Worth 'SHELL'ing out for Optimax?

[robocop]

I have just bought an early '96 XK8 Coupe with 63k miles and in excellent condition(yes I did my homework thanks to some of the threads for that-Nikasil/bushes etc)
Has anyone had any experience of using Shell Optimax in the V8? Is it worth the extra?
I used it on my last car - a 5 series Beemer - and it was a noticeable improvement, but a Jag dealer I asked put me off, saying the engine was designed to run on ordinary unleaded and Optimax wouldn't provide any gains. I am a bit concerned 'cos I think it burns slightly hotter and might effect the Nikasil linings in a slightly different way to the high-sulphur problem of the early days.

Any help you P/H's can give, grately received?
(This is my first post - so be gentle!)

Rgds robocop



>>> Edited by robocop on Friday 30th July 13:16

[jim meehan]

My xjs uses 95 ron as recommended and dont use opti. Maybe you could ring around the indep specialists or write to jaguar themselves and ask their advice.

Try Jaguar Enthusiasts Club, I aint a member but they gave me advice F.o.C. when I rang .... and I have uttered that latter acronym loudly many times recently...

[robocop]

Thanks Jim, had just done the very thing today and got a friendly reply from Chaz Whitaker of Racing Green (V Helpful!) c/o Mark Gregory of the XK8/XKR Enthusiasts Club(also V helpfull).

It seems the V8 is like the Beemer engine, in that the ECU will adjust automatically to the higher RON.

Chaz says:
"On the subject of Optimax, I don’t agree with your dealer. Optimax or the competitive BP Ultimate have a slightly higher octane rating than premium unleaded and will therefore be capable of developing more engine power – providing the engine’s timing and fuelair mixture are revised to capitalize on this. The good news is that the engine management unit will do this automatically for you. So, try it and see if you notice a difference. If you get more performance or better response or smoother low speed running, you will know whether to spend the extra money per fill up, or not. Furthermore, if the engine management detects any negative effects, it will defend against them – so I don’t think you need worry unduly about the advice given by the dealership. If Jaguar were worried they would have issued the dealerships with bulletins. If you want to be sure, ask the service manager if they have anything in writing from Jaguar on the subject."

So it looks like good news.

I am on a course for the next week and a bit, so checking with the Dealer again may have to wait until then...in the meantime...one tankful won't hurt!

Will let you know how I get on!

Rgds
robocop

[jim meehan]

robocop said:

It seems the V8 is like the Beemer engine, in that the ECU will adjust automatically to the higher RON.

then

robocop said:

providing the engine’s timing and fuelair mixture are revised to capitalize on this. The good news is that the engine management unit will do this automatically for you. Rgds robocop

Agree robocop; these EMUs really are awesome. After my recent experiences, however, it just makes it more crucial that the data & info they show up on screen is interpreted correctly, otherwise the punter can still be at the mercy of the 'wrong expert'.

Hope the fuel brings about smoother firing for you , robo May bite the bullet myself soon, if I get a few weeks out of the car running well and trade up. After the last 2 weeks, though, I have to ask myself one question. "Do I feel lucky?"

[bad company]

I ran my last car (BMW M5) on Optimax and it definitely made a difference. Now run a new type on XJ8 on normal unleaded. Seems fine.

[K.K.]

OPTIMAX - all the way! My XK8 used to run OK with normal 95 ron but much smoother with Optimax. Assuming it wasn't just my imagination, I would say it's worth the extra dosh. In my current TVR I use nothing but Optimax.

[derick]

I doesn't matter if It's optimax or XYZ fuel, the fact of the matter is that the more octane content in the mix the less fuel your car will need to push it along (most modern engines adjust them selves to the given octane of the fuel). This bring me to an interesting point; my old Volvo 740 estate goes allot further with a tank full of super unleaded 97ron. so much so that it is actually cheaper to run on the more expensive high octane fuel than ordinary unleaded 95ron..

Another point to mention; I have heard that it is possible for fuel companies to achieve over 115ron (octane content..) and if the fuel management system could cope, I could only imagine the 0 to 60 times of my old Volvo!!!

[GavinPearson]

You can only benefit if your engine uses knock detection and can advance or retard ignition to optimise the engine.

XK8 uses a Denso system that is calibrated to work within the 95 RON fuel and take advantage of better fuel by working constantly towards a baseline set using reference 98 octane fuel.

So basically Optimax works because the car & engine are designed to take advantage of it. You get better power and economy, which can often more than offset the cost.

[tomj]

Hi guys,

Just got a couple of questions..

1. I am planning to get a 1998 XJR. I assume this will have a similar system to the XK8, and therefore also benefit from 98 RON/Optimax

2. Can the fuels be mixed in the tank? I.e. if I have normal 95 RON in my tank, then want to switch to 98 or Optimax, do I have to completely empty my tank of 95, or can I put in the better fuel when there's still some 95 left in the tank?

Thanks

Tom

[robocop]

Tom,

Not sure I can answer your question in full, as I have not had an XJR, but if you look at a previous thread by Gavin, as long as you have an ECU that can sense the change and adjust automatically you will be ok.

Best advice is to burn off your 95 first(but not down to the dregs - ordinary driving will do, you don't need to drain the tank!) then fill up with Liquid Gold 98!

I can report to all, that there IS a marked improvement, especially during kickdown! So looks good so far

Rgds

>> Edited by robocop on Sunday 15th August 17:20

[V8Smith]

Regardless of any performance gains Optimax should help keep the Nikasil problem at Bay better than lower quality petrol!

Mike

[slikk]

Optimax every time as far as i'm concerned.. .. ..i dont have a Jag any more, but my Chimaera runs soooo much sweeter on it

k

[robocop]

Bloody hell!

Thats three 400mile-plus runs over the last two weeks..

First one averaged 26mpg
Second one averaged 25mpg
..so I just had to beat that for the third..27mpg!

Who would have thought supercar ownership could be economical!

And I wasn't dawdling in lane 1 like a 'blue-rinse' either

Damn impressive stuff.

Put some in your tank now!

Rgds