Thread: Tuning for Gas Mileage

Thought I would paste this in this section. In one of the Turbo section threads a person was wondering if there are any ill effects of using a 9.5:1 CR tune on a 8.5:1 CR motor.

Well that got me to look search for a DE+T and DET timing maps to see what the difference was. The fuel maps and K value were the same, including the VE table.

The only real difference was the timing table, and even then at Wide Open Throttle (WOT). That means that at cruising speeds the timing for DE+T and DET is the same.

Now DE+T have higher compression, thus at a specific RPM/Load they will be making more power then a lower compressioned DET at the same RPM/Load. Thus using a DE+T timing map for crusing speeds means you will not be having as much power as a DE+T, thus needing to use more gas to keep going the same speed.

I will test the timing maps on my road trip tomorrow

Not sure what the mileage the rest of you get but on my VE with NX stock tranny I got 38.6MPG (6.1L/100 km) over the 2.5 hr trip on the highway... how does that compare to others?

My brothers's stock classic gets 35 highway 22 city. Mine while stock got 34 highway 22 city. After the stand-alone it got 34/19. No figures for turbo yet.

Mine gets 28ish constantly on the highway and 15-20 in the city depending on the right foot.

damn 15-20 thats srt challenger numbers lol, you need to lean out that crusing air fuels that horrible gas mileage

just made a 3.5 hr trip from cincy to cleveland for a job interview and i pull similar numbers. definitely better than i was expecting.

And this is why I'm such an MPG nazi haha. My car has had MPG issues since day one.

So far I've found and fixed a few, but I still think I didn't find the root cause.

To list a few...
- Alignment was off by 1"
- Gas tank did not keep pressure, replaced one valve and that helped, but it seems like it's not keeping pressure yet again
- Bad Motor, high oil consumption.
- Fuel filter replaced twice

I'm starting to think that my gas tank might be leaking out, and or the 98-99 emissions crap that's by the gas tank, aka vapor canister, is dying.

This would explain why my highway mileage stays decent, and city is terrible. Highway mileage gets done in one day before fuel vapor escapes, while city driving it will take a week or so before I need to fuel up, thus gas can evaporate out.

Finally got to my destination... On average the car got 28mpg, at one point 35, but I think that's because that pump didn't fill in as much gas, I usually can see gas in the tube, but this pump kept on punching out before I could even see the gas, thus making the trip seem like it got 35.

Overall I'm very disappointed in the car. I did some crazy alterations to the whole timing map, did some updates to the fuel map, and it still didn't get much of anything.

While driving through West Virginia, 64 West, it would be in boost a lot. As soon as I even hit a small hill, I watched the boost go to 0 and up, A/F would drop to 11.1, timing map would show around 12-14*F. Now if I floored the car, my A/F would be around 12.

I updated the timing and leaned out that part of the map, and it seems like it stopped going to 11.1 going up the hill, it started going to 12ish.

So what I've realized is, I can't wait to get my T28, so that I would not be in boost every single time when I press the gas. This turbo is great and spools up quickly, but it has it's downfalls.

My timing map has been updated just about all over the place, the car now has a very smooth powerband/torque curve. It doesn't feel like a turbo

Just got back from the trip. My tuning both leaning out and or timing didn't seem to work out too well. I really didn't get anything above 29 MPG. Before I was saying that my average is 27-28 well actually it is 29 because I forgot to factor in bigger tires/rotational mass. Thus my trip reads 60 miles, when in reality it does 63 according to the GPS.

Well anyway while going through West Virginia, about 4 hours away form home, I started tuning in real time. Well more of I was walking my lovely wife on making changes to the map and uploading them on the fly. I must say I love the Real Time ECU for this .

I ran with a leaned out mixture for a bit, no front O2 sensor, and it seemed to drive fine at 16-17 A/F's, I did get worried when I saw a big sputter from pressing on the gas, the engine would be in boost and the A/F's wouldn't go down for about 2 seconds. I tried to fixed that, but gave up after one tune made the car just die, I quickly pulled over and had her upload my previous working tune and drove home kinda leaving it alone haha.
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Like I said I was pretty bummed because leaning didn't work and timing didn't work. Right as I entered Virginia it hit me that I should try map tracing. And it all started making sense.

At 70 MPH I'm doing 3,150ish RPM, the BIN file has 2800 and 3200 rows, thus I expected it to use the 2800 values for timing and fuel, but it turns out it actually uses 3200 as per Map trace.

Here is a shot of a steady 70 MPH cruise on cruise control. This is with going up and down some big hills.



This means if I were smart enough to map trace when I first started the trip I could have modified the values that are actually used for highway driving! Bah!

Anyway my final conclusion to my bad gas mileage.
Dual Ball Bearing T25 Turbo

How or why? Well I got some pictures for that, but I will still explain. Map tracing basically proved my theory correct. Cruise control is great and adds gas at low increments compared to the human foot. Well with my turbo, since it starts spooling at around 2k rpm and full boost usually by 3k RPM at WOT, this means any RPM range above 3k with slight press of the gas will have you in boost.

As soon as the HG's get down to 0 and the turbo builds boost, the A/F's plunge to the lowest end of the scale. After map tracing, I noticed that it goes to the right side completely. Basically the map timing and fuel designed for WOT operation.

Below are some pictures to show this phenomenon.




A good lagy turbo should help me out with this. My car would be in boost about 40% of the time while driving on this trip. That means if I stay out of boost I could possibly achieve 35+ mpg's.

Interesting articles to read.

AutoSpeed - FuelSmart, Part 1

AutoSpeed - Brake Specific Fuel Consumption

BSFC basically says that opening the throttle more in higher gear should help you with gas mileage. I'm not sure what to think of this, because as we discussed here, the goal is to keep the throttle closed. But it also makes sense on what they say.

I also don't have EGR since it is a DET, thus vacuum space is really an empty space.