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Regular Vs. Premium

9K views 39 replies 27 participants last post by  Clint 
#1 ·
A few local gas stations around here run specials on Mondays and Tuesdays where they charge regular price for premium. I bought my truck at the end of December and have been putting the premium in it ever since. I've been reading a little bit about the fact that regular is rectum-ended, I mean recommended, and I have what could be viewed as a dumb question.
Premium unleaded will not decrease my performance compared to regular, Will it?
 
#2 ·
You're just giving away extra money. If your truck doesn't require it why would use it? The different octanes burn at a different rate so you get no benefit from it. I guess the gas is way cheap where you live so it doesn't matter? LOL

Clint
 
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#3 ·
It is pretty cheap where I'm at (2.099), compared to a lot a places I'm sure. But I don't buy the premium, unless it is the same price as regular. If the stores stop running the special of prem. for reg. $, I won't have to worry about buying premium because it is so d@m^ expensive.
Also isn't it pretty sad that we have be conditioned into thinking 2.099 is cheap gas :bangit:
 
#4 ·
You might want to do a search. This has been discussed many times before.
Higher octane fuel will allow the engine to advance timing. This can increase power and fuel economy. Some think it helps and some feel it doesn't. I have about 48K miles on my Titan. The first half I used 87 and the last half I have used 91 octane fuel. Here the difference in cost is about 4.5%. My mileage increase has been more than that so I feel it is better to use 91. I have no way to compare power easily but it does seem to run better with 91.
 
#5 ·
JS02 said:
You might want to do a search. This has been discussed many times before.
Higher octane fuel will allow the engine to advance timing. This can increase power and fuel economy. Some think it helps and some feel it doesn't. I have about 48K miles on my Titan. The first half I used 87 and the last half I have used 91 octane fuel. Here the difference in cost is about 4.5%. My mileage increase has been more than that so I feel it is better to use 91. I have no way to compare power easily but it does seem to run better with 91.
Around here 91 octane premium is about 10% more than 87 octane regular, so unless I see an increase in milage greater than or equal to 10% I'll stick with the regular 87 octane stuff.
 
#6 ·
ptgarcia said:
Around here 91 octane premium is about 10% more than 87 octane regular, so unless I see an increase in milage greater than or equal to 10% I'll stick with the regular 87 octane stuff.
Same with performance here, if 93 octane doent slam me into my drivers seat @ $2.91 per gal I dont want no part. Thanks but I stick to 87 all day long.
 
#7 ·
JS02 said:
You might want to do a search. This has been discussed many times before.
Higher octane fuel will allow the engine to advance timing. This can increase power and fuel economy. Some think it helps and some feel it doesn't. I have about 48K miles on my Titan. The first half I used 87 and the last half I have used 91 octane fuel. Here the difference in cost is about 4.5%. My mileage increase has been more than that so I feel it is better to use 91. I have no way to compare power easily but it does seem to run better with 91.
Probably more to do with the truck breaking in than the octane of the gas.
 
#8 ·
Numerous studies have been done on this. Car & Driver has an editoral about it in this months issue. Basically, if the truck is on the dyno or racetrack, you can tell. (2-4 hp kinda thing.) There *may* be some validity with keeping injectors cleaner, but at a 10% permium around here, I'll stick w/the cheap stuff.
 
#10 ·
Higher octane retards your timing, and causes your engine to run poorly.

Then after you get a history of good mileage with a good gasoline, you can alter your choice of gasoline. Going to higher octane alone is like going swimming in the Everglades. Chances are,[/b] the power will drop off, your engine will run hot and mileage will decay. It seems best efficiency (or optimum pressure point) reached by the engine occurs when the fuel octane is correct. This optimum pressure occurs inside the engine cylinders when the piston is 15 degrees after top dead center. Too high an octane may cause optimum pressure to occur at 25 or 35 degrees after top center which means late timing that causes power to drop (Retards timing) . Too low an octane rating will cause peak pressure to happen at 5 or 10 degrees after top center. Such early timing leads to detonation, loss of power and even engine damage. So you just cannot beat proper timing with proper gasoline.[/b]

Detonation is a form of abnormal combustion. Combustion is abnormal when a second (or more) flame front(s) appear in the chamber. Normal combustion only has one flame front that appears near the spark plug and crosses the chamber at 30 to 100 meters per second without misfire. The octane rating of a gasoline primarily controls the amount of heat the fuel can tolerate before a second flame front can get started. Some persons have described Octane Rating as the relative speed of combustion. In other words they believe octane governs how fast a fuel burns. That is incorrect. The speed of combustion, just superficially, may or may not decrease with higher octane in the standard methods of fuel testing in a C.F.R. research engine: These are Motor, Research, Aviation or Supercharged. The speed of combustion is more a factor of the ingredients of the fuel and the actual compression ratio in the engine being tested.
 
