Discussion
I was recently persuaded by a mate who owns an audi TT to try shell optimax which he said gave better performance and an extra 15% mileage on a given tank. 5-6p a litre more expensive but what the hell. I found absolutely no difference in the performance of my 1988F 944 2.7, and on my weekly run did about 10miles less on a full tank.
Is optimax all its cracked up to be? am I not seeing the benefits because my engine is 16 years old?! (I still outrun said mate on the winding roads outside Taunton and it hacks him off bigtime!)
Is optimax all its cracked up to be? am I not seeing the benefits because my engine is 16 years old?! (I still outrun said mate on the winding roads outside Taunton and it hacks him off bigtime!)
The price premium is for a higher octane and a bunch of detergents, AFAIK.
The detergents won't give any 'instant' discernible difference but should, theoretically, keep the engine clear of carbon deposits for longer than 'normal' petrol. Given how long I tend to own my cars, this is probably not that much of a big deal...
As to the higher octane, this delays the onset of detonation, allowing higher cylinder pressures and greater ignition advance.
In my experience, Optimax makes a hell of a difference with turbo engines (Scoobies, Noble, Lotus Elan). I'd never use anything else in a turbo motor. As to N/A cars, it's a bit less obvious - my Griff was constantly running on the edge of detonation anyway and Optimax made a discernible difference, however other cars may not notice.
To get more power, you're going to need sophisticated enough engine management to notice the fact the fuel will allow more advance / boost / etc. and use more aggressive settings.
Allegedly, normal unleaded has a higher calorific value than super unleaded anyway.. though this is probably a thread for the Engines forum
The detergents won't give any 'instant' discernible difference but should, theoretically, keep the engine clear of carbon deposits for longer than 'normal' petrol. Given how long I tend to own my cars, this is probably not that much of a big deal...
As to the higher octane, this delays the onset of detonation, allowing higher cylinder pressures and greater ignition advance.
In my experience, Optimax makes a hell of a difference with turbo engines (Scoobies, Noble, Lotus Elan). I'd never use anything else in a turbo motor. As to N/A cars, it's a bit less obvious - my Griff was constantly running on the edge of detonation anyway and Optimax made a discernible difference, however other cars may not notice.
To get more power, you're going to need sophisticated enough engine management to notice the fact the fuel will allow more advance / boost / etc. and use more aggressive settings.
Allegedly, normal unleaded has a higher calorific value than super unleaded anyway.. though this is probably a thread for the Engines forum
Tim, the 944 2.7 does not have a knock sensor so it will gain no 'dynamic' advantage from Optimax (though the detergents should in time clean things up in there). The 944 S2 and Turbo DO have a knock sensor so they will dynamically advance the ignition until the point of 'knock' thereby gaining some advantage from the higher octane fuel.
To gain benefit in your 2.7 you could buy a remapped chip that has been remapped to use Optimax. Call Andrew Sweetenham at www.promaxmotorsport.co.uk/ who should be able to help
To gain benefit in your 2.7 you could buy a remapped chip that has been remapped to use Optimax. Call Andrew Sweetenham at www.promaxmotorsport.co.uk/ who should be able to help
The quality of Optimax is highly variable. I've had a good tank from a filling station, and then gone back 2 weeks later and got a tank full of fuel that felt like Tesco "Value Brand" petrol (contains minimum 10% grit)
I've found BP Ultimate to be much more consistent, although never as good as "good" Optimax.
I've found BP Ultimate to be much more consistent, although never as good as "good" Optimax.
Guys, guys, guys......
We make good money, we drive cars that we really ought to accept are never going to be cheap to run - buy the highest octane petrol you can find (use additive if you feel you need to) and enjoy the fun!
If you wan't to obsess about what MPG you're getting, buy one of those Toyota Hybrid thingies....
We make good money, we drive cars that we really ought to accept are never going to be cheap to run - buy the highest octane petrol you can find (use additive if you feel you need to) and enjoy the fun!
If you wan't to obsess about what MPG you're getting, buy one of those Toyota Hybrid thingies....
mpg who cares? quite right...but I love my old 944 so much that I want it to go on forever, so if sloshing a different petrol in it will help then great. and whilst it is true that my 944 is quite fast enough for my daily needs, I aint gonna complain if it just happens to go a bit quicker with optimax or whatever
timward said:
mpg who cares? quite right...but I love my old 944 so much that I want it to go on forever, so if sloshing a different petrol in it will help then great. and whilst it is true that my 944 is quite fast enough for my daily needs, I aint gonna complain if it just happens to go a bit quicker with optimax or whatever
Good point: well made - keep enjoying the fun and, remember; if you're not living on the edge, you're nicking too much room!
Optimax is not created as 98.6ron, but rather is normal unleaded untill octane boosters are added. These octane boosters loose there effectiveness over time, so the older the Optimax gets, the more of it's octane rating it loses.
If it was cracked (created) as 98.6 in the first place (as all other SUL's are) then it would be the same from tank to tank.
