for better mpg’s, would it be better to be at a higher rpm with less throttle or a lower rpm with more throttle?
lower rpm, more throttle
it depends.
on a flat surface or downhill, you want to be in the highest gear possible at the lowest RPM.
going uphill, you want to be at your peak torque RPM, regardless of gear.
I’m going to assume that speed is a constant. Lets see here. The only way to achieve these sinarios is to have a gearing change. Even at that, if the engine is the same it doesn’t make any cents. How to you achieve a higher rpm with less throttle then a lower rpm unless your are accelerating. Or geared to the point where your at max speed at WOT and your engine is at 2000 rpm.
Ok, think about it like this. You have an engine that will maximaze rpm at half throttle and 30% load at 5000 rpm. Your transmittion and rear end are both 1:1. Your tire circumference is 15". assuming that the power output is enough to propell your car threw the wind and other frictions, you are traveling 90 miles an hour. That would be a hypothetical optimal running condition. to deviate from that in either direction with your gearing would generate more fuel consumption. If you increase the gear, then you need more throttle/fuel to achieve a higher rpm and same speed. If you decrease the gear then you need more throttle/fuel to achieve a lower rpm, and the same speed.
I just made all the up though. so take it with a grain of salt 
higher rpm less throttle = better MPG
low rpm more throttle = shitty MPG its called city driving :doh:
my old sho got 5mpg better at 85 than it did at 65 because it was closer to the powerband of the motor.
if you have a stick, just trans brake it all the time.
rolling in gear trans braking = no injector firing = no gas usage.
Trans brake = 1st and reverse engaged at the same time.
Not to good mpg that way
Totally vehicle dependant. I get better MPG @ 85 than 65 (approx 2k rpm vs 1500 rpm) in 6th gear in my car. Though at 65 in 5th I probably do about the same as 85 in 6th (not sure since I don’t spend much time in that gear/speed combo). At 1500rpm the car pulls along just fine but the engine is out of it’s efficeint range. Now I could go 85 in 5th and barely touch the gas but I’d still get worse mpg than 6th. My car makes 300+ rwtq by 2k rpm so it’s plenty happy in 6th @ 85.
-TJ
PS- I think fshowcars meant “engine” or “compression” braking. Aka using the motor to slow the car down by downshifting. Not sure how this will help save mileage though. You have to gain the speed at some point to need to slow back down. As far as MPG is concerned I don’t think it’ll make any difference if you use the brakes or the motor to slow you down. Either way you won’t be on the gas and will be using very little fuel.
I agree …
Thats one of the great things about diesels … I have 402 rwhp - 964 ft/torque and I get 20-21 mpg … Under normal driving. If I really get my foot into it and feed her full fuel … then it goes way down.
Does anyone have access to a banked oval to test out some of these theories under controlled conditions, I’d love to go play around on an oval track, taking measurements and graphing this stuff to find out…
trans - TRANSMISSIONS BRAKING
meaning to ride down the RPM’s in gear… and you knew this…
simply because a car idling is burning more gas than a car engine braking… injectors are not firing when the tranny is spinning the motor.
some cars came with a vacuum gauge or fuel economy indicator. The best mileage occurs at the highest engine vacuum. I would imaging that a vacuum gauge could be used on a fuel injected engine and that it would indicate the same problems as when hooked up to carbed engine.
[QUOTE]trans - TRANSMISSIONS BRAKING
meaning to ride down the RPM’s in gear… and you knew this
:kekegay:
downshifting does not increase MPG :rolleyes:
so if you’re heading down a hill coming to a red light do you downshift the gears and slow down, or throw neutral?
neutral and use the brakes.
less on the drivetrain too, brakes are cheap :booty:
I use reverse to stop all my vehicles
thats fine about your brakes… but your injectors are firing in neutral burnign gas.
if you’re in gear, riding down on the transmission, it’s spinning the motor and you arne’t firing ANY fuel
so right there shows you how downshifting saves MPG… if you rolled 1 mile downhill in gear and didnt touch the gas you’d have infinity miles per gallon :booty: