Stock N/A 3.4 Powerband for Regear

I am on the tail end of doing my research for differential regearing, having lost too much torque after a lift and tires. My 04 DC TRD auto Tacoma is lifted ~3" and wearing Cooper Discover ST/Maxx 255/85R16s. Cooper has the true tire diameter listed at 32.8".

Maybe my search terminology is terrible but I have googled my brains out for the stock powerband for the 3.4 with zero success. I am hoping to use the numbers to help me decide between the 4.56:1 and the 4.88:1 gears. The only thing I have found is a generic statement about the powerband being narrow but I want to pick the gear ratio that lands an average cruising speed in that RPM window. If anyone has that information in any form I would appreciate the share.

I used the gearing-RPM calculator at csgnetwork.com that includes a final-drive input so I could compare RPMs in 3rd and OD between the gearing options. I also verified the accuracy to my current setup by noting GPS speed and RPM and inputting those values to confirm. I found the calculator to be around 20 RPMs different from what I could eyeball from the in-dash tachometer. See those numbers in the attachment.



I know there are a lot of opinions out there on which gear set to choose and each has their own merits. I hope to let the numbers decide this debate for me. Just like the old saying goes, "Happy motor happy life."

 

4.88 or 5.29 with any elevation above 2,500ft, LT tires and an automatic trans. The automatics cruise at a lower RPM than a manual trans does so I wouldn't even bother with 4.56. These trucks are gutless to begin with and an auto is even worse.

 

Have you tried using this gear calculator?

Might help you out a little.

 

Crunkbananas - Thanks, I have used that calculator. And while it has a lot of useful information I am really only after RPMs at average cruizing speed. I guess my goal is to select the highest gear ratio possible while not exceeding the top end of the motor's "powerband." What I am looking for is some sort of documentation of the efficiency vs RPM of the 3.4.

There are a few hills I drive regularly that I cannot hold 50 MPH in 3rd. I also tow a drift boat occasionally which was tough with factory tires and is now a joke with the 33s.

 

It sounds like you are looking for dyno charts. I think there are a few out there in the pre/post deckplate mod threads.

 

I have looked at several of those. They are marginally helpful but I havent been able to find a "before" dyno that was absolutely stock.

Someone shared the following dyno plot with me that compares the 5VZ to the 3VZ


Its hard to tell much on this curve because of its size and lack of graduation. What I am not able to determine is in what RPM window is the 3.4 happiest while cruising. Looking at the torque curve there is a second up-trend starting around 2500 RPMs. Obviously the motor has mechanical advantage from there up to 3500ish RPM but does that mean the motor is comfortable holding those RPMs for extended periods of time? Or does the 3.4 prefer that flat spot in the torque curve ~1800-2500 RPMs? This is what I am trying to determine.

 

I have no data to offer you, only my experience with the 3.4L with auto trans and 4.56 gears. The regear definitely helped with the underpowered-ness when running 255/85 tires, although it still wants to hunt for the right gear on any kind of hill while cruising on the highway.

If you look at your numbers above, the difference in RPM between 4.56 and 4.88 ranges from 115 RPM to 199 RPM in OD, which is negligible at average cruising speed (~65 mph) as far as available power goes. When you drop it into 3rd to climb a hill at that speed, you're already putting the motor into the powerband at 3000+ RPM regardless of the gearing. If you're worried about wear on the engine due to the differences between the two gear ratios, I think you'd have to put a million miles on the truck before that even became a factor.

All that being said, I kinda wish I'd gone with 4.88s, because I don't need the top speed, and I'd rather have the usable low end power.

 

Are you taking into account the larger tires in your chart? It seems that first one is based on stock ~31" tires. re-figuring for the change would put your RPMs lower, no?

and at least on mine with stock setup my RPMs are a little higher than the chart mentions (70mph is around 2150, 80mph is around 2500rpm)

 

I might be looking at the question wrong so apologies if I didn't get it. However from my driving it seems happiest around the 2100-2500 range. I can hit the throttle a little more without dropping a gear on the highway.

There's probably a formula that would compensate for the weight of the truck vs the torque number but I think everyone's setup would be different in the end

 

I can vouch for that!

 

FWIW it seems like people are always wishing they had gone with deeper gears but I rarely see anything that they wish they hadn't gone with the deeper gears

 

Yeah, I want to go with the highest ratio possible while keeping the motor happy at a cruising RPM of it's liking. Speed limit where I live is 70 with flow of traffic generally around 75-80.

I know driving slower is the compromise the higher you go in gearing but I feel that not being able to maintain with traffic is a safety issue.

I would love to be able to go 4.88s but want be sure I can hold the RPMs in my original post for 70-80 MPH for extended periods without melting the motor.

 

you can run the motor all day at 3k just don't expect to get above 13mpg

 

13 MPG at 3000 RPM doesnt sound like the motor likes it very much.

 

the motor or you? lol

Im jelly of you automatics 80mph at < 2500rpm? On stock tires and stock gears im running 2900rpm at 80mph, and its not very efficient there for cruising maybe 15mpg... My cousins auto 4runner is right around 2400 at 80 and its quite a bit more efficient getting about 21mpg but it also feels gutless and wants to downshift a lot on hills.

So yeah if 2400 is weak but efficient, and 2900 is strong but wasteful... pick something in between?

 

The weight of your rig should play a roll in your decision. A stock rig weighing in at ~4,000 lbs is a lot different from one with bumpers, skids and sliders weighing in at +5000 lbs.

FWIW, I am over 5K with 33s and regearing to 4.88s was by far the best mod I have done. On the 33s at 70 mph (gps) I am at 2500 rpms (corrected).

 

Digiratus - That must be an auto? I am still at a higher RPM at 70mph with 33" tires and 4.30 gears and a manual trans and my speedo is dead nuts on with the GPS. Moral of the story is, to the OP I wouldn't be afraid of 4.88. Digiratus is a perfect example, don't be afraid of a few extra RPMs as he is still slightly lower than a factory manual trans set-up.