If I was to get one I'd probably wait to see if Santa would bring it that way it doesn't cost me anything. But if it really wouldn't save me that much gas I'd look at other things.Very very little actual gain in efficiency to the engine. If you want a catback exhaust for the noise, do it for that. It'll set you back, what, $400? You'll never make that back in saved fuel economy. If you want to increase your MPGs, exercise good driving manners and self control, and spend the money on keeping your car in a proper state of tune.
You will not, ever, make money by spending money in this way. It's the same logic as taking a $5,000 bath trading down to a car with ~10% better fuel economy - its self deception at best and plain idiocy at worst.
i'd like to know why having a supercharger has anything to do with it? People buy exhausts sor either sound/style/performance. Not b/c they have a supercharger rofl. So are you saying it's a waste to do full exhaust cause all it does it sound fast? [paranoid]There are very few mods that will help mpg. The factory squeezes about as much mpg as can be had. Alot of times when you go with a "free flowing exhaust" the scavenging effect is lost and MPG goes down. Only reason to do an exhaust on these cars is if you have a supercharger or you just want it to sound fast.
Ok..I will explain a little bit more in depth. The effectiveness of a bigger freer flowing exhaust is mostly seen on high hp cars that rev to really high rpms. On a 110 hp spi motor a catback is not likely to see any more than a 10 hp gain. On a supercharged 200-300hp car you are likely to see a 20-30 hp gain. Also the hp gains are seen only in the very top of the power band and can actually hurt low end torque. Catback effectiveness increases exponentially with rpm and base hp. Price vs performance on a normally aspirated 110hp car makes it a very uneconomical mod if your doing it for performance. Alot of cars don't respond well to bigger freer flowing exhausts and actually lose horsepower and mpg.i'd like to know why having a supercharger has anything to do with it? People buy exhausts sor either sound/style/performance. Not b/c they have a supercharger rofl. So are you saying it's a waste to do full exhaust cause all it does it sound fast? [paranoid]
The buttometer can be deceiving. If you were to put it on a dyno before and after you would see that you probably lost a little torque down low and gained a little hp up in the top of the rpm band. Exhaust has a huge impact on the torque curve of an engine. Bigger is not always better. Same goes for intake runners. Long and skinny runners bring the torque curve down and short fat runners bring the torque curve up. If you want to get good mpg you design an engine with the torque curve right in the middle of the rpm you drive in the most. If you are looking to get the fastest ET at the track then you design the engine to make peak hp right at or slightly before your shifting rpm. Take a look at the late John Lingenfelters engine book some time. He explains it much better than me.[hihi]I know this because I have full exhaust on my spi and the difference in power was definitely noticeable.
Pretty nice gains from just bolt ons. I'll bet the tuning did more than anything. When you get the air fuel ratio at wide open throttle just right it can give significant gains. My Firebird will gain +- 60 rwhp just by adjusting the air fuel from 10.5 to 11.5.[burnout]My 1/4 mile times from before and after full exhaust would tell otherwise my friend.
Went from an 18.6 to a 17.4 just by adding full exhaust, all 3 motor mounts, got my car dyno tuned by Tom, and changed to lighter wheels.
I know from going with a 2.5" exhaust, I lost a little low end torque, but when I got my car dyno tuned, I gained all of that low end torque back and more. The midrange torque is damn good also, and the high end torque was improved the most from the free flowing exhaust. It also helped that I have a good intake setup.
Nope no mullet here. LOL. Just an old Army Pilot gearhead with a fade and a talent for building and tuning 600rwhp V8's. And to the original poster there is no chance that a catback will increase your mileage significantly.no way, 60 rwhp by addjusting the AFR not a chance! especialy in an old ass firebird, I could see it happening if you had a mullet, but I feel that you don't have one of those.