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Old 02-21-2009, 02:37 AM   #1
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Default Fuel economy and trigger wheel offset

I have been getting poor fuel economy. Running NA, I have it tuned so that normal driving almost never gets richer than 14.7 and often is at 16:1. I use the diyautotune base spark map and have been running aggressive EGO correction. Still, I am getting about 10 - 20% fewer miles per gallon.

So looking through my msq to see what (if anything) could be causing this, i noticed that my spark settings are 55 +22.5. I must have done this because the stock ECU at 10* Base timing did not line up perfectly with a trigger offset of 77 or 78. Could this trigger offset be causing problems?

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Old 02-21-2009, 05:05 AM   #2
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nobody has any idea if this would make a difference?
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Old 02-21-2009, 09:26 AM   #3
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The trigger offset is just an electronic version of twisting the CAS. Seems like you should have been able to get it right at 77 or 78, but if 55 +22.5 gets you at 10 degrees with "10" in the Fixed Angle box, then you should be good to go.

What does your spark map look like? Could it be that you're simply not running enough advance there?
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Old 02-21-2009, 11:34 AM   #4
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Ok, so its just as i thought ... makes no difference how I get to the correct trigger angle. Its not that it wasn't good enough with 77 or 78, just was better with 55 +22.5.

So here is the ignition advance table I have been running. It is the base map from the MSPNP. Also attatched is my msq which reflects changes i have made recently to the spark map in the idle and high vacuum areas.
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Fuel economy and trigger wheel offset-ign-table.jpg  
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File Type: msq Ryan 230cc NA.msq (35.2 KB, 66 views)
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Old 02-22-2009, 12:54 PM   #5
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145 miles of 70% highway / 30% light canyon driving with very little wide open throttle got me 21mpg yesterday. Oh well, i guess it could be worse ... its just that on the OEM ecu I would have gotten more like 25mpg
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Old 02-22-2009, 06:08 PM   #6
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what do your logs suggest? I think you can run more spark advance in the cruise cells too...not as much as mine of course, but a few degrees more.

Spark plays a huge role in fuel economy. I advanced on my stock 1.6 and scored roughly 5mpg in highway driving.
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Old 02-22-2009, 08:09 PM   #7
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I got 21.9 out of my last tank on MS about the same driving as yours.
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Old 02-22-2009, 08:17 PM   #8
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I really should get a knock sensor and an egt to really get my map dialed in. I guess I am just a bit timid when it comes to tuning spark, but ill try adding a few degrees to that map above 2900 and below 75kpa
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Old 02-22-2009, 08:19 PM   #9
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Weird deal. During a 180 mile trip that included 5 runs of near 2 min autocross runs I got 25 mpg. This is running 550cc injectors and I was seeing like 11.5:1 in boost, peak boost of 14 psi.
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Old 02-22-2009, 08:21 PM   #10
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egg is best but the headphones work well too and are a must for tuning.
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Old 02-23-2009, 07:54 PM   #11
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Maybe Ill just get a det can then ... or make one. Not like I am going to be rolling around wearing that crap all the time.
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Old 02-23-2009, 08:03 PM   #12
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I've got the same issue related to timing. Fuel economy sux nuts.

I've noticed that compared to the stock ecu, the car pulls hard as **** down low scootin' around town but up high (getting on the freeway) it seems to run out of breath. You notice this?

I've just been assuming it wont make a difference when my turbo goes on this weekend.
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Old 02-23-2009, 08:06 PM   #13
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Hustler, is there a writeup on how you built yours? Is it just simply a hose attatched to the block?
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Old 02-23-2009, 08:07 PM   #14
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I have a feeling that my fuel economy is largely related to ignition timing, so I will have to play with it a bit. Oh an I forgot to mention, that I have 3.9 gears in the differential so that is 5% difference. That means that my trip was actually closer to 23mpg which is closer. I know that on the stock ecu though, i was getting 20mpg around town and 27mpg on the highway. I would like to get back to that.
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