#11 ·
i use premium. i used it in my trans am, my maxima called for it, hell even my quad calls for it. AS LONG as it stays under $2.49 i'll keep using it in my titan, when it goes above that then i will use either 92-or 91 witch ever the station has that i stop at.
 
#12 ·
jeffs05SE said:
i use premium. i used it in my trans am, my maxima called for it, hell even my quad calls for it. AS LONG as it stays under $2.49 i'll keep using it in my titan, when it goes above that then i will use either 92-or 91 witch ever the station has that i stop at.
Damn, I just filled up with 87 regular this morning at $2.49 per gallon. And double damn, if 91-92 is not premium where you are, what is? The highest I've seen around here is 91, and its like $2.79 per gallon!
 
#13 ·
ptgarcia said:
Damn, I just filled up with 87 regular this morning at $2.49 per gallon. And double damn, if 91-92 is not premium where you are, what is? The highest I've seen around here is 91, and its like $2.79 per gallon!

well most gas stations have regular, super and premium. but some have the 4 selections of 87, 91, 92, 93. regular, super, premium, and super premium. i usually use 93 or 91 cause all gas stations around me carry both of them. there are a couple that carry the 92 also.
 
#14 ·
I think you got it backwards...

sgbofav said:
Higher octane retards your timing, and causes your engine to run poorly.
Octane rating is a rating of the fuel to resist preignition given the compression ratio of the engine. When your engine have low compression ratio... you can generally use the lower octane fuel. Higher compression ration will require you to use higher octane fuel.

If fuel octane is too low for a given compression ratio, the fuel prematurely and spontaneously ignites too early and the fuel charge EXPLODES rather than BURNS resulting in incomplete combustion. The net effect is a loss in power and possible engine damage. The operator hears an audible "knock" or "ping", referred to as detonation. Detonation may vary from a faint noise on light acceleration to a constant, deep hammering noise while driving at a constant speed.

In modern engine, with ECM truing timing continuously as you drive... it retards the timing whenever it detects 'knock'. So if you have a high compression ratio engine, running low octane fuel... you cause your engine to retard timing. If you have a low compression ratio engine running higher octane fuel (ie: our Titan V8 engine)... nothing happens. It's just money wasted since the higher octane fuel can easily hold up to the compression ratio of the engine and get detonated by the spark... and not pre-detonate.

Generally, engines with compression ratios of 9.9:1 or less will safely operate with unleaded 87 octane fuel. Engines with higher compression ratios usually require higher octane fuels. Our Titan is running 9.8:1 last time I check, so lower 87 octane should be fine.

Do you think you will get more HP using higher octane... I don't think so usless you change out your compression ratio of the engine. And even if you do make a like gain at the crank... it'll probably be lost by the time it gets to the wheel. If you want more HP... get a stroker kit (if someone make one or have one custom made) :thedevil:

My 2 cent...
 
#16 ·
Lower octane fuel out West

When I was out in Aridzona, I was surprised at the lower octane rated fuel that was available. Instead of the 87 89 93 fuel available in the East, they had 85, 89 and 91. I was driving a rental Mustang GT and wanted to put Premium in so that I could continue cruising at century speeds on the open desert on the empty hiways. The 91 worked fine.

I had never seen octane ratings so low yet apparently everyone's car was operating properly on the lower rated brew. Elevations are generally higher out west which causes lowered combustion efficiency but I never really noticed anything wrong running the lower octane fuels. With new computer controlled ignition systems, it appears engines are now more adaptable to varying fuel grades.
 
#17 ·
even though manufacturers recommend 93 for premium, 91 works just fine and is the minimum recommended grade for premium

Out west the pipeline system is different and the grades of gas carried are different than in the east. Go figure...
85 octane has something to do with altitude I believe.
 
