Supreme unleaded/high octane fuels. Any difference?
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I'm Finding My Feet Here Now
Joined: Jun 2015
Posts: 102
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From: Greater manchester
Supreme unleaded/high octane fuels. Any difference?
Supreme unleaded in an old MFI engine. Any difference?
I've read a few conflicting articles on a few different sites and videos on YouTube and was wondering what you guys think?
From what I can gather most people say higher octane unleaded fuel makes older engines running a carb or mechanical fuel injection set up (like my mk4 xr3i), run miles smoother and can eliminate some running issues, but also that it has little effect on newer engines with more sensors etc.
Thoughts??
I've read a few conflicting articles on a few different sites and videos on YouTube and was wondering what you guys think?
From what I can gather most people say higher octane unleaded fuel makes older engines running a carb or mechanical fuel injection set up (like my mk4 xr3i), run miles smoother and can eliminate some running issues, but also that it has little effect on newer engines with more sensors etc.
Thoughts??
Back in the day when you had 4/5 star etc, fuels had a higher octane, when these cars were run on unleaded, which has a lower RON (95) it is a rule of the thumb to retard the timing by a couple of degrees to prevent knock, thus engine damage. Many did not do this.
The higher the Octane or RON, the greater the resistance there is to detonate under compression, hence high performance engines and FI engines generally run on SUL and it can cause damage using regular UL.
Likewise SUL, has a higher octane (97), so this is why they run better.
Of course you will not get any advantage in an engine that is not mapped/tuned for it, however modern engines have knock sensors, so use this to 'back off' the timing if the same happens, so I would say they actually are able to take advantage of it better.
Martin
The higher the Octane or RON, the greater the resistance there is to detonate under compression, hence high performance engines and FI engines generally run on SUL and it can cause damage using regular UL.
Likewise SUL, has a higher octane (97), so this is why they run better.
Of course you will not get any advantage in an engine that is not mapped/tuned for it, however modern engines have knock sensors, so use this to 'back off' the timing if the same happens, so I would say they actually are able to take advantage of it better.
Martin
Thread Starter
I'm Finding My Feet Here Now
Joined: Jun 2015
Posts: 102
Likes: 1
From: Greater manchester
Back in the day when you had 4/5 star etc, fuels had a higher octane, when these cars were run on unleaded, which has a lower RON (95) it is a rule of the thumb to retard the timing by a couple of degrees to prevent knock, thus engine damage. Many did not do this.
The higher the Octane or RON, the greater the resistance there is to detonate under compression, hence high performance engines and FI engines generally run on SUL and it can cause damage using regular UL.
Likewise SUL, has a higher octane (97), so this is why they run better.
Of course you will not get any advantage in an engine that is not mapped/tuned for it, however modern engines have knock sensors, so use this to 'back off' the timing if the same happens, so I would say they actually are able to take advantage of it better.
Martin
The higher the Octane or RON, the greater the resistance there is to detonate under compression, hence high performance engines and FI engines generally run on SUL and it can cause damage using regular UL.
Likewise SUL, has a higher octane (97), so this is why they run better.
Of course you will not get any advantage in an engine that is not mapped/tuned for it, however modern engines have knock sensors, so use this to 'back off' the timing if the same happens, so I would say they actually are able to take advantage of it better.
Martin
Well I've now ran a full tank of BP ultimate through my car since I've had it set up (mixture and idle) and I've got to say it's been running miles better! Quieter tick over, instant start up and smoother idle. Also as you said the "knock" had disappeared although my car didn't always suffer from this just the odd occasion.
However now I feel the car is over fueling a little, maybe because the new fuel has cleared all my fuel lines and injectors of any debris. I plan to run another half to a full tank and have the mixture set up again and timing adjusted.
Proof that it does make a difference
PassionFord Post Whore!!
Joined: Aug 2004
Posts: 3,502
Likes: 184
From: Colchester,essex
Adjust your timing to suit the fuel you're going to use. I used to run 14btdc idle, and modified the distributor to lock out at 34btdc total (iirc- it was a fair while ago) on Shell V-power on my 3i
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