raukous 07

High-octane fuel

LowRyter

safe but will give no performance upgrade unless you've been using inferior gas beforehand.

Dcasole

I agree ... what octane were u using ... if you were using 87 your car was pulling timing

raukous 07

ben dover

From 91 to 95, yes there will be a small gain. You don't have 93 available?

FatsWaller

I'm sure this next part won't be controversial at all, but the octane rating of a fuel relates only to it's ability to withstand pre-ignition caused by higher compression engines, not to it's energy content. Gasoline contains, on average, 32 MJ/L. Actual energy content varies, by up to 4%, from season to season and from batch to batch (copied this last part from appropedia.org.). As an example, the V6 in the caddy that I had a CR of 11.3:1 and ran (recommended) on 87 octane gas because it was direct-injected. Just as an experiment, on a long trip (to FL), I threw a few extra $$ into the tank by filling up with 93 octane, and I saw no difference in the reported instantaneous fuel economy as reported by the trip computer. I took care to use the cruise control at the same speed on long flat runs to see if there was any difference. Nada. In short, use the fuel recommended by the manufacturer, unless you've modified the engine.

Mike's LS3

Yes, it is safe to use, but on a stock motor unnecessary.

GM recommends premium gas for the C6 corvette, 91 or preferably 93 octane (especially a Z06 with 11:1 compression ratio).

On an unmodified car, if you experience knock retard (KR), which means timing is being pulled, then using a higher octane may reduce or illuminate it. With that said, there are other reasons why timing is being pulled, air intake temps are 86F*+, coolant temps are 212F*+, etc. But these are in place to protect the engine.

You can't hear KR, but sometimes feel KR, depending on how much timing is being pulled. With my stock tune, I could feel timing being pulled and verified it by data logging KR. In CA, our premium is 91 octane, I only wish we had 93 octane.

However, if there is an audible knock, then you should absolutely use a better grade of fuel.

Dano523

LS2 and LS-7 want 93 octane fuels. On the LS3, it's compression was lowered so it only needs 91 octane to run it best instead.

So on that note, if you can get 93 octane at the pumps, it's all that is needed for your best powder. If you can only get 91, then the 95 is the ticket isntead. The 100 octane (above 93) will be a waste on the stock LS-7 instead.

Also note, check the price of the 95 and 100, since you could do a quick ratio of it, and say the 91 if that is the highest octane they have at the stand pumps, to end up with a 93 octane rating (and not end up speeding a lot more for the octane rating over 93 that would be a waste isntead.


One last thing, and make sure that the higher octane fuel is not Avgas!!!!!
AVgas has lead in it, and it going to cause all kinds of problems with the cats if you try to run it in the car.

Hence Avgas 100, 130, 150 will have a green tint to it,
Avgas 100LL will have a blue tint to it,
Avgas 82 will have a purple tint to it, and if avgas 91/95 UL , will have an amber tint to it.
And again, all the above AVgas will be leaded fuels!!!!



And no, the tint used in Avgas is not like the heavy staining pink die used in non taxed farming diesel fuel to stain the lines and tanks; so they can tell if you have used not taxed farming diesel in a car/truck that is being used on the roads isntead.

Mike's LS3

JFYI

Compression ratios:

LS-7 11:1
LS-2 10.9 (10.87)
LS-3 10.7

For the LS3, GM used L92's piston which yielded 10.5 compression. GM removed the valve relief and compression went to 10.7. GM met their performance goal and felt is was not worth the cost to increase compression by using domed pistons.

raukous 07

jrose7004

Tp put 100 octane in it would be a waste of money.

Bruze

Yup, I've made that point here before, but urban myths die hard. Also, higher octane is needed for poorly designed, inefficient combustion chambers (even low compression) which can also cause pre-ignition (higher octane burns faster). Although in modern times, there probably aren't many poorly-designed chambers.

Mike's LS3

Sonoma raceway is 25 minutes from my house and has higher octane fuels, but yes very expensive. Adding a true octane booster to 91 octane, i.e. torco would be an option for low mileage driven cars. See which option is more cost effective.

Dcasole

Guys as Dano and others pointed out it has nothing to do with fuel economy and everything about keeping the engine from pulling timing thereby giving you the maximum performance that your engine was designed to deliver ....

Sure it will run on 87 ... with a ton of knock retard .... but it will sure run better on 93 ( LS2 ) and 91 (LS3) which it was designed to run with .

I did up my timing on my LS3 so I run 93

To the OP ... 91 is fine buying 95 at that price is crazy ... lol

Dave

Dano523

FYI, but if the pump is pumping race fuel instead of avgas, most of it has lead in it as well.

Kingtal0n

I've seen engines designed for 93 with carbon buildup and oil coking that needed 98 or 100 octane to run properly.

I've also seen an engine designed for 93 get too hot and start to knock, even with timing pulled.

So, there is a time and place for the higher octane fuel than what engine originally called for. If you are going to beat on the engine around a track I wouldn't be using 93 thats for sure. It just isn't worth the minute savings when the engine is so expensive and difficult to change.

Olsarge

Couldn't have said it better.

Kingtal0n

economy goes down as octane goes up.

best economy is using lowest octane

Welker1

After listening to all the 'experts' on this topic on this and other forums over the years, as well as other sources, I've come to one conclusion ... I will follow GM's advice as outlined in the Owner's Manual.

Bruze

Are we talking about fuel economy again on the Prius Corvette forum? Attachment 48332405

Yup, you can't go wrong doing that. Pretty sure the engineers have this all figured out.