Thread: MPG help

no iridium.

Correct me if im wrong put putting more air into the engine will not get you better fuel mileage. The more air that gets in the more fuel you use.

This is all theory here, but IMO anything other than a u-bend delete wont help gas mileage that much. When you are cruising you are not giving off a lot of exhaust gas so the restrictions arent as big of a deal. I dont think you would ever make the money back in gas savings by buying headers.

Lose weight in the car, accelerate very slowly, dont use cruise control on hills, use the lowest AC setting you can or open windows, get an alt rewire and voltage booster. You could do the "Big 3" If you really wanted, dont know how much it helps. Proper tire pressure will probably help the most, and make sure your wheels are aligned.

Also, not sure if you have a supercharger or not, but if you do you could get a 4" Pulley if you dont care how fast it is.

Originally Posted by JoRoW99

Correct me if im wrong put putting more air into the engine will not get you better fuel mileage. The more air that gets in the more fuel you use.

This is all theory here, but IMO anything other than a u-bend delete wont help gas mileage that much. When you are cruising you are not giving off a lot of exhaust gas so the restrictions arent as big of a deal. I dont think you would ever make the money back in gas savings by buying headers.

Lose weight in the car, accelerate very slowly, dont use cruise control on hills, use the lowest AC setting you can or open windows, get an alt rewire and voltage booster. You could do the "Big 3" If you really wanted, dont know how much it helps. Proper tire pressure will probably help the most, and make sure your wheels are aligned.

Also, not sure if you have a supercharger or not, but if you do you could get a 4" Pulley if you dont care how fast it is.

You're wrong.

You are getting more air to the engine, but you have made the intake more effeceint because you need less throttle to acheive the same increase in speed, relative to a stock intake.

Originally Posted by stealthee

You're wrong.

You are getting more air to the engine, but you have made the intake more effeceint because you need less throttle to acheive the same increase in speed, relative to a stock intake.

So you use less throttle to get the same amount of air, hence using the same amount of gas?

Originally Posted by JoRoW99

So you use less throttle to get the same amount of air, hence using the same amount of gas?

No.

Let's put it this way as an example.

You have to hold the throttle at 15% to acheive a constant 45 mph with stock intake.
With aftermarket intake you only have to hold throttle at 10% to achieve 45 mph which means you are using LESS fuel.

Less throttle = less load = less fuel.

Headers would hurt gas mileage in this case since it lowers low end torque.

I have an 04 gp gt with 160k and like you I'm concerned with with my gas mileage as well

HERE is what you need to do:
Maintenance:
-new spark plugs
-oil change
-clean your MAF - ONLY with MAF cleaner
-clean the inside of your throttle body - TB cleaner or engine degreaser
-clean the inside of your upper and lower intake manifolds - engine degreaser I can guarantee that with your mileage the inside of your tb and intake manifolds are covered with **** and gunk and need a good cleaning
-seafoam
-keep your tire psi on the higher side (I keep mine at 40 and my tires max are 45/50)

Mods:
-remove the plastic insert in your upper intake manifold - FREE (this will also give you a small power gain in the upper RPM range)
-make your own HAI with a cone filter - $40
-get a DP or headers - $80-180 (I haven't done this yet but I've heard it will net you gains as well)
-get a tune or canned tune

Driving Habits:
-stay below 75 on the highway - the higher you get over 70 your mileage will start to drop (I try to stay at 70-72 if the speed limit is 70 and lower for lower speed limits, your best mpg will be in the 55-65 range)
-during highway driving try to stay behind another car, less air resistance -> engine does less work
-DO NOT accel at a turtles pace, you want to minimize the amount of accelerating you do and maximize the amount of cruising - even when you are accelerating slowly your mileage is cut by about 60-70% of what it is while your cruising (when going from a stop, I stay between 2500-3000 rpm until 40 when OD kicks in)
-cruise at a constant velocity as much as possible - the majority of your fuel is used during accel, the less accelerating you do the more gas you will save, this is easy physics, it takes a LOT more energy to get 3600 lbs to accelerate than it does to keep 3600 lbs at a constant velocity. so try not to bobble up and down between 40-45 mph because it will reflect in your mileage
-stay aware of your surroundings - if you see that the light is turning red ahead, let off the gas. or if you see a red light ahead and know it will be turning green soon try to pace yourself so that you will be able to maintain atleast some of your speed when the light turns green so that you dont have to use more gas by coming to a stop then accelerating back up to 40


