Super Unleaded

Never used it - Rarely fill up the disco due to being LPG but keep pondering when I fill the Laguna.

Is it worth the extra 5p a litre or is it just tosh?

Lee D

Reply to
Lee_D
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Higher octane fuels marketed to "boost performance" really do work, but only in engines that were designed to run on their octane rating in the first place. My old lotus runs noticeably better on the higher octane fuels because that's what it's designed to use, but you do have to stick to the fuel otherwise the ECU's mappings get unlearned.

IIRC they're just higher octane, and all that means is that it's less likely to cause engine knock, and at the octane ratings at our pumps it really only affects high compression engines as used in some sports cars. Sticking high octane fuel in a normal engine will just change from "not going to get engine knock" to "really really not going to get engine knock".

Reply to
Ian Rawlings

works in my saab - but that lets the boost go higher when it has higher octane so it should :)

It is however cheaper to just buy a gallon of cellulose thinners and tip a bit into the tank :) (contains toulene which is what most octane boosters seem to be). This is how i stop knock in my saab when it gets really hot and i know people using it for trackdays.

Reply to
Tom Woods

IIRC it's pretty much pure toluene. I used it 100% in my lawnmower once just for experimental purposes and it ran fine. I've always wondered about putting it in cars in case it damages rubber seals in the fuel injection system etc?

Julian.

Reply to
Julian

it depends on the thinners as to what is in it. IIRC the cheap one i can get is almost pure tuolene but the posher anti bloom one has methanol and something else in too (not that this seems to hinder its effect!)

I wasnt running it pure just adding some into the tank of sul

it hasnt damaged my saab 99, so i assume it will be fine in a saab 900 with k-jet too. There is a guy on the saab forums who is putting anything he can get his hands on in a saab 9000 too and it doesnt seem to hurt the fuel system (though he frequently blows stuff up but i think that is over exuberance and turning things up a tad too high ;) )

Reply to
Tom Woods

On or around Wed, 2 May 2007 00:25:25 +0100, "Lee_D" enlightened us thusly:

tosh, I imagine, unless you habitually want more than 90% of the rated power of the motor.

Reply to
Austin Shackles

On or around Wed, 02 May 2007 09:47:08 +0100, Tom Woods enlightened us thusly:

I've no doubt TPTB would take a dim view if they found out. Wonder if it'd up the performance of Edward II... at the rate the bloody petrol is going up, feeding him on cellulose thinners would probably be cheaper.

Reply to
Austin Shackles

"Lee_D" wrote

Only if your car is able to use it, our 330i gets about 2mpg more on a long run using Super and goes better too. Around town there isn't much difference but I always fill up with super for a long journey.

Reply to
Bob Hobden

Tosh. I've tried it (usually when someone else is paying my fuel bill) and I have never noticed an iota of difference. That would include various petrol saloons and hatchbacks, a 3.5 in a 90 and 4.6 V8 in a P38.

Performance motors, maybe. Never had the urge to try one.

Reply to
Rich B

Didnt make a blind bollocks of a difference in the Subaru & it was supposed to run on it!

Reply to
Nige

i should think it will make a difference on any car where the ECU has a knock sensor which it monitors to adjust the boost pressure or set the timing. The saabs for example let the boost pressure go up until they get knock at which point they start to cut it down (put simply) - so higher octane means more boost and more go. I was under the impression that even things like the P38 RaRo used knock sensors on the block and used them to tweak the timing? Higher octane should mean different results and thus different timing resulting in more beans or better economy.

Reply to
Tom Woods

It should make a difference in the scooby, although it might be like my old lotus, mine starts off with a set of default ignition timing maps and learns new ones as it goes along, this means that if you swap from lower to higher octane it never really gets the hang of the higher octane fuel so when the new fuel goes in it continues to retard the spark to compensate for the lower octane, or something like that. It takes a few tanks to get the hang of it. Mind you my car is running a 1989 programme in the ECU ;-)

Ask on the scooby lists, perhaps yours is ill.

Reply to
Ian Rawlings

On or around Wed, 02 May 2007 20:00:40 +0100, Tom Woods enlightened us thusly:

I assume you've got an APC Saab? I remember when that was new - they took one around Europe to test it's abilities - found petrol in Czechoslovakia where the *good* petrol was about 84 octane or something, and noted that this lost about 20 mph from the top speed. otherwise it coped fine. They then crossed into Germany and filled up with 98 octane, and it dutifully went faster again.

Reply to
Austin Shackles

ive retro fitted APC onto an older non-apc B engine - though im currently (currently actually meaning in january when i taxed the 101 instead of the 99T!) only using the APC to drive a knock LED and just setting the boost using an MBC and using SUL with thinners in it to keep the octane nice and high!.

Reply to
Tom Woods

That only applies until the maximum design octane for the engine has been reached. For something like a LR 2.25 petrol thats probably about

87 octane, for my race car engine it's around 110 octane.
Reply to
EMB

"Austin Shackles" wrote in message news: snipped-for-privacy@4ax.com...

go the David Vizard route and run on a high ethanol mixture Austin its less likely to melt the pipes on the way through and it will give a performance improvement Derek

Reply to
Derek

You really need to do some significant re-jetting to make high-ethanol fuel work properly.

Reply to
EMB

In a driving instructors little motor he tested super from Esso and got exactly the same 'pence per mile' out of both fuels but had more go with the super ... but supers do vary a lot - there was an article somewhere which I can't lay my hands on ... Put 97/98 octane in a 10.5:1 V8, add some millers VSP to bring it up to

101 ish octane and it runs at its design spec again ... equivalent of 5 star fuel and goes like a bomb.
Reply to
AJG

If you have a carb like SU's a needle change should be enough, trouble is that the people with that knowledge have either retired or gone to meet the original manufacturer. Come to think of it you can get some impressive back fires trying to get it right. Derek

Reply to
Derek

On or around Thu, 03 May 2007 19:17:06 GMT, "Derek" enlightened us thusly:

From my playing with slide carbs on bikes... the idle/slow running circuit affects the first 1/8 of the throttle movement, the needle and its jet affect it midrange up to about 3/4 and the main jet size affects the top end from 3/4 up, although there's overlap all the way through. On the SOBoxer, to cope with freeflowing exhausts and air filters, I upped the main jets from 80 to 90 and moved the needle clip to the lowest groove. seems to have survived so far, but then again, it's on full throttle a lot of the time :-)

Reply to
Austin Shackles

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