V6 and Premium fuel?

[mc_acoustic]

Originally Posted by TooCool5

We get one of these threads every few months... wow

So do you have an answer? If you don't then that explains why its asked every couple of monthes right?

[two_wheel_mayhem]

They should just do a mythbusters episode on this subject and settle it once and for all.

Of course it would come up 'plausible' anyway.

I can tell ya I've even seen this argument on motorcycle boards.

[Baba]

Originally Posted by ernie scar

I am not trying to be negative or rude. I am just trying to be helpful.

If you’re not driving your car because of storage. Make sure you throw some fuel stabilizer in the tank. It won’t matter what octane the gas has if it’s not treated it will break down over time and make the engine run like S#!T.

If you are only filling up the car a couple times during the driving season it wouldn’t hurt to throw a can in the gas tank with each fill. I have been doing this for years with seasonal drivers and have had no issues. Stabilizer is cheap engine repair is expensive.

No offense taken in the least.

I did start her up 2x week for ~15 minutes and ran her around the block once a week when the roads were dry. She has actually only been "sitting" for 6 weeks while I was recovering from foot surgery (left foot, manual trans.), but, she's also not a DD. Strictly only on Fridays to work during Spring, Summer, early Fall, weekends and holidays.

Good advice, however.

[tonyko1]

Here's something to ponder: The "fuse-pull" debate on V8's........the spiel goes that if you have run 87 octane the computer adjusts downward for the 87, but can't adjust back up for the premium fuel, hence the fuse pull reset. Many swear this works, an electrical engineer on another thread showed it couldn't possibly work by the schematic routings, but who knows. I tried it and didn't notice anything, but that's just me.

Here is the question: if you have been running 91 octane for a long-time, say after you did a fuse pull, then you find a place that sells 93 octane, is a fuse pull then required again for the 93 advantage to take effect?

[jrisebo]

I add about a gallon of water to my tank, bring that octane rating down, still doenst effect my performance.

[buckeyemike]

Unless it's tuned for 93, stop wasting your money.

There's really no arguing this.

[GretchenGotGrowl]

Originally Posted by buckeyemike

Unless it's tuned for 93, stop wasting your money.

There's really no arguing this.

He has the LLT, not the LFX. Totally different ECU. It doesn't have separate fuel/timing tables. It advances timing until it detects knock then backs off a few degrees. So, if 93 octane allows for more timing before knock is detected, it will have the same affect/benefit as TUNING for 93 octane. Your car, on the otherhand, does have different timing tables and has about 4-6 degrees of KR programmed in it. YOUR car will not benefit from 93 octane without a tune.

[MBS]

Originally Posted by jrisebo

I add about a gallon of water to my tank, bring that octane rating down, still doenst effect my performance.

You add water to your fuel tank ????? I am thinking that is a very bad ideal.

[MBS]

Originally Posted by two_wheel_mayhem

The reason the engine is designed to run 87 octane with 11.3:1 is because it is a direct injected engine, which changes things. You guys always want to argue with the engineers that design things, thinking you know better. It could handle 13.5:1 easily if GM engineers intended for it to be run on 93 octane fuel, which would probably move it's peak power up to around 350 horsepower. They could also let it turn a few more thousand RPM's with great benefit, but that's another story and is political....warranties. Anyway, the 3.6 runs at maximum performance with the designed fuel. The engineers did not crutch the timing tables just so they could say it runs on 87 octane, that would cause poor economy and emissions.

There's more to it than "this compression ratio requires this octane fuel." That only works when you are talking about a typical pushrod V8 engine with flat top pistons and wedge shaped chambers. Other factors include cylinder head/piston design and material used, bore size, altitude, engine temperature, engine tolerances (specifically piston to cylinder wall clearance), vehicle weight, and gearing.

As far as fuel additives they are all worthless no matter what vehicle you have, at best they boost your octane. If your fuel system gets gummed up no magic in a bottle will fix that. Fuel injection can sit for years and fire right back up like it was yesterday.

