I've got a 1990 Pulsar GTIR, all stock. It doesn't like 95 octane fuel, will run great for a bit but easily drops into the low octane tune. Ive confirmed this by comparing the map data off a ROM to data logs that I have recorded from the ECU. From what I am aware, the knock sensor is reasonably new and it hasn't logged any codes for knock sensor malfunction.
I have a couple of options, would like to hear about others too. One option is to run on 10% ethanol blended with the 95, this would raise the octane a couple points from what I read, but its hard to find solid data on this sort of thing.
Option two could be an off the shelf octane booster, I dont know how effective these are or which one is best.
Option three is an avgas blend, but I'm not keen on this because I don't want to rot out the factory exhaust as it will be near impossible to find another one. Also avgas not being road legal is an issue.
Your thoughts?
clark20,
Dec 24, 9:06pm
You can get leadfree race gas (so the exhaust will be OK), I would mix it with 95 (maybe 2 parts 95 , one part race) and see how that works, and full race gas for racing.
Question How fresh is the 95 you are using, octane will drop with age? (the "good stuff" evaporates)
budgel,
Dec 24, 9:46pm
I have a BMW that is supposed to run on 98, but because 98 is not available where I live, I run it on 95. The ECU adapts to the lower octane rating, it just means the car is not running as efficiently as it otherwise would. I put 98 in it when I can get it.
In your case, given that your car is standard, I think there may be something else that is causing the car to be noticeably more sluggish.
My wife had one of those Pulsars (great little car in its day) and it ran fine on the gas available here, the only noticeable difference when we got to put 98 in it was better fuel consumption. We didnt do any data logging of course.
The fact that the car is now nearly 26 years old probably has quite an influence on its performance. I would consider injector cleaners, and even a water spray decoke to see if you can enhance the performance that way. An octane booster is something that is probably worth a try.
tony9,
Dec 24, 9:53pm
Not sure what you mean by that. Iso-octane seems to be the most common octane booster now. But it has a higher boiling point than raw petrol, but has a lower energy density. This should mean the octane will rise with age, but the remaining fuel will have less "guts".
m16d,
Dec 24, 11:12pm
Going over 104 is not road legal too. so they should cancel each other out.
morrisman1,
Dec 25, 12:50am
The reason I think its fuel based is because tracing the ignition timing on the data log lines up with the low octane fuel map, but initially it will line up with high octane. There is a noticeable drop in mid range torque especially when it makes the switch.
Injectors I recently changed to see if they were an issue and it hasn't changed anything. The other set were recently ultrasonically cleaned and flowed.
Ive put about 20,000km on the engine since its rebuild so all things there are still pretty fresh. Intake is pretty clean.
I should check to see whether the correct plugs are in, perhaps they are too hot? Would that help it run on the lower octane fuel?
tweake,
Dec 25, 1:11am
what was done in the rebuild? oversized pistons? shaved the head a little bit ? could have inadvertently bumped up the compression a bit.
elect70,
Dec 25, 1:25am
Just buy off the shelf octane booster & add it to 91 at each fill cheapest way to go . I used 1 in my worked charger than ran 11:1 CR i put something called 104 octane booster& worked well .
clark20,
Dec 25, 2:40am
Ohh do they have to reach boiling point to evaporate?
robotnik,
Dec 25, 3:45am
I used to run 95 RON Shell V-Power in my Mitsi Legnum VR-4. Data from my scanner indicated hardly any detonation making it very similar to BP 98.
Not sure if Z 95 would give similar results though.
tony9,
Dec 25, 3:55am
No, but usually the vapour pressure (which allows evaporation) is somewhat relevant to boiling point.
clark20,
Dec 25, 5:39am
Anyway, it goes off, and octane reduces.
tony9,
Dec 25, 5:49am
Ahhh, no. Octane will increase as the additive to increase octane will evaporate at a lower rate than the raw petrol.
"Stale" fuel is caused by improper storage, and usually smells sour. The gasoline has been allowed to get warm, thus catalysing olefin decomposition reactions, and perhaps also losing volatile material in unsealed containers. Such fuel will tend to rapidly form gums, and will usually have a significant reduction in octane rating. The fuel can be used by blending with twice the volume of new gasoline, but the blended fuel should be used immediately, otherwise the old fuel will catalyse rapid decomposition of the new, resulting in even larger quantities of stale fuel. Some stale fuels can drop several octane numbers, so be generous with the dilution.
marte,
Dec 25, 1:17pm
Will Acetone raise the octane rating?
It did absolute wonders for a offroad motorbike I had. All that was needed was a double nipglass of Acetone in a full motorbike tank. Any more did nothing extra.
thanks everyone. I took the car up to Roxburgh over Xmas, ran good and only dropped to low octane maps doing the down running in Invercargill on the way back. Wonder if it heat soaked the intercooler?
I think Ill try an octane booster first, that should be be the easiest option as it doesn't restrict me to any particular location, then next option will be running e10. I can get ethanol from a friend but mixing it will be a bit of a pain.
sw20,
Dec 27, 10:40pm
Those octane boosters are a waste of money. When they say they raise by 7 points , that means it raises to 95.7 not 102 from 95.
designerliving,
Dec 28, 7:15pm
E85 simple
sw20,
Dec 28, 7:20pm
If you live in Hamilton or near Hampton Downs.
bill-robinson,
Dec 28, 7:45pm
if the rubber in your fuel system can cope
designerliving,
Dec 28, 8:49pm
Thankfully I do. Then your only problem becomes keeping the cyl head from lifting
morrisman1,
Dec 28, 10:09pm
supposedly a contributing factor to that is people winding too much advance into it because the e85 wont detonate resulting in too high cylinder pressures. The word is ignition timing on e85 needs to be tuned looking for peak torque rather than max advance that it will handle.
marte,
Dec 28, 10:51pm
I didn't find the real answer, just more of my findings. Like 'it works and makes the motor run and sound better' and 'you only need a tiny amount, 60mls per tank'.
I did read something new and interesting though, they think it might be because of a chemical reaction between acetone and something in the fuel.
I found out by accident. I didn't have enough fuel in my off road bike to get to the petrol station, so I poured every solvent remains I had into the tank. Tolulene (which is a major component in petrol anyway) hexane (its petrol anyway) meths (ethanol, its in petrol too, absorbs and mixes petrol and water) acetone. It didn't run great, I expected that. But, something changed for the better. So I went thru the solvents, adding a little bit to a little petrol and seeing what difference it made until I used up that litre or so. Acetone was the answer, even a small amount. I tried clean petrol, then with acetone, then without again. It was obvious, even the sound of the exhaust was better, shorter sharper quieter bang, not a 'wump' a 'bang'. Power wise, the difference between a cold and a hot engine. Or choke and no choke when cold.
marte,
Apr 21, 9:02am
Oh, tried it with 100% petrol in carby of hot engine. Is, hot engine that was run on 100% petrol. Then added acetone to tank while moving at constant throttle. I could feel and hear when the acetone mix hit the engine. Bike took off faster.
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