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Fuel Mileage and Timing

2054 Views 23 Replies 7 Participants Last post by  N0DIH
Coming home from the Des Moines meet on Sunday, I drove 262 miles. About 2 of those miles were city miles, getting to the freeway, stopping once for food, and getting back on. When I arrived home, I filled up immediately with 9.4 gallons. This works out to 27.87 mpg! Iowa and southern Minnesota are quite flat, and I had the cruise set right at 55 mph; I was in no rush, and trying to get the best mileage possible. Considering the EPA back in 1990 estimated the highway mileage at 25 (and considering the highway test is done at about 49 mph), I'm wondering how I was able to get almost 3 mpg better than the EPA figured I should. My timing is advanced 12* from the stock 0* and I'm running premium. Would the timing advance alone net 3 mpg, or do these cars simply get better mileage at 55 instead of 49?

Brian
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I run regular in my 92 Roadmaster and my timing is at the stock 0*. On a recent trip with the cruise set at 55 I got 30.12 mpg. I have 3.08 gears and everything is stock.

So I'm not sure if it's the advanced timing, or if they just underated these cars.
Is that mileage pretty typical for you? I've got 3.08 gears as well, and I typically get about 20 on the highway.
Yes, advanced timning will often help mileage up to a point.

The Epa test is not done at a constant speed though, it is a city cycle and a highway cycle. They strap the car to rollers and run it through a set speed profile that includes cruising at several speeds, slowdowns and acceleration - even in the hwy test. The whole point was to simulate highway-type driving for the average American, not steady uninterrupted cruising. So if you had smooth sailing for 262 miles I would say it is *very* easy to beat the EPA numbers.
Is that mileage pretty typical for you? I've got 3.08 gears as well, and I typically get about 20 on the highway.

30 was way out of the ordinary, but I have never set the cruise in the range of 50-55 before.

I usually get 25.5mpg on my trip to Toledo which is 140 miles with about 15 of that city with the cruise control set in the range of 65-72. If I do much above 70 it drops like a rock. Coming home from school in Michigan I was doing 80 and got 18mpg.

Driving around my town I usually get 17.5-19mpg, but keep in mind, it isn't city driving. There are stop signs and stop lights, but it isn't stop and go at all.
I saw 30.5 MPG once in my deVille....162 miles nonstop at 71 mph.
Almost everyone I have seen who has had a great mpg number the tank before and after are crap, and if you average the last say 5 tanks, you never see close to the great mpg number.

If you record you mpg, calc an average of the last 1500 miles. See if it supports the high values.

I guess the Missouri in me shows though....

Like my friend who was getting 15-16 mpg in his 96 454 Burb. Wow, great. I have one now, a 99, and I get 10-13, and 13 being quite rare. I asked him how he measures it and fills the tank. He just lets the pump shut off and that is where he leaves it. So very very inconsistent in the filling of the tank, which throws the mpg values all over the place.....

Consistency is key, and if you can't be consistent, long term averages are the only way to get some reasonable accuracy. 1500 miles or more.
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He just lets the pump shut off and that is where he leaves it. So very very inconsistent in the filling of the tank, which throws the mpg values all over the place.....
Gotta disagree on that. I always stop at the automatic shutoff and I keep a spreadsheet with each fill for my daily driver. As long as my driving conditions are consistent I see very consistent mpg numbers filling this way.
If every pump had the same pressure, and stopped at the exact same point, yes, but they don't, some pumps are slow, some are cranked up fast. This affects how much fuel is in the tank for each fill up.

If you use the same station, same pump all the time, you might be ok, but if you don't and shop around (not advisable in my book) you get a lot of variance.
I fill every tank up to the top of the goose neck. I know, topping off is illegal in some states, but it makes sure I have a somewhat accurate measurement.

Brian
I fill every tank up to the top of the goose neck. I know, topping off is illegal in some states, but it makes sure I have a somewhat accurate measurement.

Brian

I do the same thing.


And Nodih, the tank before my 30mpg was 27.5mpg, the one after that was 28mpg, and after that was 27.6mpg.

Pretty consistent.

If I am driving all highway and dont set the cruise above 65mp, I can get really good mileage in my Roadie.
I sure wish I could get some better mpg out of my FW. Probably gonna replace the coil this week, they say the 96 Vortec coil is a good upgrade, but the connectors are different.

Consistency is the key, and seeing similar results over a long time. I use Minitab (minitab.com) to crunch my mpg data. Sorta overkill, like using a 747 to go from Chicago O'Hare to Midway, or putting in a LS6 into a Chevette for a grocery getter.... But that is the tool I have and I like to abuse it to keep my skills on it up.

There is a 30 day trial, but it is a complicated program, but if you are into statistics, this IS the program to use.
How soon we forget!
Either Popular Science or Popular Mechanics made a really big splash when the idiotic 55 speed limit came in due to the fraudulent gas "crisis."
(Remember the original crap in congress was to save gas and the speed limit was to be 45? The truck lobby said HELL NO and wanted 60. The compromise was the infamous double nickel)
In any case, the magazine took a manual tranny VOLVO wagon with overdrive and showed on a series of runs that it got better gas mileage at around 67 miles per hour than at 55.
Anybody with access to LEXIS/NEXIS can check this out.
In an ideal world, yes, lower rpm's with less aero would be best. But that isn't practical either, you spend sooo much time going slow that our engines aren't that efficient, so mpg isn't that great.

Ideally, you would have to design the engines like the 307 Olds, with 2.14 gears and a stickshift. Those did pretty good. But you need to keep cruise rpm over 1500, else engine life suffers due to lack of good splash oiling so the pistons wear more than they should. So rpms keeping up higher is a good thing too.

