thericepatch

Hey guys, I read a lot more than I post, but the topic of better MPG in the big Hondas is much discussed, less researched so I figured I would pitch in what I have found using my 05 Pilot EX AWD. At purchase I was getting fairly reliable 16 mpg, nothing to write home about but not cussing it either. My first discovery was that she likes Chevron with Techron gas, like 1.5-2 mpg. I then switched to a K&N air filter and saw a small increase (.5-1mpg) putting me in the 18-19 range. As most folks have stated, running higher speeds runs down gas mileage fast, so I learned to keep it at 65 on the highway early on. I've read several things about exhaust work, but without an engineering degree, I really didn't know how much it might help or hurt MPG and power, since they are a mid size motor they need some back pressure to work optimally. I also didn't want totally free flowing exhaust to start, because it would almost certainly use more gas. So I started with just punching out the 3rd catalytic converter. If you live in a highly controlled emissions state, DO NOT do this. For the rest of us, the ecu reads before and after only the front cats on the manifolds, thus there is no tracking the 3rd cat and no extra steps; simply unbolt it (lots of penetrating oil) and punch out the ceramic honeycomb center. Just completed a roughly 800 mile trek to Georgia from Mississippi Gulf Coast area with a car-top carrier (as if it needed any more wind resistance) and managed to pull out mid 21s! I had to run Exxon for one tank on the trip and still got around 19.5-20 just verifying that the Chevron does still add roughly 2 mpg to the mix.
So brief synopsis is for better gas mileage in the large v6 Hondas: use Chevron gas (I don't work for them and I usually buy Sam's gas for everything else), K&N air filter recommended, but not a huge benefit, and eliminate the 3rd cat restriction (cheapest way is to hollow it out). Additionally I run my tires at 45psi, run 65 on the highway, and draft where I can (especially with the carrier on top).
I may run a magnaflow to replace the resonator and bypass the final muffler to get a true "truck" sound in the future, and I'll report any further gains.

tony_2018

Nice research. I didn't know the Pilot had a 3rd cat but it must be further down past the j-pipe.

thericepatch

It is just past the j pipe.

Just wanted to update since I've been driving it for about a year like this. It definitely gets better mileage on the highway, however around town it has dropped to about 15mpg. I have not regretted the change even with the drop in city mileage due to the power increase. I occasionally tow other Hondas with it, and it makes a big difference in the amount of power to tow. It doesn't really make a big difference in the sound of the exhaust by itself, but I haven't changed the muffler and resonator out yet to see how it sounds. This is the drive by wire model, I'm curious if it will make as much difference on my '03 that is cable throttle, may try that soon.

94eg!

iTrader: (2)

Oh man, 15mpg is pretty low. Our stock 04 (mechanical throttle) gets 18-19mpg combined. Worst ever (caused by brand new tires) was 16mpg. Best I ever did on the freeway was 24mpg. Usually around 19-21 though depending on wind (70mph). Never towed anything though.

Martin Young

Hello,
I bought a Honda Odyssey that also has 3 cats. The Rear cat was removed(presumably stolen) and there is now just a straight-pipe to the muffler from the Crossover pipe(J-pipe). I'm getting 3 misfire codes which from research says it could be exhaust leak or exhaust issue. Did you ever get codes from the 3rd cat not being technically causing back pressure on your engine?