5.7 vs 5.3 mpg increase

[92yukon]

Just bought a 96 2 door Tahoe (will be my daily driver when my lease goes back) with about 215k on the engine and was thinking about possibly doing a LS swap for reliability and more mpg's hopefully. What would be the expected mpg increase with a 5.3 vs a properly running 5.7 if any ?

 

[Jrgunn5150]

It's not precisely apples to apples, but my Trailblazer get's about 14.2 mpg with 4.56 gear's, a 3" lift, and 33's. My 95 GMC get's about 15.1, stock. No matter what, I don't think you'll ever save enough fuel to justify a swap on that basis alone.

 

[slowburb]

Right. How many tanks of fuel could you buy with the loot it would take to swap in the late model small block? You'd have to start counting there if you were doing it for fuel economy.

 

[skylark]

I think that you may have a hard time finding the information that you are looking for. Most people aren't doing stock engine swaps. Most likely when the VATS is tuned out there is some form of performance tuning done at the same time.

 

[92yukon]

Well im not pulling out a perfectly fine running vortec to do a 5.3 swap, but there was a good chance that this motor would be coming out due to age and mileage for at least a rebuild if not just a replacement, figured if its already out is it worthwhile to go to a 5.3 swap. Figured there would be more money involved in a swap but it may be worth it if there was a decent increase in mileage.

 

[GMRedline]

The cost could be justified depending on the price of gas.

Most people say an LS swap will cost about $2,500 on 96+ vehicles. Let's say your fuel economy goes from 13mpg to 15mpg. Those are the constants. The cost of gas is the variable. Here's an example.

100,000 miles / 13mpg = 7,692 gallons of gas
100,000 miles /15mp = 6,666.6 gallons of gas

7,692-6,666.6 = 1025.4 less gallons of gas over 100,000.

If gas is $1.50 per gallon you will save $1538 over that time.
If gas is $4 per gallon you will save $4,101 over that time.

At $1.50 per gallon you would need to drive your truck over 160,000 miles to make up the $2,500 cost.
At $4 per gallon you would need to drive it just over 60,000 miles to make up the cost.

It's impossible to know the exact payoff of an LS swap going only by fuel economy. The price of the swap might be a little more, or a little less. The fuel economy increase might be a little better or a little worse. The price of gas is the major question mark. It could stay low or it could sky rocket. We have gotten to $4 per gallon in the past.

The other thing to consider is the maintenance costs your old vortec might need. You already said it's not 100% healthy. Not doing repairs on your old engine shortends the payback period.

Basically like anything change or upgrade you make to any vehicle, you need to keep it for a long time to get your money back.