rpm/mph/mpg

[Don Jorgensen]

Pondering the number of miles, hours behind the wheel and why the Subject: varies among the Tercels I've owned and the MPG others have claimed.
So Tercel miles I'm well over 300,000 and most were at approximately 700 feet above msl. At about an average of 45 to 50 overall mph, that translates into around 6,000 hours in the comfy molded seat. My first two Tercels, "Silvie" and "Bluebelle" were FWD and used mostly on the long commute of which 100 miles per day were on Interstate highway with few hills. Neither gas guage was trustworthy so I used the trip odometer and usually filled up at 275 miles. The fuel low light would glow around 325-340 miles. Most of my highway miles were driven at speeds between 65 and 70. I kept track of mileage and the best was 37 and average was 33-34. Neither Silvie or Bluebelle had tachometers so I don't know rpm but the speedometers were correct according to the mile marker checks on interstate. I don't know how a 4WD Tercel would best these numbers much unless you had consistent high tail winds or only checked mileage going downhill from high passes.
The SR5 on the other hand is a Colorado car probably always driven above 5,000 feel elv. The original 3AC was a tired 230,000 miles logged little engine and never bested 26 mpg, mostly around 22-23, highway but I must say these trips were above 6,000 feet and with 4 adults on board with the A/C on. The SR5 now has a 4AC, all different emissions stuff, synthetic motor oil, new carb, and timing at 6 degrees btdc and the vacuum advance works. I know the speedometer is correct and the rpm in 5th gear is 3,000 at exactly 60 mph.
I figured the mileage would improve with the 4AC, new highway tires and etc. but I've yet to see above 26 mpg on the highway and I'd consider 20 mpg in city to be extraordinary.
So I'm wondering what the rpm at 60 mph in 5th gear the FWD Tercels were running if that is the reason for the difference in mpg?
Also wonder about the altitude in general and yes I've run the tests to know my compensator is working.
I must say that I do have acceptable power although I do switch off the A/C and drop to 4th on the long hard passes.

[Neu]

It really just varies between cars, from what I've seen.

The altitude could be to blame though..

[hberdan]

I've owned 3 Tercel 4x4 wagons, an 86 SR5, an 84 SR5, and now an 87 Deluxe. I live at about 6000', and routinely drive up to 9400', but most of my commuting these days is in the Denver area which is around 5-6000'.
Poor me, I've never owned a NEW wagon, all were used when I purchased them, with mileage well over 100,000 in each. That being said, I guess I have about as much mileage in them as you have in yours, around 300,000 driving miles.
I've never gotten mileage better than 31 with any of the cars, all with original 3AC engines, and for the most part averaged 27-29 mpg , that is, when they were running well. I kept the rpms below 3000 as a general rule but you know how that goes. The darn Dlx wagon has that cheaper console without the tach, but it still seems easy to drive without it.
I've always assumed that the high altitude combined with the little tiny carburated engine kept the cars from reaching better mpg. I had the Dlx carb rebuilt with different jets to compensate for the elevation, and to reduce the emission signature, and it's helped with the mileage thing. I suppose the real answer to better mileage is more horsepower, maybe a fuel injected engine, or at least a turbocharger.

[ARCHINSTL]

Well -
Following is part of a post I made back in '05 regarding MPG:
" Well, I am compelled to add my two bits.
I owned one of the first SR5s in St. Louis in late 1982, so recall the new performance.
It had no A/C or roof rack to detract from performance (can't recall if it had P/S to sap the output). It was a stick.
In suburbia driving the MPG was usually in the mid-to-upper twenties. On the highway at legal plus a bit speeds the MPG was 32-35. It never came close to 40, even at 55 steady and a tail wind."

The highway travel to which I refer was mainly in "upper MO," IL, and IN, none of which are noted for extreme altitudes...
None of the magazines at the time got any better MPG in their tests, either...
This was also the '83, with the better-for-mileage-and-noise ratio...
Oddly, Goldie, my '86 SR5 with 179K miles, gets almost the same MPG as the '83 did at the time...go figure ( I'm sure it's due to the enhanced driving skills I developed since then, right? ).
Tom M.

[takza]

My Nissan 2.4 L 4x4 truck does 25 mpg highway with 600 lbs in it and a camper cap on it. Might be seeing a little more with the sensor tweaking.

Should be seeing 35 mpg mixed again using the iso with the T4WD. Once got 47 mpg with the Terc coming home with a 25 mph tailwind over what I thought was a full tank...turned out it wasn't...was 7-8 hours of driving though.

All of the above are "facts"...so no need to all jump me at once?

As far as what you could do to see better mpg? Get Typrus to detail what the old dude did to his carb? Use additives? Mpg mods?

Pretty sure that if you don't do anything different...your mileage won't change.

