Filled up just to see what would happen


saved $3.30 on fill up

montly savings about $20

~17HP lost (read that using 87 instead of 91 usually takes about 6% HP in most cars that require premium)

Negligible affect to MPG



Overall, I missed the HP severely, definetely feels like you lost 20 HP! As far as saving a little money, ahhhh forget it!

 

but oh my god blah blah blah your gonna ruin your engine blah blah because of predetonation blah...

 

Well you see modern engines have these sensors...


(well.................... you get the drift)

 

Isn't talking to yourself (and answering) a sign of early psychosis?

 

saved 3.16???? ohhhh you put low test, well damn, sorry I wouldnt do that.

as for 20$ a month???"???? uhhhh you fill up your tank almost 7 times a month? Im at maybe twice a month, putting the savings at 6$ a month, or 72$ a YEAR. that is not gonna break the bank.

 

If you can't afford gas or tires, you shouldn't have bought the car! It really surprises me when people buy a performance car, then complain about the gas mileage. Should have bought a Civic. Or, does Nissan need to have a 4-cylinder Z like the Mustang wannabees who buy the V6?

-TB

 

Who would have ever thought that the old joke "Doc, it hurts when I do this"......."Then don't do that" would evolve into a standard response whenever anyone asks a question, or raises concerns about an issue.

Thanks for reminding us all that we have choices (as if we weren't aware of this).

 

The compression ratio, the ignition timing maps, the a/f maps, etc. are tuned for 91 octane. Yes, there is a detonation sensor (or two), but for it to work, it has to detect detonation. So you will get detonation for a (hopefully small) period of time. And when it does detect detonation, it backs down those maps, therefore, you lose hp.

Furthermore, the detonation sensor isn't completely idiot proof. On the Z32, the detonation sensor "listens" for a vibration frequency that is caused by detonation. Unfortunately, the detonation sensor is only good to 3000rpms so after 3000rpms, the detonation sensor does not work. And even still, detonation can produce a slightly different vibration frequency and the detonation sensor may not detect it.

If you want my advice: if you intend on running 87 octane, then I'd drive like grandma and try to stay at low rpms. The more aggressive you drive on 87 octane, the more aggressive maps the ECU will use.

You say you'd save $20/mo or $240/yr switching to 87 octane. A new short block should be around $3k and a new long block should be around $7k and that excludes labor and other parts. Do the math. How many years will you be rolling die?

Here's an excellent article on detonation (uncontrolled combustion after the spark) and pre-ignition (uncontrolled combustion before the spark AKA dieseling) that includes ignition timing and octane: http://www.streetrodstuff.com/Articl...e_Basics_I.php

Here's the gasoline FAQ that explains what octane is: http://www.seansa4page.com/resource/octane.html

QED.

Michael.

 

I think it's far more rediculous to buy a car that requires 91 octane and ask if it's okay to use 87 (not this thread EXACTLY, but many others). How about "Pep Boys has four tires for $99. What do you guys think? Will I lose performance?". Duh!

It's just plain stupid to use the wrong gas in a relatively high compression engine. And intentionally too.

"Doc, I'm thinking about jumping off a bridge onto big rocks below. What do you think?"...is this thread.

Your example sounds more like "The shifter vibrates at 4500 RPM. Well, don't rev to 4500 RPM. Problem solved". That's far from what I was saying.

People frequently pull crap like this. Buy an older NSX for $20000, then cry when it costs $2000 to replace the clutch. Again, DUH.

If you can't afford to make payments, maintain, fuel this car, you SHOULD NOT HAVE BOUGHT IT! There are more important things in life than a car. Do you really want to spend every last cent you have putting gas in a Z? If so, I hope you're single, not in school, etc.

I was simply stating an opinion, not evoking some standard response like a politician or lawyer.

-TB

 

I don't think it is ridiculous for some one to question wether or not premium gas is 'required', just because the manual says so.

I do think it is bold for Robert to run the test, but he probably knows more about this subject than I do. Michael-Dallas gave a good reply to the subject - info we can read, learn something from, and possibly use in making a decision.

I'm not trying to start a flame with you Them Bones, but having been on this forum for eons, I've seen way too many responses that only offered the suggesstion to "not buy the car". Someone wonders if their hockey sticks will fit in cargo area - "Don't buy the car". Someone wonders what the gas mileage will be - "Don't buy the car". Someone wonders if they can find less expensive replacement tires, use Turtle Wax instead of Zanio, fit a Big Gulp in the cupholder - "Don't buy the car".

Tell them the sticks will/wont/might fit, the mileage won't be like a Civic, cheap tires can affect performance, Turtle wax won't protect for long, and doubtful. But let them buy the car if they want to, and have fun with whatever they do.

That's all.

