What Octane fuel do you feed your Z?

[rcb280z]

Here we go again with fuel prices going way up! I currently burn 91 octane (Nissan recommended) in my 77. But, with prices topping $5 a gallon supposedly soon that will be expensive. So, what do you feed your Z's tank with? I'm thinking maybe dropping to a lower octane and adding a fuel additive every other tank. Anyone burn lower octane without issues?

[26th-Z]

I use anywhere between 91 and 93. I don't think the cost of an additive offset by the pennies per gallon difference in octane rating is going to result in any significant savings. What with gasoline at $8 per gallon (or more) in Europe, $5 per gallon is pretty cheap. I think if you really want to save money with the cost of fuel, maintain your tire pressures, change your oil regularly, drive slower and drive less. Not a real 'sports car' thing to say, agreed, but there it is. Just imagine how much you are saving over the cost of driving a Ferrari!

[Gary in NJ]

Octane is a fuel additive to reduce the rate of self-ignition in an engine. People tend to think that a higher octane fuel has more potential energy (power) then a lower fuel, but it simply isn't the case. A higher octane fuel allows for an engine to run higher compression and an advanced ignition timing. In the most simple terms, the higher the octane, the slower the fuel burns (this is overly simplified, but it helps to illustrate the point).

An engine that has been designed to run on high octane fuel (high compression) will run the same on low octane fuel, up to the point that cylinder pressure and temperature requires the slower burning fuel. This point is usually at high RPM or high load (WOT). Modern engines are able to detect detonation and/or pre-ignition and retard the ignition timing to such a point that the engine isn't damaged. I've seen an example of an Audi A4 2.0 turbo where using high octane fuel the engine produced around 200 hp on a dyno, and was only reduced to 195 hp on 87 octane. So it's not a significant difference.

The fuel injection system in the 280Z is unable to detect knock. It would be safe to use 87 RON+MON /2 in the engine as long as you avoid high RPM operation and high load conditions. Retarding the ignition timing by a few degrees would also help.

Edited February 17, 2012 by Gary in NJ

[rcb280z]

Hmmm....great info there Gary. I run with 10-12 deg. of timing so I am going to try a tank of 87 to see if there is a difference.

[rcb280z]

26th-Z, my point is; if I don't need to burn a higher octane (money wasted) then why should I? I agree....it takes maintaining your vehicle to obtain optimal fuel economy as well as performance. If I am spending more money than I have to....why am I? BTW nice avatar!

[Jeff G 78]

Here we go again with fuel prices going way up! I currently burn 91 octane (Nissan recommended) in my 77. But, with prices topping $5 a gallon supposedly soon that will be expensive. So, what do you feed your Z's tank with? I'm thinking maybe dropping to a lower octane and adding a fuel additive every other tank. Anyone burn lower octane without issues?

I don't have an owners manual handy, but from what I recall, it says to use 91 RON, not 91 (RON+MON/2). 91 RON is what we see as 87 at US pumps. I have always run 87 in every Z other than my 10:1 CR 280. My 260 race car gets only 87 and I run the wizz out of that motor with no issues. In our last race, we completed 1400 miles in about 22 hours of actual on-track time.

[Gary in NJ]

I don't have an owners manual handy, but from what I recall, it says to use 91 RON, not 91 (RON+MON/2). 91 RON is what we see as 87 at US pumps. I have always run 87 in every Z other than my 10:1 CR 280. My 260 race car gets only 87 and I run the wizz out of that motor with no issues. In our last race, we completed 1400 miles in about 22 hours of actual on-track time.

The octane at the pumps (what you see on the yellow sticker) is the average Research Octane Number and Motor Octane Number. The RON number is the higher of the two.

[Jeff G 78]

Correct Gary. When I saw your quote, I realized I had a typo in the formula. It should have read (RON+MON)/2.

[5thhorsemann]

Octain rating is an expression of the amount of pressure carburated fuel will withstand before it detonates without the presence of an ignition source at a certin ambiant temp. So high compression engines require high octain fuel.

Nitro meth has an octain of 1000+ but the combustion yeild is relatively low, its for high compression supercharged engines.

This is a simplified explanation, but our Z motors are low compression. With the alcohol we get at the pump here in the good old US of A, I find that I get some ping on hot days and run on after a hard run with low octain gas.

[LeonV]

I don't have an owners manual handy, but from what I recall, it says to use 91 RON, not 91 (RON+MON/2). 91 RON is what we see as 87 at US pumps. I have always run 87 in every Z other than my 10:1 CR 280. My 260 race car gets only 87 and I run the wizz out of that motor with no issues. In our last race, we completed 1400 miles in about 22 hours of actual on-track time.

Exactly. If the manual recommended 91 RON then 87 at the pump (AKI) will be fine.

All the octane rating is, is a measure of knock resistance, meaning resistance to self-ignition under high temperature and pressure. It has nothing to do with burn rate, energy, etc.

[tlorber]

I have a bottle of Johnny blue on the shelf of my bar. It may become cost effective to use it if prices keep on running.

More to the point, I have dished pistons and usually run 89 octane. I am looking forward to seeing if my new vacuum advance has any impact on performance.

[Walter Moore]

I would think that a 77 would run fine on regular gas since the late 70's cars were made in an era when premium just wasn't available. In 77 most gas stations in the U.S. only sold two grades of fuel: 89 octane leaded, and 87 octane unleaded.

My 71 on the other hand, with its E31 head, S130 electronic distributor, and functional vacuum advance, will ping like crazy when I try to hold a constant speed on the interstate in 5th gear if I have anything less than 92 octane in the tank.