Very interesting point you make about 5w40 given the climate and conditions around here. I might give that a try - though I would not want viscosity issues during some cold morning starts. We don't have a ton of those around here, by the way. However, I have noticed one thing about this CX-9 that I don't like. The engine is a heatsoak for sure. It really does run warm and probably hotter for those of us with warmer OATs on average. I'm going to pull over a few times after sitting in routine freeway traffic on a hot day and shoot the engine block and turbo with an infrared gun and see what comes up. I'm almost afraid to know.
Mutol and Liquimoly, I knew about prior but decided on Amsoil and their longevity in the synthetic oil business instead - though for racing applications Mutol in particular has a great reputation and following. Being in aviation as well, I went with Amsoil because I know some aircraft engines run it. Plus, I like their limited warranty which says a lot about the confidence they have in their product. If I'm not mistaken, Rotella was a synthetic blend until T6. In my research before making the switch from Redline to Amsoil, I came across a bunch of Saab owners who like using Rotella - but those always seemed to be in older Saab engines.
Regarding carbon build-up as a result of direct injection design. As you know, this could be either in the engine or in the exhaust. Most manufacturers can lay claim to solving the problem at the back end. However, this was a problem for years on the front end with many manufacturers though most of them have put forth design effort to mitigate as much as possible by now. The new iSkyActive-G engine used in the CX-9 is just that - new. Not all of it, but enough of it to matter. As such, I don't think there has been enough time to know what the net effect will be up front (valves) or out back (electronically controlled manifold that now sits between the turbo and cylinder head). In my pre-purchase research, I've come across Mazda Engineer, Dave Coleman, and his many iterations of explanations involving the new dash-G design elements.
On cold air pros and cons, a lot of that depends how Mazda encoded the fuel mapping which determines how the engine "learns" to do remapping based on air flows. Won't know until I try. I installed a Vortex cold air system in a 2000 MN6 C5 (which of course ran the LS1 V8) before I had it Lingenfeltered. That experience is what caused me to want the twin-turbo Lingenfelter package installed. I am (of course) not expecting such results with my CX-9. But, I would not mind having a little extra punch off the start. If the ECU maps right, that might happen.
Or, as you say, it could actually lose a slight amount of lower end power. That actually happened to some people who installed Cold Air Intake Systems on their C5 during the 2000 period - I distinctly remember that happening. However, many of us thought it was due to faulty installation or a damaged MAF sensor during installation. The C5s ECM too care of the rest and handled the remapping on its own. Mine in particular loved cold weather conditions throughout the entire RPM range. Of course, I also had a lemon. So, right up to about 4,300 RPM, the power curves on my LS1 began to drop like a rock (this was both before and after the Vortex - so that did not cause the problem). GM could/would never solve the problem and I decided at that point - what the heck, I'll ship it to Lingenfelter and let them rebuild it in "their own image." And, rebuild it they did indeed. This was not too long before John, passed away.
I think the only performance mods I want on my Signature is Cold Air (fingers crossed on it working), anti-sway bars front and rear (if both are necessary). I saw someone on this forum contemplating the installation of a Strut Bar on top, but conversation and debate ensued about the efficacy given the unibody design of the CX-9 not allowing much body roll in the first place. Probably bumping up slight to 265/50/20 summer performance tire as well, if I can find a good set of 8.5" rim-to-rim replacements. I've got my eyes on some Yokos, Kumhos and Michelins that might work. But, in all honesty, I do like the way these Falkens behave themselves.
Nice post.
Well I wont suggest you switch to another oil because theres nothing wrong with what you are currently using, but Id recommend you try out liqui moly, especially motul and maybe even redline one more time just to see how t compares to AMSoil. All great oils but I think Redline and Motul are the two best ones. 5w40 would be an important consideration given your climate for sure. As long as you stick to a 5w oil weight, your cold starts will always be nice and smooth unless you see -20c weather in California which I am strongly doubting. Hell, even 10w30 or 10w40 is a totally reasonable choice given your climate, but Id stick to 5w40 because its easy on your engine during cold starts yet provides good protection at full operating temp.
This is what made me particularly fond about the shell Rotella oil I tried in my BMW by the way. The cold starts were astoundingly smooth for such a heavy duty oil. I remember with the Castrol I used, the cylinder head was very rattly and noisy. This shell oil quieted down the motor on cold starts and helped the motor come up to temp quickly, yet maintained consistently lower temperatures at full operating temp and the engine ran very, very smooth with this stuff. Loved the oil, very cheap for how good it is, but I am hesitant to use it repeatedly because of all the Diesel engine detergents it has. It wears out the metals in your engine.
I believe that the 2.5L turbo engine in your CX-9 is based off the NA 2.5L found in the Mazda 6, and Mazda took precautionary steps to ensure no carbon buildup in that engine. Highly doubt they would make any backwards steps developing your newer engine, so I can confidently say that you dont need to worry about any sort of carbon buildup with your motor. I will say however, that an occasional full throttle pull will help clean out your injectors and possibly exhaust system too. If I switch cars with my Dad and he was using the Mazda for a long period of time (he never revs the engine hard) when I get the car back and do a full throttle pull with it, the exhaust smells like complete ass until its cleared out by the third redline, so this is something to keep in mind for a conservative driver.
Mazda has a super well designed intake from the factory. Not sure if your CX-9 is the same, but my 6 draws cool air from in between the hood and touching the air box after a drive, its completely cool to the touch. If yours is just a little warm but not hot, then heatsoak is not an issue in your car. If you are worried about excessive heat in the engine bay, a vented hood will do wonders. A vent toward the front of the hood, right behind the radiator will help increase radiator flow, extract hot air from within the engine bay resulting in lower oil temps and Im sure this would improve intake temperatures too.
Anyways, your stock intake is well designed so I wouldnt recommend replacing it with some metal piping unless its drawing cool air from outside the engine bay or is a closed air box design. If its not one of those two, dont waste your money.
If you want good bang for your buck and a sweet exhaust note, look into a downpipe or maybe have a custom one fabricated for your car, and dont forget the ECU tune. Much more effective power increase and you will not sacrifice any low-end torque.
The sway bars are an excellent idea, highly recommended you get both front/rear. They will improve steering precision and remove body roll without sacrificing ride comfort. If you like to corner aggressively, I would pop your alignment strut pins on the front axle or get camber plates for more negative camber. This will improve front axle grip and result in a more neutral, tail happy behaviour around corners.
I have some high performance Yokohamas on my mazda 6 that came from the factory, and I find these tires to be extremely well tuned to mazdas chassis. They are noisy on the highway, but they ride comfortably and treadwear is good. The grip, particularly in the rain ridiculously good and steering precision is spot on - cant recommend them enough.
Very interesting point you made regarding the fuel mapping adapting to a modification in airflow. Ive actually had personal experience with this modding the exhaust system on my BMW, but I am indeed very curious to see how well Mazdas ECU would adapt to an exhaust/intake mod. I am considering to delete my secondary cat and try it out on the Mazda as well.