Dark Blue

Now that gas is getting so expensive, I was wondering if it's absolutely necessary to use premium in a street diven 89 S4 auto. I know the S4's have knock sensors so in theory couldn't we get away with a lower octane gas. I always use premium b/c that's what the manual recommends, but is it really necessary. I hate to be penny wise and pound foolish, but I also hate to waste money. Thoughts?

Steve
'89 S4 Auto

Mongo

minimum 91 octane. anything below will result in detonation and damage to the piston rings.

ROG100

My 82 is made to run on regular as are most of the earlier cars.
I have run my GTS on 89 with no ill effects and she seems to perform just as well.
Providing your knock sensors are working OK it should not be a problem.
I am not an expert just reporting on my experience.

jeff jackson

Ditto...not to mention valves, valveguides, and tappets...all of which are "reverberated" about...when preignition occurs. Its worth the extra $.20/gallon to assure a healthy engine...Hell, even if the tank was empty, its only $4 more for the hi -octane fuel. Small difference,at $40+/ tank these days...Off topic, but I use "regularly"...the Lucas product..."Fuel injector Cleaner and Upper Cylinder Lubricant"...this is really not a "snake oil" product, it makes a noticeable difference in response, and performance, on my practically "stock" 86.5. I put a bottle in every other fillup, and have not looked back ....

Mark Anderson

My son has a 91 S4 and I changed the coding plug to use lower octane fuel. I never dynoed it but it probably lost about 30-40 hp and it now uses 89 octane and never pings.

deliriousga

I'm with Stig. It calls for 91 (RON+MON)/2 or better and we're talking $.10/gallon difference ($2.30 if you coast into the station). For me, it's 4 tanks/month or $9.20/month. Give up the Starbucks twice a month instead.

ROG100

Its not the money its the fact that 91 is unobtainable in certain areas.
What do you do then?
My wifes Turbo S bug needs premium but if you cant get it you have to use the best available.
Never been a problem - never noticed any difference in performance.
We use premium if it is available.

When I first got my Weissach I thought it needed premium until I read the handbook and found I had been wasting my money.

BC

A father I can aspire to be for my 3 year old Mark. Give him the car, but take the teeth out of it a bit.

borland

Apparently octane has no affect on deterioration during storage...

http://www.chevron.com/products/prod...term_gasoline/

khalloudy

Porsche 928s were made from the onset to run on ****ty low octane gas. The knock sensors will compensate and retard timing to prevent detonation. For optimal performance (and advanced timing), you will need high octane though of course. When the car was designed in the 70s with the oil supply problems, they assumed issues with fuel and designed the car to run on all fuels. 928s will pretty much run on any Octane and Leaded or unleaded. You don't want to run leaded if you have cats for obvious reasons.

Mongo

Sorry I should be more specific. You can run mid-grade (89 octane). BUT, put it this way, would you settle for a power loss and your knock sensors STRESSING to retard your timing bad enough to give your car cerebral palsy? NO? I didn't think so.

ew928

I'm not saving a few cents to trust that my 18 year old knock sensors will
be operational.
There's enough electrical issues to worry about.

Unless one's gunning for a stroker upgrade.

Ernest (NYC)

Mongo

This is true...

IcemanG17

For 20 cents a gallon in a vehicle that gets (optimistic) 20 mpg...the difference between super (2.60) and regular (2.40) 8.3% more in price...but its only 1 cent (@20mpg) or 2 cents (@ 10mpg) per mile more to use super...its a small price to pay for the extra performance and peace of mind!

If you really want to save money on gas...buy a 3-4 cylinder bucket that gets good mileage (see my sig...think 30-35mpg in town!)

deliriousga

Wow, you are optimistic! 14.7mpg here (combined hwy & city driving). Going from a Jeep Wrangler, though, that's an improvement. Add in the thrill factor and who cares what you get?