Hi Octane fuel in regular engines 1

[bam55]

Why do they recommend hi octasne fuel in regular engines?
They say it will clean out the cylinders/carb. Others say for an engine designed for regular fuel(unleaded) it is just a waste of money. Does the higher compression engines actually burn this higher octane. How high has the compression ratio to be?

 

[Knap]

Rod

I'm not convinced by that statement. An original test when Optimax 98 arrived in UK (now Vpower 99)showed no improvement for a Clio

http://fifthgear.five.tv/jsp/5gmain.jsp?lnk=601&featureid=143&pageid=273

Conventionally, enrichment for maximum power air/fuel ratio is used during full throttle operation to reduce knocking while providing better driveability; perhaps the more dense Optimax may gived the "claimed" better response.

 

[evelrod]

I'm sorry, Knap. Which statement? I think the consensus here, as I see it, is that using premium or at least a 'better' grade of fuel than the engine requires is a waste of money. As Pat puts it, run the cheapest grade of fuel that gets the job done. I see no gaines, either power or economy, in using the high priced premium or mid grade fuels (which are just a blending at the pump, anyway) when the car will operate with 'regular'. I have pointed out that in some cases,eg, early muscle cars, need premium, that's fine...they do not, however, need 110+ race fuel (I see this $5+/gal stuff used by local kids on the street...I just scratch my head.)

Rod

 

[Knap]

Rod

This statement

An additional advantage is that, due to their different composition, "premium" fuels are typically two or three percent more dense than "normal" fuel, which means that each litre contains two or three percent more mass of fuel, and hence two or three percent more energy. All other things being equal, that automatically translates into a two or three percent improvement in fuel consumption (miles/gallon or litres/100 km).

 

[GregLocock]

/If/ you are on closed loop

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[dcasto]

From GPSA data table: BTU/gal (UHV)

tolulene 132658
iso Octane (100 Octane) 119396
normal octane (0 Octane) 121428
benzene 132671
ethanol 84511
methanol 64744
straightrun gasoline (about 75 octane) 120000
iso butane 96 octane 90905

 

[MacGyverS2000]

Rod,

It depends on what "those street" kids are running under their hoods. If they're running high compression pistons, or more likely heavy boost, the high octane keeps them from blowing up. These days it's easy enough to turn an electronic dial on the blow-off valve to go from using high-octane pump gas (93) to super-octane (110+), so they can keep a high-boost blower under the hood but still have streetability when the good stuff isn't available at the pump.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[Knap]

BP sell 102 near UK race tracks for the track day enthusiast
60bhp increase claim

http://www.bp.com/sectiongenericarticle.do?categoryId=9009114&contentId=7016932

 

[MacGyverS2000]

Kind of a dumb article...

First they test with fuel 'A' with a standard RON for the baseline. Then they change to fuel 'B' with a higher RON, but modify the maps at the same time (great comparison!). Then they increase the boost for the third test.

Just what are they comparing, the engine's ability to use more power with a proper tune? If they wanted to impress me, they'd show me some power gains with a change in fuel and no change in maps or boost.


Dan - Owner

http://www.Hi-TecDesigns.com

 

[evelrod]

Knap.
I am not at all convinced by that statement either. I think it is totally bogus, or at least biased by 'fudging' the tests results. You know the cliche about 'statistics'?
As to the BP article---Am I to believe that if I put 102 in my 1930 Ford (<5:1 CR) it will boost my horsepower by 60 hp?

Dan.
I agree. However, trust that I have sufficient experience in this area to be able to tell the difference between the 'real deals' and the 'street squids'. I live just three blocks from the local high school and I see some pretty strange mods on the street. I have talked with some of these kids on occasion, especially when I'm filling the jerry cans with a race car in tow. They 'appear' to comprehend my reasoning when I tell them they are wasting their money on the 'race' fuel (Who can really tell, though). It is also quite common to see the dirt bike guys using VP and Sunoco ~110 in stock dirt bikes. The 'word' is that it gives them extra hp. Re: above statement about the BP article!

Rod

 

[TheBlacksmith]

Gee, I used to do the same thing in the dark ages by recurving the distributer, bumping base timing 2-4 degrees and using premium. Actually did see reduced ETs and better mpg. So I guess the higher octane works. Oh, did I mention recurving the distributer and bumping the base timing?

 

[evelrod]

Picky, picky, picky. There's always one. I'd give ya a "pale pink" star if I my feelings were not hurt!!! Your obfusgating the issue. ;o)

How's the kids...still doing the 'ambulance' thing?

