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Super unleaded - higher octane fuel - I don't understand!

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Super unleaded - higher octane fuel - I don't understand!

Old 31st May 2021, 11:09
  #61 (permalink)  

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The valve seat recession problem occurred in the past when low lead fuels were introduced because of poor quality exhaust valve seats, or seats cut directly in a cast iron cylinder head. The problem has largely been engineered out these days, by better materials choice.
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Old 31st May 2021, 11:16
  #62 (permalink)  
 
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Hi Mods, thank you for merging this thread. I couldn't find the original.
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Old 31st May 2021, 11:29
  #63 (permalink)  

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Often cheaper to use the bus or even taxi. Even more sobering.
I would be happy to use public transport to and from work a) if it existed and b) if it cost a reasonable amount. Hiring a taxi to take me 45 miles to work at “ohgorblimey” hours in the morning and then trying to hire one to take me home again, sometimes at an unpredictable hour around or after midnight, just isn’t practical.
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Old 31st May 2021, 14:17
  #64 (permalink)  
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True enough, ST, been there and done that too, and there are also those of who live where there is no bus service (council shut it down 2019) and a taxi is a tenner just to come to ones house, so no sensible option here either, even though I'm now retired and would happily use the bus again to go into town for a few jars with a mate. Roll on self-driving electric cars!
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Old 31st May 2021, 17:57
  #65 (permalink)  
 
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Since the banks in the UK pay SFA in interest, I have been spending my savings on Depreciation of new cars.
The fuel costs are low compared to Depreciation.
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Old 1st Jun 2021, 10:50
  #66 (permalink)  
 
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Originally Posted by ShyTorque View Post
There is possibly little or no advantage in using the higher quality fuel if not specifically required by the manufacturer. However, many modern petrol engines tend to have relatively high compression ratios and run lean, in the interests of clean emissions and fuel economy. That combination tends to put an engine closer to the point of detonation. Some ECUs have an input from a knock sensor and at the first sign of detonation will retard the ignition timing to alleviate the problem. That reduces performance, both economy and torque/horsepower.

In those cases it makes sense to use top quality fuel. In others it might make no difference.
If you have an 'older' car which has a distributor for the ignition and can be fitted with a vacuum gauge, you can often improve both fuel consumption and acceleration by advancing the distributor until you get a maximum reading on the vacuum gauge at idle. If it pinks, just back off the distributor a bit if you're already using 'super' unleaded (it's 98 octane at my locals)
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Old 1st Jun 2021, 11:58
  #67 (permalink)  
 
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fill your car up to full instead of running around with half a tank and letting it go empty
Please do not do this otherwise you are at risk of destroying your fuel pump and the associated costs, many fuel pumps are designed to be submerged in fuel. Obviously disregard if you have the non-submergible type.

I run my Swedish Brick on Super 95 RON and it runs more smoothly and I get better fuel economy ( Still drinks unleaded like a Pompey Supporter on Stella though). I had it converted to LPG which is about 112 RON. I get a smooth running engine but slightly lower equivalent MPG due to the volume of gas needed. At 1/2 the cost of Unleaded it works out much cheaper however.

Best I ever got was in Germany with 100 RON unleaded and minus 7 OAT = 137 MPH before someone pulled out in front of me on the autobahn and I had to take the foot off the accelerator

Nice to have a thread that is not enveloped in politics!
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Old 1st Jun 2021, 22:10
  #68 (permalink)  

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Chevvron,

You can do even more than that because that only advances the entire timing curve. A few years ago I got into dismantling Lucas distributors and physically modifying their advance mechanisms of my competition car’s modified engine (modifying the metal flyweights, stops and springs to adjust total advance and advance rate). I soon discovered that the manufacturer’s settings were far too conservative to get the best performance out of it, I was eventually able to get almost a 25% torque increase.

However, it was very time consuming to experiment in this way. I later locked up the mechanism altogether and converted the distributor to a digital system which I tuned using software on a laptop. Much quicker to do and more accurate.
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Old 2nd Jun 2021, 00:46
  #69 (permalink)  
 
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Question

Is there such a thing as Race Fuel these days? In the 80s and 90s I used to attend a few racing circuits here and there. Not F1, unfortunately. But I remember there was a distinct, unusual fuel smell 😶‍🌫️ 🥴 from the competitors engines. Both motorbike and car events. They were using something very different from road fuel.

I actually used to quite like the smell; much as I still like the smell of jet fuel even now! Maybe 🤔, I'm a bit weird in that regard. 🙃😉
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Old 2nd Jun 2021, 01:01
  #70 (permalink)  
 
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Originally Posted by ShyTorque View Post
Chevvron,

You can do even more than that because that only advances the entire timing curve. A few years ago I got into dismantling Lucas distributors and physically modifying their advance mechanisms of my competition carís modified engine (modifying the metal flyweights, stops and springs to adjust total advance and advance rate). I soon discovered that the manufacturerís settings were far too conservative to get the best performance out of it, I was eventually able to get almost a 25% torque increase.

