No exhaust Just downpipe. MPG loss?

[cj performance]

99 7.3L has a 3 inch lift and 35" tires. The lie o meter says about 240-250 miles to a tank.
I have no exhaust on the truck only a 4 inch downpipe right now.
Will this cause a drop in fuel mileage. The truck is all stock tuner wise.
Also do you think my mileage is off on my lie o meter cause of lift and tires?

Thanks

[nsrchofpwr]

look and see if the downpipe is blowing on the tranny lines. if it is, you will toast your tranny. the fluid will heat up. lie-o-meters are almost always wrong. different tires do make a difference.

[20stroker02]

The 4" downpipe hurts your bottom end a tiny bit but usually not noticeable. Your overhead computer will be off due to the 35's especially at highway speeds. Is your exhaust 4" all the way out or reduced after the downpipe? If so that could cause unwanted backpressure.

[cj performance]

I bought a new 4 inch turbo back exhaust. All that i have on it right now is the downpipe. im deleting the muffler out of it to have it straight piped. I bought a 4 inch pipe at a semi store but they didnt have a coupler so i need a 4" coupler.

But before this since ive had the truck it had the stock down pipe and 4 feet of piping coming off it. so thats where im getting my 250 to the tank at is with the stock downpipe and 4 feet of exhaust piping coming off.

Anyone know how big the fuel tank is. i think its 26Gals?

[nsrchofpwr]

ok. i was thinking you only had the downpipe and it could be blowing heat on the tranny lines.