Fact: modifying an engine to make more power does not in and of itself allow the engine to get better fuel economy. Before you can talk authoritatively on this subject you need to understand that fact. When one adds a CAI to an engine and it dyno's out with a few extra horse power, that power came at the expense of extra fuel, not from any perceived extra efficiency; it really is that simple, a little extra air goes into the engine and the ECU compensates by adding a little extra fuel.

As for better mileage from synthetic oil; you haven't answered the basic question, "If synthetic oil allowed for better fuel economy, why isn't every manufacturer out there screaming that fact from the top of every mountain, billboard, and banner ad?"

Edit: I will modify the above statement a bit; by virtue of the extra protective capabilities of synthetic oil, one can typically run oil a grade or two lighter and still retain the required engine protection. The lighter oil in turn can yield a slight improvement in fuel economy.

 

not true and you know it . my 2003 miata is proof that adding headers from racing beat cat back cold air intake with hood scoop and sport muffler did make power and better milage i went from the best of 28mpg to the best of 34 mpg and i raced that miata at the track for 2 years till i bought the turbo miata and raced it for two years .i now race at import shows with a all motor vw that runs 11.90 in the 1/4 mile at 128 mph i have friends that drive vws on the street with turbos on there vw motors. that run 11:30 1/4 mile and they drive them home and get 28 mpg . i have a street vw that runs 14:30s in the 1/4 mile and gets 29 mpg on the street with dual dellorto 45 carbs .and i build all my motors my self and do all the head porting my self. so dont sit there and tell me modifying a engine for power does not allow a engine make better milage . its like your peeing on my leg and telling me its rainning . we have a saying at the track when the green light pops the bull **** stops spencerfvee

 

I know it? Don't be silly; anecdotal evidence such as you've presented is proof of absolutely nothing. Don't believe me? Ask any scientist or engineer.

As you well know, one hears all manner of outlandish claims (especially on the internet); your claims are no less valid than those from device manufacturers of items like the TornadoAir (TORNADO Air Management Systems :: More Power! More Mileage!), or the various fuel treatments that claim dramatic improvements in fuel economy.

More anecdotal evidence; this time second hand. You don't really expect anybody to believe that, do you?

A couple of comments on that rant:

• For the purposes of this discussion, we're only talking about modern fuel injected engines; there is no question that carbureted engines run more efficiently (from a fuel economy perspective) with lower restriction.
• Short of redesigning the combustion chamber, adding a second spark plug to form two flame fronts, and other (typically) manufacturer only types of design changes, the lone engine modification typically achievable by the end-user which can yield both an increase in fuel economy AND power is when the effective compression ratio is increased.
• As for the rest of your rant, sorry, porting, larger valves, and virtually all other methods of increasing the flow rate of normally aspirated induction systems and heads will result in no improvement in fuel economy and normally a reduction. Why? Simple answer, fuel atomization. The higher the flow capacity of the induction system and valves are, the lower the turbulence at moderate freeway speeds; the lower the turbulence, the worse the mixture is from a consistency perspective (i.e. an even distribution of fuel and air), and finally, and the worse the mixture is, the lower the fuel economy.

Think about it this way, don't you think the very intelligent and highly educated engineers of engine manufacturers world-round haven't thought of all of the things you're discussing (and tried them in a controlled laboratory environment no less)? Trust me, they have. When it comes to determining fuel economy, calculating any given engine's Brake Specific Fuel Consumption (BSFC) at any given load, engine speed and throttle setting is the only measurement that really counts. So, when engineers put modern fuel injected engines on a test stand and hook them to a dyno, why then do the engines show virtually zero difference in the BSFC, regardless of the restriction going into the engine?

The difference between our arguments is that yours are all anecdotal with no real understanding of how the induction system of your engines actually operate; my arguments are from the perspective of verifiable scientific testing. Until you wrap your brain around the fact that the induction system of modern fuel injected cars accurately measures the density/weight of the inbound air, and adjusts the fuel flow accordingly, you will not be able to appreciate what I've been trying to tell you.

Said another way, the position of the gas pedal/throttle butterfly has virtually zero bearing on how much fuel is being injected into your engine (except at WOT for some motors which causes them to instantly switch to full-rich), the only thing the OBC cares about is the density of the intake charge. If you add a CAI and increase the density, the OBC will register that fact in the exact same manner as it would if you'd driven from the high desert on a hot day to sea level on a cold day, and as a result, more fuel will be injected to keep the air-fuel ratio in balance.

 

Just picked up our 2012 Mazda5 GT last Thursday. Still on the first tank of gas, but I'll post mileage results as they become available. We replaced a 2001 Honda Odyssey so I'm sure the mileage will be much better! Odyssey was 22hwy, 18city (winter), 16 city (summer w/ A/C on) and the transmission was ready to give up the ghost at 131k (Honda has class action lawsuit for the transmission).

Matt

 

I hope you're right. Mine has 1500 miles on it and my last fill-up calculated to 16.2 mpg (the dash gauge read 15.0). I drove mine fairly hard this tank and lots of hills, not much freeway driving. My best tank so far, driving very easy, was about 18 mpg.

 

I have 160 miles on my first tank. shows half full still. Computer says 18.4 mpg. so we'll see.

 

Humh. I'm driving city mostly, some hiway. I'm getting 26 so far, and hope to get 33+ on a strict highway. I'm up to about 900 miles total so far. I'm taking care, keeping around speed limit. mazda 5 standard shift. I hope yours improves - that seems awfully low to me

 

Our GTs have the 5-speed automatic. I definitely notice the lack of a 6th gear above 60 mph. Optimum fuel economy with the auto would be around 45-48 mph, where it's in top gear but at low revs.

 

I think every car out there will get better MPG at 45-50 mph. I just hope to get 28-30 on the hwy. The computer says 32 @ 69mph. I'd be ok with that. Mine only has 350 miles on her though, so we'll see.

 

First tank fillup results.....

Computer says 24.0, actual 25.1 mpg
Approximately 75% city and 25% highway, A/C on all the time as it's 92F in Dallas today and summer already!

I'm pretty happy with 25 mpg compared to the Odyssey's ~18 mpg in similar driving conditions w/ A/C on.


- Matt