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Old 05-12-2009, 09:57 PM   #1
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high rpm vs low rpm = mpg

in a regular piston engine I would think lower rpm range would be better mpg. thought I read a post that said rotary engines are more efficient at higher rpm ranges. even if that were true I don't know that it would amount to much of a mpg difference. for instance, on the highway in top gear (manual or stick) running at 2k rpm or 4k won't matter i would think but wished it did.

in city driving, well outside of town on a four lane each way road 4k or higher is nice but it would be nice to think just running along for a period of time at 2k would help the mpg but don't think it does really.
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Old 05-12-2009, 10:21 PM   #2
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just keep the rpms between 2 and 3k for fuel efficiency.
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how strong of a transmission do you need with 120 torque?!
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Old 05-12-2009, 10:24 PM   #3
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im so confused..
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Old 05-12-2009, 11:03 PM   #4
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Ok I'm also confused but I'll try to help u understand.....you have first set of injectors on all the time up to 3750 rpms then second set is on till 6500 rpm then 3rd set is on up to fuel cut at 9400 or so....

so yo need to keep it below 3750 rpms in high gear (6th) to achieve the best gas mileage...someone once told me that riding above that mark drops ur mileage down 2mpg but i'm not sure if that's true!
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Old 05-12-2009, 11:55 PM   #5
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So pretty much keep it around 3k
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Old 05-13-2009, 12:15 AM   #6
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Just rev the hell out of it and keep your engine healthy. You aren't really going to get decent mileage granny shifting anyway so why waste your time?
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Old 05-13-2009, 12:25 AM   #7
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im so confused..
+1...the lower the rpm, the better the mpg
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Old 05-13-2009, 12:29 AM   #8
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It is true that the rotary is more efficient at higher rpm but you are still better to run at low rpm to get better gas mileage . Does that help with the confusion ?
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Old 05-13-2009, 12:40 AM   #9
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I've actually found I get a lot more miles to the gallon if I keep around 4-5k on the highway
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Old 05-13-2009, 12:48 AM   #10
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I heard that under 4K and above 6K=best fuel efficiency. 4-6 is the worst.
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omg im an *** for telling u to learn o yes im such an *** omg this is aint my first rotary but i just dun no **** blah blah blah i dont know **** im such a baby i wanna ppl spoon feed me with stuff no matter milk or info just spoon feed me i dun search i dun look i just wanna u gimme answer omg
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Old 05-13-2009, 12:56 AM   #11
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I heard that under 4K and above 6K=best fuel efficiency. 4-6 is the worst.

Keeping it above 6k is no problem! But keeping it under 4k is a different story
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Old 05-13-2009, 01:09 AM   #12
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I have found that it is less about RPM and more about acceleration. If you are in town accelerating and decelerating constantly you get very bad MPG. If you are on the highway you get much better MPG at constant speed. So worry more about acceleration and deceleration than absolute RPM.
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Old 05-13-2009, 02:04 AM   #13
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Originally Posted by 04RX8man View Post
Ok I'm also confused but I'll try to help u understand.....you have first set of injectors on all the time up to 3750 rpms then second set is on till 6500 rpm then 3rd set is on up to fuel cut at 9400 or so....

so yo need to keep it below 3750 rpms in high gear (6th) to achieve the best gas mileage...someone once told me that riding above that mark drops ur mileage down 2mpg but i'm not sure if that's true!
there is only two set of injectors, primary and secondary. the things you talk about is intake ports. First, at low engine speeds, only the primary intake port is used, speeding intake flow for improved low-end
torque. Next, the secondary port comes into operation at
around 3750rpm through the opening of its shutter
valve, slowing intake flow to increase low- and mid range
torque. In addition, the 6-port engine’s auxiliary
port opens at about 6250rpm to maximize intake port
area and boost high-end torque and power output to the
upper limit. Finally, with the 6-port engine, the variable
intake valve opens at around 7250rpm.
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Old 05-13-2009, 07:36 AM   #14
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I think Shaunv74 pretty much got it spot on.
While RPM's do play a role, accelerating constantly versus keeing a constant speed will cut down on your MPG.

