Octane requirments for NSX?

[cfra7]

Hi,

Can I use any octane rating of gas in the NSX without damage as long as I'm not sending the RPMs above 5,000? I have a 1991 and I was wondering if the computer will retard the timing if the motor detects knock.

I know that you are saying "Why have an NSX if you aren't going to use premium?". The answer is:

1. My NSX is a daily driver with 156K miles (80K placed on there by me personally).

2. As a daily driver, I just can't see spending $3 per gal. just to drive around under 70 MPH.

3. When I go to the track once or twice a year I will continue to use the good stuff.


So before you beat me up for the cheep gas, please note:

A. I've driven more miles in my NSX than 90% of the owners
B. I've had my car on the track than 90% of the owners (one or twice per year)
C. My car has more miles on it than 90% of all NSXs

I hope that buys me some credibility. If the NSX doesn't have a computer to retard the timing, I'll go back to premium. I've only been using 87 octane for a month and I can't tell any difference yet.

Thanks

 

[cfra7]

I did find a thread that stated that the computer would retard the timing on a 1994. I'm just not sure about the 1991.

PS.

To those who say why buy an NSX to use 87 octane, I say why buy an NSX if you aren't going to drive it as your daily driver?

 

[skyguy]

Does octane rating have much to do with RPM? Don't think so. More of a compression ratio.

NSX Compression Ratio: 10.2:1

Here are some guide lines for Compression Vs. Needed Octane:

7:1 .......... 89 octane
8:1 .......... 91 octane
9:1 .......... 94 Octane
10:1 ......... 98 Octane
11:1 ......... 104 octane
12:1 ......... 110 octane
13:1 ......... 115 octane

Copy of CECIL ADAMS article:

In most of the U.S., regular gas has an octane rating of 87, midgrade gas is 89, and premium is 91 or 92. (Octane ratings are lower in the mountain west due to the effects of thin air on internal combustion.) Contrary to widespread belief, the octane rating doesn't indicate how much power the fuel delivers; all grades of gasoline contain roughly the same amount of heat energy. Rather, a higher octane rating means the fuel is less likely to cause your engine to knock or ping. Knock, also known as detonation, occurs when part of the fuel-air mixture in one or more of your car's cylinders ignites spontaneously due to compression, independent of the combustion initiated by the spark plug. (The ideal gas law tells us that a gas heats up when compressed.) Instead of a controlled burn, you get what amounts to an explosion--not a good thing for your engine. To avoid this, high-octane gas is formulated to burn slower than regular, making it less likely to ignite without benefit of spark.

 

[NSXDreamer2]

I do see your reasoning behind the "wasting 92 octane gas as you were driving 70mph in fifth gear, coasting the whole way to work everyday." But it kind of question me that if you are asking the question? or you are just looking for some confirmation?? As you had already poured the least expensive grade of gas in your engine for a month.

I've only been using 87 octane for a month and I can't tell any difference yet.

That's pretty impressive, I don't have guts to try it on my nsx, but all the other car I dare to test with the lesser grade of gas, I can feel the difference, and it's not placebo effect.

The general idea is that anything in the nsx engine is not cheap. Therefore saving $2 -$3 each tank by using lesser grade of gas could not offset the potential problem that in turns asking for thousands of dollars of parts and labor.

I say why buy an NSX if you aren't going to drive it as your daily driver?

Because it's a waste!! Daily driving within the city sucks, even though I like to drive my nsx to work too, but lets see: sitting in the stop and go traffic, lugging the engine on the on ramp for that god damn traffic regulator light, traveling 25mph waiting someone riding his/her SUV over you..(who happens to have one hand on the phone and ther other holding his starbust mocha)..... I agree the beauty of nsx do let us deal with that, but is it worth it? or at least, you can't call it pleasant drive either...

 

[cfra7]

Thanks. Based on your article below, my RPM won't matter. However I know that it just isn't compression either. Let's call it "load". What determines load if not RPM? I know that some motors knock when going up hill. The compression didn't change but the load on the motor changed. So by not spinning the motor past 5,000 RPM haven't I reduced load and therefore the motor will be less likely to knock?

I brief I guess my question is still: Under normal driving situations, will the computer in a 1991 NSX retard the timing if it detects knock and will it be able to retard it enough in normal driving situations to compensate for 87 or 91 octane?

