KLZE Fuel economy questions

[nightfire]

When would your fuel economy be better?
When driving with vris1 and 2 open or closed?

This is just a total guess, but I'd say in theory which ever state has a lower RPM (both closed, was it?).

A well running engine should easily maintain the proper AFR based on the O2 sensors, so the VRIS positions shouldn't matter. This is especially true when under low throttle (ie. highway) since naturally there's a big vacuum in there anyway.

[RX8SE3P]

When would your fuel economy be better?
When driving with vris1 and 2 open or closed?

Well they open @ 4000+ RPMS on a proper ZE ECU. I wouldn't expect good economy at 4000+ RPMs lol

Best fuel economy is probably 45-50MPH - 80kmph on a flat road. The engine has enough torque there and not much wind resistance. RPMs are not high either, throttle would be minimal.

60mph would also give good figures though. Once you break past that, it's a losing battle against wind resistance.

[Nd4SpdSe]

Well, at 4500rpms that's the peak torque for a KL01 cammed ZE, and IF i can stay around there, that's some of the best milleage I've ever gotten. Good luck to me to stay @ 80km/h on the highway. The thing is, it's not about revs, but about how hard the motor had to work....just cause your reving at 4000+ doesn't mean you'll get bad milleage. I remember that at 120km/h @ 4000rpms my foot was *barely* on the throttle. As I've mentioned, I had a trip I must of averaged 160km/h, hitting over 200 MANY times, and I still averaged almost 31mpg...

In the end, it's about matching the revs of the motor to use it's available torque to move the car. If you read the thread about cylinder deactivation, you'll see that a motor that works less is less efficient (see background and pumping loss)
http://en.wikipedia.org/wiki/Active_Fuel_Management" onclick="window.open(this.href);return false;

Thing that you need X power to keep a vehicle moving. Say you have a few Mx-3's, one with a 88hp SOHC, one with a 130hp k8 and one with a 200hp ZE with the stock trannies. Say they're all the same in terms of weight, balance and aerodynamics...because of those values, you need X hp to do certain work. Say that you need 30hp to keep the car going @ 100km/h. Now each motor is different, and Mazda from the factory geared tranny to mate with each motor, to use the power efficiently. Now I wouldnt be surprised if they sacrificed some efficienty to gain some performance, but more likely they did tailor it to the EPA 55mph. You can probably change the gearing a bit lower, but if you go too low, and you'll actually make the motor work harder. Think of it this way, what's easier, riding a bike uphill on a gear where you're pedalling quick, but it's pretty easy, or you're pedaling slower (ie: reving lower), but it's harder to get up the hill and you have to stand on your pedals and use your weight? Also choose a gear too low, and you'll burn yourself out before you get to the top of the hill.

Something interesting which I'd like to see and what had never been done, is to see the results of someone putting a Protege LX trans on a B6, and a Mx6/626 trans on a K8 and see the results.

How efficient do you think a ZE would be at 1500rpms @ 120km/h? I bet not well. It's a motor that rev's high, can do it all day and makes it's power up high. I believe my sister's H23 Prelude (auto) revved around 4k @ 120 as well. It's also why a Viper can get 30mpg despite having a V10, cause it makes so much power down low, so it can literally coast down the highway.

Just cause the motor is reving high doesn't make it inefficient, but could literally mean the opposite.

[RX8SE3P]

I totally agree but once you go too fast, the wind resistance becomes a major factor also, the more resistance, the more the engine has to work. The higher the RPMS the faster you are likely to be going too. Faster you go, the more resistance you get.

If there was zero wind resistance, like you said, peak torque would win, which is at approx 4500, the engine would hardly be working to maintain the momentum.


The rpms do make a difference though, it's all about where the engine makes it's power, then the manufacturer has to pick good gear ratios to go with it.

I'm personally using a MX6 box so I will be revving around 400-500 less than the K8 box. @3100-3500 the a healthy ZE is making about the same power as a K8 would at about 5500-6000. It has no problem moving the car at lower RPMs.

It'd be interesting to see who would win in a fuel efficiency contest. The best way to do it is if someone got a MX6 box, drove a long trip @ a specific speed then put the K8 GB in and did the exact same trip @ the same speed. I would bet that if the engine was a K8, it'd do worse with the MX6 box but if it was a ZE it'd do better with the MX6 box due to revving less.

[Nd4SpdSe]

I totally agree but once you go too fast, the wind resistance becomes a major factor also, the more resistance, the more the engine has to work. The higher the RPMS the faster you are likely to be going too. Faster you go, the more resistance you get.

If there was zero wind resistance, like you said, peak torque would win, which is at approx 4500, the engine would hardly be working to maintain the momentum.

Of course wind resistance is a factor, that's why torque/peak torque is necessary, to fight and hold against that resistance. If there was zero wind resistance, the engine would hardly need to work if not at all, so if the motor had almost no work to do...why would it need to use all of it's torque?

Yes, the higher the RPM's you have the faster you're going, but that's where you have to look at the power curve of the motor. You will always be more efficient the slower you go, no doubt about that, but to an extent you can go too slow where you're efficiency goes down because the motor isn't making enough power and/or isn't as efficient making that power.

I'm by no means saying that it's more efficient to go faster, reving lower could actually be LESS efficient and that reving high can actually be MORE efficient in comparison, at a given speed.

[fowljesse]

I seem to get best mileage at about 69mph, but no one has a setup like mine, although it's close to a proper chipped ZE. The car is lowered, which makes for less wind resistance. My best was 33mpg, but with Ethanol, the best I can hope for is about 29

[onlytrueromeo]

Well, because I live in constant cold temperature, I can use cheaper gas! I'm running 89 right now and power is BETTER than w/ 93. Gas mileage about the same. Work around the winter gas!

