100+ octane gas?

[N0DIH]

I have heard, from some reasonable sources, that higher octane burns slower. Smokey Yunick said that the slow the burn the more time for things to go wrong. Higher octane does not have any significantly higher BTU's (like a couple more), just the resistance to detonation. The lowest? Ether!! Like octane of 10! SR71 Fuel? Like 1000.....

I personally feel run the lowest octane needed for the engine. If it takes 93 then run 93, if it takes 87, use 87. Don't waste $$ on 93 in a car that only needs 87. If the car was designed for 87, and it is pinging on 87, find out why.....

[BeelzeBob]

Higher octane fuel does not burn cooler or slower. It burns at the same temperature and rate. The difference in different octane gasolines is simply the fuel's ability to resist spontaneous combustion of the end gas in the chamber....it has nothing to do with the temperature of the burn, the burn rate or the power capability of the fuel.

[amott37]

87 octane in a NORTHSTAR, no way...a significant decrease in performance. I do run 89 on occation. GM dosen't =recommend 93 it is specified.

[amott37]

Originally Posted by Ranger

No. Octane has no effect on running smooth or rough. Mine runs just as smooth on 87 as it does on 93. You said it "SEEMS to like higher octane better than lower". I suspect alot has to do with what you expect and want to see. The K&N air filter does nothing for the Northstar powerwise, yet people swear they can "feel" more power. It does make more noise. Between the "sound" of more power and the fact that they just spent $60 on an air filter and need to justify it, your subconcious is probably telling you what you want to hear.

A K/N filter kit alone won't do much, however with a modded MAF, high flow CAT and 2.5" exhaust with high flow mufflers I have gained 34 HP by dyno. 97 Deville, 4.6 N 279CI/275HP stock

[Ranger]

Originally Posted by amott37

87 octane in a NORTHSTAR, no way...a significant decrease in performance. I do run 89 on occation. GM dosen't =recommend 93 it is specified.

I have been running 87 for 3 years now and the "seat of the pants dyno" can't tell the difference. If your racing and want the absolute best performance, by all means use 93. The Northstar will handle 87 quite well. Do a search and see what bbob has to say about it.

[Eric2203]

It will handle 87 from 2000 and up. Not the earlier years.

[Ranger]

Wrong. Any Northstar will handle 87 quite well.

[Eric2203]

Fine, it'll handle it. But up to 2000, it's not optimized for it. I'll quote bbob, it's easier to explain that way than for me to try and do it with my limited knowledge.

From here:
http://www.cadillacforums.com/forums...ane#post118804

Premium was "required" for the first few years of Northstar production. Around 1997 the fuel requirements were changed to premium "recommended" and premium was removed from the dash and filler cap.

Regular fuel will run fine in most all of the 93-99 engines under most conditions. The engines have a very effective knock control system that will protect the engine is lower octane fuels are used with little or no apparent driveability impact. So, using regular is fine in a 93-99 engine. If you notice degraded drivability (sags, hesitations, loss of power) on the regular octane fuel in hot, dry ambient conditions then you might want to try a better octane grade of fuel...but the engine will not be damaged nor care.

The 93-99 engines had a very tolerant combustion chamber that was fairly knock resistant and lost very little power or driveability when the knock control system retards the spark because of detonation. For this reason and sufficient field experience running on regular fuel the "premium only" requirement was dropped.

The 93-99 engines have more compression and are definitely tuned for premium and will not make full power nor get full fuel economy if a lesser octane fuel is used. But most all drivers will not notice the difference.

Use regular and try it. Unless you live and drive in Phoenix city traffic all the time in the summer or are planning on towing a trailer thru Death Valley in the summer regular fuel will be fine. If you are planning a track day with your STS or are racing your buddy for pinks then use premium for maximum power. Otherwise, a 93-99 will be fine on regular most all the time.


A 2000 and later Northstar engine will be fine on regular period as it was designed and tuned for regular from the beginning.

