RON fuel rating for Cayman - Page 1 - Boxster/Cayman - PistonHeads UK

Hi all, Picking up my Cayman this week, and I have heard that it is meant to be run on 98 RON Super Unleaded. I wont be running any less, eg. standard 95, but does it hurt to run any higher? Like Tesco Momentum 99 or V Power Nitro? I don't mind if you gain nothing from it, I'm just worried about running the wrong fuels. I understand about running it below the recommended RON rating and it reduces the ignition timing to prevent knocking, but what happens when you run a higher rating? Around me they all have at least 99 or 100. Sorry for the noob question. I know there are many fuel threads but all I could see was people discussing whether to run 95 or 98. I want to know if it hurts running a higher figure than 98. Thanks a lot! J P.S. Here's a sneak peek of her! Edited by PorscheJW2014 on Tuesday 29th April 02:50

Higher octane is fine, and the way to go in my opinion. Cracking looking car! I've always run my cars on VPower/ Nitro but am going to give Tesco Momentum a try for the next few tankfuls. On the odd occasion I've used standard UL I've found the car to feel 'flat' in comparison - seems to have less grunt lower down and one of the reasons why I was sold on Shell is the cleaning effect of the additives it contains.

I've used Tesco Momentum in my 987 Cayman S since I purchased it 4 years ago and it loves it.

Enjoy the car - looks great. Mine seems to prefer V Power to Ultimate - more mpg, better noise and not slower. Haven't tried Tesco. S

Guys I work in car engine development. I can't say who for but our clients are prestige UK manufactures who need to outsource, we also test fuels. The RON rating of fuel will primarily limit the amount of ignition advance the engine can cope with before detonation occurs in the cylinder (pinking, knock or pre-ignition). This in turn limits the maximum power the engine can produce at wide open throttle (WOT). The Porsche engine is rated on 98RON so you'll get the claimed max power running 98. Run on 95 and you will get less as the ignition will be retarded by the knock sensor. Run on 99, 100, 102RON and you may get more power at WOT (it depends on how the engine ECU is calibrated). At part throttle you're unlikely to notice any difference in the engine's characteristics but high RON fuel may give you slightly better fuel economy. Personally I run on 95RON most of the time, just using 98 (or 102)if I want to go for a 'spirited' drive. The additives added to the fuel after it leaves the refinery are more important. These define the differences between the brands you can buy. The additives will keep the injectors clean, back of the inlet valves (on indirect injection engines) and stop the piston rings sticking in the groves. I always buy mainstream brands for petrol stations that have a high level of sales to ensure the longevity of the parts the fuel 'lubricates'.

PS - your Cayman looks good. But I'm biased, it's identical to mine... White with Graphite wheels.

The only thing that gets hurt is your wallet if you run higher than 98 octane in your Cayman. There is no benefit to running a higher grade of octane than the maker specs, with one possible exception I'll cover below... Based on my info premium gasoline can contain a few more BTU than a lower grade of octane but just not enough to make any real difference. The DME is already tuned (so to speak) to dial in the ideal amount of timing advance when the engine is fed 98 octane so there's no benefit there. Now, the engine can be sensitive to the brand of gasoline. I have run various brands over the years and not really noticed any reaction from the engine but I'm just saying if you consistently experience less than satisfactory performance from a fuel try another brand. There is a negative to running a lower than specified octane of fuel in the engine. While the DME will retard ignition to avoid detonation this ignition retardation results in less chemical energy being converted to mechanical energy. The spark is triggered late to reduce the amount of pressure in the combustion chamber/cylinder. As a result the pressure build up occurs too late in the power stroke for optimum power generation. Additionally this retarded timing raises exhaust gas temperature and subjects all items downstream to higher than normal operating temperatures. There is likely no savings in fuel costs. While the lower octane costs less the engine is less efficient and mileage suffers to the point the initial savings in buying cheaper fuel is lost because you have to buy it more often. There is the drivability factor too. I'm forced where I live to run 91 octane ( (RON + MON) / 2 ) (which is a few points below the ideal of 93 octane, or 98 RON). However, a few times I ventured into regions of the country where I can once again buy 93 octane fuel the engine's improvement in responsiveness is rather remarkable. The only time it sort of makes sense to run a higher grade of octane than the maker calls for is at the track. While this will not give you any more power it does give the engine a bit more protection against the onset of detonation (and the subsequent retardation of timing). This is on the same order of showing up at the track with fresh oil and a new filter. Just a bit of extra margin. An EVO test of fuel (now a few years past) found that buying fresh gasoline was important. Buy from a busy station to ensure the fuel is very fresh. Also, EVO found that while supermarket fuels were often indistinguishable from name brand fuels this was not always the case. Supermarket fuel stations can use a variety of fuel distributors -- to get the best price -- and the fuel quality can vary. While 98 octane is still 98 octane there are variations that one in at least a controlled test can detect, as was the case with the EVO testing.

