# HELP -- Putting Gas in 350Z



## mbarton99 (Feb 7, 2005)

HELP! I had my 350Z for 3 days and went to gas station to gas up only to find that the pump shut off immediately. My husband tried at 3 different stations to put gas in but was unable. The dealership really doesn't know what the problem is yet -- that was 1 week ago! Also, is it normal to have a BRAND NEW car and not get a loaner when there's a problem like this???

I'm VERY frustrated.

And what if they put regular octane fuel in the 350Z when they initially filled the tank? Will this cause any problems with the engine or anything down the road??? I'm thinking I just want to take the whole deal back and get my 2002 Maxima returned to me and the extra cash I paid for the 350Z -- but I love it!


----------



## Zen31ZR (Mar 24, 2004)

Interesting problem, one I've actually had on a few cars myself........

One thing you might try is changing the angle of the fuel nozzle, and holding it by hand instead of just letting it sit in the tank opening. Sounds dumb, but it can work better than you think. All fuel fill nozzles can sense pressure, they are designed to do that to prevent a fuel spill in the event of being left unattended during a long fill time. They sense backpressure as the gasoline comes up the fill pipe, and can so turn themselves off. The problem may be either the air pressure inside the tank is higher than the outside air pressure, which will confuse the nozzle sensor, or the nozzle outlet is too close to one of the fuel inlet pipe walls, that will also create the same backpressure the nozzle senses to shut off. Try various combinations of nozzle angle and how deep it is inserted into the tank inlet.....
You may also wish to sit with the nozzle in the tank for a few seconds before you start filling, this will allow any extra air pressure inside the tank to escape. 

Newer cars have more highly pressurized and better sealed gas tanks than even models made within the past few years, it's mainly to reduce hydrocarbon emissions. However this means your gas tank becomes highly pressurized even under normal driving conditions, and this excess pressure can take a few moments to vent itself after the cap is removed.

Let us know how this works out for you.


----------



## mbarton99 (Feb 7, 2005)

Thanks -- I'll try all of these, although I did try different angles -- except for totally upside down and not inserting the pump all the way. The car is at the dealership now -- it will be interesting to see what they have to say!

My other question is can damage to the motor or anything else happen if the dealership put low octane gas in when they filled it up for the first time???

Thanks!


----------



## Zen31ZR (Mar 24, 2004)

mbarton99 said:


> Thanks -- I'll try all of these, although I did try different angles -- except for totally upside down and not inserting the pump all the way. The car is at the dealership now -- it will be interesting to see what they have to say!
> 
> My other question is can damage to the motor or anything else happen if the dealership put low octane gas in when they filled it up for the first time???
> 
> Thanks!


 It would be their own fault if they did, they should know better..... I don't think it will harm the engine unless used for extended periods of time, but you may notice a small loss of power. Newer car ECUs can compensate quite well for crappy grades of gas, but the result is less power output.


----------



## 3-fity (Nov 1, 2002)

This is a pretty common problem with the new Z. I just recently had it myself. It worked when I didn't put the nozzle all the way in and tilted it to the right a little. It has only happened once to me, so I don't think it occurs everytime.


----------



## maximZ (Dec 9, 2004)

I haven't had this issue personally (03 Track) but many other have. Some reading fo ya:

Forum Thread 

Forum Thread


----------



## beth350z (Feb 15, 2005)

I've had this problem occassionally, but I just thought it was the gas pump I was at.


----------



## FSU_Z33 (Jan 12, 2005)

I've had my '03 Track since June '03. I have only had it happen at one gas station at a particular pump 3 times (I've learned my lesson!). I think it has to do with the rate of flow...? I found it was better when I rotated the nozzle about 45 degrees clockwise. It was a pain those few times...but was it really so bad you'd consider trading back for your old car?!?!?!


----------



## mbarton99 (Feb 7, 2005)

Think about this -- you spent 4 hours at the dealership getting the best deal, signing the paperwork for a trade-in plus cash deal and then have the sales manager demand your trade-in automobile that day after your salesman has agreed to get it the next day after cleaned out, etc. (keep in mind this was the 3rd new vehicle purchased at this same dealership). I was very FRUSTRATED by that point! Then 3 days later you can't pump gas into the car -- between my husband and myself we probably pumped 1 gallon of gas into the car (also knowing that the dealership put regular gas in the vehicle) -- that's never happened to me before. You then spend about 1 hour on hold with Nissan after the dealership had no idea what the problem was and was told by Nissan that the sales manager would call -- which he didn't and then you call Nissan back and they're CLOSED. The next day my hubby tried to put gas into the tank at THREE different stations -- no luck! He took the car back to the dealership and was told they would need it for at least 4 days -- oh, by the way, sorry they cannot give loaner cars out ------- YES I wanted my 2002 Maxima back.

After ranting above -- the good news. They put a new fuel tank and OVRV valves (whatever that is) in the new 2004 350Z. My husband put gas into it the other day with no problem -- I'm just waiting till the day I try to put gas into it!

Thanks for everyone's help with this matter!