 

[cfra7]

NSXDreamer2,

I do see your point. Even at 12K miles a year. I'm probably only paying an extra $180 for premium than I would for running on regular. Given that it would cost me around $10K to replace/rebuild my motor, that may be a bad bet. Now we can probably agree that the motor I'm protecting is only worth around $2K but the cost of replacement or the devaluation of my car by selling it with a blown motor probably doesn't make it a great bet. I think I'm back on the premium grade starting today.

I'm still interested from an academic standpoint on what can safely be ran in the NSX in daily driving but I agree that it isn't worth the risk because I'm not sure anyone on the list is really sure they know the answer.

As far as the daily driver thing. Your commute must be a lot worse then mine. I only drive 5 miles but I do put 12K miles on the car each year. As you can tell, most of my miles aren't from driving to work. Even at a traffic light I would rather be driving an NSX than any other car. So I guess my answer is "Yes it's worth it" to drive an NSX every day! I must like driving mine more than you do. I still think it's the best street car in the world as long as you don't mind shifting and If I'm hit by an SUV, then I get to buy another NSX with less miles.

Thanks!

 

[NSXDreamer2]

oh, don't mistake me for not having the nsx out whenever is possible. If I have a way, I will drive my car everyday... (ummm, come to think of it, I had my nsx for 3 days to work now..) and I had a nice 350 miles in it last week. (a full track day with 6 sessions.. ) I had also been putting 22k in my not-quite-2 yrs ownership of the car. looks like I'm going to put another 300 miles for the local club group drive...

It's just that if you had been through the problem of getting wrecked, and send the car to bodyshop, not satisfied, re sending it in, come back, waxing and buffing yourself... or, you don't get to enjoy the car on the daily commute, yet, your car is collecting dust, and since you are so emotionally attached to it, you want to keep it clean and shiny... So you ended up spending extra 15-30 minutes to clean it every time you took it out... It could get tired sometime. Believed me, it took me to get this feeling after a whole year. (I left my 'daily driver', my old car at home for 10 months)

Sometime it's all relative, it makes no sense of driving the car in the streets after you had driven all day long at red-line, experiencing the R tyre squeaking, stormping the brake pedal, blasting 140mph thru a kink... No matter how you drive in streets, there's no fun... not to mention my aforementioned ordeal....

oh well, I'm way off now, this is technical forum, so I do think that switching back to 91/92 is a good change. Meanwhile, I wouldn't worry about your history with the 87 gas. Think about it, if the car doesn't retart the timing, you will experience the problem already.

I heard (not a reliable source) that the lesser gas could also contribute to foul plugs and clogged fuel injection, fuel filter, etc... anyone could confirmed that ??

Even at a traffic light I would rather be driving an NSX than any other car.

Word, Brother.

 

[cfra7]

Thanks for all the info. If you are ever looking for some track time in northern California, drop me a note. It would be great to see you and your car.

 

[nsxtasy]

2. As a daily driver, I just can't see spending $3 per gal. just to drive around under 70 MPH.

The amount isn't high because of the $0.20 difference between regular and premium. It's high because even regular gas costs $2.80 (if premium costs $3.00).

Even at 12K miles a year. I'm probably only paying an extra $180 for premium than I would for running on regular.

Not even. If you average 20-25 mpg, that's 480-600 gallons, and with a price difference of $0.20 per gallon, that's $96-120, not $180. (And keep in mind that you're still driving more than twice as many miles as the average NSX owner.)

To see what other NSX owners do, click here.

 

[nsxsupra]

To those who say why buy an NSX to use 87 octane, I say why buy an NSX if you aren't going to drive it as your daily driver?

For me I don't daily drive it mainly just to avoid door dings and potential damages from people who does not respect other's properties. NSX is actually so much more comfortable and easier to drive than my daily driver, nsx actually has great gas mileage 20~30mpg it seems compare to 10~15mpg on my daily driver.

 

[mc-ca]

At the current gas prices and markup for premium - it may be cheaper to use premium gas. Here is the logic: For gas that is $2.70 for regular and $3.00 premium. You are only paying 10% more for premium. If your car gets 10% (or more) better mileage - it's cheaper.

When Gas was say $1.00 for regular and $1.30 for premium, you need to have 30% better gas mileage. When we get to $5-6/gallon, premium will be even a better deal. Having traveled to China a lot lately, you can see the huge demand for cars over there and the government is banning bicycles inside the city to encourage car ownership...

