How much does weight have to do with fuel economy???
 

I think 35-40 lbs of weight reduction will help my fuel economy on the street, what do you guys think??

Purely based on hearsay and without a shread of solid evidence (which I have not looked nor asked for) is this:

The rule of thumb from engineers on this issue is that with every ten percent of weight reduction mileage is improved by about 7%.

If my math is right, 45 pounds would be about 1.5% of a 3000 pound car. This would translate to 1% or less improvement in mpg?

Darin removed most of his interior and it looks like his mileage went up. Can anybody do some scangauge testing on this or present scangauge data???

It's not actually 45, it's around 55-60lbs. i got some other stuff removed.

But he (Darin) had a few other mods as well + temps are on the rise + the stuff was only out for a few runs + even a measly hundred pounds is a hair over 5% of a Swift-clone's weight (that equals a 3.5% FE increase according to the rule-of-thumb) + CODFISHing like a madman = a 75+ mpg tank.

I don't think he was actually talking about you compaq. I believe his 45lbs figure wasn't in reference to you.

That being said, the EPA says that every extra 100 lbs is 1-2% decrease in fuel economy.

100 lbs is noticeable. In 2004 when the car was stock it would run 17.03 was my best run with full interior and no spare/jack.

Then I removed the passenger seat and the rear seats, which was about 65-70lbs and then ran 2 runs. Which were 16.94 and 16.96, that almost a full tenth. A tenth is about 10hp difference in racing terms. The moral of the story is all that stuff removed was about 100 lbs, which made the car quicker.

I think you're right, Matt. Any mod probably varies hugely car to car. If a car starts off heavy you're going to have to remove a lot more weight to see any noticeable difference in FE. You can see a 1-2% (or higher depending on circumstances) difference in FE trip to trip.

Could it also have been that you got better at launching the car? 1/10th seems minimal to me - I know it's not in the racing world, but if your reaction time got better then couldn't that account for the same time? It could have been the weight too, but the driver accounts for a lot.

A 100 lbs will probably mean nothing on the freeway but 1/4 mile racing not constant speed, it's all about accelaration. Driving on the streets is all about accelaration most of the time.