Recommended Octane for V6?

[Jazzzed]

Originally Posted by sspade

Question...

I recently moved to California and only have access to 91 now. As afar as I know, I'm running Will's 93 tune... I emailed him to see what he thought about revising it to 91 but haven't heard back...

What are your guys thoughts?

Will's high octane tune is for 91+, so you're fine.

And I would keep your old plates on the car as some members have mentioned. You're not going to pass their inspection without putting all the stock parts back on.

[rbenotti]

Originally Posted by ChibiBlackSheep

Any increase in octane will help fight knock, and these things knock like crazy on a stock tune. If you are going to do anything besides regular, I highly recommend the highest octane you can purchase, but really any increase you can pay for will be beneficial to the engine. Whether you feel it or not is a different story, but taking some knock away is good.



The 323 power numbers come from the engine sitting in a room with sensors hooked up to it. Yes they are usually running the high octane through it, as the car's computer has a high octane and low octane fueling/timing table. The car makes less power in high RPMs on low octane. The biggest reason is the amount of timing pulled, and also with how much knock the engine has which reduces the timing even further.

Also remember, the 323 number is above 6000RPM. So unless you spend a lot of time above that, you probably won't feel the difference in day-to-day driving. You just have to trust and realize that the extra money spent is good for the engine, because you aren't forcing detonations to adjust the timing, you are letting the engine just run.

Good info. Thanks for the explanation. Kind of what I was thinking. Not used to a vehicle having two timing tables. I wonder which octanes it's actually set to.

I don't hear knock, but that just means I don't hear it. Going to keep this in mind.

Thanks.

[sspade]

Originally Posted by Jazzzed

Will's high octane tune is for 91+, so you're fine.

And I would keep your old plates on the car as some members have mentioned. You're not going to pass their inspection without putting all the stock parts back on.

Your kidding me?

I don't have all of my stock parts.

[sspade]

Actually. I don't have ANY of my stock parts.

[Dragonman]

Might want to consider leaving dear old Commiefornia.

[KenKat]

Well, now I am going to have to run a few tanks of 93 through. Need to fill up tonight after work; current tank of 87 I got 19.6 mpg, avg. speed around 31mph. I will run a few tanks of premium and see if anything changes in mileage or feel of car.

[ChibiBlackSheep]

Originally Posted by rbenotti

Good info. Thanks for the explanation. Kind of what I was thinking. Not used to a vehicle having two timing tables. I wonder which octanes it's actually set to.

It defaults to the high octane table, when the car detects knock it pulls timing. If the car is still knocking, it drops to the low octane table. If it's STILL knocking, then it pulls even more timing. Then the car's computer remembers values, and fuel trims, and stores those for future use.

When it runs knock free for a while, it will try to push timing again, and if it knocks it stops. So when you switch from low to high octane, pull the battery for an hour to reset that, or just run it with high octane for a while until the car takes the time to relearn everything.

Originally Posted by sspade

Actually. I don't have ANY of my stock parts.

Originally Posted by Dragonman

Might want to consider leaving dear old Commiefornia.

Or just sell the car in 7 years. CA sucks for any modifications. My buddy who lives out there deals with all of this crap with his Corvette and Impala. He can't even buy a CAI because none of them are CARB certified. Companies won't even SHIP him parts because they aren't certified for use in CA. It really stinks to live out there and be a car guy.

[Dragonman]

Originally Posted by ChibiBlackSheep

Or just sell the car in 7 years. CA sucks for any modifications. My buddy who lives out there deals with all of this crap with his Corvette and Impala. He can't even buy a CAI because none of them are CARB certified. Companies won't even SHIP him parts because they aren't certified for use in CA. It really stinks to live out there and be a car guy.

What really makes it a punch in the groin is how California used to be the hot rod mecca of the world, but that was 30-40 years ago. Riverside International, drag strips everywhere, dirt tracks everywhere. Can't say, after living there about 13 years, as a child and adult, I was even remotely sorry to leave and never return. If you weren't into cars, bikes, dune buggies or other vehicular entertainment there was always a day where, if you wanted to really hustle, you could go snow skiing, hit magic mountain and/or disneyland and close the day with some surfing. That'd be one helluva day but I think I can live without it and mod my car as I see fit. Not to mention an easier time of exercising my 2nd amendment rights.

[rich42550]

Hi Guys/Girls,
Great discussion on fuels. I'm a little new to the game and am old school for sure. In the 1960's all those big block Chevy's and others "HAD" to run premium fuel. From the factory they would push anywhere from 325HP to around 435HP. I went through alot of premium fuel. In my 2011 2Lt/RS Camaro that's rated at 312 HP I'm able to run regular gas. From my point of view it was one of the reasons I went with the V6 and NOT the V8. I run ONLY Mobil 87 octane and have never heard a knock or a ping as we used to call it. Thoughts, comments?

[ChibiBlackSheep]

Originally Posted by rich42550

I run ONLY Mobil 87 octane and have never heard a knock or a ping as we used to call it. Thoughts, comments?

Just read through the thread again. This is the argument, and we are showing the very reasons why these engines still need premium. You don't HAVE to do it, but the data is at least there for you to make an informed decision on the matter.

