also on side note my camaro used to get best gas mileage at around 30mph or so roughly

stupid 4.11's with a th350 didn't go well at freeway speeds

well clearly there is something radically different from your rx-7 and every other car in the world...

as in, you must have modified it, and/or it's damaged in some (good) way...

because the '87 rx7 gets 23 highway according to the EPA.

whatever you did you're getting 7 more than you're supposed to, and if you really got 40mpg that one time... my hat is off to you!

the bottom line is that a car will get better gas mileage when it doesn't have a negative force pushing against the motor, drag. Once you reach 60 or so, the drag starts to reduce gas mileage. If your car is different, then I have no explanation... but I know it's not because the rx-7 is signifcantly more aerodynamic.

EPA

this link will settle everything... no point in arguing about this anymore.

Howstuffworks.com

seems like 50mph is pretty much the best speed to go
mpg vs speed

17.5 Miles per Gallon in city....I have no clue how much it makes in highway since I installed the speedo recently.

17-20 is about what I get in city... it's quite amazing how far apart our city/highway MPGs are... SUVs and Trucks are usually only about 5 MPG apart in that regard.

that's for the auto but it's close enough
epa rated for my car is 17c/24h

but I have seen quite afew cars not fit the epa

your car alone you are quoting as better then the epa claims.
few things though to point out in one of your quoted things

"So, for most cars, the "sweet spot" on the speedometer is in the range of 40-60 mph."
not saying all but saying most

"In general, smaller, lighter, more aerodynamic cars will get their best mileage at higher speeds."
I do drive a small light weight aerodynamic car

other factors that can play a part in it though is engine efficiency
generally peak gas mileage would be around the area of peak torque. this is the point the motor can use the least amount of fuel to make the same amount of torque.

and also I do want to say I'm sorry for the long pissy sounding rant.
was trying to get to sleep for about 7 hours last night and it wasn't going well.

look at the lastest f-bodies or vettes
what does epa claim? 18c/28hwy

hell yeah, I wish I had a new trans am WS6... same damn gas mileage, but 3 times the horsepower.

another thing I never said 40mpg did I. ick I only wish for that
and the rx7 is a decent amount more aerodynamic with it's much small frontal area lower Cd. plus lighter weight then a stock f-body to weighing it at 2625 rated curb weight
another thing that might of helped though was cruise controll. just listing other things. but it's not the first and only car I have seen do that. friends parents had a little 92 civic they did a trip from cali to idaho managed on avg 40mpg which is way above the epa ratings and they where doing around 80 most the trip.

cars are weird they do weird things that's all I can say and maybe with these smaller high sprung motors they as I have been saying are more efficient in at a little higher rpm

so shove that up your little 3.1 tail pipe also


but my goal i nthe honda is 40mpg if I hope and pray long enough maybe I will get it
full synthetics maybe go to some small width tires, try to do a little with the aerodynics and full tuneup
stupid little points buggers bother me on this car. no no can't do something like my camaro had where you lift a flap and adjust them while running on the car oh no that would be too easy. you have to take the cap off and physicly move the whole points assembly
and then cause the dwell on the old points was at 44 and now it is in spec at 50* I have to change the fricken timing and I don't have a damn timing light. sorry just had to rant and rave for a moment

small, hard tires will significantly improve gas mileage.

Who cares.
You guys are getting screwed any way at the pumps.
When I went home and filled up my Z28 with premo gas 9 months ago it was about $1.80 a gallon.
I was just home and premo gas was hitting 2.50 a gallon.
Thats back home in maine.
The gas prices over here in japan have been steady for the hole 2 plus years I have been here. Steady at about $1 per liter for the cheap stuff.
I think There doing it to bail out the air lines, again.
Half of all the gas we burn comes from natural gas, whos prices have remained fairly steady and low.
Every time the price of oil goes up a little gas goes up, oil stablizes for a few days and gas still goes up and the rare event that oil prices go down gas stops going up.
That oil refinery in texas blew up, gas went up (I guess that's understandable).
You guys are getting screwed that's all there is to it.
My advice, walk.

yeah think in a matter of a week or two here gas went from 1.93/gallon to 2.29 a gallon for the cheap stuff


so my **** is going to play cheap as well and sup up my honda for gas mileage.... faster honda HA I only have 68hp gas mileage is where this thing is going to be

as far as tires think I'm running 175/75/13's right now if I remember but don't hold me to it

I only know for sure I have 13 inch rims

Today full the tank once again....20 mpg.