 

It must have been an interesting test, using 87 instead of 91. I hope you didn't take it to redline much since the variable ignition control can only retard the spark so much before pre-ignition kicks in and the dreaded pinging begins. The owner's manual recommends 91, but says if you can't find it, a lower octane may be used but you need to avoid high revs and fill up with 91 as soon as its available. Brave test, but I wouldn't do it in my new Z. I'm such a fanatic, I used 91 in my 97 Accord EX w/8.8:1 compression and recommended for 87, but I was always running it to redline to feel the v-tech, so I wasn't taking any chances with pre-igntion.

 

Why is everyone KNOCKING this guy, why KNOCK someone who went to the trouble to experiment on their car so you don't have too. I'd like to ask him if there were any other problems other than the loss of HP? like um KNOCKING?

 

This subject has been beaten down to death on other automotive forums. Some on those forums have had the unfortunate pleasure of blowing their motor due to low octane and detonation (i.e. too much boost, not enough fuel and/or not enough octane). So there is no need to risk another motor and perform any other experiments.

Octane level is very important for high compression and high performance vehicles. Read the links I've provided, search google w/ "octane detonation pre-ignition" and go through the results.

It's not rocket science.

Let me explain in layman's terms. This is simple physics. Temperature is directly proportional to pressure -- high pressure, high temperature.

What does that have to do w/ octane, detonation, etc.?

Well... octane is simply a fuel's resistance to spontaneous combustion (i.e. under extreme temperature). At some point, a/f will spontaneously combust due to extreme heat. That combustion point changes w/ octane.

Where does the extreme heat come from?

Well, how does an engine work? In a 4-stroke engine (i.e. today's cars), it goes through: 1- intake stroke (piston travels downward, intake valve(s) open, exhaust valve(s) closed), 2- compression stroke (piston travels upward, intake & exhaust valve(s) closed), 3- combustion stroke (piston travels downward, intake & exhaust valve(s) closed), and 4- exhaust stroke (piston travels upward, intake valve(s) closed, exhaust valve(s) open). Rinse, lather, and repeat.

What does this have to do w/ extreme heat?

Remember... temperature is directly proportional to pressure. The compression stroke compresses the a/f ratio. This increases pressure, therefore, increases temperature. If temperature is too extreme, the a/f ratio can spontaneously combust. This is called pre-ignition. This is how a diesel engine works. Pre-ignition will destroy a motor (except diesel engines) in a short period of time. Consider that while the piston is going up, the a/f spontaneously combusts, the expanding exhaust gas generates extreme pressure & temperature. That expanding gas wants to force the piston down, but the piston ain't going nowhere, but up. After a while, something will give.

Something else that also increases pressure is when the a/f ratio is ignited in the combustion stroke. Contrary to popular belief, a/f does not explode and the "explosion" does not force the piston down. A/F burns and the pressure generated by the expanding exhaust gas is what forces the piston down. If temperature is too extreme (from pressure generated by the expanding gas), then unburnt a/f will spontaneously combust. This is called detonation. An detonating engine will survive much longer than a pre-igniting engine because the piston is going down.

Furthermore, high performance engines have more aggressive ignition timing maps. Ignition timing merely indicates when a spark is generated, thus, igniting a/f. Igniting the a/f when the piston is at the top of the cylinder (i.e. top-dead center) will produce very little power because it takes time for the a/f to burn and produce the expanding exhaust gas to force the piston down. Therefore, the spark is generated before the piston reaches TDC; by the time it reaches TDC, there will be enough pressure to force it down. Well... consider, more pressure equals more force equals more power. But also remember more pressure also equals high temperature which may lead to spontaneous combustion if the fuel's octane level is insufficient.

Also throw into the equation that todays engines advance ignition timing at high rpms. A/F burns at a constant rate, but the piston moves faster at higher rpms.

Michael.

Oh yeah, I left out that pre-ignition & detonation go hand in hand w/ high temperature. Meaning, they are caused by extreme temperatures. But they also produce those extreme temperatures. Rinse, lather, and repeat.

 

I get your point. I really do. But, none of your examples will destroy the car. Sure, the engine will back off the timing TEMPORARILY when it detects knock. It will always be trying to return to the default timing, though.

At one point, I was trying to decide between a used sports car and a new one. After spending time on the Internet looking at stuff like this, I've made the determination that people do such crazy things to their cars that I shold stay away, far away, from used sports cars.

Picture this, you buy a used Z just out of warranty. You're thinking "cool, I can start modding it now and not have to worry about voiding the warranty". You throw a supercharger on it and start out conservatively at 4 PSI. Everything seems to be working great, then the engine just stops. It's blown. Why? What happened?

If only there was a way to know that the previous owner drove around constantly with econo 86 octane and eventually weakened the pistons from the repetetive pre-ignition.