Thats why Shell don't advertise it's exact octane rating, as they know it varies.
Still the best out there though.....when it's fresh.
If it was cracked (created) as 98.6 in the first place (as all other SUL's are) then it would be the same from tank to tank.
Thats why Shell don't advertise it's exact octane rating, as they know it varies.
Still the best out there though.....when it's fresh.
I tend to just pick a busy Shell garage as this will hopefully mean a good turnover of hte fuel so it's not standing for too long.
Bit like going into a lager drinking pub and having the bitter that only moves a few pints a night
Optimax is the only thing I'll use in my RX-7 as detonation is a little more hazardous to the rotors than it is for boingers. MPG sucks whatever I use but isn't the point of the car!
Bit like going into a lager drinking pub and having the bitter that only moves a few pints a night
Optimax is the only thing I'll use in my RX-7 as detonation is a little more hazardous to the rotors than it is for boingers. MPG sucks whatever I use but isn't the point of the car!
My experience of Optimax in my 996TT has been excellent. It is all I use now, BP Ultimate running it a poor second place. I get about 6% better economy at a steady 80mph - but the real boon is great responsiveness and definitely more power - how much I am not sure. As an aside when in Belgium recently I put a tank full of "Shell V Power" 100RON in - WOW that stuff is rocket fuel! Made no difference to my friends Griff though so I recon the more highly engineered engines get the best from higher octane. As a second aside my old Boxster S was as good on 95 as 98 RON - so maybe I have defeated my point ?
They don't seem to bother with the Optimax marketing in France to my dismay - they just sell SHELL FORMULA SUPERPLUS 98. After reading all you chaps' experiences with Optimax I wanted to try it.
Doesn't matter how much better the consumption is if I have to drive abroad to fill up...
Doesn't matter how much better the consumption is if I have to drive abroad to fill up...
cyrus1971 said:
My experience of Optimax in my 996TT has been excellent. It is all I use now, BP Ultimate running it a poor second place. I get about 6% better economy at a steady 80mph - but the real boon is great responsiveness and definitely more power - how much I am not sure. As an aside when in Belgium recently I put a tank full of "Shell V Power" 100RON in - WOW that stuff is rocket fuel! Made no difference to my friends Griff though so I recon the more highly engineered engines get the best from higher octane. As a second aside my old Boxster S was as good on 95 as 98 RON - so maybe I have defeated my point ?
no - the boxster is n/a and your 996tt is forced induction. Higher octane will let the engine management run higher boost without detonation. It's much easier to feel with a turbo - the n/a engines can't get that much more power if they're not on the edge of detonation with 95 ron...
By the way, Esso's SUL is now 98RON (was 97) and is cracked as 98. Not as good as 'fresh' Optimax, but does offer better consistency.
Many people in the know have made the switch in the past few months since Esso put thier SUL back up to 98RON (all SUL went from 98 to 97 a few years ago for tax reasons)
Many people in the know have made the switch in the past few months since Esso put thier SUL back up to 98RON (all SUL went from 98 to 97 a few years ago for tax reasons)
On modern engines with full engine management, the engine can operate safely on fuels with a wider range of octane rating, but there's usually an optimum octane for any engine under specific driving conditions. So if you're already using the optimum octane fuel for your engine, you won't get more power from higher octane fuels. The engine will already be operating at optimum settings, and your driveability and fuel economy will remain the same. The higher octane fuel always costs more, so it's just burning money for nothing.
When you're using a fuel with an octane rating slightly below the optimum, filling with higher octane will cause the engine management system to move to the optimum settings resulting in both increased power and improved fuel economy. As Porsches are sold around the world with the huge variability in available fuel this entails, there's usually gains to be had by using better fuel.
If you buy race fuel and blend it in the fuel tank don't allow the tank to become empty, and then add slugs of each fuel one after the other. The fuels may not completely mix immediately, especially if there is a significant density difference. You may get a slug of low octane that causes knock. The octane averaging from a mixture will be linear for most hydrocarbon fuels so a 50:50 mix of 98 and 102 RON will give 100.
>> Edited by turbobloke on Monday 16th August 22:27
>> Edited by turbobloke on Monday 16th August 22:29
When you're using a fuel with an octane rating slightly below the optimum, filling with higher octane will cause the engine management system to move to the optimum settings resulting in both increased power and improved fuel economy. As Porsches are sold around the world with the huge variability in available fuel this entails, there's usually gains to be had by using better fuel.
If you buy race fuel and blend it in the fuel tank don't allow the tank to become empty, and then add slugs of each fuel one after the other. The fuels may not completely mix immediately, especially if there is a significant density difference. You may get a slug of low octane that causes knock. The octane averaging from a mixture will be linear for most hydrocarbon fuels so a 50:50 mix of 98 and 102 RON will give 100.
>> Edited by turbobloke on Monday 16th August 22:27
>> Edited by turbobloke on Monday 16th August 22:29
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