93 ocT "10% ethanol" = 13.5 AFR-WOT
Feb 12, 2008, 08:36 AM
#1
93 ocT "10% ethanol" = 13.5 AFR-WOT
Just bought a tank of gas (HESS) from a station I never use and the pump had a sticker stating " Gasoline Contains 10% Ethanol". The tune will normally indicate about 12.5 AFR reported by WB at WOT, but the "gasohol" pushed the 10% claim to the limit and caused a full point of leaning to the burn to 13.5.
Even at idle the trims were maxed out with an average 14.8 AFR!
I overlayed logs recorded earlier with fuel I normally purchace (w/o alcohol cut into the gasoline) to see if IPW and airflow plots are similar confirming this isn't something else. Everything is the same, just the AFR is leaner.
Even though the leaning wasn't enough to cause knock, the burn appeared slightly lean of peak power as indicated with overlayed rpm slopes, but not enough to make any difference. One thing interesting is the power feels smoother on this side, not enough to make it a target since it's awful close to 14's - the worst possible AFR to be under load.
Just a bit of info I thought would be of some value
I can post the logs later if anyone is interested.
Even at idle the trims were maxed out with an average 14.8 AFR!
I overlayed logs recorded earlier with fuel I normally purchace (w/o alcohol cut into the gasoline) to see if IPW and airflow plots are similar confirming this isn't something else. Everything is the same, just the AFR is leaner.
Even though the leaning wasn't enough to cause knock, the burn appeared slightly lean of peak power as indicated with overlayed rpm slopes, but not enough to make any difference. One thing interesting is the power feels smoother on this side, not enough to make it a target since it's awful close to 14's - the worst possible AFR to be under load.
Just a bit of info I thought would be of some value
I can post the logs later if anyone is interested.
Feb 12, 2008, 09:32 AM
#4
Also if someones wondering why this happens:
Your 12.5 tune gives you 12.5 when you use regular fuel which has 14.7 stoich ratio.
The "gasohol"(oxygenated fuel) has approx 14.7x90%+9.8x10% = ~ 14 stoich.
So 12.5/14 = ~0.9 is the actual lambda you are now running with your tune.
And 0.9 x 14.7 = 13.23 is what the WB shows.
And while it's not the real afr (cause the wideband has 14.7 multiplier) , your lambda of ~0.9 is leaner than your desired 0.85
Your 12.5 tune gives you 12.5 when you use regular fuel which has 14.7 stoich ratio.
The "gasohol"(oxygenated fuel) has approx 14.7x90%+9.8x10% = ~ 14 stoich.
So 12.5/14 = ~0.9 is the actual lambda you are now running with your tune.
And 0.9 x 14.7 = 13.23 is what the WB shows.
And while it's not the real afr (cause the wideband has 14.7 multiplier) , your lambda of ~0.9 is leaner than your desired 0.85
Last edited by mplspilot; Feb 12, 2008 at 09:34 AM.
Feb 12, 2008, 09:42 AM
#7
Also if someones wondering why this happens:
Your 12.5 tune gives you 12.5 when you use regular fuel which has 14.7 stoich ratio.
The "gasohol"(oxygenated fuel) has approx 14.7x90%+9.8x10% = ~ 14 stoich.
So 12.5/14 = ~0.9 is the actual lambda you are now running with your tune.
And 0.9 x 14.7 = 13.23 is what the WB shows.
And while it's not the real afr (cause the wideband has 14.7 multiplier) , your lambda of ~0.9 is leaner than your desired 0.85
Your 12.5 tune gives you 12.5 when you use regular fuel which has 14.7 stoich ratio.
The "gasohol"(oxygenated fuel) has approx 14.7x90%+9.8x10% = ~ 14 stoich.
So 12.5/14 = ~0.9 is the actual lambda you are now running with your tune.
And 0.9 x 14.7 = 13.23 is what the WB shows.
And while it's not the real afr (cause the wideband has 14.7 multiplier) , your lambda of ~0.9 is leaner than your desired 0.85
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Feb 12, 2008, 10:26 AM
#11
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I have been using the Hess gas for about 2 months already. My car dynoed 361hp with Mobil 93oct and then got re tuned and re dynoed again with the Hess gas and i picked up 12hp. Just the tune changed. I am able to run more boost without knock while keeping the egt low.
Feb 12, 2008, 10:28 AM
#12
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very good info. i plan on running 100% E85 when there are a few more stations available or when tephra adds injectors scaling to the alternate maps use that one map for e85 one for 91
Feb 12, 2008, 02:51 PM
#13
I tried explaining the E5/10 thing on another forum and got this reply:
http://forums.overclockers.com.au/sh...4&postcount=41
At the time I didn't have the maths to back it up .. ;(
http://forums.overclockers.com.au/sh...4&postcount=41
At the time I didn't have the maths to back it up .. ;(
Feb 12, 2008, 04:00 PM
#14
Just bought a tank of gas (HESS) from a station I never use and the pump had a sticker stating " Gasoline Contains 10% Ethanol". The tune will normally indicate about 12.5 AFR reported by WB at WOT, but the "gasohol" pushed the 10% claim to the limit and caused a full point of leaning to the burn to 13.5.
Even at idle the trims were maxed out with an average 14.8 AFR!
I overlayed logs recorded earlier with fuel I normally purchace (w/o alcohol cut into the gasoline) to see if IPW and airflow plots are similar confirming this isn't something else. Everything is the same, just the AFR is leaner.
Even though the leaning wasn't enough to cause knock, the burn appeared slightly lean of peak power as indicated with overlayed rpm slopes, but not enough to make any difference. One thing interesting is the power feels smoother on this side, not enough to make it a target since it's awful close to 14's - the worst possible AFR to be under load.
Just a bit of info I thought would be of some value
I can post the logs later if anyone is interested.
Even at idle the trims were maxed out with an average 14.8 AFR!
I overlayed logs recorded earlier with fuel I normally purchace (w/o alcohol cut into the gasoline) to see if IPW and airflow plots are similar confirming this isn't something else. Everything is the same, just the AFR is leaner.
Even though the leaning wasn't enough to cause knock, the burn appeared slightly lean of peak power as indicated with overlayed rpm slopes, but not enough to make any difference. One thing interesting is the power feels smoother on this side, not enough to make it a target since it's awful close to 14's - the worst possible AFR to be under load.
Just a bit of info I thought would be of some value
I can post the logs later if anyone is interested.
