Joe86

So i've heard a lot about bigger gears, maf sensors, ISR mods, my question is I have a 94 4runner v6 and i have the 3.90 gears in it ( not 4.10) and from what i'm reading is if I upgrade to say 4.56 or 4.88 it would boost power, and possible to boost mpg a little.

I'm running stock size tires and it is an automatic.
I'm going to be doing a full tuneup soon and swaping in a supra maf sensor as well as doing the ISR mod.

Maybe headers? Maybe not, who knows... and of course the exhaust system upgrade.

I'm currently getting 15.4mpg and I'm a VERY light driver. So assuming I did all of these upgrades, i'm sure I could see a decent increase in power/mpg with my driving style.

However the purpose of this post is to find out would it be a waste to throw some 4.56 or 4.88 on my truck if i'm running stock tire size? Or would it actually be beneficial? Also its a 2wd 4runner.

Thanks for your advise!

aa1911

iTrader: (1)

swap in a 3.4

exhaust is probably the 'best' power mod but still weak.

Alcohol injection helps, I run a 50/50 mix of methanol and dH2O; cleans, lowers emissions, adds power, improves mpgs.... (sorry, I'm just on a mission to promote alky injection, I'm addicted)

this should get you going...
https://www.yotatech.com/forums/f116...r-3vze-220853/

aa1911

iTrader: (1)

and here's a worthy read:

https://www.yotatech.com/forums/f116...k-3vze-187741/

Joe86

Thanks for your reply however that did not answer my question.

My question again is will the 4.56 or 4.88 help the truck or not versus the stock 3.90?

Also i'm not going to do a 3.4 swap in the truck, I just can't fathom the idea of putting over $3k into a truck that is only worth $3k.

I'd rather take the $3k save it and put it towards an actual 3rd gen

Team420

Do you do mostly highway speeds, or in town driving? I ask becuz the shorter gears will def give you a boost in speed (power stays the same), but at highway speeds, the motor will turn higher rpm's, thus netting worse fuel economy. The taller gears may be worse economy for in town driving, but should net better highway speed mpg's.
In all honesty tho... there isnt much you can do to boost your fuel economy, these motors drink like sailors :-)

Duffdog

Um, not exactly. Gas mileage is defined by how much fuel goes into the engine per mile. The RPM's do not predict gas mileage-- injector pulse width does. Think of it this way: If you were going down a hill at 70mph, you would get better mileage because the force of gravity is assisting the engine, thus lowering the injector pulse width and simulating a lighter vehicle. On a flat surface at 70mph, you still have the same rpm, but higher injector pulse width and thus lower mpg. Higher gears do help mileage up until the point where wind resistance exceeds the mechanical advantage of the taller gears. Where exactly that point lies depends on many things, but can only be verified by wind tunnel testing and FEA. In a practical sense, if one only drives 55mph max, the advantage of regearing is higher than if someone drives 75.

In my 87 22re 4runner, I can't drive over 75 because I have 529's and 33's and the engine is just about revving 4k rpm if I go any faster-- my mpg has remained unchanged even with all the extra height and wind resistance. Plus I can accelerate up hills now. The tradeoff in my case was lower top speed. A lot lower.

cblackard

I find it odd that the vehicle came with 3.90:1 gears. Is that from the factory?

I think the best combination is the typical 4.10:1 gears (manual) 4.30:1 gears (auto) with the stock tire size from the factory (225-75R15 i believe).

Be aware that changing gear ratio means the speedo is out of calibration and that will effect your MPG unless you compensate in your calculations at each refuel.

My 91 truck from the factory was getting almost 25MPG with 4.10:1gears/manual trans/stock tires. Moved up to 32x11.50 ATs and lost ~ 3MPG (after corrections to the calculations due to speedo calibration) When I stepped up to 38.5x16 swampers and regeared to 5.29:1, my mileage was down to 18MPG (and this tire/gear combo corrected the offset in the speedo to almost perfect - within 1% accuracy)

The trick is to keep the engine within its optimal power band. Having the engine struggle because its running too low an RPM range or racing because it is running too high an RPM range will hurt fuel economy. Oh and you can hurt mileage running high RPMs since the computer likes to keep the engine at an optimal air/fuel ratio. More air means more fuel consumption. going downhill with your foot out of the skinny pedal means the throttle is closed more meaning less air. the opposite hold true for uphill.

bob200587

I'd get 4.88s and step up to 30 or 31 inch tires when it's time for tires.

Vudujoose

Going downhill no matter the type of trans, motor, or weight of the vehicle will always drop the RPM. So driving downhill is not the same thing as driving on a flat surface.

I understand what your getting at with injector pulse width, but to say RPM has nothing to do with it is wrong, as you drop RPM's the ECU adjusts the fuel needed (IPW), they are variables that cannot stand alone, one directly effects the other...

Duffdog

Sort of, but not really: The only time that applies is if you have an auto trans, in which case the engine is still not working as hard, thus lowering your injector pulse width. The pulse width is determined by an equation called "calculated load", not rpm. If you have a manual, speed and gearing are constants which do not change in the MPG equation--obviously if you go down a hill with a manual, the rpm's do not drop. Automatics are a different story, unfortunately for automatic owners, the losses from downshifting to go up a hill cancel out any gains derived from upshifting going down a hill. It is a net zero in both cases because we are testing at a constant speed. You cannot maintain said speed unless the injectors deliver X fuel per second to create Y horsepower.

When MPG tests are done in real life, they are done by using a flowmeter which determines EXACTLY how much fuel flows to the engine per second at a specific speed under specific conditions. It doesn't matter what the engine is doing to maintain that speed, it could be 100 rpm or 135,000 rpm, both cases are irrelevant as long as the amount of fuel flowing per second can be measured with the car maintaining a constant speed.

bolard

How can you find out what gears your running? 93 4-Runner 3.0 auto

bob200587

There is a metal plate with coded info under the hood. It has the gear ratio and transmission info among other things.

Search here or on google for the decoder.

bolard

Thanks for the info.......

TNRabbit

I thought it was on the sticker inside the driver door jamb...?

BMcEL

It is. Only the older rigs had them under the hood.

aa1911

iTrader: (1)

^yup, should be in your door. My 5speed '93 runner has 4.56 gears stock with 31" tires, I think the autos came with 4.33? dunno for sure, but 3.90 is pretty bad unless you only do highway driving. I realize it's a 2wd so the gearing is different naturally...

figure out what tire size you wish to run long term and go from there.

http://www.ttora.com/forum/showthread.php?t=56784

there are plenty of tire size rpm/gear calculators and charts floating around, the link here is one of them...

aa1911

iTrader: (1)

I guess I shouldn't say bad, but bad for bigger tires or offroading...

aa1911

iTrader: (1)

Also, FWIW, my tacoma has 4.10 gears with 32"s and does just fine both offroad and highway for power and mileage

Lycanistic

For all that, you could take your money for gears, tires, recalibration, etc and put it toward a Prius, put the saved gas mileage money toward the monthly payment....problem solved.

MaxwellE54

I just got a 91 4runner on 36 swampers and im hitting 13 mpg in town. Im jealous! Just got it so I've yet to swap off the swamps and add exhaust. I've just got an open cat and im in CA hahaha