20mpg city or highway or mixed?

mixed I get like 23mpg, but pure highway is 30 straight-up... at 80mph... I never go slower than that very often...

I bet I could get much better mileage at lower speeds.

hey rx7, do you have a 5 speed or what?

and when you are at 50, can you not use your highest gear?

yes at 50 I can use my highest gear
I usually can shift it into the highest gear at around 45 any lower then that though and if I give any gas at all it seems to try to lug a little for the mazda if you are refering to the accord yes I can shift into 5th at around 35 without really lugging it but would rather shift into 5th at 40mph

and yes I drive a 5spd for both of them

think about it like this...

you agree that there is more drag on any moving vehicle on earth, right? the faster you go, the more drag you have, right?

okay let's move on from there.

since we are talking about a 5 speed manual transmission, your 5th gear is locked and your speed is proportional to your engine RPMs.

for every rotation of the motor, you use a certain amount of fuel, so the more RPM, the more gas is consumed. since speed and engine RPM are proportional, gas should also be proportional to engine RPM... all of that would mean you would want to drive at the lowest possible RPM that will maintain your vehicle at a constant speed just below the point where the coefficient of drag causes the input/output ratio to become inefficient.

If I am missing something here, then by all means, fill me in... we are all learning something here... plus I'm tired

it's cool at least your not gettign bitter and again I'm sorry for sounding that way myself I didn't mean to.


but I don't think gas usuage is really linear for rpms. a lot of it depends on how things are designs and where they are efficient at.
so yes at higher rpms you might be using a little more fuel it might be using that fuel a little more efficiently to make that same amount of power
part of the reason could be port timing, compression bleed off, lack of intake velocity or exhuast velocity to help scavenging which can give more pumping losses,
now by itself yes that would mean you use more fuel

but you also have to think of speed
the faster you go the more ground you can cover in a certain amount of time. so lets think of a car uses the same amount of gas no matter what the speed ( think theory here) if you doubled the speed you doubled the gas mileage

we all know that can't happen though since as we both agree there are drag losses and such like that

so yes there is a point that drag will overcome the cars ability to make good gas mileage


but thta point can very from one car to another based upon things like aerodynamics, efficiency, at what rpm range the motor is efficient at and such.

one thing about my rx7 is it isn't very healthy down in the lower rpm ranges. try looking at a dyno graph of one someday down low they aren't the greatest at all. but at a certain point they actually start producing some torque to them

when I'm driving at a faster speed I'm assuming that I am getting my engine into a more efficient part of the rpm range. not really a part that uses less fuel bu tuses that fuel a little better and matched that with the faster speed it is able to pull some better gas mileage



least this is my theory

but one thing to try is lugging your motor. your at a much lower rpm now correct? but how much of the throttle are you using to go the same speed now that your lugging it? prolly quite a bit.
so now your in your motors less efficient range and even though your running less rpms your using more fuel


btw some numbers if I remembered them correctly

Cd. 0.28 and frontal area is around 18-19 cubic feet vs the later year thirdgen firebird I think was around Cd .32-.34 or so (correct me if I'm wrong) and frontal area of around 23 feet or so
quite a bit of difference there

also again just wanted to say think about speed

on my friends thirdgen firebird it was able to go into od at 35mph
but it wasn't his best gas mileage

he was moving too slow to take advantage of that once he started moving a little faster yes his rpms went up and so the steady rate of fuel consumption was a little more

but because he was going quite a bit faster it more then made it.

again his rpms are lower at 35 in od

but faster you go more ground you cover so over less fuel you use

up to a point

you're right, at 35 mph you're not utilizing the motor correctly... basically in my bird I would get the best gas mileage at 65'ish or so, (I don't know the real speed, just an estimate... that's when I start to get significant wind noise)

I can't say I know everything about your engine and transmission, but I can say that I am very confused about it as a whole..

