My experience is with Peejay. There is adequate power from 1500rpm driving in urban traffic, changing power low down improves fuel consumption. My car does not bog down in top until around 1100rpm. Even with the 12AT I can change low down without the engine bogging. My technique is to change up when the drop in revs is equivalent to the final rpm in 5th. For example in a city street, I change around 1750rpm so the final change puts me at the legal limit. Sometimes if I am head of the queue at lights and feel bored, I change far higher going 1-2-5! Around town I average 18 mpg with a 220rwhp engine.

 

Your theory is correct because you have a high HP motor. I should clarify that with stock or just above stock motors low Rpm shifitng will not improve fuel economy. The theory has always been that the more Hp that a engine has the less RPM is needed to propel it forward.
Lower HP motors have to rev higher to gain that inertia therfore at lower Rpm's bogging occurs making the motor struggle therfore consuming more fuel.

 

latly I have been putting 6 gallons everytime and I barly make it to 100 miles on the trip-o-meter, I haven't taken the car to 5+ to redline in a couple weeks and it doesn't seem to matter mileage wise.

I have a silly/obvious/dumb question but have been thiinking about it for a while and I don't really understand how carbs work so I figured I would ask.

Say your driving 35mph in the city(mostly where I drive) going up and down hills stop, go, whatever when in third gear I don't have to give the car as much throttle to keep the cars speed up as I would if I was in fourth (stock engine) now my question is would the car use more fuel running at 3ish rpm in third gear all the time or would it use more gas always staying in fourth at a lower rpm (2,100 rpm) but haveing to actually push the gas pedal down further to compensate for the lack of power and loesing speed going up hill?
Does this make any sence ? Sorry for newb question and typos

 

I have a 12A Street Port/Weber 45DCOE getting 280 miles per tank highway...

 

its a carburated sports car from the 80's...

 

... that's been radically altered to enhance horsepower at the cost of fuel efficiency, reliability and driveability.

A stock Nikki properly tuned will routinely give you 23-24 miles per gallon (about 350 miles per tank, math kids). And it drives like a first gen was meant to, plenty of pep, good progression and a reasonable number of miles between stops at the gas station.

Let's give the Mazda engineers some credit, I can't think of any other 22 year old car that could give me the service and fun that my pretty much stock 84 GSL daily driver does.

But if you prefer a race or drag car you need to expect lower gas mileage and more problems.

Ray

 

Drive like a human being, dont floor it around turns, stuff like that will keep your gas milege up.

When you think somone wants to race you or something like that, dont rev your engine up, and dont race! lol. get a tune up on your car, get a tune. and ray green......what the hell , math kids? what everrr.

 

I'm not bogging the engine at such low speeds. Trust me, the way it is tuned, it makes *plenty* of power down there. It's just like comedy - the secret is in the TIMING!

True it's under the same amount of load, however it needs less throttle with the timing as advanced as it is, plus the vacuum advance. That much advance means more time for a complete burn, so you get more from the fuel.

I shift at 2k-2500 mainly for noise reasons. I don't like making a lot of noise, so I baby the thing everywhere. (City driving, for me, is just taxiing to the highway) On the highway it's a different story - it's quieter the faster it revs, because it's under less load. Silly absorption mufflers. Fuel economy doesn't seem to be affected by cruise RPM.

It doesn't take much power to accelerate 2500 pounds to 35mph in traffic. I even save time shifting by starting off in Second gear instead of First...

BTW - Last trip I thought was 27mpg. It turns out my math is wrong. I had the speedometer error calculated incorrectly, and I was really getting 30mpg, and I wasn't cruising at 80, it was closer to 90...

Ha.
Ha.
Ha.

- Pete (Not bad for a 192k-mile stock engine)

 

doesent take much power to get 2500pounds to 35mph?


lets get our asses out there and see how fast we can get it going : P

 

I have an 88 vert and it guzzles. i get like 10-12 mpg in the city. what can i go to help this. Replace spark plugs and wires? i checked my tire pressure and adjusted it to 32psi where it should be. help me out guys i need to improve this

 

replace oxygen sensor with a factory unit
increase tire pressures a little, 32 is a little low for a heavier, sporty vehicle
clean the injectors, replace all filters (fuel, air, oil), change oil.

 

My j-bridge 13B and a Gene Berg 58mm IDA carb, Holley blue electric fuel pump, and RB streetport exhaust got me 7mpg in town, and 11mpg on the highway @ 80mph. I was LUCKY to get 120 miles to the tank.

