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Re: What if you way OVER OCTANED a motor ?
[Re: n20mstr]
#2902573
03/25/21 07:12 AM
03/25/21 07:12 AM
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Joined: Jul 2008
Posts: 30,466
Florida STAYcation
dOc !
OP
The village idiot's idiot
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OP
The village idiot's idiot
Joined: Jul 2008
Posts: 30,466
Florida STAYcation
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WOW great topic, i tell peopl e all the time, they slow down a car with too much octane. Proved it with my sons car. Junkyard 360, went 11.48 on 110 , put 93 and it went 11.15 Thx n ... but my spin here is on my Scat Pack Charger... I’m using PUMP REGULAR in it instead of 91 .. 91 is a very rare blend in these parts... only ONE STATION in this area has it. So instead of using 93 ... two points over recommended... I’m using 4 points under ... but the ECU compensates for that  ACCORDING to some members here that work at CTC. I’m curious what kind of actual 30-roll high gear press diff there would be between using the two diff fuels
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Re: What if you way OVER OCTANED a motor ?
[Re: an8sec70cuda]
#2904065
03/29/21 06:30 PM
03/29/21 06:30 PM
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Joined: Dec 2018
Posts: 88
IL
83hurstguy
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Joined: Dec 2018
Posts: 88
IL
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I am not disagreeing with the results here, but I'm curious how much of the results are not due to just octane change, but specific gravity change. Race fuel is notably lighter (less dense) than pump gas; therefore, the same jetting causes it to run leaner. The burn curves are also different so the timing requirements could change. We found this on the dyno, but ran out of time to do a full A-B comparison with jetting and timing changes.
Quite a few NHRA stock eliminator cars are running C11 or C12 fuel (or similar) on engines that have less than 10.5:1 compression, some between 9-10:1, saying its notably quicker. For heads up racing, those same engines will have a custom carb set up for C25 (or similar Pro Stock fuel) that has octane average of 117, and timing has to get pulled to make it work. It's a ton of work to optimize a fuel for a car, but somehow the higher octane fuels work for those guys and not others. I don't have any data (yet), but plan to do more testing someday. Makes you wonder...
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Re: What if you way OVER OCTANED a motor ?
[Re: 83hurstguy]
#2904140
03/29/21 10:52 PM
03/29/21 10:52 PM
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Joined: Jan 2005
Posts: 12,422
Kalispell Mt.
HotRodDave
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Kalispell Mt.
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I think those stock eliminators are getting some ram tuning effects going on that bring the actual dynamic compression up much higher than the 10.5 compression would otherwise indicate it should be.
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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Re: What if you way OVER OCTANED a motor ?
[Re: 83hurstguy]
#2904201
03/30/21 08:12 AM
03/30/21 08:12 AM
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Joined: Jan 2003
Posts: 13,380
Marion, South Carolina [><]
an8sec70cuda
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I Live Here
Joined: Jan 2003
Posts: 13,380
Marion, South Carolina [><]
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I am not disagreeing with the results here, but I'm curious how much of the results are not due to just octane change, but specific gravity change. Race fuel is notably lighter (less dense) than pump gas; therefore, the same jetting causes it to run leaner. The burn curves are also different so the timing requirements could change. We found this on the dyno, but ran out of time to do a full A-B comparison with jetting and timing changes.
Quite a few NHRA stock eliminator cars are running C11 or C12 fuel (or similar) on engines that have less than 10.5:1 compression, some between 9-10:1, saying its notably quicker. For heads up racing, those same engines will have a custom carb set up for C25 (or similar Pro Stock fuel) that has octane average of 117, and timing has to get pulled to make it work. It's a ton of work to optimize a fuel for a car, but somehow the higher octane fuels work for those guys and not others. I don't have any data (yet), but plan to do more testing someday. Makes you wonder... May very well be true in my case...I ran low on 93 at the track and threw in some 110 just to make another couple passes. Wasn't going to change anything b/c the car was optimized for 93 pump gas.
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Re: What if you way OVER OCTANED a motor ?
[Re: dizuster]
#2904547
03/31/21 10:52 AM
03/31/21 10:52 AM
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Joined: Jul 2008
Posts: 30,466
Florida STAYcation
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Florida STAYcation
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Your Scat will DEFINITELY make more power on 91/93 then it will on 87.