[WhiteFinish]

Back to the VRIS.

I think you'd use more fuel (now that i thought about it). Because the intake contains more air the ecu will try to keep the a/f ratio as perfect as possible. So more air = more fuel

Or is this wrong? hehehe

[fowljesse]

Your best mileage will be with the VRIS working properly. It is designed to cause better volumetric efficiency at various rpm.
Unless we had a mechanism that worked like a Trombone, it still isn't perfect, but it works well.

[RX8SE3P]

Hang on, I was wondering, if high rpms are just as efficient, N4SPDSE, how come people don't drive around town in second or third gear all the time?

Also if this is true, then my economy should increase during my city driving if I use 4th instead of 5th right?

I might see what economy I get off this tank using 5th gear again as usual. Last tank I got 400kms off about 34-35L. This time I will do the same and continue to use 5th gear. See what I get, then I'll post my results.

Next fill, I will use 4th gear in the city and will try my best to drive exactly the same as normal. I'll then see what I get.

In 5th I am going at about 1800-1900 rpms @ 60kmph. In 4th gear at the same speed will be going something like 2300-2500 rpms.

What's your opinion on this? Do you think 4th gear will do better?

[Nd4SpdSe]

Well, first of all, most people drive automatics, secondly cars would sound stupid driving around down at around 4000rpms. Remember too that there's much less wind resistance at city speeds, so you don't need to rev nearly as high.

I tend to have a habbit of driving in 5th around town, even in my truck, but I so try to stick in 3rd or 4th gear for exactly that reason, especially lugging around 4000lbs....however, I hit full boost around 3200rpms, and when that happens, fuel efficiency goes down, I even try to avoid those revs on the highway, which limits me to about 117km/h.

[fowljesse]

Also.. gearing. Your car is most efficient at a certain rpm, but in a less efficient rpm in a higher gear is still more efficient, because the cylinders are going up and down less times per tire rotation than in a lower gear. My car can go from a stop in 5th, and that would be more efficient gas-wise, but wouldn't last very long.
Spending time (while moving forward) out of gear saves alot of gas. I always anticipate stopping, and coast when I can, and there are more advanced methods that are more annoying than their worth IMO. Also, increasing speed efficiently helps. If there's a car in front of you, no matter how far, you can increase speed up to it gradually, unlike those half-re's (usually in huge trucks) that haul butt up to, and tailgate the car in front.

[Nd4SpdSe]

That may be true, but I'm sure you have to ride the clutch and push down the throttle pretty mucg all the way...do you really thing that's more efficient than leaving it in first and even just letting it coast off the clutch? Remember too that the ECU determines how much fuel is injected, and that's in relation to how much air is going in and required. You can rev high, but if the throttle is low, than you're only getting small amounts of fuel injected, if the throttle is opened almost all the way, the motor is taking in more fuel. Technically you can say that a motor with the throttle open 1/4 at 4000 burns the same about of fuel at 2/4 throttle at 2000rpms (have the throttle, twice the revs), but that's not necessarilly the case, and it doesn't mean that you'll be making the same about of power, not only because of the varying powerband of a gasoline engine, but also the efficiency of combusting the fuel. As it was pointed out earlier, it seems the faster a motor revs, the more efficient the combustion process is.

I'm looking at my dyno from 4 years ago, and for an example, at 2500rpms (the lowest it registered at), I'm making 60hp and 130tq, and if i double that to 5000, I'm making 135hp and 145tq. Although I've doubled the revs, I've more than doubled the horsepower, but only gained 5tq. Now, we'd have to see what the torque curve is like from 0-2500 (all the onces I have start around 2500). Now, 2500/3000 rpms is a nice city speed because of that, but also on my Dyno, my A/F ratio averages about stoich at 13:1, which is good...but at 5000, i'm almost off the chart at 10.5. Those may not be accurate because they were measured after the cat, but regardless the car should clean alot up (than my Dyno shoots past 18 after 6000)

Just to say, there is ALOT you have take into account. Although torque is something that's made by the motor, and is determined by the stoke of the pistons, you need to think too that the momentum the working drivetrain helps to keep things moving. We've also got extra cylinders compared to a 4cyl, so we've got those 2 extra hits per cycle to help keeping things moving in between with less time for it to slow down in between. Think of the same reasons why us V6's are able to get a stable idle with a lighter flywheel, but the 4cyl guys have a hard time, because of exactly that reasons


So in the end, there's MANY factors that would contribute to efficiency at a certain speed:

- Wind Resistance/Aerodynamics
- Horse Power
- Torque
- Air/Fuel Ratio
- Combustion Efficiency

And that's alot of math and alot of testing.

[solo_ryder]

I x2 what ND4SPD says about better mileage at higher RPM. It sounds like it wouldnt make sense, but on my last car I got better mileage doing 130-160km/h then I was at 80 or 100. Wierd how it works, but I think it was just a better burn with better a/f's even though the wideband readings were somewhat the same..

Anyways, I have a different ZE now, so once I get that running we will see what kinda mileage I will get...

[Nd4SpdSe]

Thank

And one more thing I want to add is that the 626 (1990 hatch w/2.2 non-turbo) would get rought the same milleage, no matter if it was 100 or 160, but the trick to doing 160 efficiently was to get there slowly. I seem to have a knack to feel how hard the motor is working, and I could keep it accelertating slowly, and it would get to 160 and stay there and get good milleage, but if i was hard on the gas, it would show quite drasticly. The Mx-3 didn't care if it was at WOT or not

One more thing, there's something i read about shifting, that in Europe, one trick they use to squeeze more milleage is to go 2-3-5. Rolling start on 2nd and skip 4th, also shifting around 2000-2500. I did that i the truck and it seems to work well.