Honestly, diesel semi's for the work they do are the most efficient. They get 7 mpg and are hauling 80K#'s. You don't see them putting in tiny engines in them trying to get better mpg. They run more and more gears with uber high compression with crappy aerodynamics.

You end up wasting more fuel on heavy throttle starts more than anything. Keeping cruise on and a more steady speed helps too.

Any automotive engineer will tell you, emissions is easy, mpg, now that is hard.... Hybirds are NOT the answer, not in the form they are now.

Diesel locomotives have the right idea that we need to do in a car. Diesel generators running at the most efficient rpm they can with electric motors that power the movement. Electric motors are more efficient across the whole rpm range, gas engines aren't.

I was wanting years ago to take my 91 Deville and add a 2.14 ratio 7.5" car rear axle to the back and a electric motor and a bank of batteries to offset my drive, even a % of it. And ideally, then yank the transmission in front and have the 4.9L power a generator that would power the electric motor and ditch the batteries.

I'll have to revisit it, I still want to do it. Finding the motor is the hard part, they are HEAVY, and wiring is an issue (big and controllers are needed)
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You're talking about my old Cordoba. When in lockup, above 45, that 360 motor got a consistent 24 - with some 26's - in hilly terrain from Hartford to NYC, fillup to fillup, over and over, per MS Excel.
I should'a bet $100 a shot with my buddies that the motor would do it. I might have made a bundle.
I didn't have a tach like the 300 models did, but I vaguely remember that the rpm at 70 was about 2100.
But the bottom line is that the laws are made by idiots who have absolutely zero feel for things technical.
Remember the 1973 Seat Belt Interlock where you had to follow a PERFECT sequence of
> Open door
> Get in/Sit down
> Close door
> Buckle up
> Insert key in Ignition, Start Car
If, on a cold day, or whatever, you tried to start the car to warm it up or anything was out of sequence, the car wouldn't start.
On one occasion, in a rental car, in a heavy overcoat, I put the keys on the dash to buckle the belt and the keys went down the defroster vents since I knew of the sequence. That was a REAL PAIN.
You could override, however, by raising the hood and pushing on a big red button like Staples "EASY" button.
So with what we have in the State and Federal guvmints, I have little hope for realistic laws regarding ANYTHING technical.
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I sure wish I could get some better mpg out of my FW. Probably gonna replace the coil this week, they say the 96 Vortec coil is a good upgrade, but the connectors are different.

Consistency is the key, and seeing similar results over a long time. I use Minitab (minitab.com) to crunch my mpg data. Sorta overkill, like using a 747 to go from Chicago O'Hare to Midway, or putting in a LS6 into a Chevette for a grocery getter.... But that is the tool I have and I like to abuse it to keep my skills on it up.

There is a 30 day trial, but it is a complicated program, but if you are into statistics, this IS the program to use.
Overkill isn't necessarily a bad thing.

BTW, what kind of mileage are you getting out of your FW. I don't know if it makes any difference because I thought the LT1's did slighty better with mileage, but I have the TBI 350.


Anyone know how far you can safely advance the timing on a TBI 350 and still run regular gas?
You sure can, the stock timing is very conservative for EPA mileage ratings and govt. regulations. I'm at 12* on premium and I could probably go to 14 or 15*, but on regular I would guess maybe 6 to 8* just fine.

Brian
You can add more timing with the more % ethanol you have in the fuel, the more octane, also more octane. More octane or more alky, the slower the burn, so more timing helps that delay.

Not much, but a couple degrees. Also, 1 degree increase per 1000 foot altitude increase too.

Does the L05 have knock sensor(s)? Got to be protective of it, pinging is damaging, it rattles the engine dangerously internally. Avoid at all costs. If it takes a couple degrees to protect it, use them.

A cooler thermostat will also allow higher timing. I wouldn't hesitate using a 160 in the summer, as the engine is fully in closed loop by 100F in warmer weather, in cooler, 130F. So a 160 stat won't hurt that (this is a internet myth that I have busted years ago....)..

Run a 10W30 oil too, not a 5W30 or 0W30, when hot they are thicker than 10W30's. So they hurt mpg in warmer weather. Synthetics are rumored to seal rings better, so you might get a 1/2 to 1 degree more with them. MAYBE....

Oh, and in most every case, when tuned properly, 87 octane gets better mpg than 93 octane. It is easier to ignite, and if you can get away with it, widen the gap on the plugs as much as you can until mpg drops, then go back a bit. A more potent coil helps too.

We get 0.045 gap on our cars, maybe if we are lucky 0.055. The 4cyl, V6 and V8 cars with the individual coils (1 coil with 2 plugs on it) get 0.060, which being it is a waste spark, is really 0.120! So more coil power can help too. If you can get a hold of a higher turns ratio coil, that might help too, with a wider gap that is.

Also, if you are the nutty experiementing type, look into the plugs for the 8.1L V8's (2000-2006 8100 pickups/rv's) and see if they will work without hitting the piston. It puts the gap farther out in the cyl so you get a better cleaner burn away from the chamber wall.
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does 335 miles/540kms for 1 complete gas tank sond right? mind you its 91 octane supreme, no catalyct converter, and just a tad advanced timing.
92 Brougham 5.7L
does 335 miles/540kms for 1 complete gas tank sond right? mind you its 91 octane supreme, no catalyct converter, and just a tad advanced timing.
92 Brougham 5.7L
City or highway driving?

Does the L05 have knock sensor(s)? Got to be protective of it, pinging is damaging, it rattles the engine dangerously internally. Avoid at all costs. If it takes a couple degrees to protect it, use them.
It sure does, and it's $22 at O'Reily's. No worries there.

Brian
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