I know that for most cars you DO get the best gas mileage at speeds between 50-60mph... now it's entirely likely that the rx7 and maybe even the thirdgens can go at higher (I just don't think its 80mph - )

On my 4-speed auto transmission, I can easily hold 80mph in OD, with the TCC engaged... the engine has more than enough torque at 1800-2100 RPM to pull me up almost any hill at that speed...

so what you're suggesting is that (for example,) if my 3.1 put out 40hp at 1800rpm, that by increasing the rpm to 2200 would MORE than linearly increase the horsepower output? allowing the transmission to output more speed per fuel burned?

I would totally agree with that if you had a CVT or a non-locking torque converter, but since the engine and transmission are locked together with the TCC engaged, it honestly doesn't matter if my car puts out exponentially MORE horsepower at the slightly higher RPM, because it already had more than enough at the lower RPM and by raising my engine rpm to 2200 is only going to result in a linear speed output... (as is the same with your 5-speed as well)

now in your case, if it truely is bogging at 50-60 in 5th gear with a little throttle... then I bet you're right about some sort of major inefficiency... I dunno, I've never driven a car that bogs like that at that rpm/speed.

but man, those twin-turbo RX-7's are some tight whips...

i'm at 25 highway...175,000 miles, no rebuilds, only new parts dealing with the drive train is little things like starters, alternators, water pump and a/c compressor.

about 40-45 is as low as I can go with my rx7 in 5th.
any lower then that I have to give the smallest amount of throttle possible.

yes speed increase per rpm is linear in any gear
but fuel burned isn't a linear 1:1 based upon rpm always
and in your car you prolly have enough low end power in mine it's a little different
hell my honda handles pulling at lower rpms then my mazda does
but then again we are talking one old honda not like the new ones that makes more torque then horsepower and is only a 2000lb car. I'm not saying faster just easier and better


so read back to another example I had way back here somewhere about the .5 lbs fuel burned an hour vs the .7 lbs fuel per houw and such it kinda explains what I am refering to

well im not sure how close this was with the rx-7s but i know that with the new rx-8 the powerband was similar to a honda s2000. u really didnt get anything out of it until u were into the 4, 5 and 6k range. the low end power was extremely low which would go along with what u say. the wankel rotory is a different engine completely and its hard to put logic to it based on a normal piston engine. ill guess that 75 mph cruising is in the ballpark of 3000 to 3500 rpm and cruising at 60-65rpm is in the 2000 rpm area. if this is true it probably uses more gas to keep it cruising as the power at that level is almost non existant

very interesting... hrm

more or less what I'm saying
though don't think it is because a rotary is so different more because as you compared it to a s2k. no powerband on the thing in the lower rpm ranges

at 45mph I'm doing around 1800-1900rpms
at 70mph it's closer to around 3000rpms

my torque peak is at 3800rpms
but at 3800rpms I wouldn't be shocked if I'm going fast enough at this point that drag is going to overtake me to the extent that I can't get as good of gas mileage out of it

I just checked my gas mileage again today... I'm more amazed then ever.

113.2miles / 3.269gallons = 34.63MPG

I get better gas mileage than a lot of 4 cylinder civics...

this is at roughly 90mph highway, with the A/C on full blast..

I wonder if the windows being rolled up helped the mileage a whole lot?

170miles on a full tank. So like 10 miles per gallon.

i would like to know what super fuel u r using to get 35 mpg at 90 mph

scrap, man i gotta call it, there is no way that you get 113 miles to 3 1/4 gallons i got a manual and i know how to conserve fuel at highway speeds, and i can't even get that with my car in 5th drafting a tractor and trailer. the highest i got was 28 miles. that was with the engine running perfectly while running at 2500 in 5th, drafting a tractor and trailer at about 70mph. even if i dropped that speed down to 65 so the tack would only show 2300. face it there is method to the madness, the lower your rpm, the less fuel you use unless you are under heavy load. if you can get someone to "pull" you down the highway you use less fuel, cause they are taking some of the load. it is a simple drafting technique that they use in nascar to pass. if the car up front is the one pushing the air and you are a foot from their bumper, they are pretty much putting you in a dead air zone, in other words your car isn't having to push the air, because of that, you can "slingshot" past your opponent as long as they don't block you.

all 80's model cars were designed to get the best gas mileage at around 55, some cars get better at 65, mine at about 60.

this was at roughly 90mph with no drifting.