Last week before taking a long drive, I cleaned my upper intake manifold, removed the plastic insert, clean my MAF and throttle body (again just because I was going to have them off anyways), and seafoamed my car. This had a BIG effect on my gas mileage, it also felt like it gained a bit of power in the upper RPMs because I removed the plastic insert. Normally when I fill my tank up before a long highway drive my gas needle will start to fall from the full positions at 35-40 miles into the trip, but after I did all of this, I was amazed to see that the needle was just starting to fall at the 50-55 mile mark, it wouldve been in the 60+ range if i hadnt done a couple of WOT runs to check my power gains from removing the intake insert. My rpms were also about 50=100 revs lower while cruising at 73ish. And city driving seems to have had a bigger improvement than that. I attribute most of the gains to removing the upper intake insert and cleaning the intake manifold because it freed up a lot of restriction. Hopefully when I get a DP I will net a few more mpg's

Hope this helps

This is turning into a fun thread. The OP should be getting a kick out of this. Anyway keep in mind people he is a kid, and I don’t really think tearing apart his D.D. is really an option for him on many levels. I have pretty long commute each day so I have spent a lot of time researching and working on mpg related items.


40 psi tire pressure = bad bad idea, been there done it. Results in an increase in braking distance (especially on wet roads). In my experience 37 psi is the threshold of when the traction loss becomes noticeable/dangerous; besides tire pressure seems only to net ~0.1 mpg per psi. Yay a I know dangerous is maybe a little strong worded but under emergency braking 40 psi might make the difference between a close call and the repair shop.

Oil = another area I've explored fairly thoroughly. What I found is a fresh dino oil change = zero mpg gain. Fresh synthetic oil change = zero mpg gain. Long term synthetic oil use = zero mpg gain. This one I know will lite some fires. Here is my spin on my surprising measurements, at commuting speeds and loads the only property of a “quality” motor that makes a difference is viscosity. Believe me I was surprised as well, I like synthetic but using it won’t give a DD a mpg boost.
In short, sticking with a regular dino oil 5W-30 GF-5 is just as efficient as a $8 a quart “super” synthetic 5W-30. Let the flaming begin.

Big 3 upgrade – I have been playing with this one myself for a while. Long story short no noticeable mpg gains from it. If you do enough reading on car electrical systems you will notice that GM vehicles often get a “note” to expect an additional ~0.2 voltage drop for testing. There is efficiency to be gained in the charging system but the gains are too small to measure in practice. By my calculations the big 3 “will” get you ~ 40 watt efficiency bonus at normal alternator loading, and ~100 watts at max load FWIW.

And my last words of wisdom are to remember GM spent money to put the pieces on your car like intake manifold runners and spare tires, so think long and hard before removing them. lol

Originally Posted by cerick08GP

And my last words of wisdom are to remember GM spent money to put the pieces on your car like intake manifold runners and spare tires, so think long and hard before removing them. lol

They also put super restrictive exhaust manifolds and a non intercooled supercharger on there to but that doesn't make it a good idea does it? lol

no temptation to speed up.

yes.

also to add, your engine is sucking the air through the stock set up, open cone lets it inhale freely.

Bingo. An engine is nothing more than an air pump. The faster and freer it can get air in, the more EFFECIENT (ie better fuel mileage) it will be.

I understand this, but the engine needs the same amount of power to hold the car at 45 mph. if you need less throttle, you could still be getting the same amount of air, hence the same amount of fuel and power. Unless of course the engine is really working to pull that air in. What does an intake gain at WOT, like 5 hp? so pull it down to 20% (or something like that) of that airflow and the restriction is not as big of a deal anymore. Intake could help mileage, could hurt it. Ill believe what i believe for now until i see tests. And I run open cone and ported TB anyway.

Originally Posted by JoRoW99

I understand this, but the engine needs the same amount of power to hold the car at 45 mph. if you need less throttle, you could still be getting the same amount of air, hence the same amount of fuel and power. Unless of course the engine is really working to pull that air in. What does an intake gain at WOT, like 5 hp? so pull it down to 20% (or something like that) of that airflow and the restriction is not as big of a deal anymore. Intake could help mileage, could hurt it. Ill believe what i believe for now until i see tests. And I run open cone and ported TB anyway.

So you are saying you'll believe whatever you want to, regardless of facts.

Tests are done all the time. Intakes are proven to increase mileage time and time again.

On my Stealth it is rated at 19 city and 24 highway. With an intake, downpipe and test pipe as my only flow mods I AVERAGED 26 mpg daily driving it. I got more mileage than it was highway rated for.