Car is a 96 ws6 with 90k miles. In the last month I have replaced:

opti
water pump
plugs
wires
fuel pump
o2's

Only mods are LT's, catback, and a Mezeire EWP.

Driving 80% freeway and 20% city netted me ~21mpg. On the freeway I generally cruise in 6th gear at approx 75-80mph. The next time I drove about 70% freeway and 30% city and got approx ~19mpg. I had no WOT runs either time.

The car seems to shake a bit at idle, but the engine holds rock steady idle so I'm guessing its just normal engine harmonics.

 

change out your fuel filter!

 

That's about what I average. 19-23 and I get on it a lot. Prolly 65% hwy 35% city. Not too bad considering my winter beater (98 Sunfire) has half the cylinders and weight and gets about 27 mpg.

 

Forgot to add that to the list. It was changed with all the other parts.

 

I don't get on it much if at all and average 18-20mpg. I normally would have just assumed it was normal, but I've read several instances where people claim to have gotten 25+mpg on the freeway. BS maybe?

 

I've read about people getting phenominal gas mileage too. The most I've gotten on a single tank was 25 mpg. But that was taking it considerably easy because my water pump was leaking so I baby'd it until I could get it changed.

I don't see CAI in you sig. If you don't have on I would definately get one. You will see a HUGE difference in MPG.

 

I got 27.5 on the hwy once. I filled up, got on the interstate and drove 4 hours. I had the cruise set on 78 and it was late at night so I didn't have to take the cruise off but like 3 times. As soon as I got off the interstate I checked the mileage. I was just curious the best my car could ever get on the interstate.

 

thats exactly what i (used) to get on the freeway (6 speed bone stock)

this coming spring-- who knows. lol

 

Best I've ever ran was 32mpg, heading to the jobsite 111 miles away. I expect to see a significant loss however, after the 383 is in

 

yea I got 26 all interstate on my last formula that was mainly stock. That was with my cruise set at 75.

 

If you have no peformance issues you are in good shape. I was getting 14-15mpg for years and was pullin high 13's in the 1/4 with a few bolt ons.
if it aint suckin gas and haulin as* its no good.

 

If you have MPG issues:

-clean injectors
-test/replace O2 sensors
-replace fuel filter
-clean out the PVC valve (carb cleaner works)
-check the gas cap area for gas smell (carbon canister may be shot)

Headers, CAI, and various other mods that improve VE (torque) should be good if you drive the same. Gears, cams, and anything that adds weight is bad.

Try not to compare MPG with people in other parts of the country. I've read those at higher altitudes have slightly different gas (lower energy), as do summer blends over winter blends... havn't seen it for myself though.

State to state will varry the ethanol content (which saps MPG... and increases evaporative emmissions at the pump... damn near the worst environmental imapact of any additive :-/) which will effect MPG as well.

finally the BIG difference will be in driving style. Some of this is the driver, but a lot of it can be terrain. Getting 25mpg in Wyoming or North Dakota is unremarkable... doing it in Western Washington or Coastal California is damn near impossible. Why? Mountains.... hills and mountains.

Hybrid vehicles with regenerative breaking should help fix this disparity, but for an LT1... the plains will get better MPG due to more highway driving and less varried terrain/hills to accelerate up.

Maybe if Al Gore shut down some of his massive engery-hog mansions we could have excess electricity to make electric cars viable.

 

Good points Steve,

First off most of my highway driving is between San Diego and Los Angeles. There are alot of hills and when cruising at 75-80, engine loads definitely change continuously as I'm going up and down the hills.

Also, ethanol content in our gas is around 10% I believe. I've also heard that ethanol is detrimental to our fuel pumps, and I've seen alot of CA owners suffer from dying fuel pumps (myself included).

I guess I'll just have to accept my mpg. I plan on doing roller rockers soon, and will be getting a dynotune afterwards, so hopefully I'll maximize my fuel efficiency then.

 

Did you gap the plugs correctly before you installed them? My car has 92,000 miles and I got 27.8 mpg on all highway driving the other week. Got to love that sixth gear.

 

I have been getting terrible gas milage as well. So far, replaced the air filter, did an oil change and filter (I know that probably wont do anything, but it needed it either way!) and cleaned the maf. It got a check engine light the other day, and I have a sneeking suspicion that its the o2 sensors, so they are on the list, as well as the fuel filter.