Megaton

I looked for a thread, but Nothing really that i could find..
so i am doing some research as to if i should get an fc or not..
i do truly LOVE the car, and rotary is just a better engine in my opinion.
But from what i've been hearing gas efficiency is pretty bad.

Around 19mpg high way and all differnt variations that people have been getting.

and like 11 or something like that for the turbo version.

I do understand a little bit of how the rotary engine works, the whole cycle so I am beginning to understand some of it.

But why would a 1.3 liter engine which is REAL small use that much gas?


Is there a way to tune it so it can be more gas efficient?

jonesfromindia

i have a streetported Turbo II that gets 20city MPG and ~25+highway MPG.

Megaton

Hey, thats not to bad..
IS it?
I mean i know its a sports car, its not meant to be good on gas, but with these gas prices, i can't afford it.

But that doesn't seem to bad.

ApexOnYou

I wish I was getting those number with my 88SE.. Last time I did the math I think I was around 17-20mpg highway, if I try really hard and keep it under 2k it gets slightly better.. But still far from good.

Icemark

the EPA gas mileage figures can be found in the "What did my FC come with..." sticky thread found at the top of this section.

17 city, and 24 highway is the expected gas mileage for an un-modified and in good tune non turbo and Turbo engine. If you don't get that on a stock engine fix what ever is broken.

fastrotaries

Stock motor BPU I was able to get up to 27 MPG. on HWY.

Megaton

27high way?
thats like normal.
the car i have now gets like 30-35..

What can i do to suppress the engines thirst? :p

musicman3x

Controle your right foot better. That is the hardess part about driving a 7. It is to fun to step on it and decrease the gas milage. The 1.3 liter in a rotary can not really be compaired to a piston engine. its like apples an oranges. Also if your are concerned about gas milage you might not want a rx 7. Or maybe you can make the first rotary hybrid (sp?).

Megaton

I have considered actually trying to create a hydrogen powered rotary engine.
I'll do some more research on it.
It would be alot of work, and i know that the fueling method is a bit differnt but i am very inteligent and this is something i would like to do, i might be able to pull it off.

Hydrogen is a extremly flamable chemical element just like gasoline, therefore combustable and just like regular gas it does combust when oxygen is added to the mix.
the problem is seperating the hyrdrogen from oxygen in liquid form from water.
therefore actually making it fueled by water as there is no hydrogen stations yet haha.
the method of seperating the chemical elements by electricity is the only way i know and i am not sure how that works, but i'll figure it out, with enough money time and effort i could probally figure it out.

OR i could just get a better job and pay for the gas prices..

musicman3x

If you are not sure of the process to seperate hydrogen and oxygen then I am not sure you are ready for that large of a project.
http://sv.typepad.com/auto/2004/11/mazda_tests_gas.html
http://www.greencar.com/index.cfm?content=features6
I think your are a bit late in the idea.

coldfire

iTrader: (1)

I average about 550km a tank. on the highway i can get around 650km a tank. which is more than the EPA rating i believe.
if i am really really pushing it for extended periods of time i might only get 450km a tank.

anyway, things i did that improved fuel usage:

- proper tune up and maintenance. make sure your TPS and timing is correct. remember to check your tire pressure also.
- going from stock cats/exhaust to RB header and basically straight-through exhaust system
- SAFCII and a wideband O2 sensor. the stock fuelling was much too rich! the SAFC paid for itself after a few months driving. and you don't need a wideband to tune your cruise. at least make sure you have a good stock working O2 sensor.
- i know it sounds a little crazy, but i swear running slightly lighter oil such as 10w30 and running a little more premix than needed in your fuel improved mileage very slightly

and for an NA (you didn't mention anything about Turbo so i am assuming here) just use the cheapest gas you can find. no need for premium. although i do notice the Ethanol-blended fuels give slightly worse mileage.

Megaton

Thanks alot man!
ALOT that helps me a whole lot, i'm sure if i do all that it wouldn't be bad at all!

and as for making a hydrogen powered rotary engine for the street from a fc 13b, well that would just be bad ***.

And i would like to do it, i am going to try :p

toplessFC3Sman

iTrader: (1)

i've hit 27 mpg in all highway driving (at the speed limit), while a mix of city and fast highway usually gets me about 20. that was with an NA 'vert. now its TII, so we'll see

Megaton

Hmm thanks for the replies..
I don't really go that far, and i do have a job so i get like 400 or so a month.
- car insurance.. 150, who knows what it'll be with a sports car.
then the rest is just for gas..

I do like to save the rest though :P
i don't spend any thing other then that..

But yeah i'd like this car, my friend has a 240 i want to compete with him ya know.
and hell having an fc just automaticly makes me cool right?


So i don't know i really don't want to get some crappy honda that gets like 50 mpg lol.
And i do want to drift, i'm also considering 300zx

supra mk2 some other crap, nothing seems to be as good as the rx7

RotaMan99

If you search for "MPG" you would probubly get 10 different threads.

Anyways, click on the link below in my sig.

djmtsu

iTrader: (3)

I get horrible mileage in town (lots of traffic) but on the highway, she shines. On the last tank of gas, I drove Deals Gap twice, then drove back home, and when I had to fill up the other day, I looked at the trip meter and realized I got 381 miles out of that tank!!! I've never gotten that much before...EVER!!

When I drive around town and never hit the highway, I barely touch 270 miles.

NoDOHC

I average 24 Highway, 21 city. I have gotten 28 highway and 24 city, but that was usually right after an autoX and I was going easy (had all the aggression out of my system.)