#18 ·
Honestly i put preimum in my Titan
when ever i tow my boat, and sometimes when i want to clean out my intakes. i honestly DO notice a diffenence.
 
#20 ·
Titan horsepower when fueled with different grades

This is a paste from a post on the sister ship Armada. The thread was discussing the differences between power rating of the Armada vs. the more expensive QX56. Interesting post:


"Beg to differ all you want, they are made on the same assembly line with the Titan. A member on the Titan forum is an engineer on the line. He says they use the same drivetrains and ECUs for all 3, except for the rear for the Titan. Mechanically, there is no difference. The differences are purely cosmetic: soundproofing wood dash, chrome side panels and wheels, HIDs, nose, etc.
Salesmen don't know their heads from their . I was at a Ford dealer with a senior salesmen who was trying to tell me the Mustang GT had a 6 cylinder. Their job is to sell cars. Read your manual and do what it says.

Last time I hope I need to post this. The ECU in all of them adjusts the engine's timing based on feedback from the knock sensor. This allows you to get more power from higher octane gas as you can advance the timing without detonation problems. If you rated the Armada or Titan motors on Super, they would be 315/385. If you rate the QX56 engine on regular, it would be 305/379. On identical fuel and rear gear ratios, most Armadas will be faster than QX56 because they weigh less. The LE 4x4 weighs almost the same as the QX56 and will be the same. "
 
#21 ·
skytop said:
When I was out in Aridzona, I was surprised at the lower octane rated fuel that was available. Instead of the 87 89 93 fuel available in the East, they had 85, 89 and 91. I was driving a rental Mustang GT and wanted to put Premium in so that I could continue cruising at century speeds on the open desert on the empty hiways. The 91 worked fine.

I had never seen octane ratings so low yet apparently everyone's car was operating properly on the lower rated brew. Elevations are generally higher out west which causes lowered combustion efficiency but I never really noticed anything wrong running the lower octane fuels. With new computer controlled ignition systems, it appears engines are now more adaptable to varying fuel grades.
Higher altitudes use lower octane fuels (a vapor pressure thing).
 
#22 ·
ECU and octane numbers

Unless you program ECU... it's hard to understand what they really do for your engine. I'm speaking from playing with Honda ECU and their timing maps, and NOT the Titan's ECU. While Nissan *may* do it differently... I really doubt it.

As for your engine taking advantage of higher octane number fuel is not true. I’ll use a 99 Honda Civic ECU as an example. The ECU retards your timing based on the knock-sensor. If your engine doesn’t ‘knock’, it’ll advance timing until it gets back up to their default maps or until it does detect ‘knock’… at which point it holds the timing at that point. BUT it’ll never go above it’s own default maps. And default timing maps for the Civic is based on 87 Octane fuel, otherwise… Regular Unleaded.

If you put higher octane fuel into the system… the ECU doesn’t know it’s higher octane, it could care less what’s in the system. As long as there’s no ‘knock’… it keeps to the default map. So when someone tells you that the engine runs better on higher octane numbers… I always wonder ‘how does the engine knows it’s higher octane and thus advance timing?’. It doesn’t… all the ECU can do is based it’s timing on ‘knock’. When there’s knock… it’ll step back the timing a step at a time until the knock goes away.

Also… going back to the root of why the different octane numbers… compression ratio. Compression ratio is how much force with which the pistons compress the mixture before it ignites and pushes the piston back away (basic engine 101). So if your engine has a compression ratio of 9.8:1… it means that it will compress the fuel/air mixture 9.8 times it’s mass before the spark from the spark-plug will detonate the mixture. As stated before… 87 octane are rated for 9.9:1 compression, which means 87 octane fuel will stand up to a compression of itself up to 9.9:1 before it will self detonate without the help of a spark.