Even when I was doing tuning "road pulls" on my Challenger scat pack, depending on where I got the 93 from sometimes it would knock and pull timing that you could see in the data logs.
For sure it knocks on 87 and pulls timing.
Worse yet, it will learn that you always put 87 in it, and when you put 93 in it you won't see gains for a long time until it knows you got off your wallet and were committed to good gas. LOL
They call this "long term trim".
You can cheat the ECU by pulling out fuse #31 under the hood for 60 seconds. That will re-set the PCM and go back to the full 91/93 octane timing/fuel maps. But if you put 93 in it without pulling the fuse to reset the PCM, don't expect to see any performance gains at all right away.
But DIZzZ... I’m wondering how much performance is lost ? ... like comparing two identical cars - just a fuel diff ? You sound like a CTC guy .. maybe even a Hpark one ! Will the ECU learn both backward and FORWARD ?
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Re: What if you way OVER OCTANED a motor ?
[Re: 83hurstguy]
#2904612
03/31/21 01:27 PM
03/31/21 01:27 PM
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Joined: Jan 2003
Posts: 11,724
Portage,michigan
B3422W5
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I Live Here
Joined: Jan 2003
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Portage,michigan
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I am not disagreeing with the results here, but I'm curious how much of the results are not due to just octane change, but specific gravity change. Race fuel is notably lighter (less dense) than pump gas; therefore, the same jetting causes it to run leaner. The burn curves are also different so the timing requirements could change. We found this on the dyno, but ran out of time to do a full A-B comparison with jetting and timing changes.
Quite a few NHRA stock eliminator cars are running C11 or C12 fuel (or similar) on engines that have less than 10.5:1 compression, some between 9-10:1, saying its notably quicker. For heads up racing, those same engines will have a custom carb set up for C25 (or similar Pro Stock fuel) that has octane average of 117, and timing has to get pulled to make it work. It's a ton of work to optimize a fuel for a car, but somehow the higher octane fuels work for those guys and not others. I don't have any data (yet), but plan to do more testing someday. Makes you wonder... I ran my 10 to 1( maybe) typical low/ mid 11 sec combo on both pump 93 and 110 for extended periods of time last year to see what if any difference might be Frankly, i noticed nothing either way regards an ET difference. People told me it would run better on pump gas, thus the effort to try it. I ran each enough to make a valid comparison
Last edited by B3422W5; 03/31/21 01:28 PM.
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Re: What if you way OVER OCTANED a motor ?
[Re: dOc !]
#2904621
03/31/21 02:01 PM
03/31/21 02:01 PM
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Joined: Jan 2005
Posts: 12,422
Kalispell Mt.
HotRodDave
I Live Here
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I Live Here
Joined: Jan 2005
Posts: 12,422
Kalispell Mt.
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Your Scat will DEFINITELY make more power on 91/93 then it will on 87.
Even when I was doing tuning "road pulls" on my Challenger scat pack, depending on where I got the 93 from sometimes it would knock and pull timing that you could see in the data logs.
For sure it knocks on 87 and pulls timing.
Worse yet, it will learn that you always put 87 in it, and when you put 93 in it you won't see gains for a long time until it knows you got off your wallet and were committed to good gas. LOL
They call this "long term trim".
You can cheat the ECU by pulling out fuse #31 under the hood for 60 seconds. That will re-set the PCM and go back to the full 91/93 octane timing/fuel maps. But if you put 93 in it without pulling the fuse to reset the PCM, don't expect to see any performance gains at all right away.
But DIZzZ... I’m wondering how much performance is lost ? ... like comparing two identical cars - just a fuel diff ? You sound like a CTC guy .. maybe even a Hpark one ! Will the ECU learn both backward and FORWARD ? They will not learn forward, only backward than back forward to where it is supposed to be but running say 100 octane in a car tuned for 93 will not get it to advance the timing anymore than the point it was set to run with 93. If you run a heavily oxygenated fuel like e-15 or higher it will detect the increased oxygen in the exhaust and add more fuel up to a point (usually 25% before it sets codes).
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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