QUOTE=FSU_Z33]I've had my '03 Track since June '03. I have only had it happen at one gas station at a particular pump 3 times (I've learned my lesson!). I think it has to do with the rate of flow...? I found it was better when I rotated the nozzle about 45 degrees clockwise. It was a pain those few times...but was it really so bad you'd consider trading back for your old car?!?!?! [/QUOTE]


----------



## Zen31ZR (Mar 24, 2004)

mbarton99 said:


> Think about this -- you spent 4 hours at the dealership getting the best deal, signing the paperwork for a trade-in plus cash deal and then have the sales manager demand your trade-in automobile that day after your salesman has agreed to get it the next day after cleaned out, etc. (keep in mind this was the 3rd new vehicle purchased at this same dealership). I was very FRUSTRATED by that point! Then 3 days later you can't pump gas into the car -- between my husband and myself we probably pumped 1 gallon of gas into the car (also knowing that the dealership put regular gas in the vehicle) -- that's never happened to me before. You then spend about 1 hour on hold with Nissan after the dealership had no idea what the problem was and was told by Nissan that the sales manager would call -- which he didn't and then you call Nissan back and they're CLOSED. The next day my hubby tried to put gas into the tank at THREE different stations -- no luck! He took the car back to the dealership and was told they would need it for at least 4 days -- oh, by the way, sorry they cannot give loaner cars out ------- YES I wanted my 2002 Maxima back.
> 
> After ranting above -- the good news. They put a new fuel tank and OVRV valves (whatever that is) in the new 2004 350Z. My husband put gas into it the other day with no problem -- I'm just waiting till the day I try to put gas into it!
> 
> Thanks for everyone's help with this matter!


 Well at least they took care of it, fixed the problem for you. Some dealerships around here mighta said, "Tough **** , you own the car now, good luck with it"..... Nice to know a few dealers still take care of new car owners without trying to gouge them in the repair shop.


----------



## FSU_Z33 (Jan 12, 2005)

When I first saw your thread I assumed it was another VERY common problem with the Z33, but it wasn't. A lot of times the fuel door sticks and doesn't open. The best solution is to wiggle the fuel door, lean back in the car and press the button again. However I suggest if this 'problem' rears its ugly head w/ your Z, that you give up on automobiles and society in general, move to the Ozarks, and live the life of a hermit.

C'mon, you have to think of your Z more than just a nice looking sporty utilitarian people-mover. The "Z community" is made up of people that love all Z's for their heritage, beauty, etc... If every time you have a little issue you run screaming to the dealership to take it back and give you something else, then the "Z community" will view you as the whiny neurotic step-daughter that they tell everyone under their breath "isn't blood related".

Show some LOVE for your Z!!!!!


----------



## Dustin (Dec 14, 2003)

heres my only question, what do you mean by low octane gas, we have 87 down here in FL, and everyone and their dog uses it. I dont think the Z would have any trouble running on a lower octane gas, unless its designed for race fuel..


----------



## Zen31ZR (Mar 24, 2004)

KaRdoN said:


> heres my only question, what do you mean by low octane gas, we have 87 down here in FL, and everyone and their dog uses it. I dont think the Z would have any trouble running on a lower octane gas, unless its designed for race fuel..


 Hmm factory recommended 91 octane, as I recall. 87 might cause detonation to set in, and if the ECU could pull enough timing to stop it, then you'd end up with a lot less Hp.....If not, then you'd end up with engine damage. I generally would not recommend using less than the factory recommended octane.


----------



## JAMESZ (Mar 12, 2004)

KaRdoN said:


> heres my only question, what do you mean by low octane gas, we have 87 down here in FL, and everyone and their dog uses it. I dont think the Z would have any trouble running on a lower octane gas, unless its designed for race fuel..


Go back to OT if you can't post useful/correct information. Like Zen said there are reasons that the VQ35DE has a minimum ocatane requirement. There is the threat of detonation, and if not that the ecu will pull timing so much the car will be limping around.


----------



## Nik33615 (Aug 3, 2004)

♣Zen31ZR♣ said:


> Hmm factory recommended 91 octane, as I recall. 87 might cause detonation to set in, and if the ECU could pull enough timing to stop it, then you'd end up with a lot less Hp.....If not, then you'd end up with engine damage. I generally would not recommend using less than the factory recommended octane.


I agree you won't damage the engine or any other part of the car by using 87 octane once in a while. If the recomended gas is 91 or higher then that is what you should use to get the most power the engine can produce. Todays cars can adjust ignition timing and such to compensate for lower octane fuel but don't produce their potential power on less than the recommended octane in most cases.on another note it seems to me that the dealer service you recived was horrible and you should at least inform them of that and maybe tell them if you recive similar service in the future you will take your business elsewhere. (just what I would probably do, but then again I like to bitch lol) hope your luck with the Z improves and good luck with it :thumbup:


----------



## Zac (Mar 10, 2004)

I have seen this happen on newer non American cars. It seems certain stations have this problem happen while other stations do not. It is no certain brand so it must be the type of pump. Certain Shell stations here have this problem while others, I would imagine they are newer, do not.

87 octane should not hurt the car as the car's electronics should retard timing if it is needed.


----------



## Dustin (Dec 14, 2003)

JAMESZ said:


> Go back to OT if you can't post useful/correct information. Like Zen said there are reasons that the VQ35DE has a minimum ocatane requirement. There is the threat of detonation, and if not that the ecu will pull timing so much the car will be limping around.


i only had a question, no need to get rude, or tell me to go back to OT


----------



## Zen31ZR (Mar 24, 2004)

Nik33615 said:


> I agree you won't damage the engine or any other part of the car by using 87 octane once in a while. If the recomended gas is 91 or higher then that is what you should use to get the most power the engine can produce. Todays cars can adjust ignition timing and such to compensate for lower octane fuel but don't produce their potential power on less than the recommