Increased MPG
 

:driving: Any of the upgrade paths actually improvement MPG as well as HP? And I mean city driving, where it hurts most.

K&N filters only, or a better exhaust seems possible... if you can avoid showing off the added HP, my novice instinct says remove obstacles to air flow and you get better overall performance.

I'm sure this is blasphemy, but I have to know!!!!:stirthepot:

Many people report better gas mileage after a tune.

The best mod for city economy is to modify the driver and tame the right foot.

I have lifetime to date economy of 10.7 litres per 100 km (sorry to those in the US, but we are metric down here) and I regularly get 550 klics per tank with 8-10 litres remaining. Most of my daily drive is outer suburban - 15 klics, then 18 klics of freeway followed by 9 klics of CBD edge stop/start on main thru roads. I cover 42-43 km in an out each day and average ~11 l/100km. The car still gets a squirt to red-line in 2nd on freeway on-ramps to get up to merge speed

The main thing is to just stroke the car along and it rewards you with efficiency. I don;t baby it, but I also don;t hit the throttle to the floor constantly either

I'd have to find out the size of a US gallon to convert but I guess you guys can do that as well as me.

I drive the car in a manner that pleases me. I don't pay any attention to my gas mileage. If that was important to me, I wouldn't be driving a 330 HP two-seat sports car.

I've noticed a small gain in economy with my new catback.

You are correct, less restriction equals more efficient which equals better mpg. I don't know what other people are reporting, but I am completely stock, and I have been able to manage 31.5mpg on the highway by only driving the speed limit. I'm very happy with that number and this alone makes me want to slow down (I typically drive 9mph over the speed limit).

Around town, this is exactly me. However, on long road trips, I love to maximize my mpg. Sometimes I compete to see if I can beat my personal best, lol.

Any mods that increase the efficiency of the engine (eg, freer-breathing intake/exhaust) will give better gas mileage ... if you drive the same before and after the mods. Most people aren't going to drive the same way after making performance mods. :driving:

For tips on getting the best MPG, see some of the hyper-miling sites and adapt/apply some of their techniques (eg, use gravity to your advantage) to your style of driving.

PS: If you drive it like a sports car, there's not a whole lot you can do to get better MPG around town. Other than quit driving it like a sports car. ;)

I squirt in first too just because it's fun and I won't be in danger of getting a ticket on local roads compared to freeways/rural areas... :bowrofl:

:iagree: Sports car and efficiency... two words that should never be in the same sentence. It's a balance beam on one end performance on the other efficiency... you decide what you want then find what suits your hand (or foot or wallet)

I had some decent mileage... went to Niagara and back with a bit of stop and go on the highway. moreso on the way back and I still managed less than half-tank used. Not bad if you ask me since I was being a bit spirited at times.

Generally speaking, power making mods increase the volume of air you take in. That means you need more fuel to mix with it in order to maintain the same AFR (maintained via ECU trimming fuel to target AFR, BTW), which means a lower MPG.

The only exception would be if the mixture (target) were leaned out via tune, which may or may not affect power -- the OEM tune is pretty rich up top ("wasted" to cool the cylinders rather than be burnt), so with no other breather mods involved, you could theoretically pick up a little power and improve MPG that way.

With breather mods and some (safe) leaning of the mixture, you'd probably break about even at best. That said, there are limits to how lean you can go to make best power, so the general rule of more air demands more fuel still applies...

Best way to improve MPG would be to drive in the highest gear possible, and to go easy on the throttle.

Next best way would be to make sure your tires are properly inflated.

Last would be to do some weight reduction.

True, unless possibly the mods increase the VE of the motor and you get some mpg gains through greater efficiency. We'll never know if the mods or the tune are what increases mpg since so few people are going to spend the coin to tune a bone stock car. Plus it all goes out the window when you put your foot into it anyway.

:iagree:

I dunno about that... turbos and superchargers effectively increase VE, so there may be proportionate improvements in MPG, but the absolute changes in air volume still mean you need more fuel to burn it, meaning the overall MPG isn't going to improve.

