Which is more fuel efficient?

[Byteme]

You'd still have the added drag of pushing the air around.  Better to just shut the valves and let the pistons compress the same air over and over.

Gotta balance the fuel savings against the added expense of such a valve train.

[Byteme]

MY RX-8 reports the same and when looking at the injector pulse width it goes to zilch

How do you know the injector pulse width?

[heelntoe]

he has a datalogger thingy

[S204STi]

Aye, Accessport. www.cobbtuning.com

[S204STi]

Y? The intake + exhaust valves are closed.

You're not paying attention. I was suggesting that as an alternative to closing the valves, but then realized it would still be an issue.

At any rate, being an air pump is the whole point of engine braking.

[JWC]

You're not paying attention. I was suggesting that as an alternative to closing the valves, but then realized it would still be an issue.

At any rate, being an air pump is the whole point of engine braking.

Jake-brake?

[S204STi]

Jake-brake?

Not sure how those work.  But even with a normal car, the engine is pumping but not creating energy, so it must be a hinderance, right?

[JWC]

Your description sounds a lot like the theory behind jake-brake.

I'm pretty sure that trying to accelerate my VW to get to a higher gear sooner will waste fuel.  I can also say that my Volvo's average mpg goes down with continuous hard acceleration.

[S204STi]

Your description sounds a lot like the theory behind jake-brake.

I'm pretty sure that trying to accelerate my VW to get to a higher gear sooner will waste fuel.  I can also say that my Volvo's average mpg goes down with continuous hard acceleration.

Ditto.  In theory is sounds feasible but in real life I do much better by driving gently.

[TBR]

I think you would have to shift very early for it to be effective which is difficult to do, particularly if your engine enjoys higher revs as much as mine does.

[Byteme]

Your description sounds a lot like the theory behind jake-brake.

I'm pretty sure that trying to accelerate my VW to get to a higher gear sooner will waste fuel.  I can also say that my Volvo's average mpg goes down with continuous hard acceleration.

Each car is going to be a bit different.  What Road and track was offering was a general rule.

Large throttle openings while shifting at low RPMs will reduce pumping loses.  I don't think they were advocating flooring it and shifting at 3000-3500.  Certainly they wern't saying run it up to near the redline and then shift.


BTW I tried coasting doen from 50 in neutral and in 5th gear.  No difference, the mileage readout went to 99.9 in both cases.

In the 3 I accelerate just enough to stay up with everybody else and shift at relatively low RPM, skipping 4th entirely, try not to change speeds often, anticipate lights and generally go 70-75 on the freeway half of our commute.  I must be doing something right.  I generally average 34 MPG in a 50-50 mix of stoplight city driving and crowded freeway driving.

[ifcar]

BTW I tried coasting doen from 50 in neutral and in 5th gear.  No difference, the mileage readout went to 99.9 in both cases.

On our fuel economy readouts, we see about 150 mpg coasting in gear in the Focus (depending on speed) and 999 (presumably meaning the fuel supply was cut off) in the Scion, while 250 or so coasting in neutral in either car.

[JWC]

Keep in mind, the VW is carburetor and I can't skip 4th. 

[Danish]

Keep in mind, the VW is carburetor and I can't skip 4th. 

Is that because you only have four gears?

[MrH]

Y? The intake + exhaust valves are closed.

He's talking about if they were kept opening and closing...

[JWC]

Is that because you only have four gears?

Yep.

[cozmik]

Hmm, so most people seem to be saying stay in gear. When I keep it in gear, the instating fuel economy gage goes to what I'm going to call infinity, and when I take it out of gear it stay in the 30-50 MPG range. The "infinity" position is also what it stays at when just idling at a stop as well though.

[MX793]

Hmm, so most people seem to be saying stay in gear. When I keep it in gear, the instating fuel economy gage goes to what I'm going to call infinity, and when I take it out of gear it stay in the 30-50 MPG range. The "infinity" position is also what it stays at when just idling at a stop as well though.

Your economy meter compares vehicle speed to fuel flow.  If the vehicle isn't moving, you're not really getting any MPG, so it must just default to the maximum value when it detects that the vehicle is standing still.

[ifcar]

It should show 0 mpg in that case; showing infinite would mean the fuel supply is cut off.

[cozmik]

It should show 0 mpg in that case; showing infinite would mean the fuel supply is cut off.

There is no 0 on BMW's fuel economy gage. The lowest it goes to is 12.

[Raza]

There is no 0 on BMW's fuel economy gage. The lowest it goes to is 12.

Heh, my Passat would show "---" when stopped, and go as high as the 300s when I was coasting downhill.  It showed 5 under floored acceleration.

[Soup DeVille]

There is no 0 on BMW's fuel economy gage. The lowest it goes to is 12.

Well, regardless of the range of the gauge, if the engine is running, and the car isn't moving, 0 MPG is the only possible accurate reading.

[hotrodalex]

Hmm, so most people seem to be saying stay in gear. When I keep it in gear, the instating fuel economy gage goes to what I'm going to call infinity, and when I take it out of gear it stay in the 30-50 MPG range. The "infinity" position is also what it stays at when just idling at a stop as well though.

In my car, it goes to the "infinity" spot when I'm off the gas (idling and coasting). Mine is an auto though, so I don't know what happens when I put it in neutral.

[cozmik]

Well, regardless of the range of the gauge, if the engine is running, and the car isn't moving, 0 MPG is the only possible accurate reading.

Right, and it goes to the same position if I'm stopped idling or coasting in gear. 0 MPG would seem impossible if I'm moving though.

[r0tor]

i do seem to get better gas mileage per my accessport when I bog the shit out of the engine