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Don't waste your money on high-octane gas - Stefan Wilkinson explains

I just finished reading THE GOLD-PLATED PORSCHE by Stefan Wilkinson. It is a bit like ZEN AND THE ART OF MOTORCYCLE MAINTENANCE, but without the philosophy lesson. Anyhow, for guys like us, it is an absolute must-read. I not only identified completely with the narrator, I also learned an incredible amount about Porsches (and I didn't think it was possible)

Anyhow, Wilkinson goes on a rant that is possibly the best description I have seen on why buying 93-octane gas when your car is rated for 89 is a waste of money:

"Many drivers think that the higher the octane, the more powerful the gasoline: if your Honda Civic is sprightly while burning regular, it'll go like snot with a tankful of premium, right? Big mistake. And it's a mistake made frequently by people who fancy themselves hot-rodders. They prowl airports in search of 100-octane aviation fuel and swear that the avgas turns their small-block Chevys into race cars.

The truth is that the chemical compounds that raise gasoline's octane rating are added simply to delay the onset of detonation. They produce no extra power. If your car never pings with 87-octane in the tank, 93-octane super will do nothing but snatch an extra two dimes per gallone out of your purse."
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Old 08-28-2004, 08:02 PM
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blah blah blah..i knew that for years...you still feel a difference tho. Besides my car runs hot if i put 89 or 91 in it and it feels funny driving it. Notice how he didnt say if you were driving a Z06 and you arent supposed to put 93 in it. Cuse if you dont, then why do you buy a Z06? that car is made to run on 93 or higher because its a performance car. Any performance car needs premium. The line is where all those honda guys with their pep boys exhaust and APC intake and body kits THINK they have a race car....so in turn they think they need 93, which does nothing but make them slower...
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Old 08-28-2004, 09:26 PM
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when you run a 3.6 or 3.8 liter engine with a 12.5:1 or 13.0:1 compression ratio, thats when you'd need 100 octane...
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Old 08-28-2004, 10:11 PM
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Ok, so I'll put in regular in my 951 and just let the knock sensor take care of business, after all, isn't that what it's there for? NOT
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Old 08-29-2004, 05:43 AM
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so you disagree, then?
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Old 08-29-2004, 06:08 AM
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Quote:
Originally posted by CJFusco
so you disagree, then?

No, you are absolutely correct. If a car does not require premium fuel, using it will not add hp.

However, some newer cars will actually get slightly better gas mileage using premium fuel. This is due to the fact that the computer is constantly adjusting the timing. Many GM cars timing strategy is to advance it right to the point of detonation, then back it up a little......then advance...then back, premium fuel raises this limit a few degrees.

Some cars will benefit from premium, for example: My VW Passat with the 30 valve 2.8 V6.

I was running regular in it and it seemed to have a strange hesitation/surge at mid throttle.
Premium fuel cured this problem and it "feels" substantially more powerful throughout the rpm range. Did it add any additional hp? who knows, but it does run better.

In fact it made enough of a difference that the wife asked me what I did to her car!!!....
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Old 08-29-2004, 07:53 AM
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I wonder if my 75' mercury bobcat with it 2 L inline 4 cylinder power plant would of benefitted. ..........
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Old 08-29-2004, 08:33 AM
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For the vast majority of cars rated for "regular" unleaded; premium is a waste of money that may actually increase carbon deposits.

Most of the people I know who run premium do it because it makes them feel better, as opposed to making their cars run better.

My 944na does great on 87 octane. I made the mistake when I first bought it and assumed it needed premium. Zero difference in performane when I switched to 87 octane and a LOT cheaper to run.

GHEN
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Old 08-29-2004, 08:44 AM
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How come that people still seem to be confused by numbers. 90% of the people i talk to about cars all claim that cars go faster on high octane fuel. This is complete nonsense. Even people in small hatchbacks with medium tuned 1.6 or 2 litre engines claim to feel the improvements. It seems that 100 just MUST be better than 96 (which is the standard over here). When i try to explain what octane actually is, they try to find excuses about how extremly tuned their car is. Explaining things like '160hp from a 1.6l is a LOT, so i really need that 100 octane fuel'. When i then tell them a rally car will get 225-250hp out of 1.6l on pretty much stock fuel they somehow seem to avoid the discussion.

The things is, over here in Europe 96 super is the regular, cheapest fuel (1.50 dollar a litre). While 98 super has been the highest (1.65 dollar a litre), now Shell introduced the 100 octane 'v-power' (a lot a litre). Now that v-power is actually only in germany 100 octane, over here it's 98. The ADAC (a german road assist company) tested the 100-octane fuel on a whole range of cars and simply concluded that only the highly tuned cars (especially with the turbo's) could improve very slightly performance wise and that some more cars improved on mileage. Nothing new here... still people keep on putting 98 in their cars and the oil companies keep smiling.
Old 08-29-2004, 09:16 AM
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Okaaay- Higher octane fuel on a computer controlled car with a knock sensor does not make more hp- True. Now for the rest of the story. Using a lower octane fuel, especially in a turbo, can lead to some detonation, which the knock sensor reads and then signals the computer to retard the engine- ergo less power produced per combustion stroke. Now within certain limitations, higher octane does allow the engine to make its maximum possible power for the given set of mechanical parameters, ie compression ratio, cam timing, ignition timing. So, an engine is setup for a given octane, reducing that octane will cause the engine to make less power. Running at the octane the engine was designed for allows it the make the designed power output. If you seriously want to bump power, and the engine is set up for it, toluene is a great additive. The crap on the shelfs of the stores is just that- crap. When they say then will bump octane a point, understand that the bump is in tenths- right tenths. So you're looking at a change of say 87 to 87.1. Toluene is 114 octane and is the main ingredient in gasoline. By adding toluene in proportions and doing the math, you can significantly raise the octane level. Is it worth it in an na car? Probably not if the fuel you're running is at the designed octane for the engine. Pays your money and makes your choice.
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Old 08-29-2004, 09:50 AM
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Quote:
Originally posted by ae1969
I wonder if my 75' mercury bobcat with it 2 L inline 4 cylinder power plant would of benefitted. ..........

