What Petrol? - Page 1 - Porsche General - PistonHeads UK

There are lots of people who are not keen on the chemicals and aditives in LRP with lots of horror stories ref how LRP has shagged engines. Overall I know more people who know their stuff in the Porsche industry who are against it, that are for it and I wouldnt put LRP in any of my fleet. Stick to super, and if you can get it always use Shell Optimax.

I second the Shell Optimax thing. My S runs the sweetest it ever has on that.

I'm new to 911 ownership (recently bought a 930 Turbo) and this forum, so Hello! Lots of the classic car mags have run tests of LRP and the unanimous verdict is don't use it. Your Turbo has hardened valve seats so doesn't need the lead in Leaded (or the crap that supposedly replaces it in LRP) to prevent the valves receding into the heads. If you want a high Octane rating to prevent pinking use Super - LRP wouldn't help with this anyway as its Octane rating isn't anything special. Optimax as I understand it is a high Octane unleaded with some special detergents etc to break down carbon deposits in your engine, and is meant to be pretty good. If you have another car that doesn't have hard valve seats I still wouldn't use LRP, you're better off using unleaded and adding one of the additives you buy separately but make sure you use one that is approved by the relevant industry body whose name I forget. I've used the Castrol one in another car and would recommend it. Hope that helps.

Thanks for that Chris,nice to see someone else with a 930. Like to see it at the Virginia Water Meet on 20/10 if you can make it! Cheers Steve

The meet sounds good, looked in the Calendar to try and find out more but couldn't find anything, am I doing something wrong? You'll see from the icons I'm beginning to get the hang of things otherwise! The car is at JZ Machtech at the moment getting a few bits sorted so should be running sweetly by the 20th! Chris

You shouldnt use any thing but super in a 930, its got no knock sensors to back off the timing like a modern injecion system and 95octane will do the engine no good at all.

Chris, Not on the calendar at the moment.Have a look on events,meets forum . Should now be on the calendar. Cheers Steve >> Edited by sb930turbo on Thursday 3rd October 16:44

I must confess I filled up with the super dooper shell stuff at the weekend to try it out. I am the only one that did not really notice any difference? * cue the "no wonder in that hairdresser-mobile" jokes..... Are we lied to by that bavarian Ferrari driver?

Would be interesting to do back to back comparison's with the fuels from BP & Esso,wouldn't it? Steve >> Edited by sb930turbo on Friday 4th October 10:57

Have you driven it enough for the ECU to have had enough chance to 're-map' using the higher Octane fuel ?

'Remapping' should occur instantly - it is usually the function of a knock sensor. As soon as the engine detects knocking/pinking because the ignition is too far advanced for the fuel, it will retard the ignition until the problem goes away. Of course, as well as the ignition being retarded, the ECU can sort the fuel mapping as well. Therefore, it should be instant. You could switch between 95 and 98 ron during a journey and the engine should instantly recalibrate its ignition and fuelling. The reason manufacturers often specify a type of fuel is because 1) not all cars have knock sensors, and 2) they will only have mapped it properly for 98 ron. Therefore, although fuelling and ignition may be fiddled with when you put 95 ron in, your car is unlikely to be working at peak efficiency or performance.

Some cars (Scooby I think for one) can take a while to adapt and it's sometimes quicker to do a manual reset of the ECU. I assume the Boxster is a bit more high tech though. >> Edited by Basil Brush on Friday 4th October 12:06 >> Edited by Basil Brush on Friday 4th October 12:35

hi i have recently brought a porsche 924 T reg (1978), i have been using LRP, would the same apply for my car as the 930. As everyone knows my car uses the k jetronic injection system, so there is no ecu. If i did change the type of petrol to shell optimax would my car be able to adjust?.... thanks

A 924 is unlikely to have any kind of knock adjustment, ECU or anything. But because the ignition mapping is less sophisticated, you may find that any weakness in your ignition/fuel system would traditionally lead to a misfire/pinking. If you run on Optimax, the higher octane rating means it burns cooler and is thus less susceptible to pre-ignition or knock. So basically, if your car is running OK I would doubt Optimax makes much difference, although the higher 'energy density' and detergent effect they claim may be of benefit anyway. If your car is, or is likely to have, a small fuelling or ignition fault, then Optimax is likely to mask it and improve matters slightly. On an old car, this may be a concern. Running on Optimax won't harm the car, although some leaded engines like lead for more than its knock-reducing effects - I believe it helps lubricate the valve system or something. Someone more tech minded may be able to help here.

I wouldn't assume that to be the case, necessarily. '80s VWs and Audis (the fuel inhected ones at least) had a knock sensor to allow them to use any fuel between 98RON four star and the 89RON muck in Eastern Europe. Wasn't the 924 engine from an Audi, and isn't it fuel injected?

You may be right, but I'd assume a 1978 engine to be running on coal... I mean carbs Don't think knock sensors work with carbs?

yes my 924 is fuel injected but there is no knock sensor, as far as i know. One porsche garage did say that for every 2 tanks of LRP i use i can get away with 1 tank of unleaded. I dont really wanna take the risk at this moment in time since i have only had the car a month and need to prove to my family that the car will be reliable. In the near future, might or should i say ill have to convert it to unleaded since LRP is gonna be switched off at the end of next year

This might be out of date by now, but worth a look. www.mgcars.org.uk/news/news545.html

The actual Porsche recomendations for '76-'79 924 is to use 98 octane then every 4th tank use leaded. I really wouldnt bother worrying, your ignition could be retarded slightly and to stop any unnesassary pinking and then just try to use super UL and pref shell optimax, which is the only 98 octane on sale in the uk at the moment.

Hi Guys, Anyone know the Pros and Cons of useing lead replacement petrol as opposed to super unleaded in my 930 Turbo? Steve