unleaded versus premium/super unleaded

[rac]

Just wondering if anyone has any views on the issue of unleaded as opposed to super/premium.
Have just treated my RV8 to some premium (only because I had a money off voucher so thought treat it )
Probably my imagination but I reckon it seemed to start easier from cold-needing less choke and a bit more responsive
anybody else had any experience or views?
Rob.

[robbo]

Hi Rob.
I always run mine on premium super unleaded with a dash of redex. The car seems to like this combination and performs very nicely on it.
Regards Rob.

[Staghound]

My Jag seems to do more mpg on the better juice.

Andrew.

[ChrisLD364]

I also use premium for the Stag. Mainly because of the ethanol in the cheaper standard fuel. Shouldn't rust the tank or separate out.

Chris

[V Mad]

You should get a bit more power on super but only if you run with timing a bit more advanced. Modern cars adjust automatically (they can retard ignition on lower octane fuel). But i find mine runs great on regular grade.

[Pete]

My car went through one tank of regular and really wasn't very happy with misfires, poor tick-over and almost unusable in slow traffic, even though I had used regular many times before. So I filled with super stuff and all was OK. Since then, I've gone back to regular with no probs what so ever. Take that as you will, but I do wonder about the quality of fuel you can get from known brands and supermarkets.

[Westfaling]

Don't RV8s come in low and high compression versions? IMHO probably not worth premium in a low comp. engine.

[flying farmer]

Petrol does seem to vary considerably, I always use regular unleaded except for track days when I use super unleaded.

All my stag engines run with as much advance as I can get away with on a normal basis, but from time to time I will pick up a bad tankful and if the pinking is too bad I will top up with super to restore order.

I avoid Morrisons petrol like the plague, I thought 4 pence per litre was a bargain the last time I filled up there, but then having to put in half a tank of super at an extra 10p per litre made it seem very poor value but I had to do it to get rid of the team of midgets that were smacking my pistons with big hammers!

The last tank of crap I filled with actually came from a big name fuel station on drive it day this year but I can't remember which brand. What was ironic was that Another Peter was filling his TR4 at the next pump with super unleaded, he asked why I didn't use Super and I said I didn't need it!

I may need Super for the project Stag as it runs a 10.5 : 1 compression ratio

Neil

[Another Peter]

The last tank of crap I filled with actually came from a big name fuel station on drive it day this year but I can't remember which brand. What was ironic was that Another Peter was filling his TR4 at the next pump with super unleaded, he asked why I didn't use Super and I said I didn't need it!

It was at the Esso garage just outside Whitchurch - expensive stuff too!

[andy p]

I only use super in my supercharged type-R as it wont run right otherwise

[73stagman]

As someone mentioned its all to do with compression ratio and octane rating. If the compression ratio is high (above 9.5 :1) then higher octane fuel can produce more power with the correct advance settings.
My compression ratio is over 10.5:1 so really I have no choice but to use higher octane fuel... I am considering using regular fuel and adding the booster separately though. I used to do this on my old spitty which needed lead additive as well. Its a fuss but makes one feel better than paying the big bucks at the fuel pump. (I dont think its any cheaper to add it in myself!)
The proper fuel makes a whole heap of difference at higher engine power but if I am prepared to trickle around on light throttle it will run on regular fuel. The problem with that is that the advance is set for the high octane fuel so when I have regular fuel with no octane booster in I am forced to drive the car like Miss Daisy.... it wont go any better!!

[Stagdad]

Al and I both filled up and went the 400 miles to ND mine was on 99 Ron , Al's was on std we both filled up at the same garage on the way back and both brimmed them. Cost was identical to fill them so super unleaded didn't cost any more due to greater mpg.

[Marco Polo]

I used to get 5% better fuel economy from my '98 Jeep Grand Cherokee, which I bought from new, using Shell VMax 98 RON, not sure what its called in the UK. So if it was less than 5% more expensive than regular unleaded, I bought it. However with the Stag I always use the highest octane fuel available, the engine seems to prefer it. I'm on standard carbs and static timing at 14 BTDC.

regards,
Raoul

[Mister G]

Generally the higher octane fuels contain lower levels of ethanol or none at all.
This has a benificial effect on carburettored engines which were not designed to cope with additives like this.
Ethanol also absorbs moisture from the atmosphere and attacks cork and rubber/some synthetic materials used for pipework.
It's not nice stuff.
However your engine does need to be set up properly for higher octane levels.

John

[V Mad]

....Ethanol also absorbs moisture from the atmosphere and attacks cork and rubber/some synthetic materials used for pipework....
John

Not just soft materials, it apparently attacks metals too like copper.