My daughter is a car nut and is close friends with an Exxon-Mobil petroleum engineer.
She and he swear that the difference in pump available 87 and 93 is so negligible that it is a waste of money to use the 93. I find it hard to believe, but they both stick to their guns. She has been using 87 in her stock performance cars for years with success.
So, just for S---s and Giggles , I gave the 87 a try with two tanks. No detonation knock, no difference at start and idle, no lights or codes, no difference in fuel mileage and no noticeable SOP or performance difference even with the Blackwing and catback in everyday use. I don't race the Vette.

So, I'm puzzled. I really don't worry about price or I wouldn't be driving Vettes, but yet don't like to burn money. I went back to 93, but again there is no,nada, zero discernible difference.

So, anyone have experience with this?
Dave

 

I use 87 too. No problems.

 

This subject comes up often and always generates a heated debate.

The owners Manual actually says:

“Fuel - Gasoline Octane

Use premium unleaded gasoline with a posted octane of 91 or higher for best performance. You may also use middle grade or regular unleaded gasoline rated at 87 octane or higher, but your vehicle’s acceleration may be slightly reduced. If the octane is less than 87, you may get a heavy knocking noise when you drive. If it is bad enough, it can damage your engine.”

E-T, who was involved in the design of the C5, will post long explanations of why the high compression of the LS1 (the LS1 has 10.1:1 compression ratio and the LS6 10.5:1) needs good gas. His advice is 91 minimum and 93 if you can get it. It has a knock sensor which automatically retards the ignition if it senses knock. If its doing that, by definition you have less power and lower fuel efficiency.

In my book, although the knock sensor may protect the engine to a certain degree, it’s still a compensatory adjustment. In other words it’s solving the problem after the event so some damage could occur however slight.

For a couple of cents a gallon, I wouldn't take the chance. JMHO

In UK Regular gas is 95 octane (RON) which equates to 91 octane in the US. The Super Unleaded is 98 octane which is about 93/94. I use the Super when I can get it but not all gas stations sell it here. And BTW, I pay way more for gas over US prices ($9+) so its even more of a decision to buy higher octane.

 

http://forums.corvetteforum.com/c5-g...as-debate.html

 

I have an 04 and an 80 and I never use hight test , if you are hard on the car I get a bit of "ping" other wise regular is fine , but I know friends of mine would never ,ever put in 87 oct. Ron

 

Just in case you don't have an owner's manual for you car - here is a link to a copy.

http://www.corvetteactioncenter.com/specs/c5/2001 2001corvette.pdf



You can use lower octane than the recommended, but the vehicle is tuned for a minimum of 91 octane. The engine has two knock sensors that are always listening for knock (or pre-detonation). If knock is "heard", the timing will be retarded. You may not notice the performance degradation based on the way you drive - but over the long term, knock is not a good thing. Also, besides the degradation of performance, you will also get a degradation of fuel mileage because of the retarded timing.

Hey - it's your car. Do with it as you see fit. My take is that the car was engineered for the higher octane by the Corvette engineers. Plus my car has been dyno-tuned for maximum performance on 91 octane. For the extra twenty cents per gallon - I'll splurge and get keep my engine running happy.

 

pay me now or pay me later.

if you can afford to own a corvette, you should be able to afford the fuel it needs.

 

I only use 93. For an extra buck or two it makes me feel better.

 

If I use 87 in mine it pings so I'll use 91 (that's all we can get here).

 

much have answered my query.
2. I can easily afford to pay whatever 93 costs; $3-4-5-6-7 + , but was curious as to why a highly placed petro engineer on the inside is so adamant that the octane diff is really nominal. He simply says, "he knows what he Knows," but does not want to be identified. I respect that.

3. The point that the annualized cost difference between 87 and 93 is very little is also certainly valid.

4. I do know that my '71 coupe 350/350 with 10.5:1 CR will knock like crazy on anything less than 93 and the former Sunoco 260 no matter what I do with the timing. When it was on the market, I always ran 260 to get it to idle and run decently. Since then I use 93 with a little octane booster per tank. Car only has 37K on it. Bought it for $6300 with 6,900K on it. Was a GM exec car. I would add that the C5 is much faster than the C3 even with A4 and 2.73 vs. M4. Probably a function of much refinement between the years or maybe a change in the way HP is calculated????
Dave

Again, most points have now been covered. Did not mean to to start anything. Just the source of the info made me curious.

Dave

 

Never put in less also run no E in it also get the gas at Sunoco...

 

Around here the price difference is about 20 cents per gallon, I seldom let it go lower than 1/4 full and usually put in about 14 gallons. An extra $2.80 to fill it up. About 5 bucks a month, I think I can afford that. When it gets to the point that 5 bucks is going to cause me to miss a meal I'll consider a different car.

Or miss the meal, I could use less of those anyway!

 

During the Powertrain class I took. The engineers indicated that if the manual reads required the engine requires that octane or higher. If the manual reads recommended the engine will perform best on the octane suggested but has programming in the computer to retard timing to reduce the likelyhood of pre-detonation on a lower octane.

IMHO if you're hot rodding your engine, spend the extra money and get the higher octane for best performance. I run the highest octane available unless it is a gas station that is in the middle of nowhere. In that case, I'll use 87 because the turn over at the station will be higher with the 87 and that gas is not stale.

 

The first gallon is regular grade to start with anyway. It's those one hose multi grade pumps that cheat you every time you select premium and have to use all the regular gas in the hose and pump machinery before you get the actual higher octane gas.

 

The GM engineers also call for.....Mobil1 5W30. But you can use dino oil if you choose. Its your call. Its a Corvette, not a Fiat.

 

The pump is the least of it. The refineries don't use separate pipelines for the different octanes but averaged out over the volume pumped, the fuel does have some differences.

 

The octane differences become much more apparent when you're running force induction. On the Porsche Turbo I had before the C5Z, you could feel a significant power difference when on boost due to knock retard. Car would ping a lot and my knock counter would go crazy.

Can't believe a petroleum engineer would claim there's no difference.

 

All I have ever used and like the peace of mind

 

One reason they may say there is little difference is if you have ethanol in your fuel. The posted octane levels are the minimum levels that garde can have and that's what by law is posted. Not the actual octane level in the fuel.

here our 87 posted octane is actually closer to 90 than it is 87. Many places here even sell the two levels the same price because they are the same fuel, while other places, (yes I'll come out and say it) attempt to gouge us as they pay the same price for the two.

I can only think of one or two places that even have 93 octane here. but as I stated, what they post by law, and what the octane level actually is are two different things.

I use 91 in my vette, but I wouldn't hesitate to use midgrade/89, because I know it's higher than 89. With fuel prices the way the are I may start using midgrade though.

I will close by saying the manual states you have to use at least 87. anyone else notice the book also referred to "posted" octane levels?

Oh, I switch back and forth between midgrade and premium in my STS Northstar all the time, and I actually get better mileage with midgrade because with fuel prices the way they are not many people are using premium and it starts going bad before it's bought. something else to consider folks.

 

Your 71 has 7 million miles on it??