Better gas mileage and performance.

[2drXmobb]

With 19 we are doing well? 19? We are getting about 10 mpg!. I was hoping to maybe hit 13 in a combo of city and highway driving? He doesn't get on the gas much, he also realizes that gas prices have spiked and the first hour he is working on the job is just to pay to fill the tank from the cost of getting to work and back.

We use standard non-premium gas I think it is 87 octane but in MI they put ethanol in everything.

Was hoping a new fuel filter might help fuel get there more efficiently.

Would a throttle body spacer help at all with mileage?

also bought the truck with a new dual exhaust. It comes right off manifolds on each side and joins in a Flowmaster 40 muffler. The stock cats were empty or disintegrated and were not replaced. The truck is running without its (single) O2 sensor which was precat I'm told. I hope to weld in high flow cats one on each pipe and one of the 2 will have a bung to allow the O2 sensor to reattached. Perhaps that will help a bit?

Bingo your o2 and cat plays a big role it's probably running rich without them. Unless you tune it out . Avg is 14 I can barely get 16mpg if I'm light on the throttle. Vacuum leaks can make it run rich also. Did you look at the old plugs to see if they were fouled or the condition when you replaced them , they can give you a brief history on the condition of the truck .

 

[Orpedcrow]

With 19 we are doing well? 19? We are getting about 10 mpg!. I was hoping to maybe hit 13 in a combo of city and highway driving? He doesn't get on the gas much, he also realizes that gas prices have spiked and the first hour he is working on the job is just to pay to fill the tank from the cost of getting to work and back.

We use standard non-premium gas I think it is 87 octane but in MI they put ethanol in everything.

Was hoping a new fuel filter might help fuel get there more efficiently.

Would a throttle body spacer help at all with mileage?

also bought the truck with a new dual exhaust. It comes right off manifolds on each side and joins in a Flowmaster 40 muffler. The stock cats were empty or disintegrated and were not replaced. The truck is running without its (single) O2 sensor which was precat I'm told. I hope to weld in high flow cats one on each pipe and one of the 2 will have a bung to allow the O2 sensor to reattached. Perhaps that will help a bit?

That’s the one! The o2 sensor functioning will help.

 

[Sean Buick 76]

How many miles are you guys driving before replacing the 02 sensors? I Kmow they go bad over time.

 

[KansasOBS]

It has 3.73 rear end and is newly outfitted with 33x12.5x20" offset rims with Kenda RT tires.

Re-gear it. Probably your best bet of getting any economy gains, and save the transmission too. Plus it will help with performance. That thing's probably struggling to get out of its own way.

 

[Sean Buick 76]

I went from 14 mpg to 17 mpg when I swapped the new crate 350 into my old 91. Never saw better than 17

 

[RDF1]

I've been spending a good bit of time tinkering with this twin turbo 4.8 in a '98 C1500 I did for a guy. With Th400 and 3.42 gears on 235/75/15s I got aggressive on timing and fueling at cruising rpms and last Saturday I took it for a trip to my buddys house.
It was a 122 mile round trip. I took an extra 12 gallons with me just incase. But the truck has a 8 gallon fuel cell and wanted to make sure I didn't run out.
Only had one good WOT pull cause my buddy wanted to hear it when I left.
122 miles and it only only burned 7.1 gallons. I mostly rode the highway at 55mph and the back roads at 50-55mph just crusing listening to the radio.
I had the timing as high as 45* and AFR around 16.5-16.7 in the cruising rpms and adjusted Injector End Angle till fuel flow decreased to its lowest point.

I was expecting the truck to get 10-12mpg being 3sp and nonlockup converter. It turns 3000rpms at 70 and about 2400 at 55mph.
Text the guy telling him he can drive it home on one tank of gas if he just cruises and doesn't listen to the turbos sing every 10 seconds.

 

[Sean Buick 76]

I've been spending a good bit of time tinkering with this twin turbo 4.8 in a '98 C1500 I did for a guy. With Th400 and 3.42 gears on 235/75/15s I got aggressive on timing and fueling at cruising rpms and last Saturday I took it for a trip to my buddys house.
It was a 122 mile round trip. I took an extra 12 gallons with me just incase. But the truck has a 8 gallon fuel cell and wanted to make sure I didn't run out.
Only had one good WOT pull cause my buddy wanted to hear it when I left.
122 miles and it only only burned 7.1 gallons. I mostly rode the highway at 55mph and the back roads at 50-55mph just crusing listening to the radio.
I had the timing as high as 45* and AFR around 16.5-16.7 in the cruising rpms and adjusted Injector End Angle till fuel flow decreased to its lowest point.

I was expecting the truck to get 10-12mpg being 3sp and nonlockup converter. It turns 3000rpms at 70 and about 2400 at 55mph.
Text the guy telling him he can drive it home on one tank of gas if he just cruises and doesn't listen to the turbos sing every 10 seconds.

Which twin turbos on the 4.8? Boost sure is an amazing thing! Once you build a car or truck with a turbo or two it’s almost impossible to imagine not adding boost to every project vehicle. I typically do twins, but I’m doing a single on a SBC to try something different this time.

 

[boy&hisdogs]

With 19 we are doing well? 19? We are getting about 10 mpg!. I was hoping to maybe hit 13 in a combo of city and highway driving? He doesn't get on the gas much, he also realizes that gas prices have spiked and the first hour he is working on the job is just to pay to fill the tank from the cost of getting to work and back.

We use standard non-premium gas I think it is 87 octane but in MI they put ethanol in everything.

Was hoping a new fuel filter might help fuel get there more efficiently.

Would a throttle body spacer help at all with mileage?

also bought the truck with a new dual exhaust. It comes right off manifolds on each side and joins in a Flowmaster 40 muffler. The stock cats were empty or disintegrated and were not replaced. The truck is running without its (single) O2 sensor which was precat I'm told. I hope to weld in high flow cats one on each pipe and one of the 2 will have a bung to allow the O2 sensor to reattached. Perhaps that will help a bit?

I'm pretty sure your O2 sensor is the issue. In my experience O2 sensor problems make the engine run rich and waste gas.

Back when I had 33s, 3.42s and no lift I was getting 13-14 mpg. If I remember right I lost about 1-2 mpgs going from a 285 A/T tire to a 12.50 M/T tire for what it's worth. This was all tank average at the pump but more highway than city most of the time.

Now I get 10 mpg but that's rolling on 37" M/Ts with 4.88 gears, 6" lift, a full toolbox, winch, etc. I dip into the single digits city driving. If you're going to burn gas you might as well make the most of it right?

The dual exhaust and big (heavy) wheels aren't helping either, taxing the engine every time you take off from a stop. The 305 needs all the help it can get.

 

[RDF1]

S366/71's
Yea I agree.
I've got friends and customers that always want to build a 408/416/427 stroker and dump tons of money into them and then get out run by one these turbo 4.8 or 5.3 trucks and get mad haha

 

[Scooterwrench]

How many miles are you guys driving before replacing the 02 sensors? I Kmow they go bad over time.

About 60,000