How do you deal with the gas mileage?
 

hey everyone.

i love the rx-7 but how do you guys deal with the outrageous gas mileage...
its supposed to run 14 mpg stock... i shiver at the thought of the mileage of a modified rotary...
with gas prices already at about $2 a gallon... how can you guys afford it?!?

NOTE THIS IS INTENDED FOR DAILY DRIVERS

because of this reason, i think i might lean toward a different car for my first...
maybe a fuel effiecient s2000... :(
i kno a lot of you only use your cars on weekends and such, but mine will be a daily driver, so maybe a change in decision might be a good idea..

Alot of highway tuning......:)
With the haltech and the WB in the car, I consistently hit over 30 mpg with the TII...Max

My stock engined car did 15 city 20 highway.

Put a street port engine in it, did about 15 city 25 highway.

My current stock engine car does 17 city 25-26 highway.

I will report on the peripheral ported engine in... two months?

btw - I don't drive much, only about 2500-3000 miles a month... :D

just did 500 miles this last weekend w a raceported motor and got 21.5 mpg... it is only partially tuned at this point... running 13.5 afrs on cruise so there is more mpg to be had.

howard coleman

13.5:1 !!!!

I dunno what AFR it is, but I tune the carb to not register anything on an O2 sensor (0.000 on the voltmeter) when on a highway cruise. Basically you lean it out until it starts running rough then add a bit of fuel back.

edit: We need to make sure w'ere talking the same units. US Gallons are 3.78 liters, Imperial Gallons are 4.5 liters. Why? Same reason we have a different accent - just because. I seem to recall the Whiskey Rebellion was involved, will have to look up when the urge gets to me.

This makes our quarts 32 ounces and our pints 16 ounces. Yet people buy 40-ounce (Imperial quart) beers, not 32-ounce, and sodas are rarely sold as 16 ounce anymore, it's either 20 ounce (Imperial pint) or 2 liter/liter/half liter. As well as 12 ounce cans (which is, well, nothing special)

But I digress. (As usual!)

Serious, get another more fuel efficient car if you're bitching about gas mileage.

I used to have an '86 Corolla GTS that got 25mpg even if I beat on it.
It regularly hit 30 to 35mpg without even trying.
It could hit 40mpg on freeway stretches.

$2/gallon?
I haven't seen gas prices like that for over a year.
$2.50/gallon for 92 on Oahu in Hawaii.
Neighbor islands have broken $2.75/gallon.


-Ted

I DIDNT SAY $2 A GALLON...i sed it was around there - if you want to be specific, my true gas prices are at about $2.78 for regular octane fuel...
yea i dont really want to drive a corolla around for the rest of my life you know...? :rolleyes:

please dont ***** to ME about your "O SO HIGH GAS PRICES"
i was just wondering how you guys run so well with a rotary...especially those of you who have gotton a 20B conversion :eek:

*shrug* Part of the cost of owning a sports car.

That said, if you haven't done a full tuneup, DO IT. New plugs, new wires, new O2 sensor, make sure the timing is set properly, replace fuel filters. That should help a good deal. Just because it's running doesn't mean it's running well. For more extreme fuel economy (hah) free up the intake & exhaust systems, and then don't whomp on it. The higher the RPM, the more gas you use. Sucks, but it's reality.

Tire inflation helps. Wash & wax, it'll help some (and look good).

There are people pulling 30mpg highway with their cars, doing 80+mph.

However, as has been said, one doesn't drive the RX-7 for fuel economy (though 30mpg at 80mph is still damn respectable - especially considering you still have power at that speed).

-=Russ=-

TUNE TUNE TUNE woot woot

So you don't want an economical daily driver, and you insist on driving your RX-7 or something more luxurious than a measly Corolla?  You want your cake and eat it too?


So this thread has turned into a bitchfest about gas prices???
Why don't you go drive to another area which has cheaper gas prices???

20B conversion almost always require aftermarket stand-alone EMS ECU's for control.  As Gibenstein mentioned, it's all in the tuning.


-Ted

what the leanest you can go on the highway while not under boost and assuuming you have a wideband and a s-afc?

thanx

Umm short of the engine dieing.

You can't.
That's the problem.
Stock ECU will always self-correct due to the closed-loop O2 function, and your adjustments on the S-AFC will do nothing to change this.


-Ted

Word, didnt notice S-AFC, but on a PFC or Haltech or other unit I think they can right?

PFC: Only if you disable the O2 monitoring function.

mazda fd3s: This thread is rediculous. We afford it because we can. If you're worried about gas mileage, get a different car, it's as simple as that.

The funny thing is, I used to have an "economy car" and it got the same mileage.

I also used to have a big huge luxury car and IT also got the same mileage.

Basically if you want to spend less money on gas, don't drive as much. If you want to not drive as much, get something dull like say a Corolla. :D

I think it's a good idea if you decide whether you want an economy car or a sports car. You seem to be confusing the two terms at this point

No, that is not true. Please lie on a different forum. Thank you.

