ok, my little 2.8 is still running like a champ, but when it dies I'm not going to put another one in.

Let's say I was going for the ultimate daily driver,and MPG were more important to me than power. If I went with a t56 with a 4.8 or a 5.3 and had it tuned properly, what MPG could I hope to get on the highway?

is 35 possible?

I love the look and feel of my car, so I'm not interested in getting a honda or a cavalier just to get those kind of MPG, but if I could drive a third gen and get way over 30 on the highway, I would be in heaven

 

When my car was in proper tune with the 305 I was getting 32mpg with a 5sp 3.08 rear. I would think with a 4.8 and 6sp you could easily get that 30mpg number.

 

I was throwing the thought around as well and had a couple of different factors in mind. One is inertia; say from a stoplight, and also highway mileage as you mentioned.

For inertia I was thinking of staying with a smaller engine (weight), smaller diameter aluminum drive-shaft and aluminum drums. IMO, you still want a decent amount of torque so you're not getting into the throttle as much.

I was thinking that highway mileage depends on a few things. First is the minimum HP to maintain your desired speed vs. your desired rpm -matching overall gearing, and optimum engine efficiency. Hills and wind are a couple of things to consider as well since dropping down a gear all the time may end up being less efficient in the end. So you might want to add a little to the desired minimum HP.
Skinnier and harder tires may help too but it may not handle as well. Little things too like checking your bearings and how freely the wheels actually rotate (brake drag etc.).

 

I was getting over 30mpg with my head/cam LS1 t56 on the highway. Around town id get 15-20 but I never "tried" to get good mileage it was just a side bonus. The car was tuned tip top mind you with 3.73's it would cruise between 1500-2000 RPM at highway speeds 65-80mph

If you want mileage id look for a 2010+ 4.8L with VVT and run one of those. They are already 304hp and the VVT bumps mileage about 1mpg or so. Avoid AFM engines though they are proving less than durable. Dont say I didnt warn you about the HELLISH swap issues with the newer gen IV stuff tho.

 

I've already been warned to stick with the 2002 and earlier LS engines for the ease of the swap.


Sounds like 35 is possible...It would take a while for the swap to pay for itself, but it would eventually happen (I'm getting 24-25 right now in my 2.8)

 

scribing to this thread........

 

On Saturday I took a "mini" road trip - 170 miles round trip. Most of it was 75 MPH interstate. Averaged 27 MPG. Stock tune.

 

GM was testing an LS2 'vette with AFM, but not VVT, and got 35 MPG from that. A 5.3 can do 1500 RPM at 65 MPH, but there's a very real possibility of doing more MPG with slightly more RPM. It's one of those things where you get a new baseline, then change something and re-test, then try something else, keep chipping away at it.