[aardvarcus]

Fundamentally, from the perspective of I4 versus V6, the I4 has less displacement (captain obvious I know) so typically it will be operating at a higher % of load, which should be at a higher BSFC. This is muddied somewhat by the fact that Toyota put vastly different gear sets in the different configurations, so for a given cruising speed the RPMs of the engine and also the partially loaded BSFC will be different. One counterpoint to that is that the V6 is a completely different, more technologically advanced engine. This should improve its BSFC figures.

One way to try to wrap our minds around the differences is to look at the Toyota provided estimates for mileage. For consistency, all the models will be the Access Cab version, for an apples to apples comparison (The double cab and regular cab figures won’t be vastly different, but are only available in more limited configurations versus the access cab which is available almost however you want.

4x4 V6 5 Speed Auto (3.73 Rear End, 0.72 Overdrive)= 16/21 City/Hwy MPG

4x2 PreRunner V6 5 Speed Auto (3.73 Rear End, 0.72 Overdrive)= 17/21 City/Hwy MPG

4x4 V6 6 Speed Manual (3.73 Rear End, 0.85 Overdrive)= 16/19 City/Hwy MPG

4x2 PreRunner I4 4 Speed Auto (3.58 Rear End, 0.71 Overdrive)= 19/24 City/Hwy MPG

4x2 I4 4 Speed Auto (3.58 Rear End, 0.71 Overdrive, Smaller Size Tires)= 19/24 City/Hwy MPG

4x2 I4 5 Speed Manual (3.31 Rear End, 0.81 Overdrive, Smaller Size Tires)= 21/25 City/Hwy MPG

4x4 I4 4 Speed Auto (4.10 Rear End, 0.71 Overdrive)= 18/21 City/Hwy MPG

4x4 I4 5 Speed Manual (4.10 Rear End, 0.81 Overdrive)= 18/21 City/Hwy MPG

I will draw a few conclusions from these numbers, realizing these are imperfect estimates from EPA.

You will notice that typically in the 4x4 versions, the V6 gets taller rear end gearing, but in the 4x2 versions the I4 gets taller rear end gearing.

You will also notice for the V6, the prerunner automatic and the 4x4 automatic which are almost identical trucks with identical gears get exactly the same highway MPG. Interpreted differently, the CV shafts, differential, driveshaft, and transfer case are not significantly hurting the highway MPG as long as identical gear sets are used. The differences in weight and friction are quite minor for highway MPGs, but you can see the city MPGs are lower probably due to weight. You can see for other configurations, different gearing is used which punishes the MPG of the 4x4 models.

You will notice for the V6, the really short overdrive gear in the manual transmission is the reason for the manual to have such poor highway MPG numbers compared to the automatic.

Comparing the I4 prerunner and the V6 prerunner, which have only a 6% difference in gearing in favor of the I4, the I4 posts over 14% better highway MPG. Most of the other configurations have such different gearing it is impossible to compare V6 to I4.

Comparing the I4 prerunner auto to the I4 non prerunner auto, notice the hwy MPG numbers are the same. Notice this is despite the non-prerunner being smaller, no wheel fender extensions, less ground clearance, 165 lbs lighter, having a lower CD of 0.368 versus 0.394, and identical* gearing. The reason is the non-prerunner has less “rubber gearing”, as the tires are roughly 12% smaller in diameter than the prerunner.

Comparing the 4x4 I4 auto to the V6 auto, you can see the highway MPGs are the same. I attribute this mainly to the 9% difference in gearing.

I hope that these comparisons have illustrated that the gearing in these trucks has a huge impact on the MPGs you can expect out of them in addition to the selection of a I4 or V6 engine.

One point of note is that there are kits for the V6 trucks to swap in a T56 manual transmission, which could give you an appropriate overdrive to make up for the less than ideal gearing. I feel that with a very tall overdrive (like the available 0.5) the V6 Manual could put out impressive highway mileage figures.

I would still maintain my opinion that the automatic transmission trucks will probably get close to their EPA estimates when driven reasonably nicely in stock trim, V6 or I4. My opinion is that the manual transmission trucks will beat the EPA estimates when driven reasonably nicely in stock trim. This is probably more true for the I4 (which I have experienced personally) and less true for the the V6 due to the stock gearing.

Remember all the above figures are all for the stock trim, aka stock amounts of drag, friction, etcetera. My opinion is that the more you mod the truck and the more you drive like a hypermiler the more of a gap will widen between the I4 and the V6 as well as the manual versus automatic.