Pontiac Firebird 1967-2002 - Getting horrible gas mileage in my 2000 WS6.. and not because of my right foot 0:)

Just as the title states, i'm getting pretty bad gas mileage in my 2000 WS6 (24-25 highway) and I know I don't have a japanese fuel sipper, but some of my friends with similar mods are getting around 30, which makes me believe something might be wrong. I usually run about 75mph on the highway (1900ish rpms). cruise control doesn't make a difference. It is a 6-speed. Does anyone have any ideas? Here are all my mods:

slp intake
bbk TB
3.73 gears
lowered 2" (which i thought would even help gas mileage a bit)
headers and borla catback (no cats)

I've already changed my 02's and spark plugs/wires and that didn't seem to help anything. It has about 108k miles. Any help is appreciated. Thanks in advance

24-25 highway with a 300hp V8 is bad?

That's about what I average at 75-80. I can get 30 at 65ish

Sounds about right for 75mph plus.

Maybe change your air and fuel filter. And make sure you use premium gas.

24-26 mpg is now considered horrible gas mileage! That's the funniest thing I've Ever heard. If your friends are saying their getting 30 then they are lying. They might get 30 in spurts on the highway but I would guess on an average it's below 24 mpg, which in my opinion anything over 20 is a plus for a 350hp car.

I agree, don't complain about 25mpg with how much power our cars have an how fast they are.

24-26 mpg is now considered horrible gas mileage! That's the funniest thing I've Ever heard. If your friends are saying their getting 30 then they are lying. They might get 30 in spurts on the highway but I would guess on an average it's below 24 mpg, which in my opinion anything over 20 is a plus for a 350hp car.

Exactly. I have a 2000 SS and a 2001 WS6 and drive them both as if they were Honda Civics.The T/A is bone stock and the SS has just a couple of mods. Driving highway at 55 and minimal red lights (drive to work at 4:00 AM) I have never even touched 24 mpg in either car. So yeah the 30 mpg is bullshit unless they are Fred Flintstone(ing) it.

I can attest to 30, my last '98 TA had 200,000+ on her and I got 30 on 100% highway at about 80 degrees keeping speed around 70. It had an FTRA, K&N Filter, SLP Lid, stock intake, manifold, cats. By '99 got around 27 MPG with mid-length headers, ORY. I was using a 6LE shaker air box, so the airflow was not really comparable with others out there. 30 is not that unusual for LS1 hwy cruising at posted speeds. I replaced my last week and hope to see 30 again in a couple of days.

Want to drive my 79TA and enjoy 16-18MPG on the hwy?

Exactly. I have a 2000 SS and a 2001 WS6 and drive them both as if they were Honda Civics.The T/A is bone stock and the SS has just a couple of mods. Driving highway at 55 and minimal red lights (drive to work at 4:00 AM) I have never even touched 24 mpg in either car. So yeah the 30 mpg is bullshit unless they are Fred Flintstone(ing) it.

I hit around 30mpg with my Formula all the time, and I've hit 34 with my Vette as it sits. Long highway driving (as in 1+ hours with the cruise set) and you will get it no problem. But for the OP, your gears and running 75mph is why you are only getting 24-25.

I checked one take of pure highway this week. Got 25.8 MPG. Lower than I got on my previous engine. I didn't have the IAT set up right and it was surging for about 50 miles, but regulated itself for the remaining 300 miles or so. May have lost some mileage with that. I am running headers and a FIPK like intake, but other than that, it is a stock M6.

In my 01' WS6 m6 with stock gears i got 29 on a nonstop 300 mile trip driving 70. Now with 410's i get about 23 24 on the highway.