my mpg sucks!
my mpg sucks!
i calculated my mpg yesterday... it seems i'm only getting 16.7 miles/gallon. i'm driving an 82 rx7, stock except for a k&n filter. i also used some gumout on the carb a few days ago. this is my daily driver, so it would be appreciated if anyone could give me a quick fix or advice on what to check. then engine has about 30,000 miles on it. i was thinking about removing the rats nest, would this help or hurt my mpg/hp?
Banned. I got OWNED!!!
Joined: Sep 2003
Posts: 2,203
Likes: 575
From: The South
When I zip around town my mileage sucks as well but on mostly highway it gets 26-27 consistently. But I've got an MSD direct fire, an electric fan, a full racing beat "streetport" exhaust, no emissions/air pump, and a number of other mods.
DSM
Joined: Feb 2004
Posts: 2,070
Likes: 1
From: Milton, FL
i have never actually checked it, but if i had to guess, i would say i get about 15-17 mpg. This is if i drive very easy and have no fun. If i get on those mech secondaries(oh yeah!) umm i dont get that good of mpg
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lol yeah i understand its one of the drawbacks of a rotary... btw i drive it like its supposed to be driven - accelerate hard and wind it to 6500 at least once every run. no wonder my mpg sucks, eh?
"A Piece of Work"
Joined: Jan 2004
Posts: 319
Likes: 0
From: Rogersville, MO
I use mine as a daily driver. 12a with RB headers, no rat's nest, rebuilt carb and I avg about 22 MPG. I usually shift about 4K RPM and run it to 65K a few times a week. For a small engine it doesn't do that well on fuel mileage, but is a hoot to drive.
TCS
TCS
Joined: Feb 2004
Posts: 838
Likes: 1
From: Waterloo & Mississauga, Ontario, Canada
I was getting around 12.5 mpg, with everything almost stock. Pretty horrible. My gas tank had a few holes near the top, rusted right through. A lot of gas was just evaporating when i had the car parked.
Swapped gas tanks yesterday, things should be much better now.
Swapped gas tanks yesterday, things should be much better now.
brilliantly stupid
Joined: Nov 2002
Posts: 1,100
Likes: 0
From: Rockford, IL
I'm lucky if I get 180 miles to a tank of gas. I used to get at least 220 or so, then suddenly it took a steep dive like so. My bro's 84 GSL, which has 61k miles on the original engine gets probably around the same, I think maybe a bit higher though.
But highway is a different story. I could pull 30-35 MPG....very odd.
But highway is a different story. I could pull 30-35 MPG....very odd.
84SE-EGI helpy-helperton
Joined: Oct 2002
Posts: 3,584
Likes: 542
From: Phoenix, AZ
Remember that fuel mileage has a lot to do with the fuel metering system (carb or EFI TB), but also has to do with the mechanical underpinnings of your vehical overall. Some things to be thinking about to increase fuel mileage are as follows;
1) Tire pressure - your tires will return minimum rolling resistance when filled to the correct pressure when hot. This is to say that bumping your tire pressures up from 30 to 34 could net you a considerable increase in fuel mileage. Lower rolling resistance equates to less fuel needed per mile, particularly during acceleration and braking.
2) Wheel bearings - older bearings may have a lot of play which can negatively impact front camber and caster adjustments and increase rolling drag. Test torque settings on front wheel bearings, and listen for rear whirring noises to see if your bearings may be increasing drag.
3) Brake dragging - do you ride your brakes when you drive? Do you downshift to slow the vehicle instead of using the brake pedal? If your brakes are poorly adjusted or in disrepair (bad calipers, leading seals, etc.) then your brakes may not be releasing fully when you let off, increasing rolling resistance and decreasing mpg.
4) Front and Rear alignment - A few degrees of 'extra' toe-in, or a canted or bent rear suspension is like dragging your tire sideways 50 feet for every mile that you drive - while hard on tires, this is also going to kill your mpg and fuel efficiency. Get a good alignment at a 4-wheel alignment shop and they can ensure that you're tracking straight. Request a dead-even alignment if you drive a lot of city streets and not much freeway - this will require more turn-in effort on your part, but reduces front friction loads.
5) Transmission, Diff and Engine oil viscosity - High viscosity oil result in mechanical loads that must be overcome by engine power. Using a higher grade of tranny or diff fluid may smooth out the sounds, but could be causing you to lose performance and efficiency. Use good quality lubes from known manufacturers to extend mechanical life with a minimum of induced drag through gear systems.
6) Aerodynamics - driving with A/C on and windows up is a dead-wash for driving with the windows down and taking on all that excess wind drag from the windows and sunroof. Either way, you're sacrificing fuel efficiency for comfort, which obviously comes into play during the summertime. Big wings and front air dams also decrease fuel efficiency, but I'm one to talk there...
7) Cooling system, radiator and oil - If your radiator and oil cooling systems aren't working right, that fan clutch on the front of your engine is going to be working overtime and taking engine power to turn it. Get your radiator flushed, and change your oil frequently to ensure that then engine runs at a steady temperature to increase mileage by a bit.
8) Electrical loads - Running a 1000 watt amp and stereo? This places additional load on your alternator and charging system, requiring more drag on the engine and dropping mpg. Running with headlights, driving lights, and neon's on will do the same thing. Reduce electrical loads to gain max mpg.
9) Shift points and accelaration - If you're shifting at redline every light, you better expect to get 10mpg! Drive more conservatively and leave plenty of braking room to conserve fuel. Also, use of your cruise control (if equipped) will help to administer only as much fuel as your car needs to maintain speed. Constantly 'chasing' the speedo leads to fuel wasted.
