rokblok

iTrader: (1)

What's better for fuel mileage and engine longevity?

A fuel injected engine is the basic. But what's better, higher RPMs with lower gears(4.88s) and 35s, or lower RPMs and higher gears (4.10s) with 33s? At cruising 70mph, I am running about 2400-2500 RPM on the 33s, and it feels very long-legged, if that makes sense. According to the various gearing/tire calculators, I will be doing about 3000RPM at the same 70mph on the 35s, but with less strain on the engine during acceleration. So what's better to do?

Long story short, I have 33s with the stock 4.10s, I'm going to get 35s and I have 2 factory 4.88 thirds to put in. And I do ALOT of highway driving, about 50-60k miles/year. With the 33 and 4.10s, my 3RZ gets about 17-18 average. Will lowering my gears and getting higher RPMs, but easier acceleration, help my mileage?

I don't care a bunch about the fuel mileage since its paid for, so I'm mostly looking for experience/expertise on the subject...

Stetson_md

Higher rpm =worse mpgs as long as it not luggin the lower the rpms the better as far as mpgs go

rokblok

iTrader: (1)

I agree with that. But on a fuel injected engine, is lugging still using fuel like a carb would? You may have your right foot shoved through the floorboard, but if its not sucking a great volume of air(as in high RPMs), will it still cause a lot of fuel consumption?

And does the TPS play a major factor in fuel mileage?

Stetson_md

rokblok

iTrader: (1)

I need some more input here guys and/or gals...

YoungFeller

The general correlation (with vehicles with typical power-weight ratios) is that a higher final-drive ratio (lower RPM at high speed) saves fuel. There is a point where this correlation reverses though, especially with an underpowered vehicle.

A powerful vehicle without an overdrive transmission, such as my previous '84 Ford with a 302 and 3-speed transmission, certainly experiences better mpg with lower highway RPMs (taller tires, an overdrive gear, etc).

In the case of 22R-powered trucks with overdrive transmissions like ours, I'm pretty sure the correlation reverses. With the overdrive 5-speed transmission and not of lot of power, lugging the engine at low RPMs can require more fuel input in order to keep the vehicle at speed than a setup that keeps the RPMs a little higher. You can tell by noting how much throttle it takes to keep up to speed in 5th into a headwind at, say, 55 mph and then shifting to 4th and comparing. Not precise, I know, but you can usually tell the difference.

Also, our 5-speed transmission ratios are spaced fairly far apart, as we experience when climbing a long grade and trying to decide whether to over rev in the lower gear or lug in the next gear up. Increasing the tire diameter effectively spaces each gear out even more, making it more difficult to obtain the optimum final drive ratio at most speeds.

With a small engine and an overdrive transmission, I'm pretty sure the best fuel economy is observed on stock-size tires with stock gears, so that the transmission gears do not get spaced further apart and the drivetrain is better able to turn the tires in the original powerband.

In the case of the 35s, there are other factors working against you such as tire weight and air resistance, but the best fuel economy is likely experienced with a stock final-drive ratio (4.10s and 28's, 4.56s and 31s, 33s and 4.88s) and the lightest, most narrow tires possible.

Oh, I just saw you have the 3rz. I still think that with the overdrive tranny, the drivetrain has to work less with stock final drive gearing.

JonnyBoy

Here's my experience, while not exactly scientific, it's as close as I could get to it in the real world.

Back when I had the 3vz in the Runner and the 31's(what was on it when I bought it) and 4.10's, I tried going the same speeds at the same stretches of road, mixing freeway and hills(my normal route from home base to work), but most all highway. Virtually no city driving. I tended to get 3 or 4 mpg better if I downshifted at the base of hills instead of flooring it up the hill til I lost enough speed i needed to downshift. The difference is less now with the 3.4 and 33's, but I do still get better mileage downshifting.

Hope that helps you out a little.

rokblok

iTrader: (1)

That helps a lot guys, thank you for the input.

I don't think I'm underpowered, just over-geared right now. It feels so long-legged. I've had it to 110mph with still some go-pedal left(granted it was downhill). When climbing hills, it will hold minor(5%) grades just fine in 5th. And at 60mph I'm only turning about 2200rpm. According to the gear calculators, if I go to 35s and 4.88s, I will be turning about 2400rpm at 60, but 2700 at 70mph. But I think it will be easier on the drivetrain with the lower gears, and my foot won't be pushing through the floorboard. Is this a safe assumption?

JonnyBoy

I feel you'd get better mileage with 4.88's than 4.10's with the 35's. I had 5.29's with 33's on my '83, 22r with a decently modified Weber carb(modded to have both barrels open a instead of one then secondary) and got around 15 mpg driving just pure highway at 70 or so.

Other thing to consider is the power curve, though. What rpms does your engine make it's peak hp and torque? The 3.4 still has about the same power curve as the 3.0, just more power. Still makes it seem to me like the ideal rpms are the same for both motors, so when I go 35's on my Runner I'll be doing 5.29's, I think.

VANCE164

iTrader: (1)

For me it was a compromise well worth going from 4.10's to 5.29's before it was alot of work to hit 50 mph (I'm on 37's) but I would still get 17-19 mpg. Now I can actually use 5th gear and go 70+ down the freeway but get 14ish mpg's I think I could get better if I wasn't trying to go 70+ but its so exciting since my yota hasn't done that since it was a baby and no sas

SCToy

I find i get beat gas mileage when running it in the optimal torque band, not the lowest rpm possible.
My dad has a 98 taco with the 3RZ, stock gears on 31s with the 5 speed. The gears are way too tall in my opinion. It doesn't make enough torque to hold those low rpms efficiently

YotaInSC

I run 2800 RPMs at 70 MPH with 5:29s and 35s. That's with a carb. Fuel mileage.... What's that?

rokblok

iTrader: (1)

Good point...

YotaInSC

I am by no means a mechanic, I know the basics. When going down the road I can smell oil burning... I was aware when I bought my runner that the valve cover gasket was shot (on my soon to do list). But I'm also smelling gas. It has a weber carb and I have no clue about adjusting them. I've been told that they are horrible to put on 22rs. I don't know if its suppose to help mileage or not but I know mine is freakin horrible without even checking to see what it is.

JonnyBoy

It's really pretty easy, and simply trial and error if your not used to carb tuning. First, are you smelling gas, or rich exhaust fumes?

Webers are great on 22rs in my experience. Search for "sync link" in the pre 84 section for some tuning and jetting info, post questions there so as to not clutter up this thread.

YotaInSC

Could be rich exhaust fumes.