Can a C3500 5.7L 4.10 beat 10 MPG?

[DerekTheGreat]

It's the tbi holding you back.
I had a 305tbi w/ 4l60e, 3.08 and got 10mpg if you were easy on it or hard on it.
Swapped in 3.73 (about this time I got another daily so thought what the heck) still got 10mpg.
Strapped on a supercharger and crammed about 7psi into the tired engine, still 10mpg.

Puked the motor and swapped in a stock 305 out of an 86 caprice with 400000 on the clock and instantly got 17mpg with my foot to the rug most of the time.
Though that's without towing a trailer but had a pair of 3 wheelers in the box from time to time and that didn't seem to change the mpg.

I'd assume by swapping to a carb you should be able to get 15mpg unloaded and around 10-12mpg loaded

This is post is laughable. It could be picked apart from so many angles such that all I'm going to say is that you will not get better MPG swapping to a carburetor and that the TBI system isn't holding the vehicle back.

 

[JCribb]

This is post is laughable. It could be picked apart from so many angles such that all I'm going to say is that you will not get better MPG swapping to a carburetor and that the TBI system isn't holding the vehicle back.

Maybe the tbi heads, but the injection system isn’t horrible. Let’s be honest with ourselves, are we really driving these things for fuel economy, or are we driving them because we are in a committed love/hate relationship with them?

 

[PlayingWithTBI]

This is post is laughable. It could be picked apart from so many angles such that all I'm going to say is that you will not get better MPG swapping to a carburetor and that the TBI system isn't holding the vehicle back.

^^^What he said x2

 

[89GMCJOHN]

Maybe the tbi heads, but the injection system isn’t horrible. Let’s be honest with ourselves, are we really driving these things for fuel economy, or are we driving them because we are in a committed love/hate relationship with them?

X2

 

[Supercharged111]

Maybe the tbi heads, but the injection system isn’t horrible. Let’s be honest with ourselves, are we really driving these things for fuel economy, or are we driving them because we are in a committed love/hate relationship with them?

Gonna disagree/clarify. The TBI heads, intake, and cam are all horrible, but they match. You need to change all 3 to make real juice and changing just 1 won't make that much of a difference. Nothing wrong with the system though, I had one and it worked just fine.

 

[JCribb]

Gonna disagree/clarify. The TBI heads, intake, and cam are all horrible, but they match. You need to change all 3 to make real juice and changing just 1 won't make that much of a difference. Nothing wrong with the system though, I had one and it worked just fine.

Yeah, I changed all three, and wow what a difference between the two. The downside to do this is all the other “little things” that are required to make everything play nice with each other afterwards. That gets expensive, but as they say, you gotta pay to play.

 

[RayHardesty187]

I have a 98 short bed k1500 its lucky to get 13. So I give on mpg and I'm looking to beef it up. Lol might as well

 

[DerekTheGreat]

Gonna disagree/clarify. The TBI heads, intake, and cam are all horrible, but they match. You need to change all 3 to make real juice and changing just 1 won't make that much of a difference. Nothing wrong with the system though, I had one and it worked just fine.

The beauty is indeed that the components match. Everything was "horrible" back then. Ford & Dodge weren't doing too much better in the HP/TQ department. Given the era and what they had to work with, I really feel they did a fine job- just as you said. They produced an engine which gives good grunt down low which is ideal in a truck. I've haven't done much towing with it but I've never had trouble starting a load or worry about stalling it. I towed more with my four-banger Colorado and that was an issue.. But I digress, compared to the lack luster crap of the mid to late 70's, power was on the way back. I've been daily driving these and Ford trucks in bone stock configuration for about eight years now. Since I don't have a bank note or the increased insurance/registration premiums that go with new cars the only reason I monitor MPG is to get an idea for how my vehicles are running. I'm pretty darn satisfied with the truck GM built as it is. I'm not against modifying one, it's just I wouldn't need the extra power 90% or more of the time.

 

[JCribb]

Here’s my mileage logs and mpg numbers. I don’t have information prior to 4/2016, but it was about 10 mpg consistently with a cracked head and worn out motor.

Everything in the attachments is after my new motor with an RV cam and vortec heads, tuned appropriately for the mods.

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[JCribb]

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