Bill Ball

I've run 87 US octane for about 100K miles. Checks with Spanner and Sharktuner have shown no knocks at all under heavy load or whatever. Now, this is only when my car has been w/o the supercharger, of course. GT and GTS and probably some other models would not tolerate this. The book calls for 90 octane US for my S4. I've seen GTS's knock like crazy on 91, although we fixed that in one case by doing a BG induction treatment (removes coke from combustion chamber), so it no longer knocked on 91. We did not try lower octane after that and doubt it would be a good idea. In my case (89 S4 stock except x-pipe) 87 is fine and I will continue to use it until I do some other engine mod. I'm planning to install some different cams later this year and we will Sharktune with 91 octane. That will likely be the end of using 87 for me, especially if we advance the timing to the ragged edge.

karl ruiter

My '88 is undrivable with regular. Pretty steep hills in my daily drive, though and dire need of an intake refresh.

But seriously, today in Honolulu a gallon of regular is $3.93 and a gallon of premium is $4.11. I seem to remember when premium was something like twice as much, at this point I'd just a soon put premium in everything.

WallyP

As a side note, based upon an earlier comment in this thread...

Octane boost additives are useless. They do exactly what the package says that they will do in most cases - add ten points to the octane rating when used as directed.

That is one octane number - a "point" is 0.1 octane number. So, your money increases the octane rating of your fuel from 87 to 88. That is known as "Truth in advertising".

Brett928S2

Hi

Usually in the UK I run my 928 S2 on Shell V-Power which is unleaded 98 octane....

Last year I found a Shell garage (one of only 5 in the UK) which was selling 5 star 100 OCTANE - LEADED !

Apparently they are only allowed to sell a small amount of this in 5 garages and its meant for "Veteran and Vintage" cars which cannot run unleaded due to their valve seats...

Soooo...I filled my tank with it and its was DRASTICALLY expensive (around 3 times the price of unleaded 98 octane) , I had around 1/4 of a tank before i filled so added around 15 gallons...

I drove off and around 20 miles later the effect kicked in.... the engine was a lot smoother and lot MORE POWERFUL.....I realise you may think it was a psychological effect, but it definitely wasnt as after 10 miles or so, I thought that I had just wasted all that money as no noticeable effect....

Once I got over 20 miles the effect as I said was startling to say the least, the engine absolutely loved it, I realise that with 10.4 compression it was designed for 98 octane but I suspect it was the lead the engine liked rather than the extra 2 octane...

Unfortunately that garage is around 170 miles away otherwise I would DEFINITELY use it all the time .... as it was a stunning difference !

All the best Brett

WallyP

" and its was DRASTICALLY expensive (around 3 times the price of unleaded 98 octane)"

Ouch! What did that work out to be in US dollars per US gallon? Or, if you don't want to do the math, what was the pump price?

aj986s

Most engines will tolerate leaded fuel just fine. However, the cats and O2 sensors will probably not.

mark kibort

ive been using regular in my tahoe and BMW 328i for over 10 years now. both are fine, no knocks. think of the 1000ss of dollars saved. I would only use 91 if i was going to do a DE with the BMW.
even my race motor for the 928 uses 91octane and seems to be fine with near 11:1 compression, but only 370rwhp. at 400rwhp plus, i will probably start to use a mix.

BILL!! lets do the shark tuning! Ive got until sept to get my HP up. I need to beat some of these AV8SS guys and all i need is a about 30hp or so!

Mark

Brett928S2

Hi Wally

It was around £2.90 per litre

All the best Brett

oaros

1 liter 95 unleaded about 1.37 Sterling where I live.
Makes it about 2.25 Dollars.
Gives you around $8.50 the gallon.

Brett928S2

Hi

So that makes my 5 star leaded around $22 per Uk gallon (roughly) ...lol

All the best Brett

WallyP

Works out to almost exactly $18/gal for us...

The payback on a twin-screw setup just got shorter.

Brett928S2

Hi Wally

I see your point, but IF anyone could afford 5* Leaded, I would bet that on a dyno after a couple of weeks of running it, it would show between 10 and 20 hp extra....

All the best Brett

Markmandude

From what I have always read and heard, the lower the octane you can use without knocking the better. The only reason higher octane would add more hp is if you engine was knocking with the lower octane and not running like it should.

SeanR

Well dang, I suppose we won't get to hear the OP and what he does next to destroy a 928.

Randy V

Oh dear - he's been banned.

That'll teach him to use regular gas!