pjr710

i always thought the lower your rpms the less gas you use, but i was driving the other day and i felt like staying in 4th gear at 3k rpms w/ -20 vacuum would conserver more on gas than say 5th gear at 2600 rpms w/ 0 or -5 vacuum

so what is better?

z6hatchboy

Theres so many variables that deal with gas consumption. But more or less i think it has a lot to do with vacuum. For ex. going up a hill in 4th at 3500 with half throttle would probably save more than going up it in 5th at 2800 at full throttle. So mainly just whichever way allows you to be easiest on the gas pedal, thats my $.02

pjr710

yea i agree .. thats pretty much the point i was tryin to make .. less throttle has got to conserve over rpms

i thought about it like this, for tuning u need more air to put in more fuel, so if you have more vacuum, like -15, that is dumping in less air so that should mean less gas. now on the other hand i'f your at 0 vacuum, your throttle is wide open, so its just dumping gas in even if you at 1500 rpms

slowcivic2k

To this end the vacuum is a problem. EGR combats this by allowing the engine to suck in exhaust gas, which does not burn, to reduce the pumping losses in the engine (so the engine doesn't have to fight sucking in air, it can simply suck in "inert" air). The Atkinson Cycle engine also reduces pump losses by reopening the intake valve for a split second. Most people hate on EGR, when in fact, it is NEVER open on WOT or idle, only at cruise, removing it makes very little practical sense unless your using a manifold that does not support it.

Lower RPM means lower engine speed, and nothing more, Ideally, you want your RPM to be in highest torque curve at the lowest RPM. This is where the engine is most efficient in the first place since it can make high torque there. You want the lowest RPM to prevent excessive friction from rotating parts, but still have good torque at the same time.

To maintain 55mph, you need to have a certain amount of power produced, regardless of gear or RPM, the lower the rpm, the more pedal you'll need to maintain it, likewise, in 3rd gear, you can have a very light pedal, but has the disadvantage of moving parts fast for no reason, hence my resolution above. Every gear is a torque reduction, and you'll make the engine produce more torque, instead of upshifting to produce it,and keep the RPM in the ideal zone.

Atkinson cycle helps a LOT
EGR helps a LOT

Anything that would reduce intake vacuum without dragging the motor is a good thing.