All this is based on getting better milage with premium - have you noticed a difference?

 

[menuserve]

i've had my NSX almost two weeks now and so far it is a daily driver for me.

i'm only using the high grade gas... after all its $2 or $3 more to fill a tank... thats less than a fast food meal! for such a small amount its worth it and not risk doing any damage to the car i love!

 

[Hugh]

Compression ratio is just one of many factors affecting an engine's octane requirement. For example, the NSX with a 10.2/1 ratio requires premium fuel, while my Hayabusa with an 11/1 ratio requires regular gas.

Design factors affecting octane requirement:

Compression ratio

Trapped Compression Ratio

Ignition timing

Combustion chamber shape

Charge Motion in the cylinder

Air/fuel ratio

Cooling efficiency

Scavenging efficiency

Spark plug location

Spark plug heat range

Operating Factors affecting octane requirement

Outside air temperature/ Intake air temperature

Altitude

Humidity

Barometric Pressure

Premix ratio (two-strokes)

Engine RPM

Engine Load

Source: http://www.eric-gorr.com/techarticles/Fuel_Basics.htm

 

[02#154]

I believe that the NSX can be driven with the low-octane gas safely. But this belief relies on whether the NSX has a knock sensor (or sensors) (I think it does). Many modern high performance cars have them and their job is to "listen" for knock from the combustion chambers. If knock is detected then the ECU will take measures to eliminate the knock. Often this is by retarding the timing until the knock is no longer detected. I just started learning about these engines so I'm not sure, but it's likely possible that VTEC equipped cars like the NSX might also disengage the VTEC lobes on the cams. What this means is that, quite literally, the maximum performance from these cars is determined in great part by the quality of gas in the tank.

The knock sensors allow the car to perform better and better with higher-octane gas up to the point where maximum timing is reached in the programming of the ECU. In other words, just because you put 114 octane in the tank doesn't mean you'll have more HP than a guy with 92. The ECU probably doesn't have the programming to advance the timing so far that that much extra octane is useful. But you might hear of people with standalone replacement ECUs using 110 and higher octane gas so that they can safely run more timing. It also allows Honda to build in a safety net that saves the engine from damaging knock if a user purposely or accidentally puts in low-octane gas.

The bottom line is, cars equipped with knock sensors can be programmed in the ECU to run more timing (more HP) with high-octane gas, and less timing (less HP) with low-octane gas, all safely.

So the question becomes: who wants to drive around their NSX with anything less than the maximum HP available?

J

 

[the nsxnut]

Hi,
... I was wondering if the computer will retard the timing if the motor detects knock...

To specifically address the original question, the answer is YES.
There are knock sensors, and the ECU listens to them.

This does not address whether or not it's good or bad or makes no difference...

 

[nsxtra]

Hi,


2. As a daily driver, I just can't see spending $3 per gal. just to drive around under 70 MPH.


Thanks

Make that $3.29 per gallon in some areas, and who knows by the time people read this it may be closer to $4.00

 

[NSXDreamer2]

Make that $3.29 per gallon in some areas, and who knows by the time people read this it may be closer to $4.00

The current inflating gas price is irrelevant in this discussion, since the difference between Premium and regular are almost constant at .30 to .40 no matter how expensive the price of gas gets.

 

[nsxtasy]

The current inflating gas price is irrelevant in this discussion, since the difference between Premium and regular are almost constant at .30 to .40 no matter how expensive the price of gas gets.

Actually, the difference between premium and regular is constant at only twenty cents...

 

[John McCain Racing]

I actually Dynoed my car with I guess you could say 97 Octane (4 gallons of 93 and 4 of 100) and it lost power all the way up to about 7000 RPMS when I guess the ECU started adjusting things. My A/F Ratio was still good, just less power. It still made 2hp less at peak. Does the ECU sense the lower grade fuel and also make adjustments I wonder?

 

[robr]

Actually, the difference between premium and regular is constant at only twenty cents...

That's been the case as long as I can remember around here.... until the past 4 or 5 months. I've seen price differences start to move to .15 between each grade, or .20 between regular and mid, and .10 between mid and premium. This makes no sense since they all come from the same crude and thus should stay consistant... unless of course there's price gouging going on.

