Rx-7Doctor

iTrader: (13)

When I first got the Se I took it for about a 650 mile round trip.
With it in stock form with stock exhaust and catalytic converter. New plugs, cap, rotor and wires. Had injectors cleaned and tested. Also had the SE trans in her.
I averaged about 19-20 MPG on the highway. This was at an average speed of 65-70 MPH with no spirited driving.



Recent mods and replacement parts.

Rb header and presilencer, still running a stock muffler. On above stock system I was running a straight thru muffler.

2nd gen coil and 2nd gen plugs for leading side.
New O'2 sensor
New Coolant temp sensor
Brand new injectors(don't think had any factor in mileage because others were in perfect condition after cleaning)
Ported UIM and LIM with pineapple racing sleeves.
Kn replacement filter for stock box
88 N/A 2nd gen tranny (For very tall 5th gear.

1st run was approx 160 miles with windows up. Average speed 65-70 MPH
2nd run about 30 miles with windows up. Average speed 75 MPH
3rd run about 120 miles with windows down. Speeds varied from 65-95 MPH.
But an average of 75MPH. The 95 was for about 15-20 seconds checking RPM at that speed with 2nd gen trans.
MPG for those above runs with previous mileage of approx 35 miles before starting trip of combo in town and freeway was 26 MPG
4 run approx 125 miles with windows down. Average speed of 65 MPH
Mileage for above 25.6 MPG


The 1st runs also included some up hill activity where the rest of the runs were all on flat land at sea level.

I hoping with maybe some tweaking to get her around 28 MPG.
I'm not sure if the manifold porting is helping or hindering the mileage. The only way to find out is to put the non ported ones back on a do a similar test. But I'm not that curious. :-)

As far as the 2nd gen trans goes. It was great to be at 95 MPH and only be taching out 3800 RPM.

EricRyan

iTrader: (4)

Nice, just more proof that says these engines need to breathe.

rxtasy3

iTrader: (2)

nice #'s. i'd be happy with anything above 20. i'm averaging about 16 with a streetported '74 13b w/holley 600. i'm hoping to soon be able to do FI on it which i know will increase my mileage. also, with a properly working A/C may yield slightly less mileage than with the windows down.

dbragg

iTrader: (7)

also, a few months ago i did a highway trip with my DD 85 GSL and my results were 27.4 mpg.

mods:

RB streetable header-RB collector-magnaflow muffler-borla muffler
2nd gen coil
RB nikki filter system

its running a little rough, not bad. i think i have a small exhaust leak around the intake manifold and i have a couple leaks around the flanges in my exhaust system.

i can hit over 30 guarenteed. ill use my new method and put it to the test the next time i have to go some where by highway.

ray green

iTrader: (14)

This is getting interesting! Doc, are those new results with the cat still in? Sounds like it since you put in a new O2 sensor. If so that's a real nice result. It looks to me like the most significant "upgrade" you've done concerning gas mileage is the 88 rear end with the higher gear, do you think that might account for most of the increase?

aws, I'm assuming you still have the stock Nikki carb. What, if anything, have you done to it? Do you still have the air pump and rat's nest?

trochoid

iTrader: (6)

That's one thing I never quite understood. Even with the 13B being a sightly larger engine, one would think that the upgrade to FI and a slightly better ecu, fuel mileage would have gone up, but the EPA stickers on the build/price sheets told a different story. The S3 12As were still rated at better fuel mileage. Good work on the improvement doc. If there was an S-AFC that was made to work with the SEs, I'm sure mpg could be improved even more since they tend to run rich with the oem settings.

With the way fuel prices are climbing. it might pay off in the long run to toss the oem ecu and go with a MegaSquirt. Leaning out the fuel mix would not only yield better mpg, it would increase performance also.

