The maual says the sedan can run on 87 octane normal and that theyu just recommend the 91+ . The coupe only says 91+

I will probably use 91+ but my old J had to have premium, are they telling me it is OK to use 90 etc?

Also the stock rims, does anyone know if they are cast or forged? Dealer did not know. Lit says aluminum

Has anyone aranged a service guideline to keep this car ticking for a good long time? In the general there is a good concensus but wanted to see what was working here. I know the manual is good to keep everything running to the end of the warranty

Thanks!

Well, I'll start by giving you a very brief explanation of the Octane rating. Basically Octane is a fuel additive that helps to promote smooth and even combustion of the fuel within the cylinder. The higher the Octane number is at the pump, the more additive there is in the fuel, and hence an increased price due to the additional processing costs.

If you are familiar with the sound of a knocking engine, you probably know why the higher octane would be necessary. As the cylinder walls heat up, it is common for the fuel to begin igniting before the spark from the spark plug. This phenemonon leads do multiple bursts of energy instead of one smooth burst from the combustion stroke of the engine. The sound this problem makes is known as "knocking" in the engine. To help reduce this problem, you would want to buy the highest Octane possible.

However, most new cars (including the G35) now come with knock sensors. These sensors automatically detect the problem and adjust the ignition timing to stop the uneven combustion. Hence, in all reality you can use any grade of gas in the G35, and the performance will be the same. Higher Octane levels often improve the performance and life of older cars, but that's because they don't usually have knock sensors in them. With all of this said, I'll probably only put Chevron Supreme in my car cuz I'm crazy like that. Maybe if I read this post a few times, I will be able to convince my self to downgrade to the mid grade.

As for your second question......I'm pretty sure that the rims are cast, not forged. I don't even think the 18s that will be on my 6M/T are forged. I did hear something about forged rims being an option in the future.....kinda like the 350Z track model.

I hope some of this helps. Again, my explination was very brief, but the point was that knock sensors = don't really have to worry about octane rating.

Dave

Understand about the octane and knock sensors, have a 93J30 too but that car stated only premium

I will use premium anyway and thanks for the rim update

Look forward to this forum as I learn more on this car

basically you get what u pay for, its always better to get the best stuff, its not THAT much more expensive anyway, all i put is 93 octane in mine

Knock sensors DO play a role in the performance of any Infiniti engine. If the sensors detect a pinging (knocking)condition due to low octane of the fuel, the ignition timing will retard to a point, thus engine performace will decline. Same goes with an EGR system that is not working, the combustion temperature will rise to a point of engine pinging therfore the knock sensors will perform the same job as if you were using a low octane fuel, resulting in a slight decline in engine performance. Also note that on hot humid days is when pinging can really take its tole due to the increase in the ambient temperature.

this is why its just better off to use highe octane gas, ive never put any lower than 93 in my car

I really hate to tell you guys this, but the only change that the ignition timing effects is the time that the spark plug fires.....hence you do not loose performance because your RPMs do not change.....the spark just fires at a different time during the stroke. I know a lot of people won't believe me anyway, but I'm a mechanical engineer that has taken a class specifically on internal combustion engines. Granted, I'm still sticking with the higher grade of fuel cuz it's only a few cents per gallon.

Super Dave wrote:I really hate to tell you guys this, but the only change that the ignition timing effects is the time that the spark plug fires.....hence you do not loose performance because your RPMs do not change.....the spark just fires at a different time during the stroke. I know a lot of people won't believe me anyway, but I'm a mechanical engineer that has taken a class specifically on internal combustion engines. Granted, I'm still sticking with the higher grade of fuel cuz it's only a few cents per gallon.

i wasnt really too sure about the whole drop in performance at all, but i did know that it retarted the timing

My understanding:

First off this has been rehashed and hashed on several different VQ boards.

The knock sensor will retard the timing if it sees preignition.

This will reduce performance in that the fuel will still be burning as the exhaust valves open, allowing some of the gas to escape instead of pushing down on the piston.

Maxima.org guys have proved this on the dyno rack.

Our timing is advanced to ~15 degrees (+/- 5 from the factory)

so advancing the timing will help 1) ensure you are far enough advanced to begin with and 2) when the knock sensor starts acting on hot days or heavy loads; that the retardation will be to around the nominal setting instead of less than the nominal

Some dealers will do this for free, others may charge you.

now that does make sense, but would it really retard the timing so much to where it wuold hurt performance, i mean, to where fuel is still burning even while exhaust valves were open?

I will read the ESM tonight

The optimum point is not where the plug fires but where the fuel has burned enough to make the maximum pressure occur at 16-17 degrees after top dead center. This is where the pistion postion is optimum to exert the most force on the rod. As the piston moves down the bore the compression ratio drops and if you were to exert maximum pressure at TDC the rod would pound down into the bearings!

The flame advance speed of gasoline varies with the charge density so at cruise plugs fire at 40 degrees BTDC vs WOT 22-26 degrees above 4,000 rpm......as you increase rpm beyond 4,000 you add 1 degree of advance per 500 rpm roughly..........the factory ecu stops advancing and hold the advance constant from 6,000-7,000 rpm........just as it does the injector open time.