From here: http://www.cadillacforums.com/forums...ane#post299623

First, several times it has been said and/or alluded to that the regular fuel burns "faster" or "hotter" or that premium fuel burns "slower" or "cooler"....it doesn't. The different grades of gas burn at the same rate and at the same temperature. Period. The difference in the fuel is the ability to resist spontaneous combustion of the end gas in the chamber. The higher the octane rating...the greater the ability to resist detonation or that spontaneous combustion of the end gas.


Changing octane of the fuel does not affect the power directly. The question is...does the engine have a knock sensor?? If the engine has a knock sensor it will detect detonation from fuel with too low an octane rating and retard the spark. That causes a power loss....the spark retard that is. If the engine doesn't spark knock on the lower octane fuel, however, then there will be no power loss. So, how close to "optimum" performance on the higher octane fuel is the engine set up determines whether it will spark knock and thus, whether there will be any performance loss on lower octane fuel.

A 93-99 Northstar is optimized with compression and timing for premium fuel. It also has a knock sensor. It also has a pretty good combustion chamber that is very fast burn and is very detonation resistent...even on lower octane fuels.

The other assumption people make is that the idea of spark knock or detonation is a black and white deal. It isn't at all. Whether any given engine is going to spark knock on lower octane fuel is dependent on the barometric pressue that day, the alitude you are operating at, the air temperature at the air inlet, the humidity that day (big effect from humidity), etc..... An engine might be fine on 87 octane fuel on a cool, wet, low baro day and knock like crazy (or have high spark retard and power loss) on a warm, dry high baro day. Same engine and same fuel...different results for diffferent conditions.

Factory fuel recommendations are always stated for the worst case. A 93-99 Northstar will always make the full power and have no spark retard from the knock sensor system with premium fuel....no matter how high the baro, how low the humidity or how hot the inlet air.... Does this mean that you always need premium. No. If you guaranteed want the optimum power then put premium in so it is there when needed. If you put regular fuel in, the engine is going to run fine under most conditions but may suffer some power loss at full throttle, peak power on a hot, dry, high baro day at sea level. This is why some people put regular fuel in a 93-99 Northstar and never notice the difference and why other people can perceive some driveability or power loss. It is very dependent on the conditions.

A 93-99 Northstar needs premium about 75 % of the time/conditions I would estimate to be able to make absolutely the maximum power. 25%of the time it can still do it on regular due to the varying conditions. A 2000 or later Northstar can be happy 80 % of the time on regular...but....in 20% of the cases it would need premium to make absolutely the last few HP. There is no cut and dried answer here...unless you want to be absoluely sure all the time under all conditions. Otherwise, you have to play it by ear with the octane of the fuel.

The Northstar for all years is very tolerante of the fuel octane rating. Even when some detonation is encountered and the knock system retards the spark accordingly, there is very little power loss when the spark retards. This is because the chamber doesn't need much spark advance (due to the fast burn) and thus , when spark is retarded, it doesn't loose as much power.

Different engines respond differently... Some engines in the past had slower combustion chambers and they would fall on their face when regular fuel was used due to the excessive spark retard. So, in those engines, running regular would impart a significant driveability penalty that was very obvious.

Try it and see. Put some lower grade of fuel in and see and listen. If you hear detonation or sense performance loss then up the octane rating next time. Otherwise, run the lower grade of fuel...it is fine.

The amount of power lost due to regular fuel in a 93-99 Northstar is not that great. Not as much as 20 HP even at full throttle , max RPM. Not enough for the old butt dyno to really tell.

Prices may be high, but personally, if I drive an early Northstar, I go the extra mile and put premium in it. I used to before I got the 95 SDV (4.9, not Northstar).

[Ranger]

Isn't that what I said (in much fewer words)? BTW, 4.9 does not have a knock sensor so you are pretty much stuck with premium.

[marc86]

i just use 91 octane, treats me well with my 93 scd.....still get 24 mpg on highway....

[amott37]

24 highway?...if my 99 deville gets less than 28 highway I start gettin busy with a wrench. 54000 mile avg is 24.6, lowest tank 19.2 and highest tank 33.4. typical highway for me - I95 N/S is 30.5 over 400 mile at 70+mph