Getting Best MPG during Cruise

[tipoytm]

Tried tonight with about 1-2* less timing compared to hiboost's map... cruise is around 40-50% load @ an average 50-60mph & 50-70% load @ an average of 60-75mph (mostly flat roads). No knocks using 91oct Costco fuel. I'm going to advance it almost identical to Hiboost's on my next flash see how that goes... will report MPG also after next fill up. Thanks again for the info! Very interesting mod :-)

[tephra]

I am actually finding having LOWER ignition advance improves fuel eco..

dunno how that works?

[Hiboost]

Originally Posted by tephra

I am actually finding having LOWER ignition advance improves fuel eco..

dunno how that works?

That seems to go against everything I have read anywhere, they always said you were a bit different from the rest!

I bet there could be a slightly different optimum MBT for each RPM depending on what mods are on the car. As someone said before the Mivec settings could also impact this quite a bit, my low end is still the same maps I posted in another thread which are slightly more aggressive then then US maps in that area.

You would think lower timing advance would mean less cylider pressure at any one time which means to maintain the same speed you would have to use more throttle. That is unless you are already at optimum or somehow past it with your setup. What mods have been done so far to your Evo X? Is it still mostly stock besides the tune?

Here is an EMS tuning guide in Google Books where it talks about timing at light loads and fuel economy. You can scroll up or down a bit for some other usefull info as well:

http://books.google.com/books?id=ze_...conomy&f=false

At Light cruise, as much as 44 degrees timing advance could enhance fuel economy.

Here is another article about Tuning for Mileage. Not sure how effective or valid all those techniques are but towards the bottom it cites this info:

http://www.fuelsaver-mpg.com/doc/TuningForMileage.html

Adjust Ignition Timing

If you have a distributor, the solution is simple. Loosen the hold-down clamp and turn the distributor. If you have DIS (Distributorless Ignition System), COP (Coil On Plug), or a distributor that doesn’t affect timing, then you have to play with the MAP and IAT signals to dial in the spark.

To adjust with the distributor, grab a vacuum gauge, timing light, and distributor wrench. Drive the vehicle down a relatively flat section of road at cruise speed. Watch your vacuum gauge. Pull over and either advance or retard the timing by about 4 degrees. If you increased the power and vacuum, adjust again by about 2 degrees. If you lost power and vacuum, crank it the other way about 8 degrees and test again. You want the least amount of timing advance needed to maintain maximum power at cruise. Any more advance than that will increase the possibility of detonation, and will fight the piston on the compression stroke.

If you have the DIS or COP, adjust the IAT sensor reading by 10° F increments for maximum power. If you start high on your reading (smaller value resistor), start adding resistance to advance timing. If you have a near ambient reading (no or large value resistor), reduce parallel resistance to retard timing.

As stated earlier, adjusting the MAP VREF will alter timing. A lower VREF will advance timing. A higher VREF will retard timing. There is a balance between finding the right lean-out limit, and maximizing the timing.

Luckily we can directly change timing advance in the specific parts of the timing maps as needed.

Some more info about advancing timing:

At low load, high vacuum, conditions the flame speed is slower. At these conditions, the engine can stand or require additional advance. Vacuum advance can improve mileage and reduce the heat load on the engine. The performance at maximum power should be optimized first, as outlined above.

Add vacuum advance to optimize low speed driveability. When you have too much the symptom will be a surging or bucking at low rpm cruise that goes away if you drive slightly faster.

[tephra]

yeah im not saying that less is more, i am saying that up until a certain point its good, then past that point you seem to go backwards...

its ultra hard doing testing in this area.. really need a dyno and just sit at various rpm's (on cruise control) and log IPW and fiddle with ignadv

[Hiboost]

Originally Posted by tephra

yeah im not saying that less is more, i am saying that up until a certain point its good, then past that point you seem to go backwards...

its ultra hard doing testing in this area.. really need a dyno and just sit at various rpm's (on cruise control) and log IPW and fiddle with ignadv

Well said, there is definitely an optimal spot and you can definitely go too far. For instance if someone had a near stock car, 41* might be optimal but you go from 40* to 44* and suddenly being 3* over optimal is worse MPG then being 1* below. All the articles that I read do say that if you exceed the optimal timing then your vacuum goes back up and you "may detect knock or see bucking/surging" where basically you are fighting the compressions stroke and losing power and efficiency again.

