I have a 2009 MDX. What are some simple changes I can do to improve the MPG or performance without doing mods? So far I've replaced the air filter with a K&N. I've heard that I should swap out the OEM spark plugs for NGK Iridium Plugs. Will that make much of difference? Is it easy to do? What are some other easy and relatively cheap ideas?

 

Do you want improvement in mpg or in performance? Generally performance comes at the price of fuel economy. You can find tires with lower rolling resistance that don't handle as well. You can inflate them to near-unsafe levels and that might help. You can ease onto the gas from stops, learn to coast with traffic better to avoid slowing down or speeding up quickly. In the end, you bought a 4600lb tank and there's not much you can do to improve its fuel economy.

 

I don't want to compromise safety one bit. Ok, if I was focused on performance instead what suggestions would you give, minus costly mods? I don't value performance so highly I want to spend a lot of money getting it.

 

Anything to do with performance will cost you a pretty penny on a naturally aspirated car.. The MDX has the highest horse power straight out of the factory in its class. For short money, you can get a NOS kit, a 100 Shot will get you plenty of hp.. but no one tried it on the 3.7 liter engines. If you want to go all out, get the rotex supercharger.. probably cost you 8k with install..

If you don't consider performance with costly mods, then your questions are useless.. NA cars are always hard to get HP from out of the factory..

 

I agree that squeezing power from an NA Honda engine gets costly...I know from experience. Might consider looking at aftermarket bits for similar 3.5-3.7 engines like thermal gaskets, spacers, pulleys, etc. The MDX is too big and too nice to drop much weight for the sake of efficiency or performance. If you want inexpensive power/efficiency in this particular chassis, that probably will not happen.

I will disagree that performance bits rob fuel efficiency especially on Honda engines. The more "go-fast" parts I put on my TSX the better my fuel economy became.

I have had my eyes on the rotex kit a friend sent me a link to recently. Not going to help fuel economy at all but damn that would be fun.

 

The MDX already comes with Iridium plugs, and they only get changed every 100k mi. (Straight from Acura's reccomendation). It is easy to do, but I will tell you I just changed mine @ 96k mi.and noticed a minute difference in preformance, which was expected. Things to consider when/ if ou change your plugs depends on how much city driving you do, additives used, and fuel quality. these are what will shorten life (or "foul" plugs sooner)....but not by very much.

Air filter won't add much, but will help a tiny bit. I put in a KN, just b/c as a preference and cost adv compared to changing a paper every few months (I travel 110 mi/ day). I also modded the OEM airbox just a touch to increase air inlet volume.

I know you don't want to dive in too far, but there are little things you can do to help the engine breathe a bit better. Like others said, without a power adder (or changing the characteristics of the internals such as cams or compression).. you won't gain much. I can't leave well enough alone, so I did a couple things:

+ Lightened Crank pulley (for TL 3.5). Nice amt of Tq freed up.

+ Intake Riser/ Spacer from a 1st Gen MDX 3.5 and Thermalbolic spacer gaskets. Polished up ports on head/ spacer/ intake and runners (porting wasn't necessary, frankly not much polishing needed either). Freed up a little more Tq.

+ 2.25" piping ran from resonators to Mufflers, also added Magnaflow mufflers (not fartcans). Freed a tad bit of hp to compensate for Tq at low end.

+ J-Pipe coming soon (To assist in HP/ Tq curve even out).

Again these are mods, but none were too intensive or costly (all < $300), and I had the Factory Service Manual right by my side the entire time (I do have a heavy technical background however as well). B/c I drive so much I wanted to free up what was available to me and add a little fun to the MDX. I do know it isn't a racecar by any means, so wasn't expecting anything of the sort. However, I do notice the MDX accelerates more freely as expected, it doesn't "feel as heavy" when you need to jump into traffic. As for MPG gains...I have noticed absolutely no increase in fuel efficiency, and I travel those 110 mi daily, consistantly on an open straight highway.