2000 Honda S2000
$19,480 Blue Book (Excellent Condition, Private Party Value, 50K miles)
20mpg City / 26mpg HWy
Rated for Premium Unleaded

1991 RX-7 Turbo Coupe
$4,810 Blue Book (Excellent Condition, Private Party Value, 50k miles)
17mpg City / 25mpg Hwy
Rated for Regular Unleaded

The latest CA averages as of 7/19/04:
Regular Unleaded = $2.186/gal
Premium Unleaded = $2.396/gal

Assuming City Driving:
2000 Honda S2000 = 20mpg @ $2.396/gal = $0.1198/mi
1991 RX-7 Turbo Coupe = 17mpg @ $2.186/gal = $0.1286/mi
Difference = $0.1286/mi - $0.1198/mi = $0.0088/mi

Vehicle Purchase Price Difference:
$19,480 S2000 - $4,810 RX7 = $14,670

Number of miles driven required to make up the vehicle price difference via gas mileage:
$14,670 / $0.0088 = 1,667,045 miles

Have fun driving your Honda :)

^hahahahahahaha simply put.

Hahaha. Nice. :D

Hey, quit cluttering up a gas-price complaint thread with facts!

Or at least compare it with something "uber-fuel efficient", like a Honda Insight.

Seriously though, I've learned through quite a bit of highway driving that an underpowered car on highways is just horrible. Can't climb hills at speed without downshifting, can't accelerate to get in front of that semi when merging onto the highway, they usually have fairly poor handling when making emergency lane changes, etc.

I drove my Mom's Saturn for a month while I was rebuilding the engine in my '7. I was getting 35mpg. My '7 gets 21mpg doing the same exact driving. Is 35mpg nice? Certainly. Would I want to drive the Saturn on a regular basis? Nope. It has no guts, and handling doesn't compare. Doing 80mph on I-80, the Saturn has problems getting up hills without downshifting. My '7 doesn't even notice the hills. Also, in at speed corners, the Saturn tends to plow at speeds well below where I track evenly with my car.

I consider it a tradeoff. Yes, it costs more to drive a sports car (gas prices are nothing compared to what I've spent on parts). Yes, an economy car will get me from point A to point B. But, will you enjoy it? I enjoy driving my car. It's the first car I've owned that I actually enjoy driving. That's worth a lot to me.

-=Russ=-

How are you able to get 30mpg?? When I had my car tuned to high 14afr, timing at 35deg and all freeway I got a bit over 22mpg. Does running 15.1-15.2:1 add that much efficiency?

15.1-15.2??? Try 16-17-18:1.

See above - lean it until it starts running rough, then add a bit of fuel until it's smooth.

