Winter fuel economy/power

[Fidelity101]

Originally Posted by yeti

I get bad fuel mileage in winter, it takes my car easily 10-15minutes to warm up.. and by that time I can be at my destination. It depends on how cold it is for me, if I want to try to have the cabin warm or not.

But my heater sucks and you can't use it until the car is warm even then it doesn't blow hard. Once with it on I drove about 30 highway miles and the car still was cold.. so I turned it off the the gauge finally went to were it was supposed to be. (who knows?)

everyone does, and its always weighing the "well do I wait 15 minutes let it warm up, then drive 2 minutes or just say fuck it and go" and your car doing 30 miles on the highway doing highway speeds was getting a lot of cold air to the radiator and such so when you stopped moving the hotter temps began to show since there is no longer a mass quantity of cold air moving past the engine, engine bay, radiator.

[NoDOHC]

Colder temperature making for increased charge air density is completely true. This is why I have trouble understanding why I observed the decrease in power when i was expecting an increase in power (also substantiated by the observed power numbers with the Haltech ECU).

I am still hoping that someone on here knows the stock AFR in cold conditions. I have a wideband O2 sensor, but is is on the '86 which is getting a turbo transplant and will need the wideband.

I can't use it on the '91 anyway as it is snowing in Wisconsin and I don't want to drive an RX7 in the snow if I can avoid it.

[Terrh]

it depends how you drive the car

if you accellerate agressively all the time, warming it up will save you fuel.

if you drive the car gently all the time (or at least, when its cold), warming it up won't.
The o2 sensor (assuming it's newish and in good order) is warm enough to be working within the first 30 seconds. It's not the issues.

Fuel mapping with cold coolant IS, and if it's cold out the injectors are DUMPING fuel. I would think with the coolant at -40F, if you were to go WOT in a TII you'd run out of injector pulsewidth with stock everything well before redline. Cold engines need a TON of fuel to operate smoothly.

[Fidelity101]

It always seemed backwards to add a bunch of fuel to a cold engine, when the fuel itself will actually cool it. But hey, whatever works I guess lol.

[vex]

Originally Posted by Fidelity101

It always seemed backwards to add a bunch of fuel to a cold engine, when the fuel itself will actually cool it. But hey, whatever works I guess lol.

more air density = more fuel needed

[Fidelity101]

Originally Posted by vex

more air density = more fuel needed

not very backassawards after all lol.

[vex]

Sorry it's been so long since I could post up some data. Here's a years worth of MPG data:

http://spreadsheets.google.com/pub?k...H8RY-8lAK1BtZQ

Preliminary data view looks like there is a slight increase in warmer weather, but nothing dramatic. Perhaps 5 miles at the most. Given that, this is through all types of driving, and is more indicative of whether I was doing city driving or freeway driving. During the summer months I was on the highway more than not, and during the winter months around town more. That alone would account for the decrease in MPG.

[Fidelity101]

Fill up while you can at the pump during the colder days, fuel is more dense when its colder so you get more bang for your buck since they have no way of calibrating or standardizing temperature with pricing and etc.

[MaczPayne]

Fuel at gas stations are typically stored deep underground. I don't think that area of earth is affected much by surface temperatures.

[Fidelity101]

Originally Posted by MaczPayne

Fuel at gas stations are typically stored deep underground. I don't think that area of earth is affected much by surface temperatures.

it depends on the state, a couple don't allow underground storage tanks.

And Michigan is cold always so its win win for me

[NoDOHC]

Hey, that google spreadsheets thing is pretty neat.

I guess that when I say running around town I mean my 11 mile one way commute to work on country roads.

I ought to figure out how to use google spreadsheets too and post my mileage numbers

I tried to summarize the data in my earlier post.

The absolute worst full-tank mileage I ever got was a weekend of drag racing (1/4 mile) and an autocross = 15.1 mpg. (This does include some normal driving). I really don't know how you got 10 mpg (although the bad tps may have been part of it). I did get 12 mpg on a partial tank (filled up, went to track, ran 12 passes, went home, filled up, checked mileage).

[Fidelity101]

Do you have a stock ported motor? I would get 14 on my street ported S4 non highway, mostly city and dicking around driving.

[NoDOHC]

Engine Statistics:

'86 (Stock ECU)
ECU: Original N326 built in October 1985
Fuel mix: Running closed loop at 14.7:1 AFR (when it was actually closed loop)
Timing: 12 degrees BTDC Leading 3 degrees ATDC trailing at idle (+17 degrees from stock)
Mileage: 178,000-192,000 miles
Compression: 104-110 psi on all faces
Block: Never touched, never had intake or exhaust manifold off, completely stock.
Coolant Seals: One may have been leaking slightly
Oil Seals: Blew clouds of oil smoke above 7,000rpm
OMP: Adjusted to the max
Premix: 4 ounces/tank
Auxiliary Ports: Functional in stock form (open at 3500 at WOT).
Air pump: Functional
Power Steering: Belt Removed
Air Conditioning: Belt Removed
Intake manifold: Stock and untouched
Exhaust: Stock 3 cats (functional) Dyna-Flow Mufflers, stock Y pipe.

'86 (Haltech)
ECU: Haltech E6X controlling ignition and Fuel.
Fuel mix: Running closed loop at 16:1 AFR (Wide band input)
Timing: 0 degrees BTDC Leading 12 degrees ATDC trailing at idle (advanced until ping elsewhere, 0 degree timing split above 2,000rpm)
Mileage: 192,000-199,000 miles
Compression: 104-110 psi on all faces
Block: Never torn down, completely stock.
Coolant Seals: One leaking slightly at first, both leaking toward the end
Oil Seals: Blew clouds of oil smoke above 7,000rpm
OMP: Adjusted to the max
Premix: 4 ounces/tank
Auxiliary Ports: Modified but functional (open at 4500 at WOT).
Air pump: Removed
Power Steering: Removed
Air Conditioning: Removed
Intake manifold: UIM deburred and polished, LIM deburred
Exhaust: Racing Beat Headers, Dyna-Flow Mufflers, stock Y pipe.

'91
ECU: Original
Fuel mix: Running closed loop at 14.7:1 AFR (when it is actually closed loop)
Timing: 17 degrees BTDC Leading 2 degrees BTDC trailing at idle (+22 degrees from stock)
Mileage: 146,000-154,000 miles
Compression: 80-100 psi on all faces (cold)
Block: in-car porting of irons to maintain runner cross-sectional area (Minimal port timing changes).
Coolant Seals: Good
Oil Seals: Good
OMP: Not adjustable
Premix: 6 ounces/tank
Auxiliary Ports: Fully Functional
VDI: Fully Functional
Air pump: Functional
Power Steering: Functional
Air Conditioning: Functional
Intake manifold: Port matched LIM and UIM
Exhaust: Racing Beat headers, ???(Stainless steel, unknown manufacturer) presilencer Y-pipe and mufflers.

I would guess that your street ported engine will not get stock port mileage. (Although I have heard some say that a street port makes little to no difference).