amartin

Oh..and for the questions "Were you using AC on the way there, etc"...

The CAR conditions were IDENCTICAL.. A/C settings, windows, etc..

JonsToy

How does using "cruze control on the HW" affect your city mpg? I find little opportunity to use "cruze control" on city streets. Perhaps your mpg could be considered mixed- %city/%highway?

amartin

In Austin, 90% of my driving is HW... we use them pretty much everywhere.

Longhornxtreme

I don't know how you use 90% freeways in austin... gross...

35 and slowpac are like the worst things in existence... i could see alot of 183 use but thats about it....

JonsToy

Then a more factual statement of your mileage would be "18-20 mpg driving 10% city/90% highway". This allows a better comparison to what our cars are achieving. Most drivers assume "city driving" as stoplight to stoplight, stop and go, and surface roads only. Hopping on a freeway and spending most of your time there doesn't qualify as "city driving" for mileage purposes.

zoom44

actually he's more correct saying city mileage as far as i care. mixed city/ highway would be when you drive for half the day in 6th and then spend the rest of the tank putzing around town. city is your normal day to day, to and from work, to the store, out for dinner driving whether it takes you on the highway or not. highway is when you fill the tank get on the highway up to 6th gear and then cruise until you get off the highway and go right to the gas station.

JonsToy

That interpretation puts me at a serious disadvantage. I have little option of doing any highway driving to get around town. The only time I can get the car up to 65 mph is if I'm exceeding the speed limit by 20 mph. The vast majority of my driving is short hop, stop and go, city street driving.
On the rare occasion that I mix in 20% highway miles (yet still stay in the city), I get 15% better mpg figures than the 16.5-17.0 mpg I posted earlier. Hence, I can equal or better the EPA city estimates posted on the window sticker.
Which begs the question, what sort of parameters does the EPA use to calculate their mileage ratings? If I recall previous threads correctly, it's either an engine-only test, or one of those cars-on-a-dynomometer tests.
I just can't see how someone who spends 90% of their driving time on a highway doing over 65 mph on cruise control can consider it "city" driving.

theclaytaurus

Define "substantially"

http://www.engineeringtoolbox.com/ai...ty-21_771.html

If you take a look around standard air pressure, a 30 degree temperature increase yields less than a percent difference. Do you mean something else by substantially?

Again, where are you getting this from? Drag is based on velocity, density, and most importantly, the so called "sail area" (as well as a shape-influenced drag coefficient). Do you have a drag curve and coefficient for the RX-8? If you do I'd like to see it (cuz I think it'd be cool to have)

Otherwise, where are you getting this from?

rotarygod

Hotter intake air temperatures also mean hotter combustion temperatures and these will affect the overall timing an ultimately air/fuel ratios as seen by the ecu which will repond in turn.

Drag isn't a 1:1 ratio with added speed. It does rise along a curve based on the cube of the airspeed. This is why it is much harder to go another mph fater if you are alreaqdy doing 150 mph vs adding 1 mph to a regular startiung speed of 40 mph. Tons more drag.

You don't need ANY info on the RX-8 as this is all fact that applies to everything within our atmosphere. Go look it allup elsewhere on the internet. If you are trying to get far more in depth to figure out exactly how much power is lost per added mph, you must first learn the drag coeffcient of the RX-8 which is .31 without the rear spoiler and .30 with it. No clue about other body kits. Of course you still don't know how much power is exactly being lost through the drivetrain either so it will still be hard to figure out how much power is lost at what speed. None of this changes the fact though that drag rises with the cube of speed. The same rules apply with a fast moving brick or even with a streamlined bullet.

Ice Blue

The gas mi was more or less the ECU adapting to the situation. A piggyback fuel manager would allow you to make it adapt each time. If you rely on the ECU you should experience the same thing.

The whole octane thing - The lower the octane fuel the lower its combustion point is and the shorter the flame burns. We are running 10:1 compression. The highest a rotary successfully obtains without a power loss due to the elongated combustion chamber. This is as well why we have a L and T plug configuration. By running lower octane you can cause nock to occur with the fuel igniting before it is designed to and burning out to quickly. As stated from Carlos at CLR and many other tuners by running a slit T first below 3krpm you can achieve more hp and quicker turbo spool "if applicable" by causing the fuel to be burned up high forcing it down into the L plug and igniting in a more compressed area causing the rotors to turn harder, creating more HP at low end. This is just another example why you should not run a low octane fuel in a high compression engine or a system running a split. The factory setup runs a 0 split for L and T. Another note is the higher the octane the hotter and longer the flame burns. This causes higher engine temps. If the flame burns past your combustion cycle then you are losing HP.

