How to safely improve cruising mpg?

[pHEnomIC]

OK, closed loop isn't workin out for me due to my setup. Cam w/ low lsa, longtube headers, and a wb simming nb.

I am going back to OL MAF. So i hear that I can command leaner a/f's than 14.7 at cruising and possibly save some gas. What would be a good strategy to do this? In addition, should i pull timing when leaning out the a/f or do i need to add more advance?

Please give me some numbers to start with and in what areas i should put them at. Also, what is a good strategy to determine the optimum numbers?

[Ackattack]

I can't help you, but I'm interested in this as well!

[WS6FirebirdTA00]

leave it alone, if you start doing that you will be right back up here complaining about how the car is surging at light throttle while cruising. Get your tune good, and leave it. So, unless you cruise at 2200+ rpms, don't mess with it.

[Billf6531]

Interesting topic.

Nothing ventured, nothing gained.

Turn DFCO off. Find a relatively level stretch of freeway. Drive at your normal cruising speed with cruise control on. Log RPM, MAP, Injector Pulse Width, Dynamic Cylinder Air, and Ignition Timing Advance for 10 miles to determine the high/low range the car is operating in at cruise. You can log other stuff too, but don't exceed 24 bits.

Then set the OLFA table to .9xxx (your stoich/15.5 afr) in the MAP range you've determined. You can add a degree or two of spark in the cruising DCA range. Your VE table has to be perfect in the cruise range to achieve the commanded 15.5 afr, so use your wideband.

Log again, including knock. If your IPW went down, your mileage improved. If the car drives to your satisfaction, you're good to go.

Please report your results, and preferably post your before and after logs.

[Dirty Howie]

Interesting topic.

Nothing ventured, nothing gained.

Turn DFCO off. Find a relatively level stretch of freeway. Drive at your normal cruising speed with cruise control on. Log RPM, MAP, Injector Pulse Width, Dynamic Cylinder Air, and Ignition Timing Advance for 10 miles to determine the high/low range the car is operating in at cruise. You can log other stuff too, but don't exceed 24 bits.

Then set the OLFA table to .9xxx (your stoich/15.5 afr) in the MAP range you've determined. You can add a degree or two of spark in the cruising DCA range. Your VE table has to be perfect in the cruise range to achieve the commanded 15.5 afr, so use your wideband.

Log again, including knock. If your IPW went down, your mileage improved. If the car drives to your satisfaction, you're good to go.

Please report your results, and preferably post your before and after logs.

I'm going to give this a try in the near future.........


DH

[WS6FirebirdTA00]

I will still put money on the fact that this is going to be WAY too lean for a cammed car and will cause drive-ability issues around town, unless he cruises upwards of 2000 rpm.

[Billf6531]

Perhaps, but a before and after log, and a statement of his impression of the driveability will provide useful data. Have you any logs of a similar test that you're willing to share?

[WS6FirebirdTA00]

I have so many logs, I could not find them right now lol

[Billf6531]

Take your time. No rush. Do your best.

Your logs and upcoming logs in the near future should be enlightening, and will leave an excellent reference thread for this topic, regardless of the results being favourable or not. At least the next user that considers doing this will have some facts to base a decision on.

[WS6FirebirdTA00]

I can tell you right now, when my fueling goes in the 15's at 1600 rpm light throttle the car surges bad.

[Billf6531]

DFCO on or off? And we're talking about open loop MAF here, correct, as the original poster detailed?

Post your tune and a log.

[WS6FirebirdTA00]

DFCO off, I never have it on, its worthless. This is OLSD.

I won't be able to find the log but won't post the tune I have too much time in it to do that.

[onecamaro1]

Right now i'm doing 16.3 up to 70 MAP because my cruising MAP was @ 50.
I have no surging issues, but this is now OLSD no MAF and no trims. IFR is 2.5 at idle/no AC and 2.9/w AC. I don't feel any surging so far.

[WS6FirebirdTA00]

Of course, you have a small cam. Any cam with a decent amount of duration on it will (in most cases) surge horribly when they lean out at light throttle.

Also remember you don't want to run the car lean past a point.

[onecamaro1]

Yeah, i was targeting 16.0 but as i did the EQ at .90 for 70 and below MAP, it came to 16.3-16.6. So i'm gonna redo my VE at in every cell i can get to.