OK - we all know the SUL / Ultimate / Optimax debate - right ? here’s some more er … fuel to the er … fire
Well due to running out of Ultimate at Bedford I had to fill up with JP’s 1 quid a litre SUL - then by the time I got back to the pits the day had ended
Anyhow driving around today I get pinking when under load ( never normally happens ) and the usual “party trick” of lifting off in 3rd at 7500 and waiting a bit before getting fourth to put unburnt fuel in the exhuast for a nice “bang” - to scare the BMW that is always on your tail - doesnt work anymore
Make of that what you will …
Probably been standing for long time and all the good stuff evaporated
Well that just adds to my Mr Palmer misgivings of late.
Brings me onto something that I had wondered about for a while
We all know that Optimax is SUL+ (98 octane if I remember rightly instead of 97 Octane)
Does anyone know how this new BP Ultimate compares? Is that also 98 octane?
I’d heard rumours (off the Scooby boys) it was as high as 100 but possibily reduced for the UK market.
ps. All in all that tells you nothing really, sorry!
gonna stir the pot somewhat now …
optimax is supposed to be 98.6 (ish) octane, this figure is reached with the addition of additives to the fuel. The base fuel used for this process is plain old 95 octane unleaded. The additives used in the process decay over time which is why tests have been done showing fluctuating octane ratings from 95-98 for optimax.
the end result of that is you could be paying extra money for bog standard unleaded fuel if it had been sat in the storage tank for any length of time.
this explains why some people experience severe detting while running on optimax
BP Ultimate uses the same process but the base fuel is super unleaded therefore worst case scenario is your buying 97 octane. Best case scenario you will see close to 100 octane
hope that helps
Very interesting. However, doesn’t the octane of fuel degrade over time as well?
Yeah I’m pretty sure it does…
Now the way I’ve always understood the great fuel debate is that unless you car is timed to run on a specific fuel you’ll never see any benefit from running higher octanes…
However if you’re forced induction then it’ll matter more under high boost to stop pre det…
But then the compression ratio is pretty high on the VHPD (I may be wrong) and so you could easily get pre det at higher RPM…
So you shouldn’t get any more power (unless you’re mapped to use that octane) but I guess will have less chance of doesng some damage
Also I heard that BP has a higher calorific content than Optimaz so you get a bigger bang for the same volume of juice… Ergo more power.
I’ve only “heard” this so don’t read it as gospel… Plus I’m learning more all the time
sounds about right
I used to run a remapped Subaru P1 which is why i looked into the great fuel debate, as det is a something you REALLY dont want @ those boost levels
I’m very damn sure that if you get SUL out of a service station in the back of beyond it will have evapourated the good stuff as no-one buys SUL unless they have to …
My local BP and Shell have a good turnround ( like its always full) so I think the stuff is relative new there …
Low octane is fine in a “normal” engine that CAN adjust itself - but the VHPD cannot ( as we all know ) so I go against the “it wont make a difference” crowd because its a highly tuned unit and thus runs closer to the det limit ( and we get them very hot dont we ) so it makes absolute sense to run a high octane to be safe ( not to increase the power )
To me that was proven by the experience I have had …
The service manual says 98 is prefered but 95 is okay.
My car used to “pink” on 95 (which, from new I only used in an emergency) & SUL particularly when hot & under load. I have used Optimax since launch, & the pinking has stopped.
Better to be safe rather than sorry, I reckon
I think safety is the key here, we don’t want to nuke a valve or something
Also I heard about octane booster is very dodgy as well, what the el cheapo stuff does is change the frequency of the “knock” (IIRC caused by pre det) so the knock sensor doesn’t hear it IYSWIM… But then don’t know if the VHPD has a knock sensor?
The stuff to go for is teuoline, that’ll up your octance I remember a guy who had a very tuned RX-7, on one trackday he done something like 7 or 8 tanks or petrol but with that about 10 gal of teuoline! Effectivly running at 102 octane!!!
I was under the impression that Optimax was the only pump petrol in the UK with 98 octane and that all other could only manage 97. Going for a better quality fuel is always a good idea as an insurance policy. When I ran cosworth race engines I always used 110 octane fuel which saves the engine if fuel sarvation occurs. I have seen plenty of blown up cosworths after fuel pump failures when running pump fuel and I have lost fuel pumps whilst running 110 with zero damage occuring.
Just throw in an emerald and get it mapped on the cheaper 95 stuff and not worry about knocking again, mine was mapped on 95 with a sports cat and still achieved 220 BHP
I bet you didn’t even sell it to Trudy as a cost saving measure!
oh yeah, and its more economical
thats a good enough reason, saving on fuel