[Don Jorgensen]

I guess by the responses so far, my SR5 isn't too far below what others are experiencing. Mine does have a roof rack and power steering.

Pretty sure that if you don't do anything different...your mileage won't change.

Well that is what I'm after. On the Subject: rpm/mph/mpg, an example is a Pontiac Firebird my son-in-law drove. His early 90's Firebird had a 350 auto with overdrive. Rpm's were around 1,500-1,600 at 60-65 mph and again few hills and elevation 700 feet or so. He often bragged about 24-28 mpg. Not bad for a muscle car! My experience with small block Chevy motors back in the 60's and 70's was any body style and a small block best mileage was in the teens at best
About the only easy way I can reduce the Tercel highway rpm is to get bigger tires. Can't go very big with stock suspension. Also the 4AC has a power curve that is probably strongest between 2,500 and 4,000 rpm. So if I were to get down to 2,000 rpm for highway cruisin, I'd probably need to be on the Bonneville Flats.

[Typrus]

Remember, when you have low enough power, a larger tire will require more effort on the part of the engine to get turning an change the turning rate of, thereby potentially reducing overall fuel economy rating, while potentially increasing highway economy, however still considering the increased engine effort the change may be offset.
Keep in mind, putting on a taller tire is like putting on a taller diff. Tall enough and it could be like you have a 2.79:1 diff. Not good when you are not even in the 3 digits for power.

I was able to get 30's with fair consistency. Live around 6000 feet and drop down to maybe 5000-5500 regularly.

My good buddy has a 74 Chevelle Malibu Laguna 4-door sedan with a 350 V-8 and TH-350 tranny (3 speed for the non muscley's)
Mods? Edelbrock Torker II intake, Holley 4160 700CFM 4-bbl carb, and an ACCEL HEI distributor.

Driving gently, he honestly makes 28mpg. No joke. I've seen it on 4 consecutive tank. GPS verified that his Odo reads right within 5% (he adjusts for his economy)
Driving hard? He used half a tank (20 gallons I think?) in 20 miles pedal-to-the-metal driving nutso berzerk.
So 2-28mpg. Lol. Someone said something about driving style effecting economy? Nah... Lol

[SR5 Tercelerator]

Just got my first mpg reading...I'm only pulling 22MPG. This is as is from sitting, just fixed the driveline. 270K with I believe about 100k on the motor. Put new plugs, wires cap and rotor on this morning when I got back from the gas station. Tires are proper. That oughta be good for a couple mpg...Of course it is nearly impossible for me to drive slowly so yeah, 30's would probably be an accomplisment. Got an O2 sensor too but going to wait till the next tank to put it in...

It sounds like the Weber carb is the key to getting 30's ???? The Weber kits have two styles listed for tercels...the 36 and the 32/34? I forget the model numbers. From weber one kit is 3something and the 32/34 is 270 ish. Anyone got a preference? The rep said the 36 was better on the hwy (Power) and the other was better in town (MPG). Or are people getting the 30's with stock carbs too?

[4wdchico]

I'd stick with the stock carb. They work really well. Lots of folk are put off by the vac system, but if you go at it one system at a time with the FSM it is not a big deal. What brand 02 sensor did you get? I strongly suggest the OE ND units only for these cars as the sensor tip extends farther into the exhaust stream so that it heats up and samples the exhaust better. Napa sells the ND 02 sensors to pro shops, but will sell them to the public if asked.

My '85 SR5 4wd averaged 28.8mpg heading back to Norcal from Colorado a bit back. Over about 1200 miles. That was loaded down with a whole lot of camping gear & a roof rack (Mtn bike is taken apart and inside the car on long runs for higher fuel economy) and driving it really hard thru lots of mountainous country. It will get over 30mpg at 65-70mph, running the AC in a 100+ degree day, without the roof rack and more lightly loaded in less harsh terrain. This is on a totally stock 3ac with about 145k miles on the whole car. The engine is in a very high state of tune. I'm pretty happy with the mileage.

[xirdneh]

i've been checking the milage on my commuter tercel 4x4 wagon (40 miles daily mostly country road some city) tercel since December 2007.
the engine has around 140,000 orig miles.
carb was rebuilt around 6,000 miles ago
has 1985 differentials , power steering and small roof rack
regular gas

started out around 26-27 mpg and gradually rose up to 28-29
seemed to increase in milage with the warming weather
the temperature here in western washington rarely gets below 30 while summer rarely goes above 90 (lots of rain)
by August i was getting 29-30 consistantly
i started out with original tires and rims
in mid August i switched to 155/80 tires on tercel sedan rims (a bit narrower rims and the tires are smaller in width and diameter)
have not noticed much milage difference due to tires but enjoy the difference in drivability
tried running the vaccum advance hoses switched around (car pings a bit more)
have not noticed much differnce in commuter driving miles but increased mileage about 1 mpg on long distance drives.

