87 octane economy tune for LNF?

[skip_jones]

hi guys, looking for some advice on this. please don't flame and hear me out. i am taking a long vacation trip this summer and was wondering with the price of gas soaring (probably gonna be $4.00+ a gal. by mid summer) can we tune our LNF's to run on 87 octane and get better fuel economy? on this family vacation trip obviously i am not concerned with performance at all. i had a few idea's. 1. disconnect the wastgate rod. 2. turn all tables in the gear vs. rpm table to 40 or 50%. 3.lower the DAL's way down. 4. lower the MALT numbers down. what i would like to accomplish is setting up the car so it cannot build boost. i would like to get 35-40 MPG on the highway. how do these ideas sound? can i accomplish this? you cant tell me with the price of gas soaring no one else has had these same feelings. help me out here guys. thanks!

[Iam Broke]

Leave everything alone and cut timing where you see knock. You will still need some power to pass, ect. I don't recommend this at all but it's your car. If you want a Prius, buy one.

If you don't boost at all, you'll have about 90 hp at the wheels and aren't going to help the cruise fuel economy.

You can't lean it out any further than 1.0 lambda at cruise with the tables we have access to, Term tried a few years ago.

[skip_jones]

so you are saying put in 87 octane and pull timing where i see knock?
also lean out cruise lambda? 90hp won't cut it, but 130 to 150hp wouldn't
bother me. if gas keeps going up, we will all be driving prius'.
do you know what kind of MPG term. was seeing? do you think i can
achieve somewhere between 35-40??

[HNRClothing]

Just put 91 in, its a difference of about 4 dollars compared to the 87 (typical 10 per gallon per octane jump .30c x 13 gallons)? Dont sacrifice possible passing power and possibly your motor depending on KR conditions due to crap gas. You can achieve high mileage from easy driving out of the hole at lights, keeping your foot out of the gas in part throttle driving, and more highway driving.

[rnjmur]

My advice if you really want to do this:

Take the stock timing tables and put in 87 and see if you get any knock on 87. If so, remove a degree or two of timing. Really, you will probably get better gas milage running 91 or better with the timing raised.

You could scale your DAL table down but this could (more than likely will) cause some airflow issues that would need to be resolved by changing the cam phasing to match with the DAL table changes. This is also going to cause your spark tables to be out of whack, so you will need to adjust the spark tables to match your DAL and cam phasing as well.


I would advise that you just tune in your timing for mileage at load airloads with 91 and keep your foot out of the gas. It will be alot less of a headache then doing all of the above, plus who knows if you may need a little get up and go at some point. There should be no reason you can't achieve around 32 MPG or higher by just keeping you foot out of the car. Even if you did adjust your DAL/cam/timing like above, I would not expect you to see much higher than 35 MPG at the absolute best. On a 500 mile trip an extra 3 MPG will only save you about 1.3 gallons of gas (about $5.00).

[skip_jones]

well, my opening line was i was looking for advice. you guys gave it. thanks. honestly i think i'm gonna follow it. sounds like its alot more work than its worth if it can be done at all. i will put the car back to 100% stock, put 91 octane in it, and try to baby it as much as humanly possible.

[Leafy]

See if you cant add more timing in cruise. You may or may not be able to pick up a tad bit more mileage there, unless gm already maxed out that area.

[skip_jones]

drove over to my buddy's house last night. it was 35 miles total (round trip).
it was about 15% city driving and 85% highway driving to get there. reset the
mpg before i left. when i got home, it was 27.2 MPG. this is with 91 octane.
i babied the car bad. no boost at all and shifting at less than 2500rpm every gear. i think this sucks.

[Pandion]

drove over to my buddy's house last night. it was 35 miles total (round trip).
it was about 15% city driving and 85% highway driving to get there. reset the
mpg before i left. when i got home, it was 27.2 MPG. this is with 91 octane.
i babied the car bad. no boost at all and shifting at less than 2500rpm every gear. i think this sucks.

I've been getting about 27 average since I bought my car. The amount of tuning I've done hasn't affected it as far as I can tell. I always run 91 too. When I had my S/C Cobalt I was seeing about 35 MPG after installing a Header and Removing the cat. I miss those numbers lol.

[Jaxon]

Didn't the ss/sc have better gear ratios all around for mileage?

[Iam Broke]

No, the final was higher like the HHR I believe. 4.05?

[HNRClothing]

No, the final was higher like the HHR I believe. 4.05?

yup.

[Jaxon]

ahh i see....

[T-Man]

well, my opening line was i was looking for advice. you guys gave it. thanks. honestly i think i'm gonna follow it. sounds like its alot more work than its worth if it can be done at all. i will put the car back to 100% stock, put 91 octane in it, and try to baby it as much as humanly possible.

Why put it back to stock? Leave the mods on. It will allow the car to operate more efficiently, so long as it has been tuned for.

[skip_jones]

Why put it back to stock? Leave the mods on. It will allow the car to operate more efficiently, so long as it has been tuned for.

i put it back to stock thinking that is where i would get my best gas mileage.
my only mods were kn drop in and a catless downpipe.

[rnjmur]

You need to see if you can raise your cruise timing. I smoothed out my timing tables and added around 1.5 - 2.25 into the cruising ranges for max-max and around 0 - 1.5 in the max-min and min-max tables (over the stock values) and if I baby the car I can average around 30 MPG, where I used to average around 28 MPG with the same driving. Once the weather warms up I want to see if I can increase the timing a bit more, but increasing it too much can cause higher exhaust gas temps which you have to be careful of.

Also, I have found that the LNF is very touchy, especially with fuel mileage, to tempurature changes. It really likes the warmer ambient air to attain the best fuel mileage over the colder denser air. I am guessing this is due to the fuel atomizing and burning faster/more efficiently in the warmer air with the DI.

[cmiller8006]

Skip I have never reset my average mpg and it's at 27.4 with the way I drive. I hVe found I get the best when I try to accelerate with the boost gauge at 0. If your in boost your burning more fuel than needed. But trying to accelerate slow burns just as much as faster acceleration because it takes five times longer to get to cruising speed. I would put that catless dp on and let it breathe. As far as the tune I can't give any pointers lol.

[Iam Broke]

The stock cruise timing tables are pretty well maxed out already, most see some KR and remove a bit, best advice is from cmiller above.

I average 27.x on the 50/50 E blend.

[skip_jones]

makes sense to let the exhaust breathe for better MPG. same with a drop in kn. might just run 91 on the previous tune and pull timing if i see any kr.
honestly i am tired of them dicking us on these high gas prices.

[cmiller8006]

makes sense to let the exhaust breathe for better MPG. same with a drop in kn. might just run 91 on the previous tune and pull timing if i see any kr.
honestly i am tired of them dicking us on these high gas prices.

You and me both. It was 3.87 for 93 yesterday. Which is why I am not in a hurry to get the car done lol.