B6T

iTrader: (2)

I've hit 26mpg with my stock GSL-SE cruising on the highway at 110km/h using cruise control. Driving in the city with fast acceleration, I've got as low as 15mpg. I just found that the throttle position sensor may need replacement or recalibration though, so hopefully that will improve my mileage as well as reduce the cloud of pollution and the horrible smell at idle. The thing runs ridiculously rich, so that's definitely affecting my fuel mileage. Aside from the TPS, are there any other ways to adjust the fuel mixture, to lean it out... A LOT?

Directfreak

iTrader: (2)

I think this is worth repeating, from an old thread:


By the way, the Best FB combo EVER for highway cruising, was the bone stock 1985 GSL-SE.

Swapping for a TII Tranny will only be a better ratio than a regular FB, but not an SE.

For THE Absolute best low RPM cruising, an Second Gen GXL tranny would probably be best, to an rear end..


So according to these numbers, my TII Tranny and SE rear end would give me a final drive ratio of 2.931, slightly worse than my stock configuration, but worth it for the strong tranny.

Also note that the tire size, diameter will have the same effect as changing the gears, so a rim/tire combo will yield better cruising RPM as well.


US SPEC MAZDA DRIVELINE RATIOS

*** FIRST GENERATION ***
……………………………………………………………….…….………………………………..AXLE..FINAL.TIRE......TIRE..ENGINE
VEH.. YEAR. 1ST.. 2ND...3RD.. 4TH...5TH...RATIO RATIO SIZE……....RPM...RPM @ 60 MPH
RX-7. 79-83 3.674 2.218 1.433 1.000 0.825 3.909 3.227 185/70-13 892...2878
RX-7. 83-83 3.674 2.218 1.433 1.000 0.825 3.909 3.227 195/60-14 891...2875
AUTO. 84-84 2.458 1.458 1.000 0.720 N/A...3.909 3.909 185/70-13 892...3487
GSLSE 84-84 3.622 2.186 1.419 1.000 0.758 4.083 3.097 205/60-14 878...2719
RX-7. 84-84 3.622 2.186 1.419 1.000 0.807 3.933 3.175 185/70-13 892...2832
RX-7. 85-85 3.622 2.186 1.419 1.000 0.807 3.909 3.156 185/70-13 892...2815
GSLSE 85-85 3.622 2.186 1.419 1.000 0.715 4.077 2.914 205/60-14 851...2480
RX-7. 85-85 3.622 2.186 1.419 1.000 0.697 4.444 3.099 205/55-14 910...2820

*** SECOND GENERATION ***
……………………………………………………………….…….………………………………..AXLE..FINAL.TIRE......TIRE..ENGINE
VEH.. YEAR. 1ST.. 2ND...3RD.. 4TH...5TH...RATIO RATIO SIZE……....RPM...RPM @ 60 MPH
Base. 86-91 3.476 2.002 1.366 1.000 0.711 4.100 2.917 185/70-14 855...2494
GXL.. 87-91 3.476 2.002 1.366 1.000 0.697 4.100 2.859 205/60-15 841...2404
Turbo 87-91 3.483 2.015 1.391 1.000 0.719 4.100 2.948 205/55-16 828...2441
Conv. 88-91
GTUs. 89-91 3.476 2.002 1.366 1.000 0.758 4.300 3.261 205/55-16 828...2700

*** THIRD GENERATION ***
……………………………………………………………….…….………………………………..AXLE..FINAL.TIRE......TIRE..ENGINE
VEH.. YEAR. 1ST.. 2ND...3RD.. 4TH...5TH...RATIO RATIO SIZE……....RPM...RPM @ 60 MPH
(FD). 93-95 3.483 2.015 1.391 1.000 0.719 4.100 2.948 225/50-16 829...2444



Man, you're not gonna believe how long it took me to get those aligned and looking right on the screen.. [/quote]

peejay

I haven't noticed gearing to matter much at all for fuel economy, for a rotary.

Spark plugs make a huge difference. I went from 30-33mpg to 22-25mpg by taking out my last set of cut-down Autolites and putting in a set of fresh stock FC plugs.

