Okay octane question
05-11-2018, 07:44 AM
#1
Thread Starter
Join Date: May 2018
Location: New York
Posts: 15
Okay octane question
The owner's manual for my '18 GT states this car takes 87 octane but that 91 is better in hot weather and towing. The fuel door and gas cap say nothing.
I've seen threads but no answer. Does anyone actually know how much power we actually lose running 87 vs 91 or 93?
No opinions, plenty of those out there. I'm running 91 name brand gas but why throw away $3 a week if it is only a few HP and doesn't hurt the car at all?
I've seen threads but no answer. Does anyone actually know how much power we actually lose running 87 vs 91 or 93?
No opinions, plenty of those out there. I'm running 91 name brand gas but why throw away $3 a week if it is only a few HP and doesn't hurt the car at all?
05-11-2018, 07:57 AM
#2
1st Gear Member
Join Date: Sep 2017
Location: Texas
Posts: 57
You're not going to find a "chart" that tells you what hp to expect depending on what gas you're using. Atmospheric conditions play a part as well. The same car using the same gas will run two different 1/4 mile times on two different days. Your engine is tuned to run fine on 87, but what they're not telling you is that if the computer detects knock, it will back off the ignition timing just enough to make it stop knocking during the event, which will cut hp. Nobody can tell you by how much. The only way us non-engineers can ensure we're always getting maximum performance out of our engines is to use the best gas we can find. If you don't find yourself going WOT, passing a semi uphill in 90-degree temps, you probably won't notice a difference. Some people claim better mpg on 93, but I don't really see how they're arriving at that conclusion. I use 93 in my Ecoboost to avoid knock, and its damaging effects. Very few butt dynos could tell the difference if I ran 87 in it.
05-11-2018, 08:32 AM
#3
Thread Starter
Join Date: May 2018
Location: New York
Posts: 15
I'm hip to how it works. I've seen a progression from "use 87 in an emergency" to "87 is fine, 91 is better" in owner's manuals over the years in different cars (Maxima, WRX, etc).
Just curious if another person or tune shop had ever dynoed this for the hell of it. I don't have access to any accurate measure of HP but somebody may have tried looking at this on a 5.0. Maybe just printed in a Ford technical document.
Honestly, I probably couldn't feel 20 HP difference in day to day driving in a car this powerful. But I suspect it's probably only a couple percent anyway.
Just curious if another person or tune shop had ever dynoed this for the hell of it. I don't have access to any accurate measure of HP but somebody may have tried looking at this on a 5.0. Maybe just printed in a Ford technical document.
Honestly, I probably couldn't feel 20 HP difference in day to day driving in a car this powerful. But I suspect it's probably only a couple percent anyway.
05-11-2018, 08:51 AM
#4
Thread Starter
Join Date: May 2018
Location: New York
Posts: 15
Haha found some internet:
https://www.caranddriver.com/feature...results-page-2
this is 2001 but shows that it can be highly variable. A Mustang gained a little. A Honda lost power on premium! Though Honda never said it should take premium.
Possibly low octane hurts the ecoBoost HP more than the V8.
https://www.torquenews.com/106/ford-...ower-87-octane
Old but interesting article with a Mopar:
http://www.hotrod.com/articles/fuel-...ng-comparison/
Just rambing. Thanks.
https://www.caranddriver.com/feature...results-page-2
this is 2001 but shows that it can be highly variable. A Mustang gained a little. A Honda lost power on premium! Though Honda never said it should take premium.
Possibly low octane hurts the ecoBoost HP more than the V8.
https://www.torquenews.com/106/ford-...ower-87-octane
Old but interesting article with a Mopar:
http://www.hotrod.com/articles/fuel-...ng-comparison/
Just rambing. Thanks.
05-11-2018, 08:10 PM
#5
Banned
Join Date: Jan 2018
Location: Pennsylvania
Posts: 2,327
You only need to use higher octane if you have preignition. If you are not
experiencing timing retarding issue, then you don't need 91.
Low octane can hurt turbocharged motor performance, and even more so
on motors with VVT. My car is designed to run on 87 octane, it is a 1.8 Turbo.
It produces 170 HP with 87 octane. When the tank is 100% 91+ octane, it
produces 190HP peak. The GLI version is a 2.0, at 200 HP, but must run 91
octane to get 200+HP. If you put 87 in it, you get 185 to 190. The 1.8 and
2.0 are the exact same engine, the 1.8 being a shorter stroke, but the 2.0 has
a slightly larger turbo. I can run +6 lbs of boost on my 1.8T, and match the
GLIs output on 87, beat it with 91 or 93 octane. If I push the +6 lbs with 87,
and stay at WOT, it pulls timing way back, it floods, and my EPC light comes
on. I also had to gap the plugs down to .028 for the extra boost.
Timing, both spark and valve is octane dependent. The spark can only
advance so far, and will retard when it detects knock, low octane.
There is a thread on this already, so I am not going over it again...
Don't fix what isn't broken...
experiencing timing retarding issue, then you don't need 91.
Low octane can hurt turbocharged motor performance, and even more so
on motors with VVT. My car is designed to run on 87 octane, it is a 1.8 Turbo.
It produces 170 HP with 87 octane. When the tank is 100% 91+ octane, it
produces 190HP peak. The GLI version is a 2.0, at 200 HP, but must run 91
octane to get 200+HP. If you put 87 in it, you get 185 to 190. The 1.8 and
2.0 are the exact same engine, the 1.8 being a shorter stroke, but the 2.0 has
a slightly larger turbo. I can run +6 lbs of boost on my 1.8T, and match the
GLIs output on 87, beat it with 91 or 93 octane. If I push the +6 lbs with 87,
and stay at WOT, it pulls timing way back, it floods, and my EPC light comes
on. I also had to gap the plugs down to .028 for the extra boost.
Timing, both spark and valve is octane dependent. The spark can only
advance so far, and will retard when it detects knock, low octane.
There is a thread on this already, so I am not going over it again...
Don't fix what isn't broken...
05-12-2018, 09:06 AM
#6
Join Date: Apr 2018
Location: South Carolina
Posts: 10
I asked my dealer what grade of fuel should I use and he said regular. I have used 93 octane but have not noticed any difference on power or MPG. I have yet to drive my car in the hot summer here in SC so I’m curious to see how my 18 GT performs in the heat with 87.
05-29-2018, 11:17 PM
#8
Join Date: Jun 2016
Location: California
Posts: 26
We can only get 91 octane in CA, so that is what I run. When I put it on the dyno, it put 360 hp to the wheels (I don't know what the atmospheric conditions were at the time). Post Roush supercharger install it put 513 hp to the wheels. Others with the same setup have put 550+ hp to the wheels, so the 91 octane is the likely culprit. As others have noted, with a modern computer controlled engine, lower octane won't hurt, but you'll probably be down on power a bit. You can probably get a custom tune that's optimized for 87, but I would think it's not worth it for most folks.
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