The throttle control is hard. You're taking off and the engine hits about 3200 rpm and it starts to pull strong, it is very difficult to not rev it out to redline and jam second gear, just for the satisfying acceleration. I have found that shifting at 2500rpm works well, because I never feel the increased torque from the dynamic tuning at 3250.

Getting the engine tuned properly is very important, when my TPS was off and my ports were wired open, I got 17 highway.

My lowest full tank is 15 mpg (autoX all day.)

My lowest partial tank is 6 mpg (about 20 1/4 mile runs consumed about 2 gallons of gas, with driving there and back I netted 6 mpg)

SpeedOfLife

iTrader: (16)

Syonyk and I were discussing this the other day. He mentioned that the closer you can drive to 3500 RPM without going higher, the better mileage you'll get. The reason being that when cruising up to 3500 RPM it will go into open loop mode and thus save fuel. He also talked a while back to another member who, with a 300+ hp beast of a '7, can also get 30+ mpg with it. So tuning and easy flowing intake/exhaust is KEY!

I haven't checked my '7's economy yet because I've only filled it once so far, but I know it's not good right now... It's running pretty rich and generally out of tune.

GeaBu88

Explanation?

RotaMan99

Now I think this could be wrong. Closed loops is when the engine uses the O2 sensor to figure out how much fuel need to be added or taken out to get the magic 14.7 number. Often this doesn't happen due to wear on the engine or something is not working the way it should.

Open loop, I never had to think of it in this way before but that just means the ECU is using sensors other then the o2 sensor and fuel maps pre-programmed in the ECU to run the engine.

I could be believe the he could get higher then 20 but not 30. I believe any modified rx7 that has stock sized primaries could get above 20 MPG. Or even large injectors that can be turned down on a non ported motor.

initial D is REAL!

I hate u! Who tuned your car? I need to go there too

Syonyk

No offense, but a '7 isn't a cheap car to own, even ignoring gas. They're old, they need maintenance, and things add up quickly. If you're tight enough on funds or driving enough miles that fuel economy is really that important, you're probably better off with something else that sips fuel.

Keeping up with the Jonses trumps personal fiscal responsibility in this country, it seems.

Also, have you ever driven or ridden in a worked CRX or Geo Metro or such on a track? I'm guessing not, because if you had, "crappy Honda that gets 50mpg" wouldn't be a phrase used. A lightweight car is amazingly impressive on anything with corners. Big, heavy and powerful works wonders in a straight line, but throw some corners in there, and it's a different game entirely.

Some numbers: My RX-7 (88SE, 140 to the wheels, crappy suspension, cheap rubber) runs around a 1:37 at the Marshalltown gokart track. My Daihatsu Charade (50hp, 1850lbs, crappy suspension, dirt cheap rubber) runs high 1:39s, and that was on cold pavement.

It's perfectly possible to have a fun car that gets 45-50mpg when you're not on it hard.

We did talk about this, and what you said isn't quite what I said.

What I *did* say was that, in my experience (and the reported experiences of others on the forum), FCs get better economy at higher speeds (say, 80 vs 70). My analysis while running on the highway (I did a lot of highway cruising for a while) is that the closer you can run to 3500 RPM without exceeding it, the better the economy will be. Below 3500 RPM, if you're light on the throttle, the ECU is in closed loop mode (using the O2 sensor). Above 3500 RPM, it goes to open loop mode, and fuel economy goes down significantly.

-=Russ=-

ericgrau

iTrader: (1)

Biggest thing you can do for mpg is to get/keep your RX-7 in good shape.

I drive crazy all the time and it never costs me more than 2 mpg compared to driving gentle. And really it's not throttle that eats gas. High throttle is actually more efficient. It's tailgaiting which makes you constantly gas & brake. Or going too fast towards a red light or slower cars which makes you repeatedly gas & brake. It's also air drag from driving at high speed on the freeway. A little bit is also engine friction from higher rpms.

Besides that, in an RX-7 you should shift when the shift light says to, and not over 4000 rpm. The auxillary ports open at 4000rpm and eat more gas, besides a couple other reasons. However, you should rev the engine high from time to time to help keep it clean.

open/closed loop: The entire purpose of the O2 sensor and closed loop is to save gas (and, as a result, emissions too). Closed loop provides feedback to allow fine adjustments for better mileage. Open loop gives worse mileage, because it relies on pre-determined estimates. Open loop is necessary when conditions are changing rapidly, making any feedback obsolete before your engine can use it. i.e., when you accelerate.

As for maintenance, get a nice one and you'll save a ton of cash in the long run.
buyer's guide: http://www.rx7.voodoobox.net/infofaq/bguide/bguide.html
I bought mine for $2500 plus $300 for a repair, before the blue book value on an RX-7 shot way up. I've spent about another $2500 since then and I've driven 10,000 miles (~500 gallons of gas). So most of that $2500 is on gas, $500+ is on bodywork from damage that occured before and after I bought it, and the rest is basic maintenance.

Ice_Wolf

My 87 GXL gets 30 MPG with highway and city driving combined. I have a few things done to it, ahd hopefully once I do a few more things I could see 31 MPG out of the car. Now tell me that's not good gas mileage for a 7.

Btw, to the guy who was talking about "some crappy Honda." I've driven a few B18 Hondas that get 40 MPG and would smoke quite a few fast cars. Even the stock motors in those cars have plenty of HP for what you need the car for, especially when you can pull 52 MPG out of them.

RotaMan99

This goes for a lot of cars (Didn't say all). I find 65-70 at 25-30% throttle is the best. Cover more ground at 70 in 5th at 3000 then you would at 3000 in 3rd or 4th.