All in all, unless you're driving around with your windows up, A/C off, no lights or electrical equipment on, you're trading fuel for convenience and niceties. If you keep your car maintained mechanically, it will help when it comes to those last few mpg that you're trying to stretch out of each tank. The biggest single contributing factor is your carb or EFI system, though - so get that checked out first, and make sure that it's running in tip-top shape before you start looking into these other things. What I mention here are only things that most people don't think about, but are nearly as important. HTH,
1) Tire pressure - your tires will return minimum rolling resistance when filled to the correct pressure when hot. This is to say that bumping your tire pressures up from 30 to 34 could net you a considerable increase in fuel mileage. Lower rolling resistance equates to less fuel needed per mile, particularly during acceleration and braking.
2) Wheel bearings - older bearings may have a lot of play which can negatively impact front camber and caster adjustments and increase rolling drag. Test torque settings on front wheel bearings, and listen for rear whirring noises to see if your bearings may be increasing drag.
3) Brake dragging - do you ride your brakes when you drive? Do you downshift to slow the vehicle instead of using the brake pedal? If your brakes are poorly adjusted or in disrepair (bad calipers, leading seals, etc.) then your brakes may not be releasing fully when you let off, increasing rolling resistance and decreasing mpg.
4) Front and Rear alignment - A few degrees of 'extra' toe-in, or a canted or bent rear suspension is like dragging your tire sideways 50 feet for every mile that you drive - while hard on tires, this is also going to kill your mpg and fuel efficiency. Get a good alignment at a 4-wheel alignment shop and they can ensure that you're tracking straight. Request a dead-even alignment if you drive a lot of city streets and not much freeway - this will require more turn-in effort on your part, but reduces front friction loads.
5) Transmission, Diff and Engine oil viscosity - High viscosity oil result in mechanical loads that must be overcome by engine power. Using a higher grade of tranny or diff fluid may smooth out the sounds, but could be causing you to lose performance and efficiency. Use good quality lubes from known manufacturers to extend mechanical life with a minimum of induced drag through gear systems.
6) Aerodynamics - driving with A/C on and windows up is a dead-wash for driving with the windows down and taking on all that excess wind drag from the windows and sunroof. Either way, you're sacrificing fuel efficiency for comfort, which obviously comes into play during the summertime. Big wings and front air dams also decrease fuel efficiency, but I'm one to talk there...
7) Cooling system, radiator and oil - If your radiator and oil cooling systems aren't working right, that fan clutch on the front of your engine is going to be working overtime and taking engine power to turn it. Get your radiator flushed, and change your oil frequently to ensure that then engine runs at a steady temperature to increase mileage by a bit.
8) Electrical loads - Running a 1000 watt amp and stereo? This places additional load on your alternator and charging system, requiring more drag on the engine and dropping mpg. Running with headlights, driving lights, and neon's on will do the same thing. Reduce electrical loads to gain max mpg.
9) Shift points and accelaration - If you're shifting at redline every light, you better expect to get 10mpg! Drive more conservatively and leave plenty of braking room to conserve fuel. Also, use of your cruise control (if equipped) will help to administer only as much fuel as your car needs to maintain speed. Constantly 'chasing' the speedo leads to fuel wasted.
All in all, unless you're driving around with your windows up, A/C off, no lights or electrical equipment on, you're trading fuel for convenience and niceties. If you keep your car maintained mechanically, it will help when it comes to those last few mpg that you're trying to stretch out of each tank. The biggest single contributing factor is your carb or EFI system, though - so get that checked out first, and make sure that it's running in tip-top shape before you start looking into these other things. What I mention here are only things that most people don't think about, but are nearly as important. HTH,
Banned. I got OWNED!!!
Joined: Sep 2003
Posts: 2,203
Likes: 575
From: The South
That's one hell of a post, longduck. You're 100% right, too. One thing about acceleration though, there's such a thing as accelerating "too slowly." I have no idea what the optimum pedal positions and shifting points are (and I imagine it varies between models) but I do know that riding it lightly and shifting at 2000 rpm ain't them.
S.F.W.C. Liberator
Joined: Jan 2004
Posts: 797
Likes: 0
From: North Carolina
Originally Posted by edwin-82/rx7
i calculated my mpg yesterday... it seems i'm only getting 16.7 miles/gallon.
getting nearly 17 mpg is extremely high for a 7. i heard of maybe two or three 7s getting that kind of gas mileage. i get like 10 mpg on my stock 7 and god knows how much on my ported 7. seriously in all jealousy though you're lucky. haha j/k--lauren
Last edited by red_blast; Aug 18, 2004 at 04:26 PM.
lol i know not to expect much... as per someones earlier post, i got my foot out of the fan and started shifting at about 3500 to 4000. but i still can't resist the urge to drive it like its supposed to be driven... :P
Undercover
Joined: Aug 2001
Posts: 1,983
Likes: 0
From: Ohio
Thats not bad for the repu. With the weber i was getting about 13-14 best. You have to consider they go down the highway at 4k +.
For my 79 with a weber i get 10-11.5. earlyier this year i was shelling out 3-$400 a month on gas. I finally went and got a mazda 323. cant beat the piston. its a gtx > 4 wheel drive turbo, and it still gets 20 + all the time and around 30 on the highway.
CJG
For my 79 with a weber i get 10-11.5. earlyier this year i was shelling out 3-$400 a month on gas. I finally went and got a mazda 323. cant beat the piston. its a gtx > 4 wheel drive turbo, and it still gets 20 + all the time and around 30 on the highway.
CJG