if we help more air get in,by improved flow,bigger pipe/no pipe,or a puffer. do we get more power/mileage just from air?
or with more air to burn does the engine control system increase fuel to maintain to some degree the same air/fuel ratio?,not increasing mpg?
i feel that most real hp increase usually comes at rpms up where we dont play very much.
i also dont see any use for 10 hp gain somewhere. the 3.7 has plenty of hp to get around and can climb any hill it doesnt do a back flip on.
if it goes back to ego, and the fun of tinkering with gas motors,hey have at it,but dont plan to get any change back...

 

A 285/70R16 would be a closer match in diameter to a 265/75R16 than a 285/75R16 it's just wider... so what you might gain in diameter, you would lose in width

A 265/75R16 is 31.65 in diameter, and 10.43 wide
A 285/70R16 is 31.71 in diameter, and 11.22 wide
A 285/75R16 is 32.83 in diameter, and 11.22 wide
A 305/70R16 is 32.81 in diameter, and 12.01 wide

I would almost bet that the GM/Hummer engineers tested various tire sizes for mpg, braking/handling and found the sweet tire to be the one posted in the drivers' door jamb for that vehicle
I have 265's and I hate everything about them...it's not a miracle mpg gainer!! I'm jumping to 305/70's the next tire purchase

 

Yes! This is exactly what I was thinking from the beginning of this thread but I couldn't articulate as well as this so I kept my mouth shut...err keyboard shut.
Well said sir

 

this doesnt make sense;
" In other words, when you increase flow to the entry of the TB, you do in fact increase flow to the combustion chamber starting as low as 2200 RPMs"

you could increase flow with a giant supercharger and the throttle plate and fuel control will still be the restriction/speed control,it has to happen somewhere.
if you use a 6 inch piece of bent pipe the throttle plate will still be the restriction point. how else would you control speed?

so if u have 30 pounds of boost and 2000 feet per minute available at the throttle your gonna need to slow it /"throttle"it somehow,,or am i flunking air flow 101??

i should let the other guy defend his position but it seems like something is out of kilter. i think hes right on.!

 

I don't believe what I said was inaccurate. What I said is just how engines work.

1. GM put a large TB on to get the low end torque. At the low end you'd need more flow to produce the higher combustion chamber pressures needed to generate the high torque this engine produces.

2. You are arguing the point of flow. That is not what we are talking about. I do not argue that a CAI will not increase flow. I will in fact agree this point. But flow means more air which in fact requires more fuel to keep air/fuel ratios correct. We are talking about MPG. A CAI, or any increase in flow/volumetric efficiency will NOT increase MPG, but will most certainly increase power because now you have more air and you can mix more fuel with it.

Understand that highly fuel efficient engines are those that require minimal amounts of air, and therefore fuel to run. Thats why cars with high MPG are those with small 4 cylinder (or even 3 cylinder) engines, with very small throttle bodies. By design they flow much smaller amounts of air compared to other engines. I know it all sounds counterintuitive until you think about the fact that the amount of fuel used is determined specifically by the amount of air you let into the engine, and it applies to every engine. It must, or if you added air and did not compensate with fuel, you will run lean and blow the engine! We control this with the throttle plate. You let more air in, the carb or the ECU adds more fuel. At partial throttle, the amount of air going into the engine is strictly metered by the throttle plate. A CAI cannot change this. At wide open throttle the plate is no longer a major restriction to flow, and a CAI may help with flow and create power, but will also cause you to use more fuel!

 

You are on the right track. More air requires more fuel to keep A/F ratios correct. The reason that gasoline engines make more HP (99.9% of them anyway) in the upper RPM range is because this is where they are flowing the most air. Most bolt on mods that increase flow can make minimal gains over the RPM range that I feel are not worth it. A set of cams, porting the head, a higher flowing intake or exhaust manifold can be expensive but will make considerable gains in HP and TQ if designed correctly, but will also require fuel and timing tuning which will negatively affect fuel consumption.

Back to topic, if you are trying to increase MPG, try to stay away from mods that increase air flow! Some people would argue that this would make the engine work less to pull in air, but this is only the case at WOT or on engines like diesels that do not restrict air flow with a throttle plate!

 

Well yes what I said was a generalization. What you did by looking up specs is what everyone should do when shopping for a tire of different specs if they are trying to compare the change in diameter for a possible new tire. Also pay attention to the "measuring rim width" that is called out, which is the width of the rim they mounted the tire to when they made those measurements. A wider or narrower rim can change the dimensions of the tire.

Just remember, all else being equal, if you only change one of the following:

1. Overall tire diameter: larger will make the engine work harder. Also remember this will throw your miles off, so if you are trying to calculate MPG after you put on bigger tires, you will need to calculate the actual miles you drove, not what shows on your trip meter! The aspect ratio (the 70 vs the 75 discussed above) can play a large role in this. For instance. I currently run a 285/75R16 on the H3. If i wanted to go to a 17 rim, but basically keep everything else the same about the tire's overall diameter, etc. I would research a 285/70R17 tire as a starting point.

2. Width of the tire (the 265 vs the 285 discussed above): changes the contact patch. A larger number increases the contact patch and thus the friction, but can hydroplane in wet conditions if you get it too big. Go too skinny and you can affect braking performance to the point that it is dangerous. This can affect MPG.

3. Rim diameter or width: A larger diameter will make a heavier wheel (more work for the engine), keeping the material the same. Changing the width can change the dimensions of the tire and can be the difference between the tire rubbing or not, or increasing/decreasing the diameter of the tires significantly.

 

It ain't worth it, your theory is flawed. I say theory, because we have real world data, from 92 trucks (all but a handfull GMs) and over 1,000,000 miles at this point. No conjecture needed.

This is a Hummer forum, I am not talking about rice burning terds and have no idea, nor do I care, how intakes work on mini vans and the like.

Power is created by EFFICIENCY, as most OEM vehicle intakes are not purely interested in efficiency (not yet any way) because they also focus on noise reduction. You can't have both noise reduction and premium efficiency. Same applies to OEM exhaust, and in an entirely different way, to OEM computer tunes. If you think auto makers have already dialed in you particular brand and model's best possible performance and fuel economy, you would be in dream land.

You guys do know that "air" does not burn, right? It is not the air charge that burns, it is the O2 brought in with the air that burns with the fuel mixed in. More O2 exists in a larger and cooler air charge and makes for a more efficient burn at the exact same fuel trim levels, which IS what makes the increased power AND efficiency long before you ever get to the point of adding in more fuel (with a PCM tune). This allows your engine to use LESS fuel under the same driving conditions. It ain't rocket science.

BTW, the capability of current GM PCMs to increase fuel trims on their own without a change in the tune itself is limited to box learning. So increased power and efficiency by adding a performance intake alone, without any other change, is NOT created by just bumping up fuel trims because your stock PCM cannot do jack by itself in that department.

Thank you for sharing your opinions, I'll stick to known facts.

 

All these "better MPG for my HUMMER" threads crack me up. YOU BOUGHT A HUMMER! You obviously don't care about gas mileage. If the latest gas prices got you down, because you fill up more than other people, then it's time to go buy that Prius that you've been looking at. lol

 

In large part you are right, but I'd rather get closer to 19 than 15 MPG.