Rod

 

[TheBlacksmith]

Rod - first daughter married a Navy man, he went to the Seaman to Admiral program and I administered his commisioning oath. I now have two granddaughters and the daughter is going for her LPN (15 months). Daughter #2 is now doing the EMT thing, including passing the emergency vehicle ops course - good for a 15% insurance discount.

 

[rmw]

Here's my question.

I drive a Mercury GM with a 4.6L V-8 engine, factory stock, second set of plugs and have put about a half million miles on 3-4 of those things in the last 15 years. I like'em. I don't think the engine has a knock sensor, or at least if it does, it doesn't work too well, because in the summer month especially that engine will ping just as long as you want to keep your foot on the foot feed at that position. I don't like to drive it pinging down the road. I do often put the next grade up in or at least do it on an every other tank basis, as I am basically in agreement with the consensus that higher octane fuels are a waste in engines not designed for them. But I do notice a ever so slight improvement in the mileage when I do it. It may be that now that the engine is not pinging itself down the road it is delivering more horsepower to the wheels, which is what I want it to do anyway.

I also have some engineering experience in fuel pipeline stations where the tanker trucks load, and I have many times seen the tankers from all brands all filling from the same tank filled from the same pipeline and have talked to the drivers as they did the additive thing. That to me is suspect, as drivers are as human as the rest of us and if his wife beat him that day before he left for his haul, he might just forget to add the package, or might do it twice. What about rainy days when it is coming down in buckets-does he bother? Who knows and where is the quality control guy checking him-I never saw one. How good does it mix? Did he add it before he filled so that he got good mixing, or put it in when the tanker was full as an after thought?

In my former life, I drove lots; sometimes requiring several fill ups a day. As a practicing ME, I think I have the ability to understand the variability of fill up levels and take into account the variations. Mostly, however, since I am basically lazy and don't count time standing at a gas pump as productive (not to mention the frustration of having to try to figure out how to operate modern pumps-the guy who designed kitchen microwave controls and television clickers designed the gas pump controls) I fill it to the brim. Multiple click off's until it is full and won't take any more (even with the occasional rocking the car). I also note whether the car is on a mostly level surface, or if it is tilted in any manner. I know just about how much it will take to get to the first click off and just about how much I can 'stuff' into it by working at it. Those of you who drive your cars lots of consistent miles know what I mean.

If I had a dollar for every time I had filled a vehicle, I'd be long retired.

That all said, every now and again, the mileage will suddenly jump noticeably. While on a good day when I am driving decently, mostly turnpike driving, not much in town driving, no excessive speeding (rare, but I can do it) I get a steady 22-23 MPG (I have the power package with a different ratio rear end so I get less than the std. GM.)

But from time to time, not often, but often enough to raise up a question in my mind, the mileage will jump to the 24-25 MPG range, and I didn't do anything in particular to obtain that. Remember determining this is always after the fact on the next fill up.

Anybody got any idea what might bring this on????

I have a theory. My theory is that if a jobber has an excess amount of higher octane fuel in stock that he has to move, that he might drop it into the 'regular' tank and sell it at 'regular' prices just to turn his inventory. I can't prove it, but I have never come up with any better explanation of why the random increase in fuel mileage. It certainly wasn't anything I did.

Usually this happens to me in a situation where I can't go back to the station where I go the 'hot' load and try to repeat the results.

I'd be curious to hear the experts on this.

Pat-I got into this thread late, but gave you a star for your first post in it.

rmw

 

[evelrod]

rmw...
I couldn't have said it any differently. One thing I do is take several tanks in a row and average instead of doing it every time. Actually, that's how I kept from going to sleep on the road, I did math problems in my head (along with the day dreaming and general daily 'worry') to project costs, etc. I'm sure your familiar with that.

One of the caveots in all this is "use the lowest grade that your engine requires"...If that baby is pinging (pinking) then, either retard the timing or go up one step in the fuel grade. I know you like the big Mercs (from earlier posts) so I am a bit surprised you don't have the pinking problem solved. Sure, it may cut power a bit, but fuel mileage does not usually change. Hey, it's a land barge, anyway. ;-)

I worked at many of the L.A. area refineries and have seen Texaco trucks loading at the Union 76 dock and observed the "Out to Mobil" lines at the Texaco tank farm, etc. I also asked about this and the driver just shrugged and said all he did was 'load it up and deliver it'...no additive, no 'nothing'!!!

Rod