But with that said there's only so much you can do to increase your MPG's above the 16/25 we average unless you start doing stuff like coasting and turning your car off at red lights like those guys who claim to get 70 MPG's....

I cannot remember what they call themselves but they all out to get good gas mileage to the point of being reckless or risking cutting the life of their engine if you ask me.
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Old 05-13-2009, 08:09 AM   #15
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We all know that the rotary doesn't get good gas mileage due to its relatively low thermal mass.

We all know that the rotary tends to build up carbon faster than a comparable piston engine (again, thermal mass related).

We all know there are two sets of plugs/injectors, due to the elongated rotary's combustion chambers, and that the second set kicks in around 5k rpm. Obviously you're burning more fuel above 5k.

We all know the RX-8 is a sportscar (ok, sports coupe).

So, whereas you can avoid jackrabbit starts, maintain momentum (plan ahead so you don't brake as often), stay around 3k rpm, and all the other typical fuel saving procedures, it's at the cost of carbon buldup and also FUN.

We all know, this is the wrong car if your intent is to get high gas mileage.
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Old 05-13-2009, 08:34 AM   #16
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I'd opt for bringing my rpms high, then coasting to the next stoplight if possible.. Of course, you'd need to really know your stoplights to do that.

I think what the OP refers to is more for highway driving, where you'd go for long distances at a set speed. In general, I like to vary my RPMs just so I know I'm loading up my engine right.
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Old 05-13-2009, 10:07 AM   #17
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the difference between 2.5k and 3k rpm going up a hill is pretty steep. its like 8mpg and 14mpg. i've driven around watching the mpg using my accessport a lot.

really. 2.5k and no higher.

on the highway, if i stay at 60mph in 6 gear, i'll get 25mpg. but i dont. i cruise at at 80mph, so i get 20mpg.
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Quote:
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how strong of a transmission do you need with 120 torque?!
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Old 05-13-2009, 12:20 PM   #18
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fuel efficient driving with an RX8 is like shooting a deer with nerf bullet or drinking non-alcoholic beer... sure you can claim to be an animal rights activist or actually like the taste of that **** in a can but in the end... it's just a waste of time, effort and money.

Drive it like you stole it or buy a honda.
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Old 05-13-2009, 12:33 PM   #19
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The best I've gotten was 28mpg going 60 MPH in 6th gear *I also had to do a mad dash through Omaha, NE so that was a lot of time sitting at 50 MPH in 3rd gear for acceleration..*. Whatever RPM I was at when I was driving around in 6th gear would be a pretty good RPM to stay at if you're going for Fuel Efficiency.
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Old 05-13-2009, 01:02 PM   #20
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Man...
28 mpg is very, very good!
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Old 05-13-2009, 01:10 PM   #21
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Quote:
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I think Shaunv74 pretty much got it spot on.
While RPM's do play a role, accelerating constantly versus keeing a constant speed will cut down on your MPG.

But with that said there's only so much you can do to increase your MPG's above the 16/25 we average unless you start doing stuff like coasting and turning your car off at red lights like those guys who claim to get 70 MPG's....

I cannot remember what they call themselves but they all out to get good gas mileage to the point of being reckless or risking cutting the life of their engine if you ask me.
16/25 we average?!

im getting 11~12 mpg 100% city driving! -- I stopped counting!

I should really get an AP!

@op: how many mpgs are you getting?
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No, 22% [drivetrain loss] makes perfect sense! Mazda recommends "sand" for transmission fluid for a reason.
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Last edited by mat128; 05-13-2009 at 01:12 PM. Reason: added the AP part
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Old 05-13-2009, 01:13 PM   #22
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6th gear, being overdrive, is of course the best fuel economy gear for highway driving. But you also need to stay at or below 60 mph. There's a reason there was a Federally-mandated 55 mph ("double nickel") Interstate highway speed limit in the gas-crunch 70's.

But again, why buy an RX-8 if you're looking for significant fuel economy? Go get a hybrid.
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Old 05-13-2009, 01:32 PM   #23
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Mileage variations on a rotary vary more between drivers than anything else. For the most part it's not a variation on the car. When we see someone say they only get 11 mpg and we see another who says they get around 18 mpg, 99% of the time it's due to driving style. It becomes really obvious who accelerates harder and shifts at a higher rpm than they need to. For normal driving with my RX-7, I shift at 3K rpm. I easily keep up with traffic so I really don't understand that the need to go higher is. There isn't one.