my friend who has 86 tercel (same 155/80 tires on stock rims, power steering, differentials, similiar commute)
noticed increase in mileage as weather warmed also (started 25-26 now up to 29-30 with occaisional wild card thrown in)

[takza]

Here is something that might be real feasible to try:

http://www.eagle-research.com/fuelsav/ecarb.html

http://www.eagle-research.com/store/ind ... ucts_id=12

(Basic) This page tells about the simplest Carburetor Enhancer, which we call the 'Basic' version. It gets the most fuel gains with the least cost and is the simplest fuel saver to install. The Carburetor Enhancer is a simple external method to significantly increase the efficiency of automobile carburetors. Once installed and adjusted, its operation is automatic. Just drive normally. This is the method I used on my previous automobile (1978 Lincoln Continental with 460 ci engine.) It went from 10-11 mpg to 13-15 mpg. The Carburetor Enhancer Manual goes into great detail about how to fix carburetors that are giving trouble and how to expand the capabilities of your Carburetor Enhancer. The Carburetor Enhancer is designed to cut back on the fuel going into the engine from the carburetor, so that the gasoline vapors have room to work.

http://www.eagle-research.com/products/pfuels.html

CARBURETOR ENHANCER MANUAL(Third edition)

The Carburetor Enhancer Manual is full of practical information on to save fuel. This book takes you, step-by-step, to a complete understanding of how to increase the efficiency of the vehicle you already have! There is no power loss and vehicle emissions usually drop below California standards.

This information is unique because it is practical, tested and easily used by anyone who drives a vehicle with a carburetor.

The Carburetor Enhancer Manual is full of practical information on how to save fuel. This book takes you step by step to a complete understanding of how to increase the efficiency of the vehicle you've already got! Based on our own results and those from testimonials; Gains of 25 percent are typical. There is no power loss and vehicle emissions usually drop well below California standards.

This information is unique because it is practical, tested and easily used by anyone who drives a vehicle with a carburetor.

What's more; your "cash out of pocket" to follow the basic steps of the Carburetor Enhancer Manual, will usually cost you less than a tank of gas.

The Carburetor Enhancer is not a fuel saving device, it is a custom tuning technique that increases the efficiency of the carburetor you already have.


As I understand it...the carb enhancer is a method of applying metered vacuum to the float bowl to enable you do fine tune the fuel that gets to the engine. You would use this rather than your O2 and ECU. At $18 the manual costs less than a Bosch O2. Parts found at a hardware store.

Would likely work with a Weber too.


I got the crankcase vac tuned in and am seeing 2 to 4" hg at cruise...depending on throttle. Had to use some 1/2" heater hose and loop it over to behind the driver's side headlight to get the regulator away from engine heat.

Also added an extension to the front air dam...bringing it down another 4" or so...using black lawn edging. Plus will be blocking off all air intake areas in the front except for right in front of the rad using alum flashing....no working AC.

You might not think this would help mpg...but it has pretty consistently made an mpg diff on a forum focusing on aero issues.

I should be seeing somewhere north of 35 mpg in summer mixed with iso....using the Toy carb.

[Typrus]

Ya'll have already heard where my economy normally had dwelled. I never had a Weber.

However, with a Weber that properly tuned and jetted, chances are you could get comperable economy and improved power. Just a matter of getting used to mechanical versus vacuum secondaries.

Biggest issue is worn diaphragms creating large numbers of small vacuum leaks. Something to watch closely for. If they are all good and functioning properly, having your vacuum hooked up right makes ALL the difference. If a bunch are leaking, time to buy a quality reman or go Weber.

Funnily enough, I have the white 85 pulling 16 inches of Mercury right now, where my EFI Camry refuses to do better than 14.5 inches... Bear in mind my altitude. At Sea-level those readings would suck. Here, 16 inches is PHENOMINAL. Its hard to get anything to pull better than 15.

[TuffGong]

I don't think thread is getting enough interest &/or love...my friend bought this manual and we did a very simple mod to my carb from it. Improved my mpg from an avg. of ~24 to around 25-32 depending on driving style (pedal to the medal - somewhat conservative).

Much fine tuning and a bit of troubleshooting needed though.





Interesting eh....

[takza]

A look under your hood looks about like mine....hoses all over the place! So you've actually tried the carb enhancer? Care to detail your other mods?

I was getting around a 10% mpg gain using 2.5 oz 91% iso from Walmart for every 10 gallons gas. I also saw maybe an 8% gain from a DIY hydrogen generator.

I do a lot of mpg testing...few things actually work all that well though....1-2% here and there for the most part.

Doing a partial grill block...but have found that the fan will tend to run more at temps above 70 F....OK for winter.