My truck (01 F250) seems to be getting worse mpg after installing my exhaust. I'm running mbrp single 4in, superchips programmer set at level one, made my own intake by cutting the plastic off the stock one, and turning 35in tires with stock 3.73 gears. Why would my mpg be going down i'm not even getting on it. Any thoughts? Also should i have reset my computer after installing these mods? Thanks

 

Ummm...if you're using the computer to figure out your MPG, then your new tires are throwing it off.

 

tire size, tire size. . for what you have done those 73's are killing you. plus i agree with with ken. if your going by the lie-o-meter it's not correct due to the tire size .

about 11 is what you should be gettin. plus this new Drainogas we have isn't helping you either

 

I'm calculating by hand, i know how many miles i should be around like half a tank and i'm way below what it used to be. I know the 3.73's arn't helping but there has to be something else that has a factor here. Do u think my exhaust is the problem?

 

You modified the intake ,problably to let more air in ,right and you also modified the exhaust to let more out right ,guess What !!!!!!!!!

The computer sees this and changes the fuel injector pulse width
There is no way to get around this


Go back to stock if you want your mileage back

Just my 2 cents

Rich

 

The programer should have compensated for the changes, I would say tires.

 

Wendell ,explain your statement.

the computer adjusts the amount of fuel to optimize your air/fuel ratio to 14.7 to 1 stoich mixture.
Constantly to keep your engine from leaning out .

So by adding more air in through the intake past the Maf and now more flow past the 02 sensors ,he's added more fuel(volume) to get that mixture to 14.7 to 1 ratio (

Rich

If his programer changes the ratio it would more than likely richen the mixture not lean it out .That would be bad news for the engine in the long run.
Lean is bad.

 

ajordan193

Way back when your stock truck had 31.6 inch diameter tires and 3.73:1 rear gears your 70MPH cruise speed was at 1975rpm

With the same gears and 35 inch tires it is now around 1800 rpm and well below the 70% torque curve of the 415 ci motor

When you added the exhaust modification you further screwed up the dynamics by reducing the exhaust gas velocity and it's scavenging effects

In order for the motor to produce enough torque to push the truck your throttle needs to be opened further

Charlie and Fred and a few others have said time and time again that large diameter tires require a lower gear ratio to keep the 415 in the 2100-2250 range at cruise for best torque and fuel effeciency....

but no matter what you do, if you need more power to move greater resistance then it will always cost you a net loss in MPG

Larger tires are heavier
Larger tires negatively effect gear ratio / torque requirements
Larger tires have higher rolling resistance
Larger tires increase unsprung weight
Larger tires require more BHP to stop

OK so they look cool... but they always cost more to run...just that simple

 

Well, I'm not going to try and convice anybody that I'm a rocket scientist, cause I'm far from it. When I got my bama programer, doug ask me what mods I had so he could create my tune. Intake and exhaust were the onlythings relevent, since I didn't have cams, or anything. I assume air- fuel ratio were the concern. To make a long story short, power, and torque did increase(butt dyno), no cel, and my mpg actually improved. Not so much around town, but highway. The programer seemed to balance the mods out, truck ran alot better than before the programer, and mpg didn't suffer, helped if anything. It wasn't a generic tune, it was a personalized tune, as good as it can be without dyno tunning it. I guess my thought was, that the mods shouldn't of hurt mpg with a good tune. I could be wrong, just relaying my own experience. When I bumped up tire size, my mpg went down a hair, also just my own experience. Sorry if I stepped out of place, I wouldn't want to give anybody bad imformation. I had a catback, headers, and intake, Doug said it wouldn't matter about the e-fan. I also switched to synthetic fluids in the motor, trans, t-case, and rear diff, it brought mpg back to where it was before the tire swap. I don't have data to prove it or anything, just personal observation, didn't mean to offend anyone. If you find anything in what I've said to be missleading, please disreguard the post, I'm to sick to argue these days, but hope there's something helpfull.

 

Hi.

A lot of you guys are talking about scavenging and how a cat-back reduces it. However, it has always been my understanding that scavenging happens at the collector (headers/manifolds) and not past the Y-pipe. Where as; scavenging is a results of exhaust pulses and the low pressure area behind them and not the velocity of the gas past the Y-pipe.

 

Wendel,sorry your not feeling good and you didn't offend me at all.
But we get these mpg threads all the time as you know you've been around here long enough.
Guys expect big mpg's because the writing on the box says it will do it.It doesn't work that way.
Unless you match everything,intake ,cam, exhaust,etc...
Even then I don't think the increase is worth the $ spent for 1-2 mpg better than had they left it alone.
These are heavey trucks not cars,Though they are going to get lighter in the future.
In the old days we used to say HP/weight ratio would improve mileage if you could keep your foot out of it.

Oh ! also after they get done doing all their mods and the truck starts to fall apart they blame Ford for there trouble.

Monsta it is my under standing that scavaging takes place all the way from the headers to the outlet of the muffler .this is the back pressure that we all talk about.

with increase or decrease in velocity you effect back pressure, which screws up dynamics of the exhaust system.

I agree tires and his gears are killing his mileage along with his other mods.
But if you want to play you got to pay!

Rich

 

Yes, you should reset the PCM after each modification that you did to your V10.

Does your PCM know that you have the 35" tires? Or does it still think they are OEM stock? That is very important in calculating the mileage.

Also, give us the before and after mileage from the exhaust install???...

biz

_______________________________
2003 F250 SD SC 142" XLT FX4 V10 Auto 4x4 3.73s

 

OK, my V-10 has had the muffler removed by the prvious owner, so I just have pipe after the cat. Are some of you saying I should put a "stock" type muffler back in it for optimum performance? I kinda like the growl when I stomp on it!

 

biz4two thanks for the info on resetting the pcm, how long do i have to disconnect the battery for?

Also i'm just judging by i'm only getting like 100 miles to half a tank (shortbox) and i used to be 130-150 depending on what i'm doing (city)

And no my truck doesn't know i have 35in tires. my programmer can't do tires or gears unfortunatly.

 

I am under the belief that by putting on a low restriction air filter, that allows the engine to draw more fresh air WHEN IT NEEDS IT....but does NOT force more air into the engine, therefore the computer does not inject more fuel.

Hence, the only time the aftermarket filters actually do anything is at WOT when there is a serious request for air....otherwise, it only draws what it needs, exactly as it does with a stock air filter.

So, unless I would drive around with the throttle wide open, or if I race a bunch, I really get no benefit from the aftermarket filters....except some noise...correct???

Exhaust, on the other hand does have a direct effect on the engine due to the change in back pressure....the less pack pressure, the higher up the rpm range the torque and power go....how many times have folks complained about a loss in low end "grunt" right after putting on a flowmaster or magnaflow or anything else....I have made the change several times, and in all cases lost at least a little low end power

Since I pull a 5th wheel, I need all the low end I can get, so I left the exhaust alone....works for me...