The factory measures the pressure [with sensors under each spark plug on the dyno] and reverse engineers the time to fire the plug at each rpm and load condition and temperature with varing fuel charge densities. The build charts and equations into ecu memories from lab tests which have the desired timing.

Once they get a maximum advance for maximum power they back off this number [less advance] as a safety factor !

Generally Nissan have 3-4 degrees less advance than that need for maximum power in the 4,000 to 7,000 rpm rage......The point of peak pressure occurs LATE at 20-23 ATDC instead of 16-17 ATDC.

Modern ecu advance to knock and keep records [adaptive learning] so in a way they test the fuel for octane number.

When the KS counts per 100 [and 500] millisecs exceed a certain threshold the ecu first reduces ignition advance by 3 degrees then if that doesn't reduce the knock it reduces another 5 degrees.

Important to understand that you must reduce advance more to stop knock than that required to keep it from starting in the first place!

If the KS don't pass their diagnostic test then the ecu permanently reduces the advance by 3-8 degrees depending on rpm and amount of calulated advance. Just like the amount of advance is reduced when the coolant temp exceeds 195F.

From the above if plug fires at 26 BTDC and the peak pressure occurs at 16 ATDC [42 degrees later] the entire combustion event takes maybe 80 degrees [so all the burning is complete by 55 ATDC] and the exhaust valve doesn't open until 120 ATDC........and it does flow any significant amount until after BDC or 60 degrees later.

Impossible for a burn to take place while the exhaust open unless the plug didn't fire [misfire]

Q45tech wrote:The optimum point is not where the plug fires but where the fuel has burned enough to make the maximum pressure occur at 16-17 degrees after top dead center. This is where the pistion postion is optimum to exert the most force on the rod. As the piston moves down the bore the compression ratio drops and if you were to exert maximum pressure at TDC the rod would pound down into the bearings!

The flame advance speed of gasoline varies with the charge density so at cruise plugs fire at 40 degrees BTDC vs WOT 22-26 degrees above 4,000 rpm......as you increase rpm beyond 4,000 you add 1 degree of advance per 500 rpm roughly..........the factory ecu stops advancing and hold the advance constant from 6,000-7,000 rpm........just as it does the injector open time.

The factory measures the pressure [with sensors under each spark plug on the dyno] and reverse engineers the time to fire the plug at each rpm and load condition and temperature with varing fuel charge densities. The build charts and equations into ecu memories from lab tests which have the desired timing.

Once they get a maximum advance for maximum power they back off this number [less advance] as a safety factor !

Generally Nissan have 3-4 degrees less advance than that need for maximum power in the 4,000 to 7,000 rpm rage......The point of peak pressure occurs at 12-13 ATDC instead of 16-17 ATDC.

Modern ecu advance to knock and keep records [adaptive learning] so in a way they test the fuel for octane number.

When the KS counts per 100 [and 500] millisecs exceed a certain threshold the ecu first reduces ignition advance by 3 degrees then if that doesn't reduce the knock it reduces another 5 degrees.

Important to understand that you must reduce advance more to stop knock than that required to keep it from starting in the first place!

If the KS don't pass their diagnostic test then the ecu permanently reduces the advance by 3-8 degrees depending on rpm and amount of calulated advance. Just like the amount of advance is reduced when the coolant temp exceeds 195F.

From the above if plug fires at 26 BTDC and the peak pressure occurs at 16 ATDC [42 degrees later] the entire combustion event takes maybe 80 degrees [so all the burning is complete by 55 ATDC] and the exhaust valve doesn't open until 120 ATDC........and it does flow any significant amount until after BDC or 60 degrees later.

Impossible for a burn to take place while the exhaust open unless the plug didn't fire [misfire]

:withstup , yea, what he said

"The point of peak pressure occurs at 12-13 ATDC instead of 16-17 ATDC."

I made a typo here the point of peak pressure occurs 4 degrees later than optimum at 20-21 degrees ATDC [not 16-17 nor 12-13]so the power is less. The piston has moved farther down the bore so the combustion space is 4% larger so the pressure is less.

The more the static advance the earlier the peak. Different gasolines have differing flame speeds depending on components as the following shows.

http://www.erc.wisc.edu/modeli...r.pdf

http://autos.groups.yahoo.com/.../3733h ... /ignition/

thanks for all of hte useful info Q45tech, now all i have t odo is figure it all out and put it into lamen's terms for myself

Actually guys, only put the gasoline that is recommended by the manufacturer. Don't put the good 93 octane gas on a car with a compression ratio of 9:1 or so. Heres why....

The higher the octane in gas, the slower it burns because it is more resistant to combustion. That is why high compression cars (11:1 for example) require high octane. As the air-fuel mixture is compressed more and more, it has a greater chance of spontaneously combusting(knocking). So you need the higher octane gas to prevent this. If you have a car with an engine that doesn't require high-octane gas, don't hurt performance by making the air-fuel mixture burn slower.

well the vq35de motor has many different forms, and therefore different compression ratios, the lowest ive seen is 9.8:1, i know my QR25de has a compression of 9.5:1, and all VQ motors are recommened to use premuim unleaded fuel only, so i figure with .3:1 compression difference, i mite as wel use premuim as well, not to mention ive heard a lot of stories about altima knock sensors and they're sensativity, so until someone can prove to me its hurting my car, ill stick with 93 octane only