I am at 1900-2100rpm at those speeds, and I calculated the mileage from maps.yahoo.com, which I've found is pretty dang accurate.

Assuming some leniancy in their measurements, that still gives me 32-37mpg... because it could go either way.

The best way to measure would be some sort of GPS unit, but I don't have one I can borrow for a long trip..

listen man, a auto should not be getting that kinda gas mileage, i got a stick and i don't even get that kinda mileage. i would deffinately have to see it to believe it.

well, what RPM are you at cruising highway speeds? I may have a more calm rear-end ratio than you.

I'm at about 2000rpm at about 87mph, if that means anything.

Also, I checked it again, with my windows down and I got 33MPG just the other day... so I will check it again today on the same 112-mile-trip to Waco.

I wish I had a better way of measuring the gasoline used... because I'm depending on the pump's accuracy...

What I do is I let it fill up until it stops automatically, and I use the same brand of pump once I get to waco, so hopefully they are configured at the same PSI for auto-stop.

I guess the best way would be to drain all my gas and put in 5 gallons, and drive until I ran out of gas, while tracking my journey with a GPS unit... but I can't do any of that.

19-20 city, 31-32 interstate-much better than my 6-7 mpg R-30
4 door truck!

city I get about 16mpg... as a delivery driver mostly.

no car ever made will get twice the fuel economy on the highway compared to city. you will maybe get a 20-25% increase. your saying that your 15 yr old car gets the highway fuel economy of most newer 4 bangers. and unless ur running a magical tranny and rear end ur not gonna cruise at 87 mph at 2000 rpms

11.325 mpg
.....wrong car lol I MISS MY CAMARO :'(

Hmm, this got me thinking, if you have the info from the ALDL port and a laptop(or maybe some other device, like a PDA) then wouldn't it be possible to calculate mileage using some kind of software? That way you could get mileage info even if you do not have a digital dash.

i am gonna have to agree with 86bluebird on this one guys, cause i do get almost 28 mpg on the highway at about 2300rpm doing about 70mph and i get about 16 in town, but i don't granny shift in town, i shift at about 4000-4500 in town. so i get 16 mpg due to my driving style, not cause that is all the car gets in town.
when i go 65 i get about 30 mpg at about 2100rpm

what all you yungun's(below 20yrs old) don't realize is that your driving style has ALOT to do with the gas mileage that you get.

I'm 17 and I agree. If you keep your foot in it you get less mileage. I know when i get on it alot or floor it around corners my milage goes down to about 18 mpg. If i baby it and occasionally get on it. I get about 21 mpg. And not flooring it at all and shifting like granny I get 24-25 mpg. All about your driving style and the shape of the motor.

Well I can't tell you for sure what changes have been made to my tranny or rear end, but for sure I am at roughly 2000rpm at 85mph...

I will settle this once and for all this weekend, because I'm going on a long trip with a bunch of people, so we can all compare odometers and such.

I have no reason to make this up.

What's funny is I actually had a VERY low tire, 25psi, front driver side when I last checked my mileage... I had no idea.

I just had my center link, tierods, and steering coupler replaced, along with the necessary alignment... is it possible that this is helping my mileage signifcantly?

I'm curious, what is different about my car that allows me to be at roughly 2000rpm@85mph??? I have a strong suspicion that my torque converter is falling apart, because when I try to maintain 90mph on a long hill, I increase the gas, but I don't give it enough to break it free of the TCC, but I hear a slight grinding sound, so I think the TCC is slipping and heating up. I'd probably get even better mileage if I had everything rebuilt.

