your friend drives a RX-7 right? He is the last person who should give you advice about gas milage. I would love to have a rotory motor but and this is a big BUT[bootyshak RX-7's get terrible milage they are great for power to wieght they make alot of power for there size and weight but they burn more gas than a piston driven engine also they make no low end power they like to rev and be in there power band which is why he probably told you to down shift cause in his car it probably does alittle better at higher rpms in its power band they don't like to be lugged around at low rpm.
you can find rx7s for around 10k all day long... and im talking nice ones with freshly rebuilt motors and single turbos. its the supra that hold their value....
as for this discusion, honestly i dont think you will notice a difference. i think if you tested your gas milage never downshifting to slow down, and then tested it with downshifting to slow down you probably wouldnt be able to tell. yes granted downshifting will use a bit more gas but think about it you arent even hitting the throttle, it really isnt going to be much fuel. you should just tell your friend it is a stupid discusion and the idea of whether or not to downshift should be left up to however you see fit to the situation.
actually its true....u do save gas downshifting....ur friend is right....sorry guys it is true....when u fully left off the gas in gear you are using ZERO gas.....the momentum of ur car is keeping the engine alive, and no it dont hurt ur clutch because its hardly putting any more stress on it then starting off into 1st is.
cliff notes: it does save gas downshifting (as long as u dont rev match....)
markysparky66 is right. Modern day fuel injected motors basically shut off if you leave the car in gear and coast to a stop. As long as the motor is reved above idle speed while coasting it's not using any gas. If you have an AFR meter you will see that the AFR drops off the scale when you are coasting to a stop with the car in gear.
i still dont understand...if the car is coasting then it uses no gas right?...so if i decide to put it in neutral or just hold the clutch and let it coast...is that the same thing?
cause if it is, then theres no difference between rolling/coasting at idle and just sitting/parking at idle (other than the speed)...which means that if it uses no gas coasting then it uses no gas at idle...which is wrong cause if i started my car and let it sit all day i would eventually run through the tank...someone please explain it to me!