Thanks for all of the great replies everyone! All of the petrol stations around me are always busy, so no worry about fuel that's been left stagnant for days. Really interesting replies, I'm glad I asked the question! Thanks a lot! I pick up the car on Thursday around 3.30pm. I will post pics on a new topic when I get a chance! J

Rockster said: An EVO test of fuel (now a few years past) found that buying fresh gasoline was important. Buy from a busy station to ensure the fuel is very fresh. Also, EVO found that while supermarket fuels were often indistinguishable from name brand fuels this was not always the case. Supermarket fuel stations can use a variety of fuel distributors -- to get the best price -- and the fuel quality can vary. While 98 octane is still 98 octane there are variations that one in at least a controlled test can detect, as was the case with the EVO testing. Where are you based Rockster? I agree with your comments with one exception but that may be due to our relative locations; I'm in the UK. Here in the UK the major supermarket retailers fuel (think Tesco and Sainsbury's) is good to use (although I usually buy BP or Shell). In the UK all petrol comes from the same refineries, its just the additives that define the brand. our major supermarkets put a lot of work in to ensuring their fuel meets the EU standards and competes with the long standing brands like Shell, BP, etc. There are subtle differences between brands. I've been involved testing different fuels to determine the differences. The effort that goes in to getting just a few %points difference in fuel consumption is amazing and expensive. I wish I could tell you more. You need to avoid the small independent traders who 'spot buy', they sell fuel straight from the refinery sans additives. Finally in the UK you can get 95 & 98 almost everywhere (we don't sell less than 95), higher RON is available a selected outlets.

engineermk said: Rockster said: An EVO test of fuel (now a few years past) found that buying fresh gasoline was important. Buy from a busy station to ensure the fuel is very fresh. Also, EVO found that while supermarket fuels were often indistinguishable from name brand fuels this was not always the case. Supermarket fuel stations can use a variety of fuel distributors -- to get the best price -- and the fuel quality can vary. While 98 octane is still 98 octane there are variations that one in at least a controlled test can detect, as was the case with the EVO testing. Where are you based Rockster? I agree with your comments with one exception but that may be due to our relative locations; I'm in the UK. Here in the UK the major supermarket retailers fuel (think Tesco and Sainsbury's) is good to use (although I usually buy BP or Shell). In the UK all petrol comes from the same refineries, its just the additives that define the brand. our major supermarkets put a lot of work in to ensuring their fuel meets the EU standards and competes with the long standing brands like Shell, BP, etc. There are subtle differences between brands. I've been involved testing different fuels to determine the differences. The effort that goes in to getting just a few %points difference in fuel consumption is amazing and expensive. I wish I could tell you more. You need to avoid the small independent traders who 'spot buy', they sell fuel straight from the refinery sans additives. Finally in the UK you can get 95 & 98 almost everywhere (we don't sell less than 95), higher RON is available a selected outlets. I usually fill my Boxster up with 98 at Sainsburys. If this doesn't have the additives of the Shell or BP equivalents, would it be worth me adding a bottle of something periodically to compensate?

Pretty sure Sainsbury sell 97 RON (ours does), but that aside, I wouldn't be bunging stuff into the fuel - that idea reminds me of 1970's 2 strokes.

IMO the 98 (or 97) you buy at Sainsbury's (or Tesco) is fine as its comes out of the pump, no need to use additives.

engineermk said: IMO the 98 (or 97) you buy at Sainsbury's (or Tesco) is fine as its comes out of the pump, no need to use additives. Thanks.

Nice colour combo, very similar to mine (my wheels are meteor grey):

You bring that back from Dubai?

yup, been on the road for about a week now. Still need to go for a proper drive in it, and also keen to try spirited driving in the rain, should be interesting!

S1MMA said: keen to try spirited driving in the rain, should be interesting! You won't have to wait for long back here.

I always seem to sit on the fence slightly with fuel topics. Supermarket fuel quality is no different to Shell etc. it's all out of the same tank essentially. The additive quantities they add are so small, their claims are frankly absurd. It does not change the RON. The biggest difference in 95 RON fuel from a petrol station would come from a driver turning up with 7,000 litres of Super, only for it to not fit in the station tank..... So it goes in the 95 tank.... Increasing the RON. Claims of supermarkets sourcing sub standard fuel..... What happens when a refinery has a "shut down"? The fuel is imported and all the majors use it. If you want to use 95, use the cheapest available. Tesco or V-power if you want 98+ I run a fuel terminal, no doubt someone will know someone who works in the deli at morrisons who knows the truth.