shitty mpg. supercharger to blame?

I do my best to educate people to make informed decisions.

 

Was surprised today when I filled up and checked my fuel mileage , I got almost 17 mpg city driving . That's up almost 1.5 mpg better than last tank and this time I had the ECT switch in normal mode . Last fill up was with the ECT in power mode

I know this is a 1rst gen 4cyl with a gen II Black case supercharger , K&N CAI & Gibson cat back . Have been on the loud pedal quite a few times as I could clearly hear the blower whine so not driving efficiently at all . I'm also slightly under geared with the 265/75-16 tires as my truck came stock with 225's . With the bigger tires and 4.56 gears I'm down about 400 rpm . If I go up to 4.88's I should get a substantial increase in fuel mileage

I do have plans on installing a Doug Thorley header and increase boost to 8psi . I already have pink injectors and looking at a Aeromotive A340 Stealth pump

 

All while wanting stock or better than stock MPG

 

No they dont.

 

When driven for max mpg they do. All of the numbers I listed are actually lower than what my truck gets/ got in those situations - I was being consevative.

 

What is involved with regearing?
Should you do it whenever you increase tire size?
Does it recalibrate the odometer?

 

Regearing will possibly help with city mileage, but raising your rpms at highway speeds will decrease fuel milage

 

Yes, they do. I consistently averaged 20 mpg before wheels and tires. I mainly 80% highway driving 55 mph or less. I still get around 18 or 19 with the new setup.

 

Highway 55mph, thanks grandpa. You would get run off the road around here .

 

I averaged 22.5 mpgs on my last 3 fill ups. I don't drive over 60mph on my daily commutes. It might be "driving like a grandpa" but you have to understand that the EPA mpg tests don't drive vehicles much over 60mph on the highway tests (average is like 40mph). So driving slower IS how the EPA mpg calculations are done. If people drove like that with a stock vehicle they would do very well on mileage. Just because you don't drive that economically doesn't mean stock vehicles don't get projected EPA numbers.

 

Well considering the posted speed limit is 55. Typically drive 5 over. Excuse me for understanding how fuel economy works. Pretty ignorant comment to say would get run off the road.

 

It's not ignorant its a fact.

 

As long as you are only one on the road, otherwise it's pretty ignorant to think that you won't have vehicles all on your ass til they can go around or think that driving on highways below posted speeds isn't going to cause unwanted disgust from others or safety issues. Also pretty ignorant to not know what he meant.

 

Wasn't that bad when you do everything correctly

 

Exactly, go big or go home! Lol

 

Gears in your diff determine your driveshaft revolutions to tire revolutions ratio. When you increase your tire size you change the amount of distance each tire rotation covers on the ground, and is effectively like reducing gear ratio, meaning your truck has to work harder for every tire rotation. Regearing changes the diff ratio to account for the larger tire size to put the effort back near what it was stock for each tire rotation.

Regearing should be considered when changing tire size significantly over stock, I would start to consider when going to 33s, no earlier.

I believe the speed sensors are different for the manual vs auto. One does it on the output shaft and the other on the hub. It would correct for the one on the output shaft but I do not recall which one that is.

Not necessarily the case. If the engine struggles to maintain speed on a slight grade or is constantly downshifting on the highway due to larger tires, you can still achieve real world mpg improvements on the highway as well.

 

Thanks!

 

No shit. I know what he meant. I am not talking about driving below posted speeds...duh. Talking about reasonable speeds. As far as safety issue....well what the hell do you thinking not following speed limit is? I get it, I don't live in a highly populated area but do visit larger cities. Traffic dictates your pace a lot of times. The whole point is the 4.0 is more than capable of getting 20 mpg.

Back to helping OP with his issue.

 

I think that not following the posted speed limits either above or below causes safety issues & I agree that traffic dictates speed in some situations & agree that 20 mpg is obtainable with 4.0 depending on set of variables. Whether or not you knew what the other dude meant wasn't obvious based on the response.

Topical...........

Basically if you are adding a pwr maker you shouldn't expect mpg to go up. Not saying it can't and hasn't but it will come at a cost.