Just last month someone started a thread that asked why they were getting crappy mileage. They couldn't figure it out as they were always shifting by 6K rpm. What! Why 6K??? There is no need to go that high for normal driving. I will actually cruise around at 30 mph in top gear. The engine does it just fine. A rotary engine uses a lot more fuel when pushed just a little more. It doesn't take much to really affect mileage. For me the difference between shifting by 3K and 5K is about 3 mpg or roughly a 12% improvement and that's not including any spirited driving. Keep in mind I don't get anywhere any faster by shifting higher. There is no more fun in it. It's just waste. When I want fun, I drive it like I do. Commuting isn't it.

You definitely don't have a fuel efficient car but to suggest that you shouldn't be concerned with fuel economy is just plain ignorant. Fuel prices add up. I drive 2000 miles per month to and from work. Let's say my average mileage was 18. Let's say gasoline was a constant $2 a gallon. Tha's basically $222 in gas per month. Let's say I could get 21 mpg through conservative driving keeping in mind it would still take the same amount of time to get where I'm going. At 21 mpg that's averaging $190 in gas per month. A $32 a month savings which is basically a tank of gas saved each month or roughly $384 saved a year. I don't need to buy a hybrid to know I can save money by not driving my car inefficiently.
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Old 05-13-2009, 02:22 PM   #24
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I took a 100 mile trip to PA and back twice these last two weeks. On the highway, going from 3K to 7K rpms (I like to vary my rpms, as I said) and I definitely got 20-22 MPG. This was mostly done in the 6th gear, with the higher RPMs in 4th gear.

I'll say that I probably got great MPG when I was in 6th and low RPMS, and got terrible MPG in 4th and higher RPMS, and it ended up averaging to 20 MPG.
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Old 05-13-2009, 05:06 PM   #25
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Debating whether an RX-8 can be highly fuel efficient is ignorant to its inherent design weakness in this area. Hopefully the 16X will live up to its expectations for better economy tho'.

There's no question you can drive an RX-8 more fuel efficiently. Just do all the things you would do in any gas powered vehicle to conserve.

For long trips, and all Winter, I take my little gas sipping 4-banger and take it slow. I drive my '8 for fun.

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Mileage variations on a rotary vary more between drivers than anything else. For the most part it's not a variation on the car. When we see someone say they only get 11 mpg and we see another who says they get around 18 mpg, 99% of the time it's due to driving style. It becomes really obvious who accelerates harder and shifts at a higher rpm than they need to. For normal driving with my RX-7, I shift at 3K rpm. I easily keep up with traffic so I really don't understand that the need to go higher is. There isn't one.

Just last month someone started a thread that asked why they were getting crappy mileage. They couldn't figure it out as they were always shifting by 6K rpm. What! Why 6K??? There is no need to go that high for normal driving. I will actually cruise around at 30 mph in top gear. The engine does it just fine. A rotary engine uses a lot more fuel when pushed just a little more. It doesn't take much to really affect mileage. For me the difference between shifting by 3K and 5K is about 3 mpg or roughly a 12% improvement and that's not including any spirited driving. Keep in mind I don't get anywhere any faster by shifting higher. There is no more fun in it. It's just waste. When I want fun, I drive it like I do. Commuting isn't it.

You definitely don't have a fuel efficient car but to suggest that you shouldn't be concerned with fuel economy is just plain ignorant. Fuel prices add up. I drive 2000 miles per month to and from work. Let's say my average mileage was 18. Let's say gasoline was a constant $2 a gallon. Tha's basically $222 in gas per month. Let's say I could get 21 mpg through conservative driving keeping in mind it would still take the same amount of time to get where I'm going. At 21 mpg that's averaging $190 in gas per month. A $32 a month savings which is basically a tank of gas saved each month or roughly $384 saved a year. I don't need to buy a hybrid to know I can save money by not driving my car inefficiently.
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