The best thing I can say is, Unless you are going to spend the money to RND your motor for the temperatures you drive it in and driving conditions and octane levels to fined out what is optimum for your car at your place of residence, why argue with the factory who obviously did the RND to find out the best octane all around to be? If the motor has to pull back the timing to stop the nock then your putting something in it that is not right. Stop relying on the ECU to take care of your pore judgment.

EDIT: lol I didnt notice there was 6 pages and some good NFO posted allready.

theclaytaurus

You are correct and incorrect. While it isn't a 1:1 ratio (which i didn't intend to claim) it also isn't a cubed ratio, but more realistically based on the velocity squared. Basic Bernoulli's.

Refs:

http://hypertextbook.com/physics/matter/drag/
http://www.insideracingtechnology.com/tech102drag.htm
http://www.audi.co.nz/liveupdater/Ar...rtID=192536165
http://www.getfaster.com/Techtips/Aerodrag.html

I could keep listing them, but you get the point.

I did. Now show me where you're getting this velocity cubed stuff, as well as where you got the drag coefficients for the RX-8. I wanna know if those are actually the Cd's or not, cuz it'd be cool to have em!

Seriously though, think about it. If the drag was proportional to speed cubed, then you would be increasing your drag 64 fold between 60 and 15 mph. Speed squared is only a 16 fold increase, much more reasonable.

rotarygod

Actually I did mean to say squared and not cubed. I read the word cubed in a post you quoted and apparently typed it that way.

theclaytaurus

nhnf

at least i didn't waste all that time studying for nothing...

where did you get the drag coefficient numbers though? is there a resource for this kind of stuff?

theclaytaurus

Also, this is not true.

If you do the math, it's more like 1.5 the drag. You can't just cube (or square, for that matter) 75 and 95 and compare the two numbers. There are other factors.

rotarygod

There is an RX-8 book out written by Jack K. Yamaguchi. It is a really nice coffee table book with tons of great info and pictures. It was originally given to the people who first preordered their RX-8's in the beginning. I haven't seen it in any bookstores anywhere but that doesn't mean that it can't be found somewhere. It is probably about $50 or so if you do find it. Actually, check eBay. They pop up there every once in a while.

mmats69

Yes, speed does have a lot to do with how much mileage you get. I would believe the 27 mpg claim. Going at 55 mph over a long distance may achieve that. It is scientifically proven that you get optimal gas mileage at 55. That's why it became somewhat of a national speed limit after the gas "crisis" in the 70's.

theclaytaurus

Where is it "scientifically proven?" What does "scientifically proven" mean?

You are referencing 30 year old legislature. The bathtubs that dominated the auto market back then certainly don't apply to cars like the RX-8.

I agree with what you are ultimately trying to say, that MPG is probably the best somewhere in the 50-70 mph range, but people need to stop saying things like "it's scientifically proven" without then offering up a reference.

In reality, you can't set your speed always to 55 and expect the best gas mileage. If you are truly looking for the optimal point, you would need to calculate the speed at which you are traveling through the fluid. You would need to install an apparent speed indicator (as opposed to the true speed speedometer), one that measured how fast (including head or tail winds) the air was flowing over the car.

This would have limitations based on other losses from wheels, etc., but in general would be more accurate then always going 55.

Longhornxtreme

Any true scientist will tell you that science CANNOT prove anything. It can only falsify hypotheses.

MazdaManiac

iTrader: (3)

Uh, no.
The 55 speed limit was imposed for financial reasons. The only thing "scientifically proven" was the ample revenue speed limit enforcement provides.
The most efficient speed for every motor vehicle design is different. On the RX-8, it appears to be around 70 MPH or so.

bryrx804

Well you have to take in that the diffent in gas one station could of had 10% ethonal in 87 or 92-93 have less like 6%., and the more ethonal will hinder the mpg. Gas stations 2 years ago had to label the gas pumps, there was a new law that took off the labels cuz gas stations were upset ppl found out and stopped going.. Many gas stations are switching to ethonal cuz its about 4 cents cheaper..