However, it was very time consuming to experiment in this way. I later locked up the mechanism altogether and converted the distributor to a digital system which I tuned using software on a laptop. Much quicker to do and more accurate.
Yes I'm well aware of that having read Petersen mags like 'Hot Rod' and 'Motor Trend' where they tested 'Dyno Tune' kits which, as you say, gave you a modified advance curve, however what I did was what anyone could do in their driveway without dismantling the distributor; I also fitted electronic ignition kits and 'played' with spark plug gaps and different heat ranges
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Old 2nd Jun 2021, 02:59
  #71 (permalink)  
 
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Generally the higher the octane the less Sulfur in the fuel. Sulfur is bad for engines.
91 RON limit is 150 ppm
98 RON limit is 10 ppm
Engines with a gasoline particulate filter need ultra low sulfur fuel (98 octane 10 ppm) or you will destroy the gpf. They generaly mandate ultra low sulfur oils as well....especially in diesels with a DPF.
It has been tested that 98 fuel will produce less noxious emissions in an old engine but no increase in performance.
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Old 2nd Jun 2021, 16:25
  #72 (permalink)  

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98 Octane might give a bit more if it allows more ignition advance.
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Old 2nd Jun 2021, 20:49
  #73 (permalink)  
 
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Originally Posted by Out Of Trim View Post
Is there such a thing as Race Fuel these days? In the 80s and 90s I used to attend a few racing circuits here and there. Not F1, unfortunately. But I remember there was a distinct, unusual fuel smell 😶‍🌫️ 🥴 from the competitors engines. Both motorbike and car events. They were using something very different from road fuel.
When I was racing Classic F3 in the late '80s some in the class had sources of 100/130 avgas, that could have been it. Strictly illegal but there was worse cheating going on. I stuck to 5* and had to accept 2-3% fewer horses.

'a
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Old 2nd Jun 2021, 23:15
  #74 (permalink)  
 
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But I remember there was a distinct, unusual fuel smell 😶‍🌫️ 🥴 from the competitors engines. Both motorbike and car events. They were using something very different from road fuel.

Then there was Castrol AAAAAAAAAAARRRRR.....
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Old 3rd Jun 2021, 05:26
  #75 (permalink)  
 
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Originally Posted by Out Of Trim View Post
Is there such a thing as Race Fuel these days? In the 80s and 90s I used to attend a few racing circuits here and there. Not F1, unfortunately. But I remember there was a distinct, unusual fuel smell 😶‍🌫️ 🥴 from the competitors engines. Both motorbike and car events. They were using something very different from road fuel.

I actually used to quite like the smell; much as I still like the smell of jet fuel even now! Maybe 🤔, I'm a bit weird in that regard. 🙃😉
It's still out there, but it's harder to get (and costs ~3x the stuff you buy at the corner gas/petrol station). Most of what I used was 108-110 octane leaded (at least on this side of the pond, quoted octane numbers are nearly always (MOR+RON)/2), although some classes dictated unleaded - which you could get in ranges from 100 - 110 octane. Interestingly, you could not use 110 leaded and 110 unleaded interchangeably - they reacted totally differently in the engines although I couldn't say why that was. For that matter, all 110 rated leaded wasn't created equally - changing brands but with same octane (without changing anything else) could easily result in a burned or holed piston from excessive detonation (been there/done that - I once blew up 2 engines in four laps when I switched brands of 110 octane leaded fuel)...
Oh, and yes, I do remember that unique smell of racing gas.

The current trend towards turbocharged engines has changed the equation for what octane fuel you want to use. Modern fuel injection systems are quite sophisticated, and have very finely tuned detonation sensors (ping/pink is the initial onset of detonation - the occasional ping/pink isn't harmful, but left unchecked detonation will quickly result in holed pistons or burned valves). Detonation is inefficient - even if it doesn't damage the engine, it results in inefficient combustion and costs power. So on turbocharged engines, the engine control system will advance the spark until is senses the onset of 'ping/pink' then back it off a touch - that's the most efficient for both fuel burn and power. Hence higher octane can result in better mileage was well as greater power. If you drive 'hard' - it may well be cheaper to use higher octane, while if you drive like the proverbial little old lady the difference in mileage between low and high octane would be insignificant.
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Old 3rd Jun 2021, 06:10
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In the interests of the environment it helps to have a small everyday runabout, with something a little more interesting parked most of the time out of sight, ready for special occasions.

Watching ‘Suspicion’ yesterday, a 1941 Alfred Hitchcock film, it was educational to watch the needle on the large Lagonda dial creep alarmingly towards 50 mph along the cliff road.
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Old 3rd Jun 2021, 07:45
  #77 (permalink)  

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Originally Posted by jimtherev View Post
Then there was Castrol AAAAAAAAAAARRRRR.....
Iíve still got a gallon can of that in my garage. I occasionally put a small amount in my motorbikeís tank, just for old timeís sake. Trouble is, if you overdo it it causes excessive carbon to form which can cause problems.
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