Best Octane For E31 Head

[Nismo37]

Hey Guys,

I just bought my first Z this month and drove it 500 miles home. Runs great. I'm new to the 240Z though and don't know a ton about the engines. Mine is a series 1 with the original E31 head. I know this one is a higher compression head.

What is the best octane to run on a stock motor to avoid detonation? Also, if the engine hasn't been re-built (I'm not sure if this one has) what do you do about the unleaded fuel?

[Dr. 240Z]

Hi Matt,

Good question...The 1971 Series 1 owners manual (page 24) recommends '95 and higher'. From that it would appear the higher, the better, and that of course depends on local availability. So, adjust the timing (knocking??)accordingly.

Cheers,

George

[madkaw]

Congrats on getting a Z with a performance head like the E-31. Run the highest available in your area as said. Are you aware of what detonation is and what it sounds like? If not, get familiar so you can avoid it and avoid replacing head gaskets. I probably run the same compression as you and run 93 octane and run full ignition with no detonation.

Welcome to CZCC

[Nismo37]

Congrats on getting a Z with a performance head like the E-31. Run the highest available in your area as said. Are you aware of what detonation is and what it sounds like? If not, get familiar so you can avoid it and avoid replacing head gaskets. I probably run the same compression as you and run 93 octane and run full ignition with no detonation.

Welcome to CZCC

I drove the car 600 miles home to Boise from California and I'm starting to get more familiar with how the car sounds. I had to fill up with 87 in the middle of nowhere because it was all that was available and I was running low. I think I might be getting a little detonation because the motor has that old school VW beetle sound under load. I'll fill up with highest I can find. If the highest isn't 95 what do you think about Octane boosters?

Also do you guys run a lead attitive?

[madkaw]

You shouldn't need octane boosters, just run premium. Eventually no lead gas will take it's toll on a stock early head, but do you know if anything has been done with that engine?

Don't fret about the no-lead, just run good gas, keep your coolant system clean and working good and keep your engine in tune and timing checked.

Oh, and start reading the Z forums and studying these cars and their characteristics. There is endless info here, just need to do some searching

[bartsscooterservice]

I use unleaded euro95 here on my Z with E31 head.

Octane rating - Wikipedia, the free encyclopedia

To convert that to US rating it should be 90 or 91..

I don't know what fuel grade they had in the past when these cars came out of the factory but I suspect a lower octane fuel.

Edited May 19, 2014 by bartsscooterservice

[LeonV]

Bart is right, the manual refers to RON which is the octane standard the US used back then (and the rest of the world still uses today). The US now uses RON+MON/2 (AKI) which is a lower number for the same octane level, i.e. 95RON is equivalent to 91AKI, as Bart already pointed out.

[Dr. 240Z]

Bart is right, the manual refers to RON which is the octane standard the US used back then (and the rest of the world still uses today). The US now uses RON+MON/2 (AKI) which is a lower number for the same octane level, i.e. 95RON is equivalent to 91AKI, as Bart already pointed out.

The same for Canada...eh!!

George

[Nismo37]

Bart is right, the manual refers to RON which is the octane standard the US used back then (and the rest of the world still uses today). The US now uses RON+MON/2 (AKI) which is a lower number for the same octane level, i.e. 95RON is equivalent to 91AKI, as Bart already pointed out.

The highest octane i can find without ethanol in it is 90. I'm also at a higher elevation too which should help.

[LeonV]

The highest octane i can find without ethanol in it is 90. I'm also at a higher elevation too which should help.

That should be fine, as long as the head hasn't been shaved.

[ajmcforester]

104 was the octane level I could get at one time.  your right if you calulate the octane need its between 95-97.  However the argument that 91 is 95 try running the higher octane and lission to the engine with a scewdriver along the valves you will hear a difference.  I can't here a differnce between 98 and 104 octane on these engines.