That’s why when tuner rise the compression ratio of a given engine, for this example… still a Civic, you have to redo the ECU with a timing map that’s suited for the compression ratio. And on top of that… pump in higher-octane fuel. Same as in anyone that has ever put a turbo/supercharger into a stock engine without having the ECU re-map… you need some form of manual timing control that will allow you to advance the timing. The key word is still compression ratio and not higher-octane fuel. If you have a 9.8:1 compression ratio engine… and you pump 93-octane fuel into the system and advance the timing, NOTHING will happen. The only thing that will result from higher-octane fuel into a low compression engine is ‘unburned fuel’. If the engine cannot make enough pressure to overcome the octane present in a fuel, an incomplete burn may result. You may end up with lowered performance or fuel economy as the engine struggles (and fails) to take full advantage of the fuel present in the cylinders.

SO... stick with what Nissan recommends, just use Regular Unleaded and be happy it’s not $3/gal yet :thedevil:
 
#23 ·
You're are right about all you just said about the Hondas and their ECUs work just the same as Nissans. However, the reason the Titan will make 315 HP with 91 octane because Nissan sends it from the factory that way. Thats exactly what that guy was quoting from the Nissan engineer. The Titan, Armada & QX56 all use the same engine, drivetrain and ECU. Which when you think about is a very economical way to manufacture since everything is the same with no worrys about making parts for basically the same engine to make different power figures.

A good example would be another 1999 Civic this one being an Si model which requires premium fuel. It will happily run on 87, if it has to. However it reduces power accordingly to compensate for the reduced octane. The Titan ECU is probably setup in the same way, only the Titan doesn't need the extra octane, it's basically used as a key to unlock the premium fuel map which provides better power.
 
#24 ·
Titank said:
Unless you program ECU... it's hard to understand what they really do for your engine. I'm speaking from playing with Honda ECU and their timing maps, and NOT the Titan's ECU. While Nissan *may* do it differently... I really doubt it.

As for your engine taking advantage of higher octane number fuel is not true. I’ll use a 99 Honda Civic ECU as an example. The ECU retards your timing based on the knock-sensor. If your engine doesn’t ‘knock’, it’ll advance timing until it gets back up to their default maps or until it does detect ‘knock’… at which point it holds the timing at that point. BUT it’ll never go above it’s own default maps. And default timing maps for the Civic is based on 87 Octane fuel, otherwise… Regular Unleaded.

If you put higher octane fuel into the system… the ECU doesn’t know it’s higher octane, it could care less what’s in the system. As long as there’s no ‘knock’… it keeps to the default map. So when someone tells you that the engine runs better on higher octane numbers… I always wonder ‘how does the engine knows it’s higher octane and thus advance timing?’. It doesn’t… all the ECU can do is based it’s timing on ‘knock’. When there’s knock… it’ll step back the timing a step at a time until the knock goes away.

Also… going back to the root of why the different octane numbers… compression ratio. Compression ratio is how much force with which the pistons compress the mixture before it ignites and pushes the piston back away (basic engine 101). So if your engine has a compression ratio of 9.8:1… it means that it will compress the fuel/air mixture 9.8 times it’s mass before the spark from the spark-plug will detonate the mixture. As stated before… 87 octane are rated for 9.9:1 compression, which means 87 octane fuel will stand up to a compression of itself up to 9.9:1 before it will self detonate without the help of a spark.

That’s why when tuner rise the compression ratio of a given engine, for this example… still a Civic, you have to redo the ECU with a timing map that’s suited for the compression ratio. And on top of that… pump in higher-octane fuel. Same as in anyone that has ever put a turbo/supercharger into a stock engine without having the ECU re-map… you need some form of manual timing control that will allow you to advance the timing. The key word is still compression ratio and not higher-octane fuel. If you have a 9.8:1 compression ratio engine… and you pump 93-octane fuel into the system and advance the timing, NOTHING will happen. The only thing that will result from higher-octane fuel into a low compression engine is ‘unburned fuel’. If the engine cannot make enough pressure to overcome the octane present in a fuel, an incomplete burn may result. You may end up with lowered performance or fuel economy as the engine struggles (and fails) to take full advantage of the fuel present in the cylinders.

SO... stick with what Nissan recommends, just use Regular Unleaded and be happy it’s not $3/gal yet :thedevil:
I measured my titan timing once using a scan tool and different grades of gas. the higher grade gas let the engine run more advanced timing. the advanced timing gives the higher octane fuel the time needed to fully burn. the longer burn and push on the cylinder results in more torque and horsepower. I never checked timing advance for premium but mid-grade definitly will add some power and get better mileage.

juma
 
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