I guess there are a lot of people who buy sports cars just for the look and don't care about the performance. Doesn't compute in my mind.

To each his own, I guess.

One final comment and I will leave this topic alone for good. People really should take manufacturer recommendations for fluid type, quantity, etc. at face value. They designed the car, not you. They know what will work best and over the long run. Lots of aftermarket stuff is made to be compatible with OEM types, so I'm not saying you have to use Nissan stuff. The recommendations you can take with a grain of salt are all of the safety comments peppered througout the owners manual. "Don't adjust your seat while driving. Don't use cup holder while driving. Don't change your oil while driving." These are designed to protect Nissan from lawsuits and don't have anything to do with the actual functionality of a certain device. Just use common sense folks.

Peace. -TB

 

This would seem to be the place to ask the converse of the original question: what happens if I put in higher octane than 91? Do I get more horsepower, or do I just do a different kind of damage to the engine?

I'll be taking the car to the track a few times a year. Should I use the higher octane fuels available there (at only $4.00 a gallon or so!!!) for better performance? How do I determine how high to go? Is there a simple linear correlation between octane and power? Is it possible to go too high?

Are there any problems to be expected from using 91 most of the time and switching to higher octane for a day at the track every month or so?

Thanks.

--James
Columbia, MD
Lemans Track

 

You put 87 Octane in your Nissan Z? Id stop that, right now..

one of my buddies was putting 87 Octane into his Cobra ( Also tuned for 91 octane, just like the 350Z due to Compression )

Guess what happened? Detonation, and he blew a piston when he was dragging the car.. He can afford the car and the insurance, but not the 20 cents a gallon?

I mean, really.....

Like people said.. you bought the car and you have to take care of it...

Atleast you dont HAVE to run 93 Octane ( specific tune ) I have to skip certain gas stations because they only offer 91-92 octane.

BTW,

Any of you guys run your Z on 91 octane, and then compared it when you add Octane booster? If it is anything like my car, it will be like an air conditioner difference.. ( it will feel like you were running the car before with the air conditioner on.. Know what Im saying? )

-Ryan

 

You should first ask WHERE these people live. In higher altitudes, such as here in Colorado, 87 octane is sufficient when 91 is required.

I, personally, will stick with 91, as I always have. My Toyota requires 86 octane, but I run 91. The cost is neglible.

 

Fuels higher than 91 octane should not damage any modern-day motor as long as the fuel is unleaded. If anything, higher octane will reduce the chances of detonation. Contrary to popular belief, octane is merely a fuel's resistance to spontaneous combustion -- it is not the burn rate of fuel or "explosion" level of fuel.

To actually gain power from an NA motor using higher octane: 1- the ECU needs to be re-programmed to incorporate and/or default to the higher octane fuel; and/or 2- the base ignition timing should be advanced (very carefully). For forced-induction motors, higher octane allows you to run higher levels of boost.

Advancing base ignition timing is a common mod. For example, 87 octane is recommended on my 94 SE-R, but because I've advanced my ignition timing by 6 degrees (from 15 degrees BTDC to 21 degress BTDC), I run 93 octane. Another example, 91 octane is recommended on my 300, but because I've advanced my ignition timing by 4 degrees (from 15 degrees BTDC to 19 degrees BTDC), I run 93 octane.

On a dyno, I have gained 10rwhp on the 300 by simply advancing base ignition timing so, yes, it does work; I've never checked the gains on the SE-R, but I'm guessing it's good for a couple of rwhp and other people who have dynoed their SE-R have seen results. BTW, factory spec for both is 15 degrees +/- 2 degrees (i.e. you should be able to advance or retard ignition timing and still run on the recommended octane).

The 350 poses an interesting problem for advancing base ignition timing. The spec is 15 degrees +/- 5 degrees, but there is no way to adjust it. Oddly enough, the crankshaft angle sensor is bolted onto the oil pan and not adjustable. And from what I've read in the service manual, the base ignition timing is determined at startup -- it starts out at 15 degrees and continually adjusts accordingly to certain situations and/or sensor readings (i.e. if the detonation sensor detects ping, then it will retard base ignition timing and use less aggressive maps; if the o2 sensor detects a rich condition, then it may "slowly" advance base ignition timing and/or use more aggressive maps). So, in theory, if you continually use higher than 91 octane, the ECU will eventually "learn" and hopefully advance base ignition timing.

Michael.

 

Yes it is. Remember, I have a list of sanatariums that would perfect for this case. Just willing to help a fellow member.

 

This a test nobody needs. Why take a chance when you don't have to? 91 octane is the recipe for sports cars, you use lower octane too much you can use your engine for a boat anchor. I thought everyone knew and understood the need for it. This really surprises me, I had put the practice into the folklore category as common knowledge.