[Dragonman]

Originally Posted by rich42550

Hi Guys/Girls,
Great discussion on fuels. I'm a little new to the game and am old school for sure. In the 1960's all those big block Chevy's and others "HAD" to run premium fuel. From the factory they would push anywhere from 325HP to around 435HP. I went through alot of premium fuel. In my 2011 2Lt/RS Camaro that's rated at 312 HP I'm able to run regular gas. From my point of view it was one of the reasons I went with the V6 and NOT the V8. I run ONLY Mobil 87 octane and have never heard a knock or a ping as we used to call it. Thoughts, comments?

You don't hear knock because the timing is being retarded to prevent it. Premium fuel is generally used for high compression engines, no matter their size or horsepower.

I've been running 93 since Jun 30 and while I'll have to look at my previous data to be absolutely certain, it appears I'm getting about 3MPG more than I was with 87. Think I'm on my 4th tank of 93. It needs way less pedal to get going and runs much stronger with the AC running.

The more I run 93 the more convinced I am to keep running it, even though it's a bit more expensive and I'm not sure the increased mileage will counter the expense. The car runs better when it's drinkin' the good stuff.

[rbenotti]

Originally Posted by Dragonman

You don't hear knock because the timing is being retarded to prevent it. Premium fuel is generally used for high compression engines, no matter their size or horsepower.

I've been running 93 since Jun 30 and while I'll have to look at my previous data to be absolutely certain, it appears I'm getting about 3MPG more than I was with 87. Think I'm on my 4th tank of 93. It needs way less pedal to get going and runs much stronger with the AC running.

The more I run 93 the more convinced I am to keep running it, even though it's a bit more expensive and I'm not sure the increased mileage will counter the expense. The car runs better when it's drinkin' the good stuff.

If the timing is being retarded to reduce knock, then doesn't that mean engine any damage is mitigated?

The more I read about it, the more I myself go back and forth. It boils down to the cost difference. It's about $6 a tank or more.

Now - IF I got 3 mpg more, the cost per mile is almost a wash (1 penny per mile higher).

I track my mileage, so this could be a real world experiment. Taking into account it's really the previous fill-up.

[Dragonman]

Originally Posted by rbenotti

If the timing is being retarded to reduce knock, then doesn't that mean engine any damage is mitigated?

Certainly.

While I'm not gonna pretend to know what's an optimal detonation point in the compression stage, I imagine it's at that point where the ratio achieves its designed 11.5:1, I do know that's what adjusting the timing does. Not sure if the LFX has variable valve timing or not but if the intake valves open to soon or remain open to long can also contribute to "knock", which is detonation of fuel/air outside the point it's supposed to be exploding and is not good for the motor. Pistons and valves are in the wrong place when it happens. The lower the octane rating of a fuel usually means it can be fired simply by compressing the mix, think diesel engines, the higher it is requires external stimuli to achieve explosion.

So, the car is designed to give it's full power within a single cylinder with a air fuel mix containing 93 octane when the piston has compressed it all to that 11.5:1 ratio. Putting 87 in it causes pockets of the A/F mix to detonate before or after the ratio is reached. When the computer senses it happening it adjusts the timing which will change the compression ratio the A/F mix gets to when fired. Either before, at or after the piston reaches top dead center (TDC). I don't know which way it adjusts but I'm sure someone here can tell us.

In my experience, however limited, retarding timing makes the engine output less power while advancing the timing has the opposite effect, up to a certain point. If the timing is advanced to far the spark will not hit the A/F mix during any amount of ignitable compression and the car won't run.

Just thinking about it, I wouldn't think you'd want the explosion to hit while the piston is traveling up. TDC probably isn't really all that good for the rods or crank either, but, it can't be very far past TDC on the down stroke or you lose the compression ratio needed.

Alright, I've probably rambled ignorantly on long enough.

Still about 4 1/2 months away from the end of my 6 month 93 octane study.

[CamaroFred]

Advancing the timing does mean beginning the burn before TDC. So by the time the piston is passing TDC the majority of fuel is burning.

It isn't as if all the fuel explodes in an instant. One of the most important aspects in engine design is the burn pattern. Air and fuel are still being introduced to the chamber when ignition begins and the way it swirls determines the rate and efficiency of the burn. Higher octanes burn slower and thus ignition can begin earlier. This allows more of the fuel to burn, thus increasing power and MPGs.

Anyway, with direct injection, the computer controls when and how much fuel is introduced along with the spark timing. Thus detonation can be avoided by delaying the introduction of fuel. But this means there is less time to add fuel and still expect it to burn effectively. Resulting in lower power and lower MPGs.

The main way to control the burn and the way the air/fuel moves involves the shape and length of the intake and exhaust ports, the placement and size of the valves, the rate and height and time at which valves open and close, the size and shape of the combustion chamber, etc.

And that is a simple explanation

As you can see, it is quite involved and it used to be all trial and error. With the advent of super computers and dynamic equations much of the guess work can be avoided, but it still comes down to building and testing, tweaking, repeating.

Of course, cost and reliability are always factors affecting the final product. There comes a point of return on investment. The masses do not want to spend another $1,000 on a car for 0.1 more MPG or 1 more HP.