Would Higher Octane Gas Make Your Car Slower?

DFG 5OH · Nov 5, 2005

Well in an attempt to solve my pre-detonation problems I put $20.00 worth of 93 octane in my car. Right off the bat I noticed that all my pinging problems were gone, and on a side note, the smell of higher octane gasoline is . Anyways, i went out to run it up in the RPMS, and my car did not feel as fast as it did with 87, AND it seemed to get really hot, and smell different (not the exhaust). My temp. guage didnt reflect a change in tempature, but i could feel it outside my car. Even on a cool night, where my car would run the best, and stay cool, it would not be as fast and get hotter than usual. Is this all in my head, or could this be true?

Thank You Fellow Stangnetters,
Matt J.

deadlast · Nov 5, 2005

i have heard higher octane can lower your mpg, buts thats ill i know off. i put in some 93 like yourself, and didnt notice any performance changes, but it did start and run smoother.

HISSIN50 · Nov 5, 2005

Higher octane, WHEN NOT NEEDED, can diminish performance (it is akin to having ignition timing too retarded).

The difference in octane is so minimal, I would not sweat anything temp-wise you notice. It would take a lot more octane to notice a temp delta, etc.

The issue IMHO comes down to the fact that our timing tables are not consistant. We ping at lower and mid loads but not at higher loads (it seems to me). So we shadetree-tune (timing, octane, etc) for the Low-RPM ping, for instance. But now we dont have maximized high-load total timing. So it is a trade off.

With it pinging at lower loads for you Matt, your high load total timing was probably pretty optimal (in stock tune) for performance. Now the timing is essentially a little retarded at high load (but you dont ping at low loads).

Now if you were only pinging at higher RPM's, that is different than my experiences so I wont comment. That would actually probably be a little easier to deal with and tune around.

Good luck man.

DFG 5OH · Nov 5, 2005

thanks for the help hissin, my tank is nearly empty, and i'll stick some 87 back in it, and see how it is.

Nobody · Nov 5, 2005

5.0 Mustang did an article on octane and ran a motor on the dyno on different octane fuels and also tested with octane booster. The conclusion was that there is a sweet spot when it comes to octane. The higher octane fuels burn slower than the lower octane stuff and therefore, the motor was making less HP beyond a certain octane rating, even with more timing.

mo_dingo · Nov 5, 2005

matthiasj said:
thanks for the help hissin, my tank is nearly empty, and i'll stick some 87 back in it, and see how it is.

Yeah, good idea.......more octane = less volitile = less explosion = less power...pretty simple.
Scott

DFG 5OH · Nov 5, 2005

well maybe i'll try to fix my pinging somewhere else. Hissin, i'm pinging more up top, under normal driving, no ping, but when i get on it, especailly in 3rd and 4th gear it pings pretty bad past 3k on 87 octane, none with 93.

sage2k · Nov 5, 2005

today i changed my spark plugs and at the same time sprayed electric cleaner on my MAF wires
my car stopped pinging (only had minor WOT pinging) and idles alot smoother now
also more powerful up top in rpms

i dunno if it was maf cleaning or spark plugs, i went from 4 prong bosche to the 1 prong autolite 25's and now everything is much nicer

dstanggt50 · Nov 5, 2005

sage2k said:
today i changed my spark plugs and at the same time sprayed electric cleaner on my MAF wires
my car stopped pinging (only had minor WOT pinging) and idles alot smoother now
also more powerful up top in rpms

i dunno if it was maf cleaning or spark plugs, i went from 4 prong bosche to the 1 prong autolite 25's and now everything is much nicer

I would think it is a mixture of both, I've heard that those platinums don't work very well.

HISSIN50 · Nov 5, 2005

Matt, I have played the same games you are. I wont bore you with it, but I have Low RPM/low load ping. I know several factors which are involved and need a TwEECer to get around them.

So I run the higher octane for low RPM ping even though I dont ping at higher RPM's no matter what.

I am sorry if my previous post came across misleading. I would tune so you dont have any ping at ANY time. If you need to run more octane to accomplish this, do it. If 93 octane takes care of your high rpm ping (and all other pinging you ever might have), I would:

a) run the 93
b) Run a lower octane but also lower timing till you dont ping.
c) do a little of both.

Scott, I know you know this, but your post is a little misleading IMHO. Higher octane most definately has as much potential energy as lower octane (actually more). But because it is less volatile (octane rating being a measure of knock resistance), it can handle more heat and pressure before igniting. My advice would be that if someone never ever pings on 87 octane, but runs a higher octane because they feel it helps (on a non-piezo equipped car), that is a waste. In that case, the 87 is sufficient and the higher octane is a waste of money and performance - just like you said.

But for anyone with ping issues, the higher octane definately is helpful. Your comment quoted Matt's quote, and he does have detonation issues at high RPM (and his issues diminish with more octane if I read him right). I would not run 87 in that case.

Matt, also do be sure your pump is not leaving you dry at high RPM (high demand). A dirty fuel filter or weak pump reveal themselves in that situation.

Sage, good call on getting those plats out. Annealed copper is much more conductive, but at the expense of greater wear (gap erosion) over time.
Good luck to all.

CManT1914 · Nov 6, 2005

Matt, have you tried 89 octane? It'd be kind of a compromise. What is your base timing at anyway? (didn't read the whole thread) Of course, the only REAL solution is to figure out why it's pinging and fix it, but I know that can be very elusive and frustrating.

wytstang · Nov 6, 2005

Pull the plugs out and see what they say, they willl tell you what's a matta wit jou......

DFG 5OH · Nov 6, 2005

i'll check the plugs today, i havent checked them since i got my car fixed. I put a full tank of 87 in last night, it does run better, havent checked if it still pings. My timing is suppost to be set at 8*. The previous owner really messed up the dizzy and timing, and me and a good mustang mechanic got the dizzy supposedly at the right place, and got the timing set right. He told me be tried the timing at 10*, but pinged REALLY bad in higher RPMS. 8* is a compermise i guess. I'll be dynoing Nov. 12th, and i'll post numbers, and charts, hopefully the wideband will tell me something.

ROLLIN5.0 · Nov 6, 2005

Why does everyone on here seem to accept the fact that their car is pinging ? If your car is pinging on 87 onctane fuel, there is something wrong with it, period. Either there is a component in your fuel delivery system that is malfunctioning, or your mods have gotten to the point that you need a bigger fuel delivery system, or a tune. Running a higher octane fuel to eliminate the problem is like straping a bandaid over the knub after your finger gets cut off. Find out why your car isn't running right. Secondly, detonation, or preignition will make your engine run hotter than it will when these conditions are not present, so you should have seen a decrease in temperature when you ran the higher octane fuel.

Brandon

DFG 5OH · Nov 6, 2005

I understand that Brandon, but there is so many different things that cause predetonation that its hard to track down. I'm going to yank a few plugs today, see how those look. I'm still stock, COULD be a fuel prob, but my pressure is fine.

HISSIN50 · Nov 6, 2005

Brandon, it would be nice if it was that simple. The stock GT tune leaves some to be desired (I think it was an attempt to clean up a dirty motor - that was one reason the 5.0 went away).

FWIW, there is a difference between detonation and pre-ignition.

Would Higher Octane Gas Make Your Car Slower?

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