Possibly one way to test this is to find a stretch of road where you can do a steady 65 or 70 mph cruise for a couple minutes repeatably and log with Evoscan. You could test timing in 1* increments and the output from evoscan will let you average out the values for timing, psi (will read negative), AFR, load, and IPW which should result in a trend of where vacuum should increase on average and load decrease until you reach optimal timing then start going back down again. A dyno would be likely more controllable but I think it could be done.

If someone has time you could likely test 34*, 40*, 42*, 44*, 46* and see a trend of where you would have highest vacuum and lowest load which should hopefully result in what the best timing advance is for your setup. Then you could try a 1* change if it lands between two of the tested timing numbers.

[tipoytm]

Report:

Increased my cruise timing load cells now nearly identical to hiboost's. Everything is the same as his except on 40% load column max at 43* instead of 44, and at 70% load column, all changed cells are 1* lower... together with a few other load cells in between for smoother transitions.

Happy to report that I never got any knocks. Cruised around town with my family earlier, usually I'd get an average of 19mpg on the MFD, but after we got home tonight... I got 21mpg on the display! This is 30 mins. of normal driving (cruise+occasional boosts), still using Costco 91oct gas.

[Methodical4u]

has anyone tried this with an AP by chance? I would work on it myself with the ATR... BUT I don't know what the hell i'm doing

[GST Motorsports]

You guys really need to not go by the MPG display and go more by the "fill up the tank, drive so and so miles, note miles, pump gas, note gallons, divide miles by gallons it took to fill up" test

[tephra]

the MPG display should be accurate, flat/straight road, limited distance, cruise control...

live mapping would be awesome for this

[Hiboost]

Originally Posted by GST Motorsports

You guys really need to not go by the MPG display and go more by the "fill up the tank, drive so and so miles, note miles, pump gas, note gallons, divide miles by gallons it took to fill up" test

I agree that getting actual mileage from refilling the tank after driving 300 miles is the most accurate. The problem is that usually you are seeing mixxed driving so the max highway mileage will be hard to calculate unless you do a long trip. So when you compare mileage from a previous date with various driving conditions, the variables of how and where you drove and at what speeds will make the results pretty random but over time you should see an increase in MPG. I suppose that you could fill up at the same gas station and pump, then do a 10-15 min loop and come back and repeat with the different settings. I'm not 100% sure the pump would be accurate enough based on where it would shut off for such a small trip though.

The in dash display is accurate enough to get a good feel for averages if you drive a similar stretch of highway for 10 minutes such as a commute to work at a similar speed. Cruise control would take most of the speed variables out even if it isn't quite as good MPG as manually feathering the gas as needed. Usually actual usage is a bit more than what the MPG screen will indicate but it can still be usefull for comparing before and after changes.

[Hiboost]

Originally Posted by Methodical4u

has anyone tried this with an AP by chance? I would work on it myself with the ATR... BUT I don't know what the hell i'm doing

If you know how to access the timing maps you should be able to alter the timing advance table in a similar way. I've never seen the AP interface so someone else would have to help further.

[tipoytm]

Originally Posted by GST Motorsports

You guys really need to not go by the MPG display and go more by the "fill up the tank, drive so and so miles, note miles, pump gas, note gallons, divide miles by gallons it took to fill up" test

The route we took yesterday was a very familiar one, same roads, same part of town, same destination (Borders bookstore+shopping area), and back. Also, I drove the same way, not actually "feathering" it.. just normal cruising + accelerations on stoplights. So I know what to expect to see on the MFD. Seeing 21MPG kinda surprised me since I would only get 20+ on the display if I'm on the freeway for at least 15 mins... and this was all city driving.

But you are right though, the most accurate way to tell the actual MPG would be calculating it after the next fill up.

[tipoytm]

By the way, with my carputer "setup" and evoscan gauges, when cruising 55-60 mph on a long stretch of flat road (ie. big multi-lane avenue), I saw the timing bounce around 43-41 (occasionally 44)... maybe the A/C was affecting load too since it's usually stuck to 60%-40%, rarely below.

[Methodical4u]

Is knock the biggest thing to watch out for when making adjustments to timing and such?

[tipoytm]

Originally Posted by Methodical4u

Is knock the biggest thing to watch out for when making adjustments to timing and such?

Yeah, that's what the experts said on prior posts above.