100k

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robin
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Re: 100k

Post by robin » Sun Jan 05, 2020 9:43 pm

I think you're wasting your time. 98/100 RON have longer hydrocarbon chains (at least that's my understanding) meaning they burn slower - so you can advance the ignition timing a few degrees on 98/100 and the flame reaches the "top" as the piston reaches the "top".

What I don't know is what happens when the ECU doesn't know it's running 98/100 - I assume that the combination of the misfire detection and O2 sensor in the exhaust trim the engine so that it still runs OK, but I doubt it makes any more power.

I could easily be completely wrong though!
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Tim S
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Re: 100k

Post by Tim S » Mon Jan 06, 2020 9:09 am

No idea of the chemistry behind any of this, but always super if it's available. Costs more, so must be better - right?!

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rawsco
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Re: 100k

Post by rawsco » Tue Jan 07, 2020 3:15 pm

pretty much wasting your time on 98/100 unless its timed/mapped for it, certainly on N/A, I believe RON is the resistance to ignition, i.e. higher RON harder to ignite.

for a N/A engine my understanding is that the map will be optimised for a RON rated fuel (say 98) and timed accordingly, if you stick 95 in it, it will knock this will be detected and the timing will be retarded as a safety measure, not ideal as to return timing to normal the engine would need to periodically advance timing until it knocks, prolonged knock will eventually damage the engine so its not a good plan to have this happening routinely. Where I understand it might benefit is when engines get old and soot buildup in combustion chamber or hotspots can create glowing ignition sources other than the spark plug that can cause pre spark ignition which is very, very engine explodingly bad, higher RON would resist this and allow the spark to ignite. If you stick 100 in it it will run with the map for 98 with no benefit other than noted above.

Turbos I believe are different as higher RON can allow higher boost for a given timing before knocking and the ECU can play with that variable in a safer way than advancing timing and seeing what happens, why I'm not sure. So turbo, yes benefit, if the ECU can increase boost till it detects knock then back off as it would with timing, N/A no benefit.

My understanding could of course be utterly crap and I await any corrections, id certainly like to understand more.
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robin
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Re: 100k

Post by robin » Wed Jan 08, 2020 9:22 pm

The turbo engines need knock sensors to run I think ... I wonder if they are just quicker/better because the engine was always going to knock repeatedly ... where the NA engine can have a slower knock response because basically it's not supposed to happen.

I cannot remember the last time I saw an engine suffer from "dieseling" (pre-ignition due to glowing coke in the chamber)! My old Ford Cortina used to do it - had to stall the engine to stop it (also: only had 2nd gear). Not sure I've ever seen a fuel injected engine suffer from this though :-)
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campbell
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Re: 100k

Post by campbell » Wed Jan 08, 2020 9:24 pm

Cortina eh. Well we never knew about THAT one!
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Sanjøy
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Re: 100k

Post by Sanjøy » Wed Jan 08, 2020 9:26 pm

Cortina? Is that not where Kristian Ghedina was from?
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rawsco
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Re: 100k

Post by rawsco » Wed Jan 08, 2020 10:00 pm

robin wrote:
Wed Jan 08, 2020 9:22 pm
The turbo engines need knock sensors to run I think ... I wonder if they are just quicker/better because the engine was always going to knock repeatedly ... where the NA engine can have a slower knock response because basically it's not supposed to happen.

I cannot remember the last time I saw an engine suffer from "dieseling" (pre-ignition due to glowing coke in the chamber)! My old Ford Cortina used to do it - had to stall the engine to stop it (also: only had 2nd gear). Not sure I've ever seen a fuel injected engine suffer from this though :-)
I think it boils down to turbos being effectively variable compression engines and the ecu needing a mechanism to manage compression to prevent auto ignition or knock (RON is resistance to compression auto ignition not what I initially thought. It’s lab tested, in a variable compression lab engine.) so I expect Robin you are correct. Managing and optimising the engine using the knock sensor is routine for a turbo and this it can take advantage of the higher RON fuel by increasing compression. For a NA engine of a given compression ratio and fuel rating only has a very narrow operating window. a turbo engine will be very wide. I think.
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robin
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Re: 100k

Post by robin » Thu Jan 09, 2020 9:07 pm

campbell wrote:
Wed Jan 08, 2020 9:24 pm
Cortina eh. Well we never knew about THAT one!
I am sure it featured on my submission to the "all the cars I've ever owned" post. Though maybe that was on onelist or e-groups or something. Without Tut to lookup the archives, we'll never know :roll:

When I bought the car it was one shade of orangey brown but had clearly been resprayed. I was still an apprentice at Renault dealer in those days and so I used the high pressure steam cleaner to clean it. Took the paint off :-) So it was browner and less orangey after that.

The thread for the gear stick gimble had stripped, so you could only change gear with a screw driver shoved in the hole and some fairly violent movements. So it was easier to leave in 2nd (60mph indicated after full throttle run).

Eventually it blew the core plug out - probably because it had so much blow by and because it was revved to death every day due to no gears :-)
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campbell
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Re: 100k

Post by campbell » Thu Jan 09, 2020 9:40 pm

Love these stories, Robin.

Keep em coming.

(Tut may not have heard some of them either so he’ll get a good old chuckle too)
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robin
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Re: 100k

Post by robin » Fri Jan 10, 2020 9:22 am

Tut won't be hearing anything ... he was deaf enough when he was alive ;-)
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campbell
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Re: 100k

Post by campbell » Sat Jan 11, 2020 2:45 pm

His Jedi powers will be in play
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