 

You know there is a recall for that right? Passports are rebadged Isuzu rodeo's and they have the same problem.

 

In a recent 1100 mile road trip I averaged 17 MPG, in an 84 GSL-SE, 160 K, stock everything, wired open 5/6 ports. (need a pressure source for the actuators).

It idles at 1000-1100, and it seems to run rich based on the fumes in the garage that burn my nostrils.

I hope to improve things...

 

Welcome to the forum amigo. You might want to post up in the second gen section though. Although the theory is the same the 2nd gens are completely different injection systems and have there own inherent characteristics.

 

Heavy beasts, too.....simply dropping ten miles per hour on the highway will supposedly garner an average 10% improvement in mileage all by itself, BTW....I decided to test the theory after Car and Driver, then Autoweek tried it and got positive results. Simply dropping from 85 mph to 72 - 75 mph on the 25 minute drive to and from work had this result.

From 17.34 mpg, about 230 to 235 miles on the odo, to 18.65 average, about 255 to 262 on the odo...a real world improvement of 7.55% in mileage while still goosing the gas pedal when I need to...

 

Are there any carb mods you can do to improve gas mileage? It's really hurting my wallet, and I'm afraid if i cant get better fuel mileage, i'll have to sell her.

 

Before I swapped out carbs I was getting damn near 25 miles per gallon. And that was mainly in the city driving. Now I don't know what I am getting as I never have the cash to fill all the way up. Damn carbs, starters, and fuel pumps going out on me at the same damn time.

 

I got 19.7mpg on this tank that I just refilled. I went from a pilot jet of 72.5 to 60, and it made a world of difference. I still need to do some tweaking on it, maybe going back up to 62.5. It bogs and stutters while under 3k rpm if you press the throttle just a bit too much. I also changed my shift pattern from shifting at 3k in every gear to taking first to 4.5k, 2nd and 3rd to 4k, and 4th to 3k. By doing this, I don't have to press the throttle as hard to reach the same speed as I would shifting at 3k.

My mpg would most certainly been higher had I not driven as hard as I did on this tank. Normally, I'll really get on it just a couple of times per tank, but on this last tank, I redlined it at least a dozen/dozen and a half times. Also, my mpg would be hire if my A/C worked. 70mph with the windows down does horribly for mileage. However, a nice little box appeared on my door step today with a new compressor and multiple other things.

BTW, the vast majority of my driving (mile wise) is on the interstate or highways. I only encounter 6 stop lights one way to work, and most of the time, half of them are green.

 

"Before I swapped out carbs I was getting damn near 25 miles per gallon. And that was mainly in the city driving. Now I don't know what I am getting as I never have the cash to fill all the way up. Damn carbs, starters, and fuel pumps going out on me at the same damn time."

-Normality Glitch

Here's the best argument for keeping it stock that I've heard in a long time.

Ray

 

So smaller jets, should help fuel economy? Whats stock size in the nikki carb? Coz i can just order a set of smaller ones for every day driving, and bigger ones for track day for $9 ea. and save from selling the car. Any suggestions for sizes on a stock 12a with headders?

 

So running more rpm earned you more miles per gallon? rather then shifting low rpm and making the engine work more and pressing the peddle further down. This has been my thoughts for a while but I haven't been able to test it out.

 

My 79 SA is completly stock and I get around 20 in town and 24 to 28 on the freeway.....

 

5.0 gallons got me 140 miles stopping half-way up on a trip from Chesapeake, VA with my 1980 12a - foot in the throttle the whole way when not stopped in traffic - interior stripped out of the car, Kumho V700 175/60-13 tires at 32 PSI - built for racing but gets great gas mileage - engine is mostly stock though there might be some emissions stuff not hooked up and the exhaust is modified.

The second half of the trip was 130 miles and I am getting about the same mileage - I haven't hit the mechanical secondaries a lot but am not afraid to get into the throttle.

A 1986 13b I had a few years ago used to get between 17 and 25 mpg.

If you want good gas mileage get a Prius, if you want a grin on your face when you are driving, the only Rx for that is to get in your 7 and wind up that nice 1.1 or 1.3L...Zoom Zoom

Live Free and Drive,

Keith

 

I have found this so true, the 7 really drives nice and brings a smile. I am happy I found this car last spring...even though it needed much TLC, things are good now.