[N0DIH]

Has anyone done any power or fuel economy evaluation on running higher octane vs lower? As the LT1 was designed to run on 87, was it factory lowered timing to keep it from pinging? Does it bring timing up when higher octane is introduced?

I put in Shell Vpower (they claim to have better mpg than others) today, and initial impressions are that it runs a slightly better. But in this cold of weather, it might be just that too.

 

[Katshot]

You might start a long "discussion" here. In the past, long threads got formed when people started posting their opinons about octane.
My experienece has been that the LT1 runs fine on an actual quality grade of regular. I say it this way because IMO, not all fuels are the same. You can fill up at several different stations, making sure to select the same advertised octane fuel yet end up with the car reacting differently to some of them. Why? If they are the same octane, why would the car run differently?
I'm told it's due to a couple different factors:
1. Even if the fuels ARE the same octane, the additives can have an effect on the overall performance of the fuel in a given car.
2. Quite often, even though a station might "advertise" a specific octane, that may not be exactly what comes out the pump on any given day.

My way of dealing with these issues is to find a brand of fuel that seems to satisfy my particular vehicle (some engines seem to be more picky than others), and overall, I tend to run one grade higher than is called for by the vehicle OEM. I do this to give me a buffer against dishonest station owners that skimp on the fuel they sell.
In my FTS, prior to doing any re-tuning of the timing tables in the PCM, I found that occassionally the PCM could be found to be pulling timing on certain low octane fuels. After I started "playing" with my car and doing mods, I started running preium fuel only and found that I could push my timing a bit. Right now, I think I'm sitting at a 4 degree increase across the board but I'd have to check my laptop to be sure (I keep a log of my changes), and I still have no knock retard evident. SO I know I can still push it more, I just haven't gotten around to it yet.

 

[JAKE91]

Nothing Less Than 93 Octane

I AM ON MY FOURTH 5.7,IN VARIOUS CARS, AND THE ONLY GAS THAT THEY RAN PROPERLY WITH WAS 93 OR 94 OCTANE.:alchi:

BETTER STARTS IN THE WINTER TOO. THE HIGHER DETERGENT LEVEL IN 93 IS USEFUL FOR THE FUEL INJECTORS..

TWICE A YEAR I WILL FILL UP FROM ALMOST EMPTY AND ADD A PINT OF 108 OCTANE(RACING FUEL) BOOST. YOU REALLY TELL THE DIFFERENCE IN PERFORMANCE FOR THAT TANKFULL.:bouncy:

 

[ShadowLvr400]

These days I have to run premium, have aftermarket programming that bumps the need up some.

 

[BCs71]

As Katshot stated, there are long threads on the LT1 engine needs for octane on other boards. It turns ugly usually with a lot of angry people.

My thoughts are that the LT1 was so great not only because of its power, fuel economy, and good emissions. The best part was that it was DESIGNED to do all of the above on 87 octane. This is what your car should be running on unless you messed with the PCM and bumped timing a bit to make more power with higher octane.

If your PCM is running the stock program, then putting in higher octane will give zero gain since the PCM is dumb to any changes in fuel you just made. The extra money in higher octane will kinda be thrown away.
Katshot however makes a good point that some station owners may 'fudge' their gas quality and octane which could result in poor performance. Buyer beware...

If your car has many miles and is running poorly, as in excessive carbon build-up, then you can experience timing changes by the PCM which takes some timing to prevent detonation. If you run 89 or 93 octane and the car drives noticeably better (gains back some timing), then with an LT1 engine you are kinda only putting "band-aid" on the problem. It's time to figure out the real problem and fix it, and then run 87 octane again.

That said, I do run 89 octane in my Fleetwood. I have a different PCM tune however for performance and I'm trying to get some more power with a little timing. I opted to forgo the 93 octane tune in order to save money at the pump. I also have some software and a laptop that I can hook up to my vehicle to monitor vehicle performance and condition, however.

In my LT1 96 Caprice (stock) I run 87 octane with no issues at all. I have the stock PCM tune and don't want the compromise for extra power at the expense of price at the pump since this is my daily driver.

My Two cents

Katshot said it pretty well. "My experienece has been that the LT1 runs fine on an actual quality grade of regular."

 

[Katshot]

I think there IS one thing that most people forget about. Octane is NOT the only difference between the "Regular", "Plus" and "Premium" fuels out there. Although octane gets the nod quite often as the "Power-Maker", there are other points to ponder here. The fuel suppliers also put a better additive package in their pricier fuels. These additives can also aid in faster cold starts, cleaner fuel systems, and a general feeling of crisper performance. Even though the PCM will not be adjusting timing due to the knock sensor if there's no knock present, it IS adjusting for other things that move your BLMs around and can effect the way the engine will react to throttle input at any given time.
Bottom line, OCTANE is not the only reason you might want to buy premium fuel.

