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GT86 Cosworth
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Discussion Starter · #1 ·
Does anyone have any thoughts on RON95 vs RON99(or 97,98 ect..) and what about using Tesco Momentum 99 vs Shell V Power (Both have 5% ethanol I believe). V-Power apparently according to Shell, has more cleaning agents.

Looking at the K20 I would predict a 5% power loss when using RON95 over RON99.

I was thinking about running it on RON95 while runnnig it as I wouldnt be ragging it anyway and then using Momentum99 most of the time with a tank of V-Power every 3-4 tanks.....

What are your thoughts....
 

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You're highly unlikely to be able to detect anything beyond placebo between any of the 97+ RON fuels. If the car has been calibrated for super unleaded (apparently) then running anything less may reduce engine output. This shouldn't affect the running-in cycle.
 

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Actually if you go above the rated RON you may get worse performance. Higher octane fuel burns slower and the ignition won't be optimised for it.
 

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Discussion Starter · #5 ·
gt_sjo said:
Actually if you go above the rated RON you may get worse performance. Higher octane fuel burns slower and the ignition won't be optimised for it.
Im not expert, but can't it retard or advance the timing to account for that? Im not saying running RON101 will be better than RON98 but shouldnt it be able to advance the timing in order for it not to reduce performance?
 

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I don't have the Subaru strategy infront of me, but typically you have a spark angle target (which is based on the fuel the engine is mapped on), and then you have a knock retard table which is adaptive based on the amount of detonation the ECU monitors. If you advance the spark angle too far, you'll lose power again. The ideal is what's known as Mean Best Torque (MBT). Most N/A engines can be tuned for MBT, although this high compression engine it is possible they couldn't quite get to MBT. In this scenario, running a higher octane fuel and advancing the ignition slightly may generate a slight gain, but I doubt the ECU can do that. They would have had to have mapped it on a high octane fuel and put some maximum advance values into a table somewhere. But again, i've not seen the tables, so can't offer a factual reply. :)

This is a very simplistic view of it as modern ECU's have hundreds of tables and complex strategies, but at a basic level this is how it can work.
 

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It really won't make much of a difference. On a high power turbocharged engine you can see the differences between the fuels but on something relatively low power like this you just won't see it.

If it mattered, i'd use Shell Vpower.
 

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I think it could probably make more power on 101, but above 98 you're into the law of diminishing returns, plus its expensive and who knows if it actually turns 98 into 101...?!


(previous post was... rather wide of the mark... thank you GT86Owner for pointing that out...)
Edited by: Sideways?
 

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Discussion Starter · #14 ·
Sideways? said:
Argh!!! This really winds me up......
There is no way on earth that using the recommended fuel would give you lower power - that is total and utter nonsense.
I think you need to read the posts again sideways, he was trying to explain why using a higher octane than recommended, such as RON101 instead of RON98 can in some case reduce power (when compard to ROM98).

Edited by: GT86Owner
 

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GT86Owner said:
lordgrover said:
ICantAffordAnLFA said:
Even on vpower it will be about 10% down on power
Compared to what?
I think he's going by the dyno results giving 145hp at the wheels....
Yes



More power very shortly.
 
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