If I get only 26mpg when I put the -SE engine in the new car, I'd probably have to go postal. Fortunately, the design of the intake manifold is conducive to installing a false-air device so I can adjust fuel mixture on the fly.

peejay

I *hate* the FC trans and cannot wait to go back to the FB unit.

There's an enormous hole in between 4th and 5th. It ends up that to go up hills, you're either running near redline in 4th or running with heavy throttle at 4000 in 5th. There's no useful in-between like the FB unit.

Note that 4000 in 5th for my car with the FC trans is only 80mph or so. In fourth, that speed is around 6500... kind of a crappy choice to have.

With the FB trans, of course 4th will still be useless but 5th becomes usable.

murdo

Are you basing this on an Imperial gallon or converting to a US gallon?

If it is an Imperial gallon, your figures are nothing to write home about.

I took my 85 GSL-SE on a 500 plus mile road trip when I first got it 10 years ago (about 80k miles on the clock) and I got 25 mpg (US gallon). That is the best I have ever had with it. However, it seldom sees a lengthy road trip.

In any event, the fuel economy of the GSL-SE is superior to both the 79 RX7s I owned before buying it.

Rx-7Doctor

iTrader: (13)

With the 12A engine you would have more of a problem with the taller 5th gear because of the difference in power between the 12a and the 13B.
I had no problem going up a hill in 5th gear because I'm making alot more power than a stock 12a and alot more than a 12a with a header system.

So It is not a benenficial thing for you to be using a FC trans.

As far as fuel economy goes. The fuel that we had when these cars came out was much better than the fuel we have today. The winter fuel we use takes away a considerable amount of fuel economy away from us and California fuel is even worse.

I am going to be experimenting with lower gearing and timing changes like you did to see if I can increase my fuel economy. There are also some other experimental things that I am working on.

B6T

iTrader: (2)

More details please! Are you saying you were getting 30-33mpg with cut-down autolites? I currently have FC plugs in my -SE and am getting similar fuel mileage to you (22-25mpg).

rxtasy3

iTrader: (2)

i want to know what is meant by "cut down"?

JKM

That's funny, I'm running an almost identical setup to the "after" car, with the exception that mine is a S5 transmission, and I got nearly the same results, I clocked in at 24 MPG highway at 70-75 MPH with the windows down.

Then I flooded my car it got 14 mpg with fouled plugs. I currently get around 17 MPG (city or highway) with a huge exhaust leak.

dbragg

iTrader: (7)

all details about my car:

85 GSL
82-83 engine, not sure which. had a rebuild done it beofre i got it. should have around 10K or less miles on it. the tranny is a stock 12a tranny. i thought about switching to the SE tranny, but havent. if i find one cheap enough i may. i have the stock rearend. im running stock wheels and tires. the tires are complete **** and cant keep air for anything.

as for the engine. the is no rats nest. i have the vacuum advanced hooked up. i have the line running to the first line(fartherest to the left) on the carb. i have AC and PS. i wasnt running AC that day, as i have never ran it. it have the belt off of it for now. i have the stock nikki with a RB filter set up. i have a carter fuel pump and holley FPR with the PSI set around 2-2.25. which is about what the stock pump puts out. as when i had the FPR hooked up on the stock pump the gauge read right 2 psi constantly i believe. the day i got these results im not sure what milage i was running. im assuming around 60-70 with a few stop lights and such. it wasnt 100% highway driving. i also had the sunroof cracked open and the windows down. the only other mods i have done to my car are the 2nd gen coil and a FD alt. i hooked up a relay for the fuel pump but i think thats a joke as to me it seems now the power fluctuates more than before. im not sure what plugs im running, i think some densos. i need to buy some NGK.

i am running a test currently with a new factor that i dont want to speak about until i am finished with my testing. just a tad bit of info. i am doing 100% city driving currently(the daily home to work to work and etc). i cant be definate as everyone knows our fuel gauges run wild, but it appears to me the gains i am seeing now are tremendous. i will post more results probably later this week or next. depending on how long the rest of this tank lasts me.


i had also thought about going with an FC tranny at one time. after realizing i live ine GA. we are a mountainous region and the 5th gear would kill me i decided against it. MAYBE an SE trans, but im 100% satisfied with my 12a trans.

peejay

cut down: i took standard spark plugs and cut the ground straps and bent them to convert them to side-gap. Mandatory if you don't want to munch the rotors and apex seals.

