As stated in the title, I am looking for ideas to improve economy, I have one car I am using as a test bed and am looking to try to acheive 30 mpg out of a 12a.

Base is a 83 GSL manual, 126,000 good mechanical shape.

Done

Regular tune items including: plugs, wires, fuel filter, coolant flush and replace

Weight loss/diet: a/c removal, non power steer, wind up windows and stripped interior.

Amsoil into engine, transmission and rear end.

2GCDFIS

Planned exhaust upgrade (current isn't stock but is restrictive)

Thinking about a 3.6 diff ratio but not sure that'll help as RPM will be around 2600 at 60 mph.

Most of my driving is highway.

This is a project with stock engine so any ideas welcome.

So far I'm getting about 24 mpg.

 

Sounds like you are on the right track. An e-fan may help slightly. Also tires and air pressure are important. Make sure they are properly inflated. Softer/stickier tires will tend to give lower MPG than hard compound tires. Also make sure carb/fuel system is in good shape/tuned. Anything to reduce aerodynamic drag will also help, especially on highway. A good exhaust setup will increase the MPG as well.

 

For everyone's benefit, I thought I'd throw in our PM exchange from earlier today;

I seriously doubt that you'll be able to exceed 30 MPG, however.

First off, you should know that I've done some statistical analysis on the 84SE and even with it's EFI system, efficiency mods are not going to yield a process capability which exceeds about 26 MPG - the car just isn't able to perform at better MPG than this under my test conditions. The 12A may have a better shot with a bit less displacement, but 30MPG is a very high target. As a point of reference, my best MPG ever (84SE EFI) has been 24 during the summertime (low air density), and all highway driving. Have never been able to do much better than that, but here are the statistically correct 'Critical Factors' for fuel economy in an 84SE w/13B and EFI:

Tested:
Driving Conditions (City/Highway/Mixed) a critical factor
Day of Week not a factor
Season a critical factor
Level of Performance also a critical factor (though slight) and,
Oxygenated Fuels not a factor - you may not have Ethanol added to your gasoline there.

This is with 89 octane pump gas and Oxygenated Fuels mandated by EPA from 11/15 to 3/31 seasonally. Test vehicle base mileage = 193k miles on original engine with performance mods listed in signature line. Data collected from every refuel receipt back to 1/2003.

Of the critical factors which I tested for, Driving Condition (city driving vs. highway driving) was the single largest contributing factor to improving MPG. Next was Season - high outside temps mean less fuel must be burned to balance air intake. Also, less critical, but a consideration is Level of Performance and Repair - the better condition your car is in mechanically, the better MPG you will get.

Translate this into real-world as follows;
1) Drive highway as much as possible, city driving reduces MPG
2) Drive during the heat of the day, or during the summertime, if you have a choice,
3) Keep your car in good operating condition, new plugs, new cap/rotor, tires to 35psi (or as rated), and new wheel bearings, non-dragging brakes, etc.

Hope this helps, and reply back if more questions.

 

I would try some "Ricer stickers" and maybe some Fuzzy Dice......

Reality.... A high quality air filter (oiled sponge type) will make a difference....

Jay
1984 FB

 

Any ideas on carb alternatives for improved economy or is there a Sterling that is made for economy.

I am using 10-40 Amsoil due to weather

I have almost new all weather tires, not sticky at all......lol

temperature range here is extreme low zero degrees to high 95 all farenheit for our non US members.

 

You could wire your secondaries SHUT - that will improve MPG! In all seriousness, the critical factor of Level of Performance that I talked about before, can be misleading, because it is only critical due to a 2-way interaction with Seasonality. In other words, the statistical tests (ANOVA Table of Subgroups and a Design of Experiments, if you're interested) shows that as Level of Performance=increases combined with Season=Summer, MPG goes up. Season is the Main Effect contributing to the output (the MPG).

So, to boil this down; as you increase performance, don't immediately expect that it's going to be beneficial to your MPG - in many cases, it will increase HP and HP costs fuel. If you're going for all out efficiency and don't want to buy a Toyota Prius, then I would look at routine maintenance and repairs as a way to increase 'performance' rather than changing out stock parts for 'race' parts. Just want to clarify on that point.

Routine maintenance and repair would include those things that contribute to overall vehicle friction when driving. A short list would include; wheel bearings, aero (keep your glass hatch - my Mariah hatch cost me 2 MPG along with Airdam), brake components, tire pressure, A/C use, oil viscosity (wasn't able to test this), and most of all, your right foot. HTH,

 

Megasquirt controlling fuel and spark.

