I would say throttle position has more to do with fuel economy overall than speed.

As long as you can keep your vacuum at -15 to -19 inhg, your fuel economy will be spectacular.

 

I can get it down to 20 in/Hg if I really try, but its mostly at 11". lol.

 

I can get it to 19 or so, but even on flat ground i slowly loose speed. So 15 inhg seems to give me around 22-24 mpg on the scangauge2.

 

i got 25mpg at 70mph

 

The torque peak of our cars is around 5500rpm. How do these scenarios compare in terms of fuel economy then? The TPS would be lowest at 4th gear, then 5th, then 6th?

a) 6th gear, 105 km/h, approx 3200 rpm
b) 5th gear, 105 km/h, approx 4000 rpm
c) 4th gear, 105 km/h, approx 5000 rpm

I think I remember that staying below 3500rpm, the engine will only use the first set of fuel injectors. Between 3500 and 6000 rpm, the engine will use the first and second set of fuel injectors. Beyond 6000 rpm, the engine uses all 3 sets of injectors?

 

The torque peak is where the engine is most efficient. That doesn't mean it's getting the best gas mileage there though. You need to factor in time. Higher rpms require more fuel per unit time than lower rpms. You can actually lose some efficiency runing at a lower rpm but you may still come out ahead mileage wise.

 

Yes, sadly the gas consumption is very rev-dependant - cut the revs and save your gas.

I did an experiment after finding the torque peak was at 5300 - tried to maintain those exact revs for a whole tank-full!

The results were entirely predictable, the mileage was crap, but it sure was fun!

S

 

doesnt the secondary ports opening have an effect on fuel milage at 3750 rpms?

 

I do not think so. Why do I say this?
I have a MPG analog gauge. Its a plastic one from JC Whitney. ( a vacuum gauge bought for 1 buck at the local flea market)

It can be calibrated to fit your car. It says "relative" so its not that accurate.
The main point is to drive with the needle as far to the right as possible
I have it installed on a 4 cy MX-4

It all depends how I drive, not the speed I am driving. Ie, I sometimes get better gas mileage at 65 than at 55. Yes, at 70 and above it tends to go down.

It takes some getting used to, how much pressure one puts on the gas pedal, even at the same mph.

In stop and go traffic, its more important, how one starts and stops than the actual MPH
In highway traffic, its a bit different story.

So I say, get some kink of MPG gauge, ie vacuum gauge, and try it out.

 

Were you being towed by a tow truck or were you going down the mountain side

 

Interesting.......what is illegal and dangerous about it?

Are we talking about coasting in neutral doing 65mph on the highway, or like I often do, coast to the stop sign when in residential neighborhoods.

 

You missed the throttle position bit.
If you do the math (or actually try it) the torque peak with minimal throttle is ALWAYS the best fuel consumption.
Problem is that it is difficult do drive low throttle/high RPM.

 

I agree that it seems to be revs more than mph - there seem to be 'sweet spots' on mine at different speeds - I can get some very good long haul milage at about 85, but easy revs - just letting her settle in, I get a good spot at about 48....

But all this may be moot - CNN just announced that the Senate is debating a federal limit of 55 mph - for our own good - just like they did during the simulated gas crises during the 70s. Rumors say they are responding to electric car and Prius owner demands that they slow traffic down enough to allow them to catch up!

 

But what happens when you are goin back home for the day and ur at the bottom of the hill? lol Gas mileage I try to keep it under 9000rmps for the best gas mileage thats about it I bought this car to have fun and the government is not goin to ruin my fun by jacking up fuel prices for no reason!!!

 

QFT.

 

any more info the accessport? i haven't heard much about it. i guess i'll search

 

https://www.rx8club.com/mazdamaniac-183/cobb-accessport-discussion-140117/

 

while a general rule can be lower rpm = less fuel... it's not always the case.

depending on engine rpm and/or idle positions, the fuel injected can be any percentage of the max flow rate of the injectors.

now if you're cruising in 4th gear at 2,000 rpm - you could be getting 50% of max fuel flow of the injectors. but if you were 3rd gear at 3,000rpm (same overall mph), you would have a 50% increase of rpm but perhaps the injectors aren't pumping out as much fuel because it's in a more "efficient" power range...

I'm not going to create a formula on the spot because i don't know the actual numbers that the fuel is being pumped at what rpm and what load... but theoretically a higher rpm "can" be more fuel efficient in certain cases.

Also i believe that when coasting down a hill, it's better to leave the car in gear as the fuel will be cut completely rather then becoming an engine idle situation to keep the car running.

 

Where coasting can be illegal is going down a hill with either the car out of gear or the clutch pushed in. It was a law designed more for trucks since you have no engine braking and if you need to do an emergency stop or maneuver you don't have time to think about finding the right gear since brakes alone aren't going to stop you.

Coasting is bs anyway, the fuel injectors stop injecting if you coast in gear with no accelerator input as long as you keep above the RPM threshold. Even an engine with a carburetor won't be using much fuel since the high vacuum is below the butterflies. To maximize your fuel economy coast down to your stop in gear, pushing the clutch in when you're getting close to idle.

 

immmm soooo guilty of that.

my girlfriend lives 30 minutes away on the freeway.

i have needs. and those needs cannot be fulfilled legally with 4.98 gas at shell .

 

It all depends on how far you're coasting--if you can coast longer than engine braking slows and stops the car, coasting can of course be much more efficient.

WRT the original question. I just back from a 500+ mile mostly highway trip at mostly 65 mph cruise control and got 26-27 mpg with AC on/off and lots of state troopers out for the holiday weekend.

 

none...0mph

 

A person would have to be a mathematical genius to decide if the idle fuel consumption during coasting would be less than what it took to get you back to speed after a certain point, plus have complete knowledge in the road ahead. You are right in that it theoretically can be more efficient, but the likelihood of getting it right is a factor of luck, not skill.

 

then you get 0 miles to every gallon you burn idling...

 

It's really just common sense if you know your car and watch the road ahead of you then you can see if you can coast further than the engine would stop you. Hypermiler fools will even turn the engine off if they can coast a significant distance. Can be dangerous if you don't realize you have power assist brakes, 'though.