Fuel Requirement? - LotusTalk - The Lotus Cars Community
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post #1 of 29 (permalink) Old 03-27-2004, 05:04 PM Thread Starter
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Fuel Requirement?

Hi all, I’ve been an observer for some time now and have enjoyed the posts. I was wondering about the recommended octane requirement.
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post #2 of 29 (permalink) Old 03-27-2004, 05:29 PM
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The Toyota engine requires high octane (91+?).

Welcome to the machin...er.....forum.
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post #3 of 29 (permalink) Old 03-27-2004, 05:32 PM
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Do you think the east coast people have a power advantage because they can get 93+ octane at the pump, whereas stupid CA forces us to use 91?
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post #4 of 29 (permalink) Old 03-27-2004, 05:38 PM
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When are they going to have the power advantage?
When you drive your car to the east coast to race them, or when they drive their car here?
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post #5 of 29 (permalink) Old 03-27-2004, 05:42 PM
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Quote:
Originally posted by Robert Puertas
When are they going to have the power advantage?
When you drive your car to the east coast to race them, or when they drive their car here?
Excellent point

I'm just bitter that we cant get higher than 91 here.
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post #6 of 29 (permalink) Old 03-27-2004, 05:43 PM
 
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I was under the impression that octane over the 'stated manufacturer's level' actually adds nothing. I do remember reading that octane must be no lower than the recommended amount but that
additional levels were a waste of money.
Any confirmed data on this?
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post #7 of 29 (permalink) Old 03-27-2004, 05:54 PM
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I thought that the ECU adjusts for octane (senses pinging). This retards the timing so manufacturers dont have to pay for engines when someone puts in 87 rather than 92. So wouldnt it work in the opposite scenario?
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post #8 of 29 (permalink) Old 03-27-2004, 05:55 PM
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Quote:
Originally posted by Ridgemanron
I was under the impression that octane over the 'stated manufacturer's level' actually adds nothing. I do remember reading that octane must be no lower than the recommended amount but that
additional levels were a waste of money.
Any confirmed data on this?
there are usually gains to be had using higher octane, up to a certain point.

94 would almost certainly give better performance than 91, even if 91 is the recommended number
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post #9 of 29 (permalink) Old 03-27-2004, 05:58 PM
 
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post #10 of 29 (permalink) Old 03-27-2004, 06:15 PM
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Octane is a measurement that indicates how resistant the fuel is to predetonation = pinging. Typically the higher the compression the greater the demand for a higher octane number. Thus putting higher octane in an engine that requires 87 is pretty much a waste of money since you can't change the compression ratio on the fly. However, for engines with Turbos or Superchargers the ECU can potentially control the boost and raise it until reaching pre-detonation (pinging).
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post #11 of 29 (permalink) Old 03-27-2004, 06:49 PM
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Quote:
Originally posted by khamai
Octane is a measurement that indicates how resistant the fuel is to predetonation = pinging. Typically the higher the compression the greater the demand for a higher octane number. Thus putting higher octane in an engine that requires 87 is pretty much a waste of money since you can't change the compression ratio on the fly. However, for engines with Turbos or Superchargers the ECU can potentially control the boost and raise it until reaching pre-detonation (pinging).
I think they are going with the theory that the car will advance timming to max. With the higher octane the vehicle would be less likely to ping under heat and stress thereby allowing max advance and avioding any timming retard issues. If the timming is at max advance the vehicle will make more power. Although your boosted thoughts are correct, you can get more power up to the vehicles max advance from higher octane fuel. Higher octane fuel allows for certain gains in non-boosted conditions. It is also not limited to just compression ratio issues as it is only one of the controlling factors. Basically, cars with variable timming control can maintain higher power output (up to max) through a wider range of operation. There is a benefit. The only difference is the higher octane fuel will not give you more power then whatever the max power is for the car. It will just make sure you always get it.

PS: East Coast folks get 94 octane not just 93! So when are they releasing that turbo

Last edited by Lotus F1; 03-27-2004 at 06:52 PM.
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post #12 of 29 (permalink) Old 03-27-2004, 08:41 PM
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Agreed. ECU can adjust timing, valve timing and on the Elise 111R, valve lift. But like you stated, an engine can not extract more HP than the fuel octane it was designed to take. All of the above + compression dictates that limit. Thus in light of the question, "does using fuel with a higher than recommended octane produce more power?", the answer is "no". If an engine is spec'd for 115 hp w/ 87 octane you won't get 120 hp by putting 92 octane in the tank. You'll still get 115 hp.
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post #13 of 29 (permalink) Old 03-27-2004, 08:45 PM
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The S54 engine in current M3's has shows gains when using 94 octane vs the recommended 91.