 

[I~LUV~Caddys8792]

I ran 87 octane in my LT1 Roadmaster, It ran great

 

[N0DIH]

My primary reason right now, is to validate the claims of better fuel economy (through cleaning deposits). But initially it does seem to run good, nice crisp throttle. Can't say it is in there long enough to clean anything yet. Heck, could be the pstop hp increase. (psycological seat of the pants)

After talking to my local station where I consistently buy fuel, they said there is 3 grades of each octane of fuel. Which depends on where it is in the tank in the ground. Lower in tank is cheaper, but often picks up more dirt/sediment. The name brands get the top, or should. If you carry a name brand, you have to buy x% of the fuel from the actual name brand, the rest can come from wherever you want.

So, if I am buying "VPower", am I really getting it? No way to know.



http://www.shell.com/home/Framework...ists/fuels/optimax/optimax_about_ga_1602.html

I ran 87 octane in my LT1 Roadmaster, It ran great

I have been running 87 octane from only a small handful of stations for the last 9 months. No issues. I try to keep it with ethanol or without for long periods at a time. Trying to keep that variable tamed as best I can. Once in a while I run 89 octane, only because Road Ranger stations have that as the low octane fuel. Same price as everyone else has 87 octane.

Well, we will see how it goes for a month or 2 at 93 VPower and see what I can come up with for mpg #'s. And see if it really matters in my car.

I eventually want to use LT1 Edit or Tunercat to mess with my programming. Mainly for efficiency, not all out power.

 

[ralphb]

There is another factor to consider in addition to those already discussed here :

Many years ago, I had a boat with an outboard motor. OMC, the maker of Johnson & Evinrude outboards put out a bulletin advising all owners of their motors to use only a good quality premium gasoline (even tho the CR of most of their lower HP machines were such that they could almost run on kerosene in third world countries). The reasoning was that the better grade fuels had fewer additives that might crud up the engine (both before combustion and after); they tend to break down and lose their qualities more slowly; and they were less likely to turn to varnish and gum up the carb or injectors.

These factors would be of particularly concern to those that may not drive their vehicles regularly, as is the case with many of the pre 90's vehicles which are kept as vintage or collector cars.

I have followed OMC's advice, and use the top grade Amoco (now part of BP) which is so clean it doesn't even have a fuel dye in it, in all my lesser machinery such as lawn tractor, etc.

 

[N0DIH]

I have always heard that higher octane burns slower. Now, does that mean, slower as in milliseconds or microseconds slower? Or tenths of seconds?

And, as we do know, there is still crankshaft rotation in ever microsecond, how much DOES this actually make a difference? If the fuel @ 87 octane is completely consumed with the A/F present in say (an arbitrary number) 0.1 seconds. And in 0.10 seconds that crankshaft has moved and the piston is now say 1/4" down in the chamber (a guess here, just numbers). Now we introduce in 93 octane. And it is consumed in 0.15 seconds, and the crank has moved, and the piston is now down 3/8" down in the cyl.

How much does this matter? Is it more efficient to burn longer or shorter? We can get a higher spike of pressure if it burns faster. This theory says it will create a higher force to start moving the piston down and the crankshaft earlier or quicker, but at a weak point for leverage.

But if the design of the engine is short rod/long rod/long stroke/short stroke, etc, which ends up being better for power or efficiency, or even economy?

In theory, it seems that higher octane might be a little easy on the bottom end of the engine. And in theory, might the slower burn allow a long flame to reach more cracks and crevices in the chamber to reach every atom of fuel molocule, thereby reducing emissions and increasing fuel economy due to more BTU's of fuel being burned and exhausted. The longer burn might take more advantage of an increased lever of the crankshaft being moved farther before the burn stops.

Ok, yes, I am sick, I think WAAAYYYY to much on these things.

 

[Katshot]

Longer or shorter isn't as important as the "consistency" of the burn. Lower octane fuels are closer to an explosion which is basically an uncontrolled burn. Whereas the higher octane fuels burn slower and more evenly. The whole point of the burn is to increase cylinder head pressure, right? Well in a perfect world you'd be doing it at a perfectly consistent rate which allows you to predict exactly at which point the piston needs to be at TDC to take advantage of the perfect pressure. This is why ignition timing is SO important. The higher octane fuels just give you the best chance of hitting that "perfect" timing consistently.