Do N/A cars really require 91 or higher octane?

[Frogger]

I just bought my car two days ago. The guages say "premium fuel only" I thought that was a bit weird so I looked it up in a chiltons manual and it said all 2.0 DOHC engines require atleast 91 octane. Is this true for even NON turbo eclipses? I filled it up with 93 the first night I got it.

 

[Catbox_95]

Maybe for absolutely best performance, but it won't hurt anything to put 87 in it. My wife's Maxima says the same thing, and there's no way I can get her to put 93 in it, so it always has 87 in it. If I listen very carefully, under acceleration at certain rpm's I can hear a little valve clatter, but if I run the 93 in it I get no clatter.

Just run the 91 or 93. It may cost more per gallon, but it's better for the engine and you will get a little better gas mileage, off-setting the higher cost per gallon.

 

[Defiant]

My wife's Maxima says the same thing, and there's no way I can get her to put 93 in it, so it always has 87 in it. If I listen very carefully, under acceleration at certain rpm's I can hear a little valve clatter, but if I run the 93 in it I get no clatter.

That's ping. The valve noises won't change.

Just run the 91 or 93. It may cost more per gallon, but it's better for the engine and you will get a little better gas mileage, off-setting the higher cost per gallon.

It's slightly worse for the engine, as the higher amount of additives and octane enhancers increase the amount of ash while reducing the energy per gallon. Any benefit to perfomance will arise out of the engine's timing running more advanced than it can on the lower octane fuel.

An NT should be fine on regular. My turbo does. I waffle back-and-forth on which I get. I don't see a peformance difference on the stock engine.

 

[Frogger]

Thanks I'll stick with 91/93

 

[Catbox_95]

That's ping. The valve noises won't change.It's slightly worse for the engine, as the higher amount of additives and octane enhancers increase the amount of ash while reducing the energy per gallon. Any benefit to perfomance will arise out of the engine's timing running more advanced than it can on the lower octane fuel.

An NT should be fine on regular. My turbo does. I waffle back-and-forth on which I get. I don't see a peformance difference on the stock engine.

Yes, but "ping" is the valve stems slapping the rocker arms do to unburnt fuel, so ping and valve noise can be one in the same.

I disagree on your stance on higher octane fuel. I'm not a chemist, but have slight knowledge on the subject. That being said, I know I may be wrong, but then how come higher compression engines must have higher octane fuel? I do not think it's wise to run boost with low octane fuel, as it is the same effect as high compression. I am a pilot and so know a little about airplane engines, and they have a lot of compression and therefore must run on 100 octane low-lead fuel. You put 93 octane in there and you cut your horsepower in half and increase detonation.

Lower octane burns faster, that is why high compression engines and engines with advanced timing detonate on low octane. Higher octane burns more complete and fuller, which is why it is required in high compression, so that there is no unburnt fuel in the cylinder which cannot be compressed.

(With respect, virtually nothing in this post is accurate -Defiant.)

 

[ran-o-matic]

Yes, but "ping" is the valve stems slapping the rocker arms do to unburnt fuel, so ping and valve noise can be one in the same.
...

Ping is caused when the air/fuel mixture self-ignites before the spark plug fires. Valve stems are not involved.

 

[i1nk83]

hate to break it to yah but a/c engines dont have higher compression, granted the acrobatic engines might,they tend to run anywhere from 6:1 to 8.5:1. (not very high for an n/a engine) why do you think they burn so much fuel because the compression is so low and they rediculiously uneffecient, but they are reliable so they get used. damned avation.

 

[KGB Pilot125]

actually 87 octane has more power per gallon but it is unstable you squeeze it and it could go off at any time, higher octane 91-93 not race gas, produces less power per gallon or less energy but its more stable do to the additives so you can actually sqeeze the mixture more ie: more combustion and thats how you make the power.

 

[2GeNTSi]

ugh I feel so stupid, yesterday I accidentaly put 87 in my car. I was in a hurry because I was late for work and it's those kind of stations where one pump handles all the octanes. I didn't boost at all on the way to work so I hope I'm fine...only put two gallons until I realized my five dollars of gas was going a long way so I got about 20 more miles till I'm on empty.

 

[Doug99RS]

The stock 2gnt should run the 87 octane and if I'm not mistaken there should be something in the owners manual about it. However, if someone has replaced the computer then it may require a higher octane. I would check the computer.
Doug

 

[psychlow]

Yes, but "ping" is the valve stems slapping the rocker arms do to unburnt fuel, so ping and valve noise can be one in the same.

You need to read this:
http://www.dsmtuners.com/forums/showthread.php?t=153144

Ping is a product of detonation, which is much like slapping your engine with a hammer. What you're hearing is a result of detonation, not unburnt fuel. If it were unburnt fuel, your engine would backfire every five seconds from unburnt fuel making its way into your exhaust.

Detonation occurs when the flame front travels faster than (or equal to) the speed of sound. It is usually coupled with multiple, uncontrolled flame fronts that all have their own shock waves. This is undesirable, as in an IC engine, we want the flame front to travel, in a controlled fashion, from the spark plug to the piston, from the middle of the cylinder outward.

When combustion events transition from deflagration to detonation, they have much more brisance, which allows them to start destroying (and sometimes even shattering) parts. This is what causes the sound you hear. The cylinder pressure rises extremely quickly, and it usually occurs when the piston is in a position that is undesirable for that amount of pressure. When coupled with multiple flame fronts, the shock waves will bounce off each other, which increases the effects.

but then how come higher compression engines must have higher octane fuel?

Because they are looking for a resistance to detonation.

I do not think it's wise to run boost with low octane fuel, as it is the same effect as high compression. I am a pilot and so know a little about airplane engines, and they have a lot of compression and therefore must run on 100 octane low-lead fuel. You put 93 octane in there and you cut your horsepower in half and increase detonation.

It all depends on how the engine is tuned. If you run boost on an engine that has a rich enough A/F to compensate, you'll never see adverse side effects because the extra gasoline can cool the cylinder enough to keep detonation from occurring, up to a certain point. You can't run 40PSI on 87 octane if you have a 3:1 A/F ratio, for example, but you can run 12PSI on 87 octane with an 11:1 A/F ratio in most cases.

Lower octane burns faster, that is why high compression engines and engines with advanced timing detonate on low octane. Higher octane burns more complete and fuller, which is why it is required in high compression, so that there is no unburnt fuel in the cylinder which cannot be compressed.

Not true. Higher octane prevents detonation - that is octane's only function. In both situations, assuming a 14.7:1 A/F ratio, ALL of the gasoline will be burned, regardless of the octane. The 93 octane will burn slightly slower than 87 octane, and have slightly less energy per volume, but it will also resist detonation longer. The tradeoff is that the increased boost, timing, and leaner A/F you can run can net you more power than lower boost, timing, and a richer A/F at a lower octane.