I'm not 100% sure on 300hp Northstars. But the Northstar for 275 horsemotor starting in 2000 was able to use regular unleaded. I have been doing this with no problem. My eldo runs fine with plenty of kick. The difference between using premium and regular is power. The onboard computer can determine with sensors the gas quality and adjusts acordingly. With higher octane the Northstar should provide higher performance. So it depends on what you want from you car which grade of gas to choose.
On ANY computer-controlled engine system equipped with a knock sensor (in other words, your car), the PCM retards base timing to compensate for engine knock brought on by low octane. As the timing is retarded, the engine will:
1. Run hotter
2. Run cleaner with regards to emissions
3. Run weaker
4. Get lower MPG
The lower grade fuel will also tend to build carbon in the combustion chamber faster which will further aggrivate the situation.
Bottom line: I ALWAYS run AT LEAST what the recommended octane is (I run premium in my Fleetwood even though it only requires regular).
The following is quote from Cadillac. Since 2000 the Northstar was designed to run on regular. It is more than just nox sensor adjustment by the on board computer. Before 2000 Cadillac did not allow the use of regular.
"What's more, Cadillac's Northstar V8 has been redesigned from the inside out to achieve better mileage with regular fuel, smoother and quieter operation, and certification as a low-emission vehicle (LEV) for California and certain Northeast states."
Running Premium will give better performance, but 2000 and newer Northstars were designed operate with a min of 87 octane.
Well i traded it my Lincol Navigator for a Deville and that was it for me when the sales person told me i can put regular gas in their. In my Navi i had to put 93 nothing less, i was spending 75 as week in gas it sucks
My 94 eldo has been using 87 for years with no ill effects and I'm getting avg of 21.6mpg. 145k miles. No carbon build up what so ever due to plenty of WOT. I think if you due a search on "octane" with user "*********" you will find all the info you need to dispel all the myths about what grade of fuel to use.
eh... if you are getting a newer Cadillac DeVille, then just run premium... don't cheapen out on it...
yeah, the knock sensor can retard the timing.. but it is more of a safety thing to prevent further damage to the enigne.... in other words... you can use cheap gas, and have the knock sensor do it's job, but Kat said the end result of what would happen...
... think of it as being an object... any object, this object has a primary system and a secondary back up system... I dunno... lets say a motor mount... if the motor mount breaks, there is still a bolt built into it to prevent the enigne from jumping too much... and practically coming out of the car.... insead of fixing the mount, you just keep driving around with it, everytime to accelerate the engine jumps around... until one day after abuse, that secondary system will fail and that bolt will snap... a corny comparison, yes, but that is what is basically happening when relying on the knock sensor to prevent pre-ignition....
... Last winter when my Olds was my only car, I ran premium all the time, dosn't even require it, but I did... the 3800 has a knock sensor too... now I run regular, as that engine will not get any benifit from premium... I used to run premium in my '79... then as I got thinking about it... with a lousy 8.2:1 compression (for NA car) it shouldn't need premium.... so I use regular, and every once in a while fill up with Sunoco Ultra 93... even under the most demanding driving, the enigne never pings or anything... stock 425 runs fine on 87.... my '93 requires premium, dosn't ahve a knock sensor either... plus we advanced the timing a little... that car has never seen anything but premium sicne I owned it (don't know about it's history... I would say form everything, it always had premium) Sunoco Ultra 93 is what it likes best....
All in all, use what the owners manual says to use.... most forced induction or high performance enignes require premium... IIRC the 4banger in the Sentra SE-R needs premium as it is similar in design to a race enigne... just like the NorthStar....
... but be kind to the N*, give it premium gas, becuase it is a grerat engine in a luxury car, and it'll treat you great for years to come...
I have been running 87 for two years on the advice of ********* (GM powertrain engineer) and I have notived no difference in performance. I still get 23-24 MPG. The knock sensor system works very well. If your gonna race it run premium. That said the 2000 had the compression ratio lowered to "recommend" regular. DO NOT use fuel system cleaners. They can eat away the insulation on the fuel pump and injector windings. For a detailed explanation do a search for fuel injection cleaners or fuel additives and read the posts by *********.
You'll get 20 different answers to this question. I have an '00 Deville DHS. Started running 93 octane until prices jumped like crazy. Read recently it doesn't make a difference, but I do think performance is a bit different. I really don't think it makes much of a difference, although I'm still running 93. A good comment I read was: If you're going to drive a high-end vehicle, why put low-end fuel in it. Makes sense to me.