Mike903L

This question appeared in another thread and kinda got lost/ignored. Not trying to take credit but, I thought I'd make it the topic of it's own thread, as I think it's kinda of an important question....

Like many other Californian's, I am on a list anxiously awaiting my turn to order my 2006 ZO6...

Unlike many others, however, I failed to notice that 93 octane is the recommended fuel for this engine... (I have not seen this information in print myself, but I believe it is accurrate)... Also, it has also been reported that Dave Hill strongly recommended a fuel of this octane rating for the ZO6.

The problem is the highest octane fuel readily available to the general motoring public here in California is 91 octane.....

Is this going to be a problem?

Scissors

You'll lose HP. The computer can adjust for the lower octane, but your engine will produce less power.

Mike903L

Does anyone know if there is a formula that will allow you to accurately compute how much of a HP loss can be expected???

racerns

I think the correct answer would be that you may lose HP. The octane rating is an average rating of the ability of the fuel to resist knock. There are many other factors in the combustion that have effect on knock like engine (head) temp, inlet air temp, and carbon build up. So depending on the conditions you may not see any knock with 91, but if you do then the computer will retard the timing a set amount. Taking a SWAG I would guess you could lose 10 -15 hp, depending but I am not sure how much retard GM has set for knock conditions. It is not a guarantee that you will lose hp with 91 just a possibility. My guess is that the compression ratio is high enough and the timing agressive enough, on the LS7, that if you want to ensure no knock (or retarded timing) under all conditions they recommend 93 octane gas.

hlv

Dave Hill recommended 93 for the C6 , he did not recommend you use
it on the Z06 , he said you must use it . I was there at BG when he said it.

LS6v

Not that it matters to me because we have 93+ here in PA. But they have to be retarded releasing an engine that MUST have 93 octane. If my area only had 91 I'd still run it, and if it throws a rod or just generally screws things up I guess it's GM's problem.

I just find the 93 hard to believe when engines that make over 850HP can run on less than 93 or 91. I'm talking about Mercurys new 850Sci racing engines that'll make 700HP on regular gas. So the LS7 must be tweaked a bit to much if it can't pull the timing enough to safely run on anything less than 93.

Mike903L

Thanks for jumping in with that information!! Doesn't sound too good for us California drivers.....

vetteship

If 93 is a must, then what are we going to do in California and other states with 91 octane as the highest, GM... what the heck

lateapex

I agree that 93 octane is desirable (probably necessary) if you will be driving hard. But I don't think it should be. Saleen’s S7 twin turbo is rated at 750 hp, has an 11:1 compression ratio (before 5.5 psi of turbo boost), and requires only 91 octane per their web site.

On the LS7, when the engine is cool, there would probably not be any significant knock even under maximum load. Once the engine is at normal operating temp, or more elevated than normal, you would probably see some timing retardation at WOT. Timing retard is not a fixed amount. The computer always monitors knock counts. If it sees so many knock signals in a certain period of time, it will take out so much timing. When it calculates that the knock count is back under that threshold, it will restore timing.

There are many complications to this simple explanation which I won’t go into, but here are a few. If it sees a very high number of counts, it can pull significant timing; 10-12 degrees was common on LT1’s. It can restore only some of the timing. Some GM ECM’s will not restore full timing until the gas tank has gotten below a certain level and then been refilled. It assumes that you got a tank of bad gas, or filled it with a lower than recommended octane.

The pulling of timing is not always a smooth, linear occurrence. It is very abrupt, and if it happens frequently or if the computer pulls a large # of degrees, the engine can feel very rough. One 5 degree episode usually just feels like a slight flat spot. When I observed knock retard on the dyno, it usually cost me about 10-15 rwhp, with a ragged looking curve. I found that in road racing in the summer, with water temp around 220*, I had to use 100 octane to maintain full engine power.

racerns

I too have a hard time believing that 93 is a must to run the LS7. My 396 LT-4 has a compression ratio 11.6:1 and makes about 500hp. I have run it on 92 plenty of times and a few on 91 without any problem. I have had no problems open tracking it on 93, though I do have a big radiator that keep my engine temps down on track.

shaky

Highest octane I have seen at the pump in Alberta is 91. My 02 Z knocks with 91 so I'm thinking the 06 Z will have knocking issuses as well especially if you have to run less than 93.

Michael A

I think this is a classic example of why Hill and crew need to get out a Michigan once in a while, and see how the other half lives. That's why we don't have a good front license plate mounting either (Michigan has no front plate). So. Cal. has to be one of their biggest markets. There are Corvettes on almost every street corner here. I saw five just on my way to Lowe's Sunday. It's time they come out, and check things out.

By the way, the Saleen runs on 91, because their operation is in So. Cal., and that's all we have for premium.

Michael

Mike903L

May have found the answer to my own question re: the LS7 fuel requirement...

Was searching for LS7 engine specs and came across a web site "crateenginedepot.com and it stated the fuel reuirements as follows:
"Premium required. 91 octane minimum..."

Michael A

I question the accuracy of their information. On the Corvette Museum website, it says "Recommended Fuel: 93 octane" for the Z06. For the LS2, it says "93 octane (recommended but not required)." Check it out at Corvette Museum Z06 .

Michael

Z11409

When Chevron was tested couple months ago it turned out to be 91.9 octane.Have no idea what other brands are in the real world.Normal stop and go city driving should be no problemo but for track use we will blend in some 100 unleaded.

Michael A

That's going to vary with each batch of gas. The county tested Chevron Supreme, a few months ago, and it was lower than that, but still just above 91.

Michael

dollarbill

I was just in Europe and found their premium was 98 at all stations and even found one with 100. Solution to the problem could be to ship 'em all to Europe. LOL

SWCDuke

Europe uses RON, which is 4-5 points higher than our PON. So where does that get you?

GM has quoted the Z06 octane requirement as "91 octane, minimum", and "93 octane". In both cases they are referring to the commonly used in the US PON, not RON, MON, AON, PN, or any other measurement method.

Depending on ambient temperature, pressure, humidity, engine coolant temperature, manifold vacuum, and other variables in the detonation equation, 91 PON may force a little spark retard to prevent detonation. The loss of power will likely not be noticeable.

And it only took seventeen posts to get here.

Duke

Kelly100

I would worry more about them adding more ethanol to the gas than 91 octane. I don't know how much the hoses etc can more ethanol. Just a thought. In CA, they will be adding more ethanol

SWCDuke

Fuel system elastomers have been designed for up to 10 percent volume ethanol for the last 20+ years.

No, the sky is not falling!

Does anyone REALLY think that GM (or any other major manufacturer) would build a car that won't operate satisfactorily from both a performance and reliability standpoint in California, which is 30 percent of the US car market?

Well, okay, if you really believe that you better add another layer of aluminum foil under your hat!

Duke