Power gets lost as heat and fuel gets "wasted" (at least in terms of producing work) if unburnt. The former doesn't really factor much into MPG in real world conditions relative to the latter.

On that note, for a boosted motor, an intercooler will both condense the charge and also chill it -- meaning more grams of air consumed per sec (i.e., more efficient) and also less fuel needed to cool the charge and prevent autoignition. But... the greater volume of air still needs more fuel to produce power, so MPG is either going to break about even or go down.

I really don't understand how a freer flowing anything will improve MPG -- you may get less pumping losses, but if the AFR is fixed, fuel consumption will change with air mass taken in.

Arguably, if power is lost as heat, it would make just as much if not more sense to say that higher flow means a cooler charge. I'm sure that's true, but the effect is negligible.

Or am I missing something here? :confused:

My wild-*** guess is that the cooler charge allows the ecu to use less fuel as a safety margin. At the end of the day, it's probably all statistical noise and the gains all come from the tune leaning things out.

It depends on if you are looking at comparing MPG to throttle position or power output. If you use the same throttle position, then yes, miles per gallon will drop because you are moving more air/fuel and producing more power. If you use the same power output then, because of increased efficiency, fuel consumption will drop. Of course, there are many other real-world variables (especially that right foot) and we are talking about a sports car, so it's kinda like arguing about how many angels can dance on the head of a pin. :P

I'm pretty sure you just hit the nail on the head.

If one of the factors that affects target AFR is IAT's then that would certainly be true.

I think it gets confusing in part because power and MPG are kind of unrelated issues when you get down to it.

You could coast downhill consuming very little fuel and engine power, and improve MPG, or you could destroy a new set of tires with a smoky burn out, consume tons of fuel and produce lots of power (or, well, torque more precisely), go nowhere, and have terrible MPG.

Fuel consumption comes into play on the basis of fuel consumed to make so much torque over a period of time, but it doesn't necessarily translate into distance traveled.

That's why gearing and drag (either in terms of tire inflation, weight, or the ability to deflect wind) all wind up being such surprisingly important factors in MPG (those little plastic wind deflectors in front of the front tires come to mind...).

That's also why city MPG is always lower than highway MPG; taking off from a dead stop (i.e., stop and go driving) requires more energy than rolling along with the help of inertia.

I don't know about heat losses related to airflow, but losses as heat matter definitely in some aspects of MPG. A fluid coupling trans, for example, will lose power in the form of heat, and therefore have a poorer MPG than a solid connection to the driveshaft operating under the same conditions (although gearing and time spent in a given gear will affect MPG too).

The IAT is located in the MAF and used by the MAF circuit as part of the density calculations. Details are in the FSM.

Good explanation. :tup:

Any effect on MPG/efficiency due to cooling from airflow is pretty insignificant. Keep in mind that the air is "cold" only until the piston starts up.

Any heat loss means less efficiency. The "perfect" engine wouldn't have a radiator (and the drive wheel would be bolted to the crank). Some of the hyper-milers run their engines very hot, but that will lead to detonation problems (plus increased wear) for a "normal" driver.

Sounds like I need to lighten my foot a bit and enjoy the ride, thanks guys!

Fixed

Edit: There was a real-time MPG monitor in my '09 Touring; if you have that, you may find it helpful. Or get an app for monitoring different variables. Also check out some of the hyper-miling sites. I doubt if anyone here would go to the extremes that they do, but there is still a lot of good info.

I can say with some certainty that a supercharger and upgraded injectors/fuel pump do not help your gas mileage so you can cross those off the list.


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How about this.... HFC and CBE. Better flow but no change to the air/fuel mixture. Nice performance increase too? Of course, Fast Intentions seems like the winner for both parts.

Better flow (i.e., more air) + same mixture ratio = more power and poorer MPG. It will add fuel to maintain same AFR via fuel trims to target. The faster exhaust can escape, the more air can be sucked in, so same result whichever side you improve flow on.

On a related note, everyone will make less power and have better MPG in the summer and more power/worse MPG in the winter, all else being equal...

Oh well. I guess I'll just get a gas card with a discount and floor this motha.