Header and good exhaust helps on the highway.

 

I am trying to keep my RPM under 4500 at all times, although I do clean out the carbon in second every now and then, it is a rotary after all, hehehe.

With regard to the carb, I am not looking for a performance carb, I was wondering there is a more economical choice out there, probably two barrel as you indicated, or is a well tuned Nikki as good as it gets or close enough to not be an issue.

This is meant to be a low cost project for those who drive these cars a lot, I do up to 2000 miles a week, average about 1000 lately.

 

i think ultimately fuel injection is the way to go, but either way leaning it, in addition to the other stuff being talked about, is helpful.

also freeing up the exhaust helps a bunch, timing is prolly also key.

here are some examples from my personal cars.

my black gsl-se with the s4 block (larger ports) and the rb street port exhaust, would get about 26mpg on the freeway, 20-22 in mixed driving

the 3 rotor fc when leaned out to 14.5:1 in vaccum, ALL the vacuum ranges, with the haltech, would get 19.9mpg freeway. the engine will run leaner, up to about 15:1, 15.5:1, depending.

my 1983 limited edition, would run about 13.3-13.6:1 @cruise, its a little rich, theres room for improvement, that got 18-20mpg in the same mixed driving the gsl-se got 20-22mpg

at some point though you have the simple fact that there are 2 rotors @x number of rpms and they need a certain amount of fuel per revolution.....

 

the next step is stuff like what honda did on the 92-95 civic vx, skinnier wheels and tires, its got more aero stuff, its a little lighter.

 

What a lame RX-7 project.


LMAO, I'm on the edge of my seat reading all this.

 

Who asked you...........I have four 7s drive about 1000 miles a week and wanted to try something different, your positive input is well received, dumbarse.

 

LOL, sorry.


Good luck.

 

You won't see any benefits of taller gearing (as if you could find any) UNTIL you do something about the IGNITION TIMING...

I haven't played with low-load negative split, some people swear by it, HOWEVER i can tell you that running locked 20/10 timing will give you lots more below-4000rpm pull and the engine runs better. And make sure that the ignition advance is hooked up!

I've easily done 27-28mpg, and that with energy-sucking wide tires and a non-optimal wheel alignment.

Without locked timing, you can get the same MPG in 4th gear as 5th gear at a steady 60-70mph cruise, because the engine isn't working to best efficiency at the lower RPM. It's why a lot of early cars were 4 speed... they didn't *need* 5th gear. But people whinged about spinning 4k to tool down the road so a 5 speed became standard.

 

Ok I know this might sound funny but I have a streetported 12A with a header back pipe, prisilencer and a flow throu muffler runing only the alternator. Going on the highway at about 80-90 it gets 29mpg. And I have 2 12" subs in a big box witch probablly is about 70lbs.

 

I can believe it... many forms of porting can and does improve fuel economy. It makes the engine more efficient, after all.

The added weight wouldn't enough of a difference. Steady state cruise drag is bearing and tire drag, and aero drag, and at highway speeds it is mostly aero drag.

 

PeeJay, can you give me more info on how to go about doing the locked timing deal, is there a post on this? I have a 3.6 ratio center available if I want it.

Your post seems to address exactly why I hadn't done this diff change yet as my revs will drop below what is a reasonable rpm range for a 12a in cruising mode.

 

All you *need* to do is remove the springs on the advance weights. As soon as the engine starts turning, you get full mechanical advance. No need to weld or do anything like that.

Takes about 10 minutes, and a lot of that is dealing with the fiddly little clips holding the vacuum advance rods to the pickup plates. Remove the ignitors and vacuum advance pots, unscrew the pickup plate and remove that too, remove the advance springs (VERY CAREFULLY if you intend to ever re-use, they distort easily!), then pop it back together.

I remember there was one difficulty... I think the upper distributor shaft (what the rotor pushes onto) needs to come out with the pickup plate, and to do that there is a screw hidden in the top of the shaft, usually that area is packed with grease. Then when re-assembling, you have to ensure that the tabs in the advance weights are in the slots in the upper shaft (will make sense when you have the pieces in front of you). Easy way to verify after you get it together is to rotate the upper shaft back and forth, you should see the advance weights moving in and out.

It does mess up the idle quality a little bit, and isn't the best for emissions. But it works... everyone who's driven or rode around in my cars comments on the way the thing just pulls at any RPM.