You had me till the last paragraph , Saying fuel additives are worthless is wrong, GM recommends only top-tier gasoline which has more additives than the other stations sell ,

[SC2150]

He is pretty correct on the additives as far as DI engines, but there are advantages to say stabil types for storage.

The reason a DI engine can run a higher CR w/out as much detonation danger is the fuel mixture on a port inj or carbed car is drawn into the combustion chamber on the intake stroke and through the entire compression stroke, so a glowing piece of carbon deposit can easily detonate prematurely. On a DI engine, the fuel is injected directly into the combustion chamber at 2-3000 PSI in the final 20% or so of the compression stroke so it is in the combustion chamber for milleseconds. That is why these will run fine on 87 octaine at that CR, and watch, I expect to see above 12:1 in the future. DI allows more power, better fuel economy out of smaller dispalcement....but that does not take away from the fact that it WILL run better, make more power, etc. on 93. We have seen this dozens and dozens of times on the dyno. We find some buy the VMax CNC patteren ported TB and see poor power....ask and find the owner has 87 in it. Run the 87 out and fill w/93 and see 8-15 rwhp more and far better response.

So no mythbusters needed. It is a personal choice.....they run fine on 87, just not as efficient as on 93.

[rtcat600man]

Originally Posted by SC2150

He is pretty correct on the additives as far as DI engines, but there are advantages to say stabil types for storage.

The reason a DI engine can run a higher CR w/out as much detonation danger is the fuel mixture on a port inj or carbed car is drawn into the combustion chamber on the intake stroke and through the entire compression stroke, so a glowing piece of carbon deposit can easily detonate prematurely. On a DI engine, the fuel is injected directly into the combustion chamber at 2-3000 PSI in the final 20% or so of the compression stroke so it is in the combustion chamber for milleseconds. That is why these will run fine on 87 octaine at that CR, and watch, I expect to see above 12:1 in the future. DI allows more power, better fuel economy out of smaller dispalcement....but that does not take away from the fact that it WILL run better, make more power, etc. on 93. We have seen this dozens and dozens of times on the dyno. We find some buy the VMax CNC patteren ported TB and see poor power....ask and find the owner has 87 in it. Run the 87 out and fill w/93 and see 8-15 rwhp more and far better response.

So no mythbusters needed. It is a personal choice.....they run fine on 87, just not as efficient as on 93.

I always like reading your GREAT explanations Tracy.....

Those who THINK they know will NEVER believe.......

Those of US who have run and seen the differance BELIEVE......

[911medic]

Originally Posted by GretchenGotGrowl

He has the LLT, not the LFX. Totally different ECU. It doesn't have separate fuel/timing tables. It advances timing until it detects knock then backs off a few degrees. So, if 93 octane allows for more timing before knock is detected, it will have the same affect/benefit as TUNING for 93 octane. Your car, on the otherhand, does have different timing tables and has about 4-6 degrees of KR programmed in it. YOUR car will not benefit from 93 octane without a tune.

Can you explain this a bit more, or point me to a discussion regarding the LFX/LLT differences that make using 93 in the LFX (w/o a tune) worthless?

I'm not questioning the truth of your post, I just want to know more and understand.

[SC2150]

The LLT with the Bosch ECU is constantly adjusting timing where as the V8's and the LFX with the Delphi PCM have 2 timing tables that dictate max advance timing so unless the high octaine table is tuned to make use of the 93, you wont see much power improvement like w/the LLT unless of course it is in the low octaine table.

These tables as Gretchen states, are preset from the factory. You will still see some benifit, but not nearly what the LLT will.

Biggest issue for either is the intake valve coking that degrades the volumetric efficiency on all DI engines if not prevented with a good catchcan.

[911medic]

OK. So, for us LFX'ers:

• slight benefit from higher octane fuel
• two separate timing tables instead of multiple, on-the-fly adjustments
• need a tune to access the higher timing table

That about sum it up?

Can I assume that we aren't so lucky (as the V8 crowd) to be able to do some kind of fuse pull to reset the table to the higher octane one?

BTW, my used catch can & breather just arrived today. Gonna try to get them cleaned up and installed in the next few days.