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Old 05-28-2010, 07:36 PM
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Question Engine Octane Ratings

So....I let my brother burrow my 2003 3.5 Altima (automatic) earlier today. I left him with 1/4 tank of gas. He only had to drive a few miles. When he brought it home he mentioned he filled the tank up for me. A very nice gesture, but when I asked what fuel he used he mentioned 'regular?' - meaning 87 or 89 octane gasoline.


Question.

1. What octane do you run in your VQ35DE? I know premium is recommended.
2. Should I throw a bottle of octane boost in the tank? Or will it do more harm than good?
3. What engine MAPs does the engine computer have for fuel?
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Old 05-28-2010, 07:47 PM
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Quote:
Originally Posted by Swim100flyy View Post
So....I let my brother burrow my 2003 3.5 Altima (automatic) earlier today. I left him with 1/4 tank of gas. He only had to drive a few miles. When he brought it home he mentioned he filled the tank up for me. A very nice gesture, but when I asked what fuel he used he mentioned 'regular?' - meaning 87 or 89 octane gasoline.


Question.

1. What octane do you run in your VQ35DE? I know premium is recommended.
2. Should I throw a bottle of octane boost in the tank? Or will it do more harm than good?
3. What engine MAPs does the engine computer have for fuel?
1. Premium since day one over 8 years ago.
2. No (doesnt matter really). No.
3.
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Old 05-28-2010, 07:50 PM
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Originally Posted by *Whore-Jay* View Post
1. Premium since day one over 8 years ago.
2. No (doesnt matter really). No.
3.
The reason I ask is because one of my mechanic friends worked at a Nissan dealership as a tech for a few years...He told me that 93 octane is the highest I should put in because the Engine computer didn't have any air/fuel maps for anything above 93 octane.

Yes - you could receive more power from 100 octane race gas only if you had an aftermarket ECU that had been tuned/programmed for the high octane gasoline.
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Old 05-28-2010, 08:07 PM
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I put in 87 no problmo. Just let it run out and then put the premium stuff you like.
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Old 06-02-2010, 05:42 PM
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Dyno's on the Max board say you lose about 20 hp form using reg octane, but it does not harm the engine.
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Old 06-02-2010, 06:36 PM
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That's what a knock sensor is for. Your engine will be fine but will probably be less responsive.
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Old 06-02-2010, 06:46 PM
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Originally Posted by GPS View Post
Dyno's on the Max board say you lose about 20 hp form using reg octane, but it does not harm the engine.
I can't see losing 20HP between regular and premium on a stock VQ35DE...
But I'm looking into other tests.

Here's an interesting article on the Mopar 360:
LINK

Here's a short youtube clip...Since they didn't list any of their testings I don't trust it.
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Old 06-03-2010, 01:18 AM
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Originally Posted by GPS View Post
Dyno's on the Max board say you lose about 20 hp form using reg octane, but it does not harm the engine.
20 hp!!!!! I hope you were just kidding.
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Old 06-03-2010, 01:30 AM
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Quote:
Originally Posted by Swim100flyy View Post
I can't see losing 20HP between regular and premium on a stock VQ35DE...
But I'm looking into other tests.

Here's an interesting article on the Mopar 360:
LINK

Here's a short youtube clip...Since they didn't list any of their testings I don't trust it.
LINK
No offense Swim but that video you linked is the most misleading load of crap I have seen in a while. First off they didn't even tell you what kind of motor they used to "test" the fuel additives. They could have been using a low compression ratio engine which will lose power if you use to high of an octane rating. Why you ask? Well first off the octane rating is pretty much how well the fuel stands up to being ignited. Meaning lower octane rating the easier it is to burn the fuel. Why is this important to the compression ratio? Well high compression ratio engines and force induction engines during the compression stage of the pistons stroke can, if the octane rating is to low, cause premature ignition. That is why high octane ratings are needed so the fuels is more stable and is ignited by the spark not the compression and heat of the motor.

Long winded I know, however that being said 87 won't hurt your car. Don't put an octane boost in there now, it will not get properly mixed into the fuel and wont do anything for you anyway.
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Old 06-03-2010, 01:40 AM
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Quote:
Originally Posted by Swim100flyy View Post
...Since they didn't list any of their testings I don't trust it.


Exactly my point.
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Old 06-03-2010, 02:14 AM
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always try and use the recommended octane that is listed in your vehicles manual.
cars nowadays are built with a certain octane in mind to get the best performance and economy out of the engine. too little will cause problems and so will too much. most likely, youre not going to kill your engine on one tank, but should you hear any knock, back off the gas a tad. my best advice - add higher octane once the tank is at about half full.
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Old 06-03-2010, 04:20 AM
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when you get to 1/2 a tank fill it back up with 93 , that will give you around 90 octane , you'll be fine .
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Old 06-03-2010, 04:24 AM
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Right. Since I took a 300mi drive this past weekend on the highway I watched for any unwanted engine noises. It turns out the engine was fine. I took the tank down to about 5gal and then filled up with 92 (the highest they had in the middle of bumfcuk nowhere).

On the way home; I drove as conservatively as possible and managed to get 31mpg highway on the 92. Not bad at all. That's the best I've ever gotten. Ever.
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Old 06-03-2010, 04:32 AM
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Quote:
Originally Posted by Swim100flyy View Post
Right. Since I took a 300mi drive this past weekend on the highway I watched for any unwanted engine noises. It turns out the engine was fine. I took the tank down to about 5gal and then filled up with 92 (the highest they had in the middle of bumfcuk nowhere).

On the way home; I drove as conservatively as possible and managed to get 31mpg highway on the 92. Not bad at all. That's the best I've ever gotten. Ever.
your car will run great on anything above 87 octane , no need to over think it .
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Old 06-03-2010, 04:39 AM
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Quote:
Originally Posted by jimnolimit View Post
your car will run great on anything above 87 octane , no need to over think it .

Yes; this is true. But more specifically - I know many engines have separate air/fuel/pressure maps depending upon the grade of fuel it determines to be in use.

Example. I read an article once in car&driver/motortrend/etc... in regards to the Honda Odyssey's 3.5L engine. Like our VQ35DE - the honda motor could be run on regular or premium, but premium was recommended for higher power output [for towing]...They tested the engine on both regular and premium fuels. They ended up finding a dramatic increase in power output when premium was used.

Now. As to how the engine computer determines octane ratings (via knock sensor / O2 readings / etc...) I am not sure.

I talked to a Nissan tech once who did tell me that there was a limit to the octane where the engine computer simply didn't have any fuel maps over a certain octane. If we could find out what this number is it could save us a little cash we thought was adding performance but was really wasted.
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