In fact, it keeps gaining until about 96 or 97, where gains are maxed out.

Last edited by atyclb; 03-27-2004 at 08:51 PM.
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post #14 of 29 (permalink) Old 03-27-2004, 09:02 PM
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What it really comes down to is the Lotus reprogramming of the ECU has timing tables that go higher then the power that can be had for 91 octane. If it keeps advancing and it's threshold is higher it is concievable to make more 189HP. Someone needs to find out. I think I'll stick with 93!
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post #15 of 29 (permalink) Old 03-28-2004, 04:23 AM
 
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A member on newcelica.org used a OBD scanner to monitor ignition advance with 91 and 93 octane on the Celica's 2ZZ-GE. There was no observable difference between the two.

I don't know if a more careful and scientific test would reveal any difference.

Also, I doubt the Lotus changes make a difference since they seem to be minor or non-existent.
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post #16 of 29 (permalink) Old 03-28-2004, 05:24 AM
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If the octane number is lower in California can you use an octane enhancer like 103 or Vortec Octane Plus? I have never used one or heard much about them, so I don't even know if they work.
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post #17 of 29 (permalink) Old 03-28-2004, 08:22 AM
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good question- after spending way too much time reading bottles of octane booster labels, I have yet to see actual quantities or mix ratios that would support adding x ounces to y gallons to get octance boost from 91 to 94 (or any other boost). At this point it would seem that the octane bosting game is a scam.

btw, not only do we have a 91 octane limit in CA, it costs more than anywhere else in the US! Our progressive CA legislature has created an off-spec gasoline only used here.
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post #18 of 29 (permalink) Old 03-28-2004, 10:01 AM
 
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California does have an octane disability problem- the best we can do at normal pumps is 91 octane.

However- Union 76 stations in some areas have been carrying race gas, and the trend appears to be acclerating. In the SF bay area, for example, there are several stations that I know of that do this, one of which in San Jose actually dispenses race gas from the pumps, and others of which will sell it to you from drums or in containers. A bit of a hassle, yes, but at least it's becoming easier than fueling at a track. (One of my prior vehicles needed a minimum of 93 to be happy, or it would substantially retard the timing and get sluggish on me)

And let me add another data point to the "high octane is better in any car" debate- in a relatively low compression car under normal operating conditions, going to higher octane will actually LOWER your fuel mileage without offering any performance gain at all. High octane does not imply more energy in the fuel, just more resistance to igniting, and if the engine isn't designed for that, it's actually suboptimal. (As far as our Elises, I don't have any experience with that engine, and am inclined to think that higher-than-the-minimum-specified octane will be helpful, but I don't agree with prior comments that higher octane is _always_ helpful)

-Knute

Last edited by Knute; 03-28-2004 at 10:04 AM.
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post #19 of 29 (permalink) Old 03-28-2004, 10:35 AM
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I think the old car debate stems from some older cars having pinging/detonation problems and benefitting from using higher octane to curb that problem. But you are right in that a car not designed and running correctly will not gain anything from higher octane rating. This really is the oil companies doing as they lead most of the public to believe higher octane means power and cleaner running fuel. Almost every girlfriend I had would fight with me when I told them to stop putting 92 octane in there family sedan cars rated for 89. It's amazing how well they have trained most of the driving public.
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post #20 of 29 (permalink) Old 03-28-2004, 11:46 AM
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There is more flexibility in the ECU timing than one might think. Honda actually lists two different maximum power outputs for the Odessy based on 87 or 91 Octane. The difference is 15HP and that is a NA engine. I have an lightly modified Audi 1.8T (15psi) that dynoed 220HP on pump gas here in the NE. The compression is high and realtime ECU mapping revealed a retarded timing. The performance shop predicts I could do another 15-20hp on race gas with the timing advanced.

I have been experimenting with mixing my own race gas. I add Toluene (118 octane) 1 gallon to 9 gallons of 93 pump gas. If you do the math it comes out to about 97 octane. The toluene increses the percent aromatic carbons significantly as well. Aromatic hydrocarbons release more energy per volume but may cause overheating problems so there is a lit to how much you can add. Commercially available race gas maintans the aromatic hydrocarbons at 45% while increasing the octane to 104. It's hard to find around here in the unleaded version.

In short the "rocket fuel" I mix makes a noticeable difference. I plan to dyno it this summer. My main purpose was to avoid predetonation but the extra power is a nice.
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