Can anyone offer a definitive answer to this quesiton? I have heard from a few dealers and mechanics that yes you must use Premium unleaded in pre 04 Supercharged Engines and others that say no it will run fine on 87 Octane. I assume higher Octane may be needed to realize the full performance potential of the engine/supercharger and perhaps get better mileage to a degree but other than "retarding" the timing as one fellow put it, does regular unleaded fuel actually do any damage to the SC or engine or wear parts out faster over time? Splitting hairs now i guess but I will ask...can regular fuel be used safely and without performance decrease if I am also going to use a high octane fuel additive at every fillup. And YES, the additives are cheaper than paying the 10 cents more for the fuel on a full fill. Gas prices are killer here in Ontario most of the time. Went up to $1.31 +/- PER LITRE a couple months ago (roughly $5.25/gallon), and now sits at $0.79-$0.91 per litre. Needless to say I try to leave my "BIG GREEN PIG" with the 160 litre tank (yes ONE tank) in the driveway more often now that I have the Bonneville. One last thing, does anyone have anything to say about Lucas Oil Additive/Stabilizer VS Synthetic. It seems like a cheap alternative and I have heard nothing but good things about it. Thanks again for all your help. I am excited to be apart of such an informative forum filled with such passionate Bonnie Lovers

yes, sorry but you need premium fuel or you can have long term problem.

And yes gas is expensive , 1.07$ premium gas here in montreal right now.
Higher the octane will be , better the engine will be.

YOU MUST USE PREMIUM!!! if ya can't pay don't play.

Plus your milage will suffer too.

Hmm..how can I put an equation on this...

87 Octane in L67 = My little ponie horse
89 Octane in L67 = Quarter Horse
91-94 Octane = Mustangs or Clidesdale horses.

Get the picture?

wish you goodluck.

ok, i wish some of the members here would actually tell him why, not just say he must use premium. so heres the gig.

With forced induction ( supercharger or turbocharger ) a higher octane gas is always recomeneded. The supercharger increases cylinder pressure, and when under load, wide open throttle, high boost, and hot coditions, this extra pressure can cause the engine to ping or even prmaturely detonate resulting in a burned valve or piston. The use of premium fuel makes the likelyhood of this from hapening lessen greatly.
However, if pinging does occur, the computer measures this through the knock sensor, and will retard the timing to help correct the problem. Sometimes this is not enough however, and the pinging will continue and cause serious internal damage, also fuel mileage and performance will suffer.

This is also dependant on the vehicle, some 3800s will run beautifully on 89, and some dont run well at all. If you dont have the equipment to monitor how much "knock retard" is being applied to the timing, STICK WITH 93

IMO Lucas oil stabilizer is not helpful at all, it makes your oil thicker than the manufacturer recomends, and will not benefit anything that can not be accomplishd through proper maintenence.
I have used lucas, but only to help slow down a pretty serious oil leak in a previous vehicle.

If you don't run at least 91 octane and your knock sensor fails, you WILL cause damage. Maybe instantly, certainly over time.

I WOULD NEVER DO IT...
but my mom had ran 87-89 in her 97 ssei for years...runs like a champ, but she never gets on it