what upgrade are you planning on?

So far I have tuned the car, replaced O2 sensors, replaced water pump, replaced Cat, and done induction system cleaning.

Upgrades to follow for performance and hopefully gains in gas mileage will be the CAI, a 160* T-stat, and I am researching if there is a more aggressive CPU that will give me more performance and better shifts.

the only thing you can do is buy a new e-prom (chip) for the computer, or have your old one re-flashed. and if this car is a daily driver, i wouldn't go lower than a 180 stat.

Firemouth, we have the funky OBD 1.5 year PCM so any drop in chip is out of the question. Apparently GM Tuners is our only option to flash our PCM, although I haven't looked into yet. Our cars are twins so I'm interested in all you do to your cars cause I'll probably follow you down the same road in mods. I'm already dealing with a bunch of codes before any mods tough. I get 16 city right now with practically no highway driving. I'm curious to see yourm "new" mpg with the cat.

Boss455,
new mpg=24 combined. I am taking a trip to Chicago next weekend and wil try to run at 75mph on cruise to see how far 15g gets.

Alright I don't feel so bad about my mileage now...

I usually average 21-23 mpg combined State Hwy (speeds of 60-70, multiple stop lights) and city/residential. When I've been working (delivering pizzas) it'* gone down as far as 17, but on an all-freeway, cruise-set trip, I've gotten as high as 29!

I miss my 35 mpg Cavalier at times, but then realize it'* worth the mileage drop to drive a Bonneville!!

I drove to chicago and back this weekend and got 410 miles out of 15g of gas. That'* 27mpg highway!

I was very excited to see this thread on mpg. I've been looking for reasons why my 1995 Bonneville got better mpg avg than my 99 (26 vs 24), and both got better than my current (2005 & 22/23 mpg). I pride myself on good gas mileage, and have been pretty disappointed in my decrease over my cars. Perhaps it is only my experience, but it seems that you get the better mpg when you get > 100K.

I've been told that hollowing out the catalytic converter can help airflow, but was also told in the same breath that it isn't legal. Anyone doing this type of thing, or know if it is worthwhile (or worth the risk)?

I'm also interested in CAI and what the mpg possibilities are with it. And can someone give me the quick rundown on what a different themostat will get me - I saw 180 vs 160??? What # is OEM, and is it good - or could it be better?

I don't know what you have for laws in Columbus, but watch gutting the kitty if you have a tailpipe test. Here in PA, they're law and a PITA. Now if a car is running well, it can pass, but it don't take much to screw it up (at least to fail here). Maybe look into a high flow cat. While it'* still a compromise, it will still do the job intended. My 87 GN has one and it passes the test every year with flying colors...yet can still fly on the road.:P

Plus, if your exhaust is cleaner, my air will be cleaner as the prevailing winds are from the west.

took a trip to NH in februaary

and drove around there and in town for a little while and got 38 mpg on that tank!

i was shocked