peejay

195/50-15 gumball tires
Slightly higher than stock ride height
4.78 gearing
Stock carb, 2.25psi fuel pressure


25mpg.

BUT

I discovered today that when I popped this engine in, I neglected to reconnect the vacuum advance. That's good for about 2-3mpg... plus I don't know right now where the mix is under cruise. If it's rich, I have a handy-dandy driver-controlled enleanment device that could bring up another MPG or two.

I will know next month what the 1/4mi times will be, but it surely feels like it's mid 15's. I'll also have updated fuel economy info after I reconnect the vacuum advance and schlep on over to aussiesmg's place on Saturday.

- Pete (cackling softly)

diabolical1

iTrader: (3)

[scottish accent]Boss-tarrrd[/scottish accent]

trochoid

iTrader: (6)

Not bad at all for the gear set. How much total change do the gears and tires make in the speedo? I managed 23 mpg hwy @ 75 mph on the bridgeport, correcting for the taller tires and I know the carb is rich.

steve84GS TII

Yea.....well.....I can drive more than 10ft on only a quart of $3.10 GAL premium,so there!!

25MPG is pretty impressive for any rotary.Getting everything dialed in nice,huh?
I kinda miss those days,tweaking carbs to the max,playing with distributors and such.....nowadays I let my silicon based buddy under the floor mat handle those duties.

I sure am glad I only have to go 10 miles a day to work and back.I can burn up an entire tank of gas on my days off,but the rest of the week I do pretty well.I can still eek 20MPG on the highway,but around town....forgetaboutit!!!

clean85owner

When my motor was running, it was extraordinarily rich. It would manage 15-17mpg.

I'm sure with everything dialed in and me driving like a normal human being, 20 mpg is doable.

peejay

I went 61.4 miles indicated on two gallons. Slightly *less* than two gallons, but we'll be pessimistic with the gauge.

3.909 / 4.778 is .818something which is what you need to multiply by *indicated* to get actual.

Times 61.4 = 50.something divided by 2 gallons = 25.something.

When driving, figuring actual speed is easy. I take the indicated speed in kilometers and divide by two. For example: 4.778 / 3.909 (to convert actual to indicated) is 1.22something. 1.22something times 60 is 73.something. 73.something converted to km is 122, which is about twice 60.

Or, 60mph is damned close to 100km/h, which times 1.22 is 122. Much simpler to do.

Note that with non-gumball tires, I've done close to 30mpg on numerous occasions.

It's just nice to note that gearing has rather little to do with actual fuel economy.

trochoid

iTrader: (6)

LOL. I wasn't asking for a math lesson. I was curious what the total difference was, percentage wise, with the taller tire and gear combo. My rear tires have a 10% longer in circumference than the stockers, so I have to adjust reading the speedo accordingly. If I installed at set of 4.44 gears, the speedo would be near dead on. 4.88 would have the same effect as installing a 4.44 set with stock tires.

I don't see any adjustment for the taller tires, which would reduce overall mileage. I have heard that the shorter gears won't make that much of a difference in hwy mileage before. Good thing to know if I ever get around to changing mine.

Paradox

iTrader: (1)

i dont even want to know what my mileage is with the holley.

RX7145

iTrader: (1)

i'm glad thoes gears worked for you Pete. I wish I could get 25mpg:-(

peejay

The 195/50-15's are actually slightly shorter than the stock 185/70-13's.

PaulFitzwarryne

When the 84 came out its official fuel consumption was 30mpg highway, 21 mpg city. Forum members must have a unique driving style! Perhaps there should be another consumption measure, gals per Honda kill.

With an 85 12AT i get 29 mpg highway running on stock 205 60 14s on normal tire pressure. I run 430 miles from home to my first gas station on the way to work so get an accurate consumption. My fuel bills are tax deductable so I need to keep a good record!

What is really interesting is if there is a 26mph headwind consumption really falls, but with the wind behind there is no corresponding improvement. I found heading into a cold 0 degree storm for six hours had a major impact andnearly ran out of fuel.

rbf41182gt

hmmmm

i'm getting like 16mpg. I can barely squeeze 200mi. out of full tank. Must be my driving- I'd rather pay a little more and have fun


~b.k.

Pele

iTrader: (28)

We've got a better drag coefficient in reverse? Sweet! I'm gonna P-port it and mount the manifolds on backwards!

Wait... Can I make a carb work upside down? Damn you Isaac Newton! DAAAAAMMMMN YOOOUUUU!!!!

aussiesmg

iTrader: (1)

Pete that black car you've been cutting up with me got 25 mpg for the past 10,000 miles, I also keep records for my taxes.

Where the hell are you living Paul? Sounds like the Nullabor....lol

Paradox_Racing

Man I am envious! I get about 20 or so on the highway, but in town it's more like 8! With the porting I have done, it doesn't like to idle lean, and if I lean out the midrange (where it generally sits while driving in town) I get horrible bucking and hesitation. Oh well, that's why it's not my DD! She is purty fast though!

peejay

I forgot to add this...



195/50-15 are slightly smaller in diameter but they are close enough for gummint work. Less difference than the difference between new and worn tires, anyway.

rotary_sex

13b 6 port, weber 48mm dcoe sidedraft, gsl-se fp, holley fpr @ 3.5psi, rb header, presilencer, straight "cat" back. managed 24mpg highway on average unless im speeding then its about 17-18mpg

vxturboxv

iTrader: (2)

So what is this handy driver controlled enleanment device?

kgray

Stiffer spring on the accelerator linkage? lol

vxturboxv

iTrader: (2)

I was thinking of a vac switch inline with the secondaries? That way you could turn them off for high way and MPG cruises and turn it back on for "spirited" adventures.

Or maybe an inline rheostat to the fuel pump to lower the voltage and drop fuiel pressure? Dunno I'd be nervous to do anything to drastic w/o a WB02 sensor. Wouldn't want to run to lean and scorch up the rotor housings/seals/etc...

Kentetsu

I get about 10 mpg, but I blame that soley on my right foot.

aussiesmg

iTrader: (1)

Back from the dead thread

mar3

iTrader: (8)

Stock 12A, stock carb, stock fuel pump, stock exhaust = 20 mpg.....it may be an old thread, but it's also an opportunity to find out what kind of mileage peejay is seeing these days since you know he's had to tune to optimize his combination.

Jeff20B

iTrader: (13)

Yeah, and what about that bellhousing of mine you're always pining for, huh peejay? When I test the tranny in the MG and it checks out good, I won't need the spare anymore - its bellhousing will go up for grabs. Oh, and good job on the mileage or whatever. (try driving a rotary truck with 4.625 gearing and short tires)

two79rx7's

peejay
2nd the motion for info on enleanment control reather than reinventing,
I would want to use this on longer cruising trips.
suggestions on best place to monitor exhaust gas temp?