I use 3923 because they're the first thing I tried and they happened to work awesome. They're the correct seat, diameter, reach, and they are 5/8 hex (main reason for use) so no fancy socket is needed for use with FB rotor housings. Oh, and four of them cost about the same as ONE BR8ET. They also last about four times as long, the main wear problem being undercutting of the center electrode at the porcelain.

I think I was gapping them at .035".

rx7doctor, I'd say you need to ride in my 12A to believe the torque, but you can't, since the engine finally wore out last week. Only 211k on it, too, think Mazda should comp me for the early failure? The header actually increases midrange. It felt much beefier than any 13b 6-port I'd ever driven or rode in, and this was confirmed by several other people who drove it/rode in it.

Stock 12A cars feel like absolute complete **** to drive, they have no power down low, no power up high, and no power in the middle either. Anything you do to a rotary seems to increae power *everywhere* not just one place.

B6T

iTrader: (2)

Could you take a picture of the electrode, just so we know how to do it properly?

You were getting 30mpg with these plugs? And they improve power over the FC plugs?

j9fd3s

iTrader: (3)

my gsl-se would do 26 freeway too. mods are the RB streetport exhaust, fc block, and aluminum flywheel. car is an 84 too, so it doesnt have the tall 5th.

current ride is the all stock 79 sa, i'm getting 16mpg....

peejay

http://www.mazspeed.com/sidefire.htm

I can do them in one shot, cut with the whizzer (i hate dremel cutoff wheels, they break so easy) a quick file to roudn the corners and smack with hammer and done.

Glazedham42

iTrader: (4)

You guys that are getting 25-30 mpg, what oil weight are you using? How about the tranny? Just wondering how much impact this would have. I know that 5W oil has become increasingly popular in new cars b/c of the decrease in parasitic loss which will subsequently increase MPG.

j9fd3s

iTrader: (3)

not much, but then again every little bit helps.

Mills

iTrader: (1)

I always used 10w-30, the lightest oil Mazda recommends. Stock SE block with emissions removed, full RB header/exhaust setup and 5th/6th port sleeves from pineapple.

I consistently got 24mpg, just what the original window sticker said when new! (and I redlined it ALL the time ) Can't complain about that!

peejay

5W20. I switched to 20W50 the last couple oil changes and the engine seemed to make more power (kinda scary) and fuel economy didn't change. Weird. I am running the beehive oil "cooler" so that may enter into it.

Transmission - Redline Shockproof Light

Rear - Redline Shockproof Heavy

At least, I think that's where they are. The red stuff is in the rear, the blue-green stuff is in the trans. I want a thick synthetic sludge in the rear because I run 80mph everywhere with gear backlash set to a half thou' less than minimum spec (maybe prevent the breakage problem) and I want everything to keep things cool, and keep things tolerable when they do get hot.

Trailing split under cruise and timing under cruise are huge for fuel economy. I detailed this in a previous post, in a nutshell some experimentation is required and right now I've forgotten what works best. I remember that fuel economy took a plunge when timing got higher than 22 degrees, not including vacuum advance. (I run straight distributor timing, make heaps low end)

Also, get rid of the gumballs. Sticky tires on my Golf cut fuel economy from 40+ to about 35mpg.

rotaxrave

so far mine has almost doulbed to about 18 to 20 after dlidfsdfilsd and air filter, plugs, rotor, cap