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4.6 3V - MBT tables lower than Borderline??
It looks like the stock factory MBT table for my 2007 Mustang GT has lower spark values in many regions than the Borderline knock. I understand MBT is supposed to have been developed by the OEM for maximum brake torque. I've read Eric's tuning guide and he showed a Borderline/MBT that wasn't the same as stock. For example he mentions the 3V produces the most power at 31* of advance at WOT. Stock Borderline and stock MBT is set to about 15-17* at the high load / high RPM cells. Nowhere close to 31*.
I thought it might have been a fluke, but the MBT for the 07 Shelby GT (not GT500) was the same. The Explorer/F-150 4.6 3V had similar MBT tables where they max out around 19-20*.
Am I losing power running the 3V at 31* timing? I had been running SCT's 93-octane value file for the longest time and they too set the WOT cells to 31* or so.
The knock sensors pull a lot of timing in the 2250-3000 RPM cells at 50% or higher loads, but I think they might be false knock? Then again with the stock BKT values in the negatives for that area, the ECU was adding the max 8* timing.
On my GTDI engines (EcoBoost SHO / GM LNF) I don't touch the non-WOT areas and just add however many degrees timing I want for the 4k+ RPM / high load region, but the stock MBT table on the 3V seems goofy.
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Stock BKT and MBT, notice how MBT is lower in value than BKT in many regions, and check out how low the high load / high RPM cells are in BKT compared to what we typically see on a Ford I4, V6, or V8 (EcoBoost or non-EcoBoost). My SHO at 16 psi and LNF at 24 psi run more timing than the stock 3V MBT.
2017-07-09.png
SCT 93 octane value file:
2017-07-09 (1).png
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IMRC correction gets MBT to right around 31*
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That's a lot of correction... I don't recall seeing 14 to 15 degrees added by the imrc tables? I have the cmcv deletes as well. Maybe that's why SCT just sets the BKT and MBT directly to 31 with their cmcv delete 93 octane files?
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This is from a 4.6 2005 GT.
2005imrc corr.PNG
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Ok - now Eric's original article on using HPTuners on the Mustang makes a whole lot more sense. And that also explains how SCT developed their 93 octane value files. Thanks murfie.
Would these modified tables (with the advanced timing) be better for fuel economy or just for power? I'm noticing a hit in MPG if I set my Spark Decel very low (this impacts the 10% load row for actual spark). If I set that table to high values, the MPG is better (by about 1 MPG using full E85). I got tired of 14 mpg with full E85 but going back to E30, my mileage hasn't really improved all that much.
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With DFCO enabled there should be no fuel consumption on decel so the spark shouldn't affect MPG. I've seen higher cylair multipliers over ride DFCO.
Comparing your SCT to the stock spark values in the area where you would be cruising and trying to get the best MPG 1500 to 3000RPMs and .2 to .5 load I see the IMRC values make the borderline much higher than what the SCT tune has. I don't know if the higher timing was useable because the IMRC and the SCT values were pulled back because of knock. Throttle response, power, and MPG would all be effected negatively if with out the IMRC you run into knock in this area. the higher ethanol should actually be able to make up for some if not all of it so I would say add as much timing advance in that area as you can.
Last edited by murfie; 07-09-2017 at 02:24 PM.
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Fuel consumption during decel is low, instantaneous MPG calculation is like 60+ mpg. However, I have data that shows I get about 1 mpg better if I use normal or high/advanced spark decel versus retarded spark decel.
Isn't Cylair Mult set to 1.99 or recommended that high?
For the stock BKT w/ IMRC added, it is nowhere near as high as SCT's value file (which is the MBT w/ IMRC copied straight over). Using E30 or E85, I get minimal knock retard in the 2250 RPM column at high loads but otherwise is all zero. It looks like the IMRC adders only impact 3000 RPM or lower for the BKT.
But for fuel economy, would I want more advanced or retarded timing? I always thought advanced timing yielded better power (to a certain point) while retarded timing yielded better fuel economy (to a certain point).
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Raising those multiplier are spouse to help with getting the SD to work with boosted applications.
For fuel economy you want the timing that makes the most torque as thats when the engine will be using the fuel the most efficiently. This is MBT. When talking about WOT Most fuels have too low of octane and will be detonation limited. That said I would think that values for BKT IMRC would get lower on a diagonal axis from high load low RPM to low load high RPM, rather than a vertical RPM cut off.
When talking about low partial throttle areas where cylinder pressures start much lower with much less air, fuel, and final pressures do not get as high it is possible to exceed MBT advanced. E85 more so than 93. Along with its knock resistance E85 burns slower so the cylinder pressure doesnt climb as fast as 93. This means with more advance the pre-tdc cylinder pressures work less against the piston robbing the engine of torque so its MBT will be a higher advance as 93 will be lower. With out a cylinder pressure sensor or dyno, tuning the spark advance in these areas is difficult.
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Why wouldn't the OEM do this for maximum fuel economy? It seems stock BKT is very low in the sub-4250 RPM region.
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This is from a 2009 file, the base IMRC values are lower than from 2005.
I added the tables up to compare BKT vs MBT. You can see where it would be using MBT as borderline is higher, then there is a transition to the BKT values where the fuel would be detonation limited. As you can see and already know the MBT table is the same as the SCT values. I drew a line where the borderline is higher than the MBT. The ECU would then use the MBT values. The borderline being higher in these areas most likely is so if the other spark correction factors come up to be a negative it doesnt immediately pull timing below MBT when it is not necessary. Vise versa when it comes out positive, but then MBT value will be used anyway. The OEM calibrated it better than SCT did.
2009BKTvsMBT with IMRC.PNG
Last edited by murfie; 07-09-2017 at 05:51 PM.
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I noticed from driving that the spark values from BKT at 3000 RPM and lower (all the rows) are used in normal driving. When I have to do a full WOT test run, it would then start to use the cells from 4250 RPM and higher, mainly at high loads. I noticed the 2009 values you posted have several cells lower than the 2007 values, mainly by a few degrees. Perhaps it is due to the different spark plug design used in the 2008.5-up heads?
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They hold the IMRC closed a bit longer in the 2009 than the 2005 files. late (dec.) 2007-2009 had different heads, a better plug design, better coolant hose routing with thermostat relocation, and just a beefier chassis for the GT500. Probably changes for emissions purposes more than MPG.
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MY2007 is when they did the GT500 chassis update and coolant hose reroute (I see both in my 07 that was made late 2006) but MY08.5 is when they started using the new plugs from what I recall. I'll run the BKT plus IMRC for sub 3k and see if there's any change in fuel economy.
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