tire size. The difference between a 26" tall tire and a 31" tall tire is pretty significant.

In general for most stock to mild V8's if 65-70 MPH ends up around 2000 RPM or a little more, you will be fine. It is possible to go lower and many new truck do go lower than that, but you must carefully consider the torque curve and the intended use of the truck.

[JohnC]

Great info Pyro.

If it were me I would go 3.73's

[watahyahknow]

Originally Posted by dan76

http://www.grimmjeeper.com/gears.html


Use this chart to compare the two axle ratios with your trans. Consider how you'll use the truck (cruise night, freeway cruising, towing) and match the ratio to your engine's torque curve.

thanks for that link
i was wondering wat rpm's my engine would run at certan legal speeds with a 4l80e and 3.73 gears
i wanted to know when its best for the chosen turbo to come on boost with that setup

that link helps a lot
it whont help driving a car on the street if the boost enters at 2000 rpm , you just be spinning out of controll in corners and all that
sumtimes a little turbolag is actually good
for street driveabillity its better to choose a bigger turbo that comes in slow and a little higher in the rpm range ..... hmmm i think thats why nelson is having so mush succes with his turbosetups
from the rpm reading per speed that turned up using that link i need the boost to come in at about 4000 rpm or so to be able to drive the truck normally without the bucking bronco effect under that rpm at highway speeds , and still have a pretty fast reaction with downshifting or pushing the trottle to over 4000 rpm

[Jonboy]

I would suggest 3.73's. Probably not all that hard to find in a 12 bolt, also.

[N2TRUX]

Great reply Pyrotechnic.

[STOCKISH]

Absolutely, thanks, 3.73s it is then.

[MikeB]

An engine that makes lots of low RPM torque can pull the 3.42 without a lot of downshifting. That would be a 350 with a small cam, say less than 210 intake duration @ .050" tappet rise along with a 500-600 CFM carb (or a Q-jet). A 383 or a big block (with relatively mild cams) will easily pull a 3.42.

Oh, yeah, tire diameter comes into play here, also. The difference between a 31" and 28" tire is the same as the difference between a 3.42 and 3.73 axle ratio.

So, no one should choose or recommend an axle ratio without having the above info.

[watahyahknow]

i did put a stock size tire in the calculation , might need to redo it later when i know the propper sizes i'm going to use

should be simple using the same data and change the end gear in the diff

[Kinze]

I could care less about the gearing until I know the tire size. I love to have all the power right off the line so 3.73's or 4.10's are my general go to gear but for all we know you are running some really short tires.