Any tips for my long trip for getting accurate mileage readings to satisfy you guys? Do you typically let the pump stop on it's own, or do you top it off a certain amount or what? I doubt most people would put in an exact amount and let it run dry.

use your trip odometer to get actual mileage and than fill it up completely. some pumps push out faster and will shut off earlier, especially if no one around is filling up at the same time. if the pumps run slow it will shut off later as the pressure wont build up as rapidly. and u must have a magic ride cuz at 80 my car is closer to 3k rpms

you must not have a TCC, because that would be nearly impossible.

I haven't driven at 80mph and checked the gauge so I am not sure but thats like 130km/h, I used to get like 1900-2000 at 100kph(60mph), now though I can get 1800rpm at 60mph.

I think that at 80mph I think it'd be around 2300 or 2500 rpms, just guesstimating though.

not necessarily, i got a 3.42 rear of the auto cars, but i got a 5 speed. i run 2,000 at 55 and 3,000 at almost 90. my fifth is really loong, and i only had it above 5,000 in 5th about 10 times, and let me tell you, i was clocked at 162.6 by a buddy of mine in his high speed persuit 95 mustang cobra police intercepter(he works for the pa state police) on I-81 between carlisle and I-581 cross connect. he about crapped himself, and i almost pi$$ed myself when he told me the speed

divine, is that in a v-8 car or a v-6. cuz my old formula used to cruise at 65 mile/hr in third gear at around 1600-1700 rpms. the bigger engines make a big difference

It must have taken all day to get up to that kind of speed in a 2.8... This is more unbelievable than getting 40mpg in a thirdgen.

I might use a little more gas per mile when I'm doing 75

but less time on the road is worth it to me

i gotta call scrapmaker out on this one too

that is total BS

NO CAR from our time period got that kind of gas mileage except the best running of 4 cylinder motors. even those were hard pressed to get above 30 in the 80's, it is simple fact.

A brand new 4 banger w/6 speed (basically an overdriven manual) Civic is getting what you claim... I should know, I drove my brother in laws brand new Civic (10,000 miles on it, he's original owner, babies it always) from Sacramento to San Diego. San Diego to Tijuana, then Tijuana to Sacramento. I had ALOT of spare time to calculate gas.

Either you're really bad at math, or you aren't keeping accurate mileage, or you are getting way more gas than you think you are at the pump.

C'mon now, be reasonable... The MOST EFFICIENT HYBRID (the toyota prius) gets 55 city, 45 highway (they get better mileage in city because they use the electric motor more, you should read up on those cars they are very interesting stuff)... You're telling me you're almost matching that?

I have a perfect running 3.1 with a perfect shifting 5 speed transmission. Perfectly aligned, no shake or rattle at any speed. Brand new tires, just greased all my bearings and front end.

I do tuneup's every 2,000 miles (very dusty area and I drive it ALOT, about 40,000 miles a year, alot of freeway time)

It drives straighter than an arrow and has no kind of vibration, the smoothest stock thirdgen I've ever drove or even ridden in my entire life...

If I'm being very modest and concious about gas I can ALMOST pull 26 mpg on the highway. If I sit dead at 65 with cruise control. That's the most efficient I can get the car to be, ever. Frankly, people have a hard time believing THAT even, but it's true. THAT is with a concious effort of saving gas the entire time.

Normal highway is about 21 if I'm driving normally.

I get about 18 in the city, and it drops drastically to about 15 or 16 in the city if I drive it hard everywhere I go from light to light.

Okay, allowing for inaccuracies in the pump, and maybe even the mileage, it's still easily 30mpg... my question to you is what rpm are you at on the highway at 85mph? I seriously think I have some gimp-*** rear gears... hell, I can't even burn out with my brand-new motor.... friggin' pathetic. I can MAYBE get a little squeak on some road surfaces... that's IT. I always hear of you guys being able to "light them up," and that's something I've just gotten used to not being able to do.

btw I'm going on a several-hundred-mile trip tomorrow morning, along with several other drivers. I will compare mileage with them, so I can make sure I'm as accurate as I can be.

The only thing that sucks, is all the other cars are vintage muscle, that probably won't go over 60mph due to the lack of overdrive. Maybe I'll get even better mileage?