cornish6544

Fuel octane wants the truth?

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So my hatch is currently being built by Scooby clinic and I'm about to collect it to do some running in miles. Where I am at the moment down south I can easily fill up with vpower but when I move back to the Lake district in January I won't be able to get hold of vpower or Tesco 99 as the closest one is a 90-mile round trip.

This means I will have to use a lower fuel such as BP ultimate or Esso supreme at 97. I will be running one of these for my final map and I've been told it could actually make a 30BHP decrease because it's not vpower. How true is this or are they just being cautious not to get my hopes up? 

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I am not entirely sure what exactly it will do to your car. I can only speak from experience with a lot older import.

I have been using tesco 99 for the last year with occasional shell vpower top ups and had no problems.  I recently changed jobs and started using texacos 97 ron performance fuel. Thought it would do the job. The car slowly started running like a bag of nails, kangarooing in low gears when approaching traffic lights slowly etc. This went on for a week and a half before i finally realised that it wasnt a mechanical problem. Filled up with half a tank of shell and half of tesco 99 and the problems disappeared. 

This to me backs up their claim. There is a difference between fuels. Im no scientist or engineer, but read that higher octane fuels react differently under high heats and combustion pressure. It would make sense that higher bhp targets include higher heat and combustion pressure....

When my car was mapped yesterday the mapper asked me what fuel i had in my tank and what fuel i was going to use regularly. I had my shell, tesco mix in it and said I would continue with that.  It sounds like you dont have a choice about the fuel you will use, but thankfully above 280bhp imo 30bhp wont make an extreme amount of difference, get an aggressive map and you will still be really happy.

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Higher octane reduces the fuel's potential to pre ignite, so the higerer octane rated fuel the more timing you can run and more power the engine will produce among many other things so if you can have two maps put on then i'd do that (I did) had a v power map and a emegrency **** fuel map, (never used it)

The lower quality octane of the fuel the less power you'll make



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I’ve no doubt that 99 fuel does make a difference but I’m curious how much we are talking. I have no choice but to run Esso supreme 97 but I’m thinking my car should still produce 330bhp as Subaru map them with 97 fuel? 

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my dad didn't want to get force to run 99 so had it mapped for 95, dropped from 330 to 300 so about 10% drop.

 

However even being mapped it did eventually drop a valve.

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I think using the right fuel for the map, or getting a remap if you're going to use a specific fuel, especially if it's lower than 99RON, is very important. It's not just about the power. Since getting my car in July I was only using VPower and it was fine. I had to use some Tesco 99 in an emergency and found the engine ran distinctly smoother, suggesting the map was done on Tesco fuel.

Back to the OP - yes I wouldn't be surprised if running BP fuel will 'cost' you 30bhp. That said if it's what you're going to use, best to get the right map. 

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From what I understand , vpower is by far superior to any other on the market , even Tesco 99 , the odds are you wouldn't be able the run as much boost as safely as you can with v power , depends on who maps your car , may make the same power as a car on 99 but could fail prematurely , I think 30 hp is a realistic loss between the different fuels I think between 5-10 % is a reasonable figure , your power can fluctuate by maybe between 1%- 5% on a day to day basis so I wouldn't be that bothered , a well tuned car that running really well at 300 bhp could well be faster more drivable and most importantly more reliable than a car that made 330 once one time on a dyno ,,, but that said I know Martyn Jeffries last week mapped an rs6 running on 95 Ron 🤦🏻‍♂️, ( some people are unbelievable haha) but that made just shy of 700hp so it is the tune that is most important but just be aware that there will be limitations to 97 compared to 99 but hey it's better than 95 ;)


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