Hmm essay time.... :soapbox:
Its not so much of tuning to one rpm range for cruise, but using closed loop across all ranges, effectively.. In all the early Microtech/Haltech arguments, the microtech guys always insisted they could tune to 14.7 to cover for no closed loop, the problem is, is you can't do that at all rpm ranges at all possible vacuum points/oad points..
Say you have a stretch of road you drive every day that is kind of windey, its got a few straigh sections, so you drive it at (these numbers for example purposes) at 3rd gear 70 km/h so at 3500 rpm, its got a few straight sections, to keep the power crisp, your a/f's at part throttle are 13.4-14.0 then fall to high 12 under slight accelaration , if you notice its rich in the straight parts, alot of people think to lean that area out thinking "hey I am cruising here , it doesn't need to be that rich", so you lean it out 14.7 .... Then on a different road, in a different gear , under slight load, you cross that map point you made lean to suit the other condition, and you feel the motor flatten out then come back, you see the lean blip and richen it up, eleminating the tuning done for the other road/gear/situation, you never can tune in the return to stoich under such vast conditions as closed loop can, and maintain that "pure" efi driveability that its known for, efi without closed loop is really no different nor better than having a remotely jetable carb IMHO...
I tuned my base maps with closed loop off, so the car had no off idle hesitations, no lean spots in the part throttle ranges, and across as many temperature ranges as I could drive the car in. Then I turned it on, and played with the lean/rich +-, and cycling rate, which you need a voltmeter or a plain autometer a/f guage to see, most widebands will not show the closed loop cycling, as they are sampling in averages rather than than reprenting the hils and valleys of the cycle. Once you get the cycling rate set right with the haltech, you will notice the car going into closed loop where you never thought you would, and start looking at the wideband when you are doing none freeway cruising... I noticed when I was puttering along in 2nd gear in a playground zone, the car would lock into closed loop and go to a perfect 14.7:1 at 2000 rpm in 2nd gear, basically whenever I was not into the pedal the ecu found its way to 14.7:1 with no stumbles or lean spots having to be put into the fuel map deliberatly for any given light load cruise situation.
I even run closed loop at idle with a partial bridgeport. Not only does this save gas, it has a couple of other effects, it allows you to run a pretty cold plug with premix and they won't foul, with the fluctuating a/f's the plugs stay clean at idle, something I discovered by accident, you will also notice the carbon stops accumulating above tailpipe on the bumper. The first motor in my car was a 3mm motor that on its best days pushed 80 psi per rotor, compression on a motor has a ton to do with its overall efficiency and it shows up in your gas reciepts, I could never push that first motor out of the 11.5-12.0 range for idle, it would start to sputter, run rough and surge on the bac valve as it tried to stall..
After that motor I moved to a s5 j-spec motor, although I had the j-spec motor apart 3 times, for porting, and seal changes, it was the same internal parts I used over and over again, at its best it pushed over 115 per rotor with mazda 2mm seals, even with the partial bridge , it would idle fine as high as 14.5:1 with no surging or stalling, when I first started the j-spec, with the map from the 3mm motor, it wouldn't idle right, I had to use the page down key in the maps to knock out a ton of fuel, compression and internal sealing has a such huge effect on power output/efficiency, its really where the money should be spent, I think that sealing and motor health is really overlooked,I also think thats why in Japan, when they rebuild a motor, they actually rebuild it, its not really that the parts over there are any cheaper, on the retail level, they are about the same price as they are here, there are shops there, that don't even like to use the irons over again, they insisted on new housings, ALL new seals, everything towards the tight end of the tolerances, they also charge alot for a rebuild , it worked out to be between 5000 and 7500 canadian for a 13bt, but every car I heard had a very "crisp" and tight sound to it, no misses, no flat spots etc etc...
I used to notice the fuel gauge drop rapidly in my car prior to tuning it to the point it is now, but now even with boost runs and 550/1600's seeing high 90% duty cycles, its not a bad car to drive for fuel mileage. On its last major highway cruise I drove it over 700 km's on one tank, I could have stretched it farther, but doing boost runs on a low fuel tank is not a good idea on our cars generally, so I stopped a tanked up about 50 km's from home..
I use to be under the conclusion the my n/a was better on gas than my TII, thats not the case though, the TII would outshine the n/a on mileage and was cheaper to drive than the n/a, however I have since added a gen 1 safc to my na to see what it would to for mileage power...
Ted says that the safc will have no effect on the cruise condition with the stock ecu , and this I would also think to be true seeing as thats how it works on the e6k, it doesn;t matter if that map point is 12.5 or 13:1, at closed loop, it will go to 14.7 or what its target fuel rate is, however the safc does have an effect on the stock ecu for cruising mileage, I have driven my na over the same stretch of road with and with out the safc, installed with no other changes, I turned back the fuel 15% just for kicks to see what it would do, and to my amazment it had a huge effect on gas mileage, even with the stock ecu going into closed loop . I stretch an extra 100 km out of that tank, when you come a hill and the cruise kicks out the closed loop, the ecu goes back to the map point and having it set 15% lean is probably when it makes the difference, so its leaning out the fuel map for that range which is having the effect in a non closed loop condition, however like the microtech leaning it out all over the place tends to start making the motor flat in places, I limit the leaness to one rpm range with the n/a, also doing that to a turbo car will amount be 15% leaner on boost in that rpm range as well, be careful.
I don't go for way wacky lean conditions, I notice on the 13b, if you go lean on cruise much over 15.3:1 it takes more throttle position to maintain a given road speed on cruise , and the duty cycle ends up being higher, than it would be by maintaing a 14.7-15.0, the 13b doesn't have the lean burn range as some other engines, due probably to its poorer thermal efficiency, take a mopar 440, you can push that thing to 18:1 with a whole stack of timing on cruise conditions and maintain the same throttle position, the old thermoquad carbs have an en"lean"ment valve on them that takes them to ridiculously lean a/f's under cruise conditions/high vacuum situations, those motors don't show lean surge to nearly 20:1, no chance on that with a 13b..
ok I am done... Max

Thanks for all the info Max, it's got me thinking.
I'm assuming you are running a heated o2 sensor? Where do you have your's located in the exhaust? I had a single wire too far down in the exhaust (end of DP)and I coulden't get a good reading unless I was running higher rpms to heat it. Also, what timing values are you running with closed loop at idle?! I've noticed it I bump up the timing I can get away with leaner mixtures. Right now I'm running 9btdc with 12.9afr @ 900rpm. I'll run out to the garage in a bit and take some compression readings. When I got the engine it would hit 120psi but that was 5000miles ago. I'm assuming it's about the same today because it still pulls the same vacuum it did back then (17.5"hg @900rpm). Couple more questions.. What throttle % do you have it go out of closed loop and What would be a good starting point to set my engine cycles between correction?

Thanks again for the info/help!

Just be glad you guys don't live in the UK, Super Unleaded here is now at 89.9p per litre, yes I said per litre:( Good job I only do 6000 miles per year!

Wav;)