Does this sound right? I drove the car as nicely as possible just to see how much I could squeeze out from it. This is city/highway driving combined.

I once got 350 straight highway which is good, but my city value sucks!

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89 GTA G92
305 TPI WC 5spd w/3.45
Accel Cap & 8mm Taylor's
Custom 4" Cold Air Induction
Jet Airfoil
K&N Airfilter
160 deg stat/fan switch TB Bypass - Steel Rad
Cat back 3" Exhaust w/Terminator Muff.
HiGh FlOw Dynomax Cat
Spohn LCA's - KYB GR-2's
Moroso Crank Bolt and roller pilot bearing.
Autometer Vac+Oil Temp

 

I get around 425km in the city driving like a bitch. My usual tank lasts around 375 km to 400 km tho.

On the hiway, I've squeezed out 510 km, but that was pushing it.

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1991 Firebird Formula
305 TPI,Auto,Custom 3" Mandrel bent I-pipe, Flowmaster 80 series muffler, 3" hi-flo cat, Accel Cap & Rotor, K&N Filter, Grant GT Steering Wheel, 5% Rear tint, Pontiac Windshield Decal, Fresh paint

Former owner of an 88 2.8 Firebird....RIP

 

Depending on which gas I use I get different results. The best I got was around 340 km on 87 octane in the city and I was suprised because I was driving it faster than usual. On the previous tank I was driving like a wuss and got around 280 km. I think there's an optimal speed for gas milage and its possible that you were driving too slow. Also, it depends how much gas was left in the tank. Sometimes I go below empty and when I fill up I find out there was like 5 L left.

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'90 Red Formula Firebird
305 TPI 5-speed
TB Bypass, Ported Plenum
UBC Sports Car Club

 

I get about about 300KM's (city) to around 50-55L of gas. That's about 15-16MPG. On the highway, yah, anywhere from 350-400KM to the same amount, (22MPG). I have a 5speed with a mildly built 305. (comp 260h, world 305 heads, edelbrock performer, tes headers, catback) I usually drive nicely, with the occasional tire shredding/road manic.
I think it's a reasonable compromise between power/economy.

Later,
Hype.

 

You guys should get into eprom burning. I have leaned my engine to 17.4:1 with 47* spark advance in "Highway Mode". I get 12Km/litre (over 600 km @ 50 liters) with this setup. The gas savings alone pays for all the equipement (which isn't that expensive).

I cannot comment on "city driving" as most of the driving I do is highway.

BTW, I have an L98, 4L60 and 3.23s.