Oh, ABSOLUTELY............it would of been a real contender!!!

But, it still would of been green!!!!!!!!!!!...
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Old 08-29-2004, 09:52 AM
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Quote:
Originally posted by Wolf1

I was running regular in it and it seemed to have a strange hesitation/surge at mid throttle.
Premium fuel cured this problem and it "feels" substantially more powerful throughout the rpm range. Did it add any additional hp? who knows, but it does run better.

In fact it made enough of a difference that the wife asked me what I did to her car!!!....

BTW....this car does call for premium fuel.
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Old 08-29-2004, 09:55 AM
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The "truth" about premium fuel: If the manual calls for it, use it. If the manual doesn't call for it, don't use it. That's it. While a modern engine with a knock sensor may be able to adapt to lower octane fuel (knock sensors can only do so much, so even with a knock sensor your car can still knock and ping on a hut day under a heavy load if it calls for Premium and you use Regular), the knock sensor works by retarding timing and retarding timing lessens power. So if your car calls for Premium and you run regular, you will absolutely make less power than if you ran Premium. However, the converse is not true. If your car calls for regular and you run Premium, all you're doing is increasing carbon deposits.

Believe it or not, the '89 944 with the 2.7 litre engine calls for 91 Octane (R+M/2) in the manual. I know my 924S didn't, and I was surprised to find that the '89 944 did.

Aaron
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Old 08-29-2004, 11:11 AM
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So, how come, everybody in here agrees on the same simple facts a lot (as i pointed out in my case 90%) of people think that the higher the number the better. And why is it that the word 'octane' has so much of a 'racy' feel to it and for instance words like 'viscosity' or 'cetane' or whatever other word that is in essence just a specification of a product. I think octane has been regularly misused by stuff like games and movies. Maybe it's because race car engines run on high octane fuel to avoid the earlier discussed problems low-octane fuel might cause in high-performance applications. Or is it a marketing question? Or just a combination of all of it. Somehow 'octane' seems to make people think 'power' as the word 'porsche' somehow seems to do
Old 08-29-2004, 11:34 AM
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I think that a lot of it has been marketing. Instead of simply marketing gasoline by octane grade, stations have "Regular", "Extra", and "Premium" or some variation of that theme. The names lead people to believe that the "Premium" must be better in all instances.

Plus, there's also the general lack of automotive knowledge among the general public. People don't understand what Octane is and they see that more powerful cars use higher octane fuel. From that they incorrectly reason that Octane must be one of the reasons that those more powerful engines make more power.

At least, that's my theory on things.

Aaron
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Old 08-29-2004, 01:26 PM
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I second that and disagree with the author completely. I think Wilkinson is getting away from the point and is assuming that people get higher octane gas for power only.

I certainly do not. My car runs smoother and stumbles less on higher octane but is not "faster". I expect as much, and its the absolute truth - not simply a feeling that "jeez, I SWEAR it feels more powerful" as the afore-mentioned hot rodder types believe.
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Old 08-29-2004, 01:29 PM
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Probably... and that marketing theory is further supported by the fact that the german v-power was promoted with 100 octane and the dutch is promoted on cleaning additives and smoother engine performance. People in holland actually drive to germany ($$$) and tank the 100 octane version of the identical fuel ($$$$) in their simple hatchbacks and claim they gained power. How much better can it get for the Shell company. People use the fuel to get to the fuel and then pay more for it as well. EXCELLENT!
Old 08-29-2004, 01:30 PM
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I've got a fairly well modified Audi TT for a daily driver. Factory specs call for 91 or higher. Car runs "THE BEST" at 93. I tried using 104 once it ran awful. I am sure the carbon deposit issue comes into play eventually...
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Old 08-29-2004, 01:32 PM
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So what did you modify? Complete new head and camshaft on the 3.2 V6 engine... don't think so. Or is it just a matter of chipping the 1.8T 225hp engine up (in which case it is actually adviseable to drive a higher octane). I know a guy who runs the 1.8T with a simple chip giving him around 260hp and he runs on normal fuel. No problems of knock or anything, but on of his quattro driveshafts broke a few weeks ago... nice one
Old 08-29-2004, 01:39 PM
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_____________________________________

So what did you modify? Complete new head and camshaft on the 3.2 V6 engine... don't thinkso.

_____________________________________
Below is a list of my performance mods.

-K04 Turbo
-GIAC Chip
-Forge adjustable diverter valve
-Forge Intercoolers
-BMC TT Carbon Dynamic Airbox
-Exhaust manifold cast out of high-temperature nickel alloy
-Cast Aluminum Crossover Pipe and Turbo Inlet
-Cast Exhaust Downturn
-SAMCO hoses
-Upgraded plugs
-Upgraded injectors
-High flow fuel pump
-9lbs aluminum flywheel
-dual fiber street compound sprung center clutch disc
-heavy sprung pressure plate
-upgraded throw out bearing

The list goes on...and on. So, no I didn't just "chip it"
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Old 08-29-2004, 01:57 PM
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