 

[nsxtasy]

That's been the case as long as I can remember around here.... until the past 4 or 5 months. I've seen price differences start to move to .15 between each grade, or .20 between regular and mid, and .10 between mid and premium. This makes no sense since they all come from the same crude and thus should stay consistant... unless of course there's price gouging going on.

Around here, the difference is 10 cents between regular and mid, and 10 cents between mid and premium. Hasn't changed at all. And every photo I've seen in the national news stories, with photos showing gas prices at stations all over the country, seems to show the same thing. I haven't seen those differences widening, even as the prices themselves have skyrocketed.

 

[NsXMas]

Comments from Tom & Ray on Cartalk on using lower octane gas in high performance cars:

"Dear Tom and Ray:

We purchased a '97 Nissan Maxima automatic in January and love it! The owner's manual recommends "unleaded premium gasoline with an octane rating of at least 91." It also says, "If unleaded premium is unavailable, unleaded regular gasoline with an octane rating of at least 87 can be used." Whenever I fill up the car (which is most of the time), I follow the manual's recommendation and use premium gas. But when my husband fills her up, he uses regular gasoline even when premium is available. So my question is, am I spending money needlessly on premium gasoline? And why would Nissan recommend premium gasoline if regular is OK to use? -- JoAnn

Tom: You're doing exactly the right thing, JoAnn.

Ray: This car has a high-compression engine that's designed to run on premium gas. But since there are places where premium gas is not available, and because premium gasolines can vary in octane, most manufacturers, including Nissan, use a "knock sensor" to protect the engine.

Tom: The knock sensor detects -- that's right -- "knocking" (also known as "pre-ignition" or "pinging")! Knocking is bad for the engine, and it often results from using lower-than-recommended-octane fuel. So when your cheapskate husband puts regular unleaded in the Maxima, the knock sensor kicks into action and retards the ignition timing to protect the engine.

Ray: Retarding the timing prevents the knocking, but it also reduces the engine's power, decreases fuel economy, probably increases the emissions, and may lead to a buildup of residue on the valves. So it's not an ideal situation. It won't hurt the engine if you use regular gas occasionally, but it prevents the engine from performing at the specifications at which it was designed to perform.

Tom: So I'd either take away your husband's keys, or increase his allowance by a few bucks a month so he can afford to buy premium. And if he's unhappy about having to spend the extra money, remind him that a car's fuel requirement (which can add many hundreds of dollars to the cost of owning a car over the years) is one of the things you should find out about before you put down your deposit."

 

[NsXMas]

I believe that the NSX can be driven with the low-octane gas safely. But this belief relies on whether the NSX has a knock sensor (or sensors) (I think it does). Many modern high performance cars have them and their job is to "listen" for knock from the combustion chambers. If knock is detected then the ECU will take measures to eliminate the knock. Often this is by retarding the timing until the knock is no longer detected. I just started learning about these engines so I'm not sure, but it's likely possible that VTEC equipped cars like the NSX might also disengage the VTEC lobes on the cams. What this means is that, quite literally, the maximum performance from these cars is determined in great part by the quality of gas in the tank.

The knock sensors allow the car to perform better and better with higher-octane gas up to the point where maximum timing is reached in the programming of the ECU. In other words, just because you put 114 octane in the tank doesn't mean you'll have more HP than a guy with 92. The ECU probably doesn't have the programming to advance the timing so far that that much extra octane is useful. But you might hear of people with standalone replacement ECUs using 110 and higher octane gas so that they can safely run more timing. It also allows Honda to build in a safety net that saves the engine from damaging knock if a user purposely or accidentally puts in low-octane gas.

The bottom line is, cars equipped with knock sensors can be programmed in the ECU to run more timing (more HP) with high-octane gas, and less timing (less HP) with low-octane gas, all safely.

So the question becomes: who wants to drive around their NSX with anything less than the maximum HP available?

J

If you're not sure what lower octane gas does to the NSX, I'd advise you pay a few extra dollars for the Honda recommended gas for the NSX.

 

[robr]

Around here, the difference is 10 cents between regular and mid, and 10 cents between mid and premium. Hasn't changed at all. And every photo I've seen in the national news stories, with photos showing gas prices at stations all over the country, seems to show the same thing. I haven't seen those differences widening, even as the prices themselves have skyrocketed.

Here ya go Ken, stations around here are all over the place with pricing now. Some are still .10, one I passed yesterday was .28 between 87 and 89, then .02 between 89 and 93.