Might possibly be the worst question but do mods like exhaust and CAI use more gas then stock? gas is getting ridculous... 90$ a fill up here

 

It's not that they kill gas mileage, it's the "oh my car sounds so nice" and you end up using a lot of gas like that.

If you are complaining about gas prices. Don't spend your money on mods then.

 

Shit then I guess I'm modded out then, cuz I enjoy my base stock sound as is. :P

 

^lol, Before i left i relized what my exhaust*stock* sounds like, and i liked it. just have to be outside the car while someones reving lol. Cant hear it otherwise :\

 

No, mods don't require more gas, we drive just like everyone else.......

 

^ well said, driving a function of gas

 

smart ass.

and Omnuts didnt get it.

 

 

in an ideal world some mods should actually increase mpg as it allows the car to "breath" easier. however, everyone with mods likes to floor the accelerator after they mod to hear there car so they lose mpg

 

hahahahha love my tl-s....my buddy said that its a fact that his fuel economy has got better after removing his pre-cats, j-pipe, exhaust and intake for parting out his car...i believe its the sound and fulfillment you get when mashing the pedal feeling that extra HP causing your mpg's to go down not necessarily the addition of the modifications themselves

 

Saw a silver TL here in town six months back with a chrome nut sack mod dangling on the back. I don't think that required more gas.

 

awesome

 

Any sort of mods that drastically alter the engine's air-to-fuel ratio will cause you to use more fuel no matter how you drive the car. Things like ported intake components (heads, manifold, throttlebody, etc...), superchargers and turbochargers are some of the bigger culprits.

Regarding the CAI and exhaust that you're talking about, the exhaust most likely won't change anything, though the CAI has the potential to. Especially if you relocate the IAT sensor. Your car will think it's being fed cooler air than it actually is and will enrich the fuel mixture. It's not likely to change it by much, but there still would be a difference.

 

Would that change be a positive or negative change on effects of gas mileage?

 

 

 

just dont put any stickers

 

ooh okay thanks guys all your comments helped =)

 

:aman:

 

Compression and exhaust are the only two things that will make a difference. Intake mods don't make a bit of difference. The throttle body is used to restrict air flow at everything besides full throttle. If intake mods increased mileage, it would only make sense that driving at full throttle increases mileage since that's a significant restriction reduction.

The engine has to force exhaust out so freeing up that restriction not only frees up power from the pistons not having to push the exhaust out as hard but you get a better charge (not as diluted with exhaust) during cylinder scavenging.

Turbos won't decrease mileage as long as you don't exceed stock power levels. Superchargers will since there's more drag on the engine at all times.

 

uhm more air into engine = more gas no way around it....mods will impact gas milage negatively if you are heavy footed

freeing up restrictions in the intake and exhaust will result in less pumping loss

max fuel economy is reached when max engine efficiency is reached and some mods will increase engine efficiency by removing those restrictions...thus allowing the engine to use LESS fuel to acheive the same accelleration....because you get more power at a given RPM.... some mods will actually result in power loss at specific parts of the rpm range.....

 

The only part I disagree on is the intake restrictions. They have no influence on mpg. The throttle body's purpose is to limit airflow through the intake tract. You can free the intake up all you want but you will have the exact same restriction caused by the TB in every condition except full throttle. It goes back to what I said earlier, if freeing up intake restrictions caused better mpg, driving at full throttle all the time would give the best mpg since that's the least intake restriction.

 

We get most of our oil from Canada but they pay more. Lol

 

it does take effort to suck air into an engine via it's intake straw... try this little trick

grab a mc donald's straw and then a coffie stir stick straw and tell me which one is easier to suck air in through......

same goes for your engine because after all the intake pipe that the engine's straw and if it is restricted (as most stock ones are) there will be a HP loss due to less air making it into the engine

btw I never said an intake would give you better mpg as most of the time freeing up restrictions results in poorer mpg.......

 

If you get a shorter gas pedal, theres less leverage to press on, saves gas.

 

Ugh, I'm 100% sure I'm going to regret arguing with you, but I guess there's no other way for me to learn.

A CAI will increase MPG, however insignificant. Your air fuel ratio will increase TOWARD the ideal ~14. This will allow a more efficient combustion process. Also, according to Le Chatelier's principle, it will also push the combustion reaction more toward completion (already pretty complete though). Your response regarding the throttle being kept wide open is refutable as well. When opening the throttle all the way, the car knows that more moles of O2 is being allowed in. The car will then inject more fuel to keep the AFR down. Keeping your throttle wide open will however still increase the AFR a bit (just like the CAI). However, unlike the CAI, the engine will now be at a very high RPM causing increased heat and decreased efficiency. Only ~20% of the gasoline's chemical potential energy is being harvested, while the rest is lost in mostly heat. Thus, also according to Le Chatelier's principle, the heat will hinder the combustion reaction, as it is a product of the reactants. Also, at high RPM, the engine's internal resistance will significantly increase, leading to more parasitic HP loss.

A CAI can NOT decrease MPG. Saying that it will not affect MPG is not entirely correct either. It will increase it, but just not by that much.

 

There's no need for it to be an argument. I would say 99% of the population believes that freeing up the intake tract gets better mpg.

I think we need to separate a CAI's cooler charge and intake restrictions into two separate topics.

There is one way a CAI can increase mpg. That is by delivering cooler air, the ECU can add more timing without detonation. This is debatable on the TL specifically but that's another argument. The TL's stock intake tract is not a restriction, it's invisible to the engine. Freeing it up is pointless with a stock or lightly modded engine when it offers no restriction in the first place but that's also another discussion.

Every car built today uses closed loop fuel feedback. The air flow is calculated in our cars (measured by the MAF meter in most others) so the ECU knows how much fuel to inject but that calculation is checked post combustion by the 02 sensors. If you add more airflow, the 02 signals the ECU to add more fuel even if the ECU did not catch the additional airflow. Air fuel ratio is kept the same no matter how much airflow you have within the limits of the LT trims. You flow more air, you get the corresponding increase in fuel.

These cars and most others run at or very close to stoich under normal conditions from the factory. You can't maintain stoich under heavy loads and full throttle or you would run into drivability issues and pinging. Some times they will run slightly rich at idle to get a smoother idle but I doubt that's the case with the TL. Judging by what you wrote, you're assuming they run rich when stock.
Again, referring to the AF ratio, it stays the same with or without mods.
The ECU knows the mass of air entering the engine at all times, not just WOT. Fuel injection rate is faithfully follows air flow and can vary many times a second. At idle, fuel is injected into EACH cylinder 500 times a second. Each one of those times is calculated and checked and the ECU can vary the rate 3000 times per second on an SFI system if needed and that's only at idle. There is no problem maintaining the desired AF ratio.

Full throttle richens the mixture to prevent detonation. Adding more airflow (as you suggest with the addition of a CAI) in a non feedback speed density system would lean the mixture but luckily we don't have to worry about it since ours is closed loop (feedback via the 02) most of the time.
I'm not real sure where you're going... I said the car would get better mpg under full throttle to refute those that said freeing up the intake restrictions would increase mpg. Obviously the car will get it's worst mileage at full throttle the way it's set up from the factory. This is the case nearly 100% of the time but there is one exception.

What I was getting at is you can't say that freeing up an intake restriction will give better mpg and at the same time say that full throttle will not give better mpg too. It's the same thing on a gasoline engine or any engine that uses a throttlebody to throttle the car. If you say freeing up intake restrictions gets better mpg, and full throttle frees up the most restriction, you have to say that full throttle gets better mpg. You can't use the argument only part of the time.

Our cars are throttled by a huge restriction in the intake tract which is the throttlebody. This is by far the largest restriction. Remove this "restriction" and the car is at full throttle all the time. This is the only way power is controlled, by limiting airflow into the engine. Pretend the air filter is this huge restriction and you free it up. Now you can make more power at full throttle, but.... If you want to maintain 65mph on the freeway say it takes 30hp to maintain that speed. You've now freed up the intake by using a better filter. At the same throttle opening the car now makes 35hp. The result is the driver letting up on the throttle, closing the throttle valve somewhat and bringing overall restriction back to where it was before you replaced the air filter in order to maintain 65mph and 30hp. You're exactly back to where you started in both mpg and power.

This is why freeing up the intake tract can not give you better mpg. If you decrease restriction, you increase power and since AF ratio stays constant, you use more fuel. Under partial throttle it's all the same. MPG stays exactly the same whether you have a huge restriction before the TB or if you have none. Under full throttle, the additional airflow of a less restrictive intake tract will get worse mpg because you're not flowing more air and fuel than it was capable of when stock.

A CAI has the possibility of increasing mpg but not for the reasons you gave. It would be purely a matter of additional timing due to the cooler air but nothing to do with restrictions. Of course the denser air helps in power but not mpg. Just freeing up the intake tract can not give an increase in mpg, only power. It does have the potential to decrease mpg if the additional power over stock is used a lot. This would never be significant enough to be measured but it's a lot more real than a supposed increase in mpg.

If you want to talk about extremes and the exception to what I've said, best mpg can be attained in a car tuned for this setup with the throttle all the way open (WOT) in an extremely high gear that requires full throttle just to maintain speed. Whenever the TB is closed, manifold vacuum is high. The higher the manifold vacuum, the more energy is lost in pumping losses. Get rid of this vacuum and efficiency goes up. This is one of the reasons diesels get so much better mpg than gasoline engines, they are unthrottled, no restriction in the intake tract.

In practice, this is seen with smaller engines. Ever wonder why the same car with a 4 cylinder will get better mpg than the V6 version when cruising down the freeway at the same speed? Both cars require the same hp to maintain speed so both engines are making the same power. Part of it is friction but that's a very small percent. The 4 cylinder will be under heavier throttle with the throttle valve more open than the V6. The 4 cylinder will have less manifold vacuum than the V6 so pumping losses will be less. You could say less total (combined) intake restriction, throttlebody included, at the same power level will equal better mpg. The small engine allows you to have less restriction at the same power level. This sounds at first like I'm contradicting myself but read it thoroughly.

If you search around, I've posted a government study that shows dirty air filters (intake restriction) has no effect on the mpg of a fuel injected car. It will decrease power of course. This way of thinking started with carbureted engines where having a dirty filter acted like the choke and significantly richened the mixture. In the case of a carbureted engine, reducing restriction before the carb can lean it out somewhat.

While Chatelier's principles still apply, we're light years ahead in internal combustion engine design and efficiency from when that was written in the late 1800s. Cylinder scavenging is so good right out of the box, af is so precise, and thermal efficiency is about as good as it's going to get without turbocharging that these principles have less of an effect in regards to the IC engine.

 

Wow ok, that was an informative post. So, from what I can understand, your saying the AFR will stay the same regardless of stock intake vs CAI. Rather, a CAI will allow denser air with more moles of O2 and the car will react by increasing fuel. Thus, the AFR is maintained.

If this is the case, then the gas consumption of a car with a CAI will be greater than a stock car at the same throttle position. At the same throttle position, the CAI car is allowing more moles of O2, and the car is injecting more fuel to maintain the AFR. The car with the CAI will produce more power at this same level of throttle, so this driver could reduce the throttle to match the same amount of power.

As such, only at WOT could a CAI car do something that a stock car couldn't. Hmm, that's interesting. I always thought that a CAI just leaned the AFR, but it seems that it just increases the amount of potential O2 consumption.

Edit: Also, are you implying that stock TLs don't run rich? I thought the stock AFR was ~8-9, while the ideal was ~14. Do you know what the stock AFR is for the TL?