Unleaded vs Super unleaded

[monkeyhanger]

I've posted this before but it seems appropriate to do so again.

All about Octane and how some cars will never take advantage of higher RON fuels.

https://www.youtube.com/watch?v=D9nhXNarFdg

Some people will still disbelieve it though, unfortunately.

Putting RON 98 fuel into a RON 95 optimised car just makes the cylinder ignite it earlier and at a lower compression ratio than the fuel was designed for. RON98 fuel isn't more calorific, it just resists a higher compression ratio without pinking. The timing on a RON 95 car may well be able to advance, but it can't alter the car's compression ratio to make it compress the RON 98 fuel more.

Definitely more opportunity to cause damage to a RON 98 optimised car running on 95 than a 95 optimised car running RON 98, having to ignite the RON95 fuel prematurely to avoid pinking.

[CraigW]

This thread is right up there in my top 5 of most mundane topics yet.

[mcmaddy]

Is that mundane or pointless Craig 

[CraigW]

Both sum it up nicely Chris 

[corgi]

Contrary to popular belief, RON98 isn't any more calorific than RON95, it is less volatile so it can be squeezed further  (greater compression ratio, or same compression ratio at a higher operating temp) without pinking before it is intentionally ignited by the spark plug. Running a RON95 optimised car on RON98 fuel just means that the fuel isn't being compressed to its full potential before ignition and at best will ignite in the same way as RON95, at worst you could get an incomplete burn (unlikely, as petrol of both types have a low flash point). The only obvious advantage then is running a tank through for any detergent cleaning benefits.

MH,

The compression ratio does not change. In order to avoid pinking with lower grade fuel the car retards the ignition timing to avoid pre-ignition (pinking/knocking) using (in most cases) knock sensors. When the ECU detects pre-ignition it retards the ignition until none is detected then progressively in small increments increases it until it reaches a pre-programmed limit or pre-ignition is detected again. However, in a car optimised for 95 RON fuel it will never advance the timing to a point where it can take advantage of the more expensive fuel. Pre-ignition is bad and can cause serious damage to an engine - holed pistons etc.

You are correct to say that the calorific value of the 98 RON petrol is little more than 95 RON; however, you will generate more power if the car is optimised for 98 because you can run more advanced timing...

[monkeyhanger]

Contrary to popular belief, RON98 isn't any more calorific than RON95, it is less volatile so it can be squeezed further  (greater compression ratio, or same compression ratio at a higher operating temp) without pinking before it is intentionally ignited by the spark plug. Running a RON95 optimised car on RON98 fuel just means that the fuel isn't being compressed to its full potential before ignition and at best will ignite in the same way as RON95, at worst you could get an incomplete burn (unlikely, as petrol of both types have a low flash point). The only obvious advantage then is running a tank through for any detergent cleaning benefits.

MH,

The compression ratio does not change. In order to avoid pinking with lower grade fuel the car retards the ignition timing to avoid pre-ignition (pinking/knocking) using (in most cases) knock sensors. When the ECU detects pre-ignition it retards the ignition until none is detected then progressively in small increments increases it until it reaches a pre-programmed limit or pre-ignition is detected again. However, in a car optimised for 95 RON fuel it will never advance the timing to a point where it can take advantage of the more expensive fuel. Pre-ignition is bad and can cause serious damage to an engine - holed pistons etc.

You are correct to say that the calorific value of the 98 RON petrol is little more than 95 RON; however, you will generate more power if the car is optimised for 98 because you can run more advanced timing...

I think you misread my post. I know the compression ratio on an engine does not change (the fundamental reason why a RON95 optimised car cannot noticeably take advantage of RON98 fuel even if ignition timing is advanced), I was stating that RON98 fuel can be compressed further without pre-ignition than RON95 i.e. in an engine with a higher compression ratio that is optimised for RON98 fuel.

[GrahamFR]

I dont care what you all say, I get double shell points with V-Power and I have a fuel card, so god bless pointlessly expensive fuel 

On a serious note tho, I have to admit I am in 'notice a difference' camp when it comes to V-Power, even when I tried it in my old megane as a young idiot once, and I swear it was a nicer car to drive on that tank.

[GeoBog]

I dont care what you all say, I get double shell points with V-Power and I have a fuel card, so god bless pointlessly expensive fuel 

Best part is when you come home from work, open the door and find the fuel vouchers on the doormat 

[JB GTI]

This thread is right up there in my top 5 of most mundane topics yet.

I agree
Fuel tanks empties. Fuel goes in.......And repeat !!
......Next 

[mcmaddy]

I think shell are s4ite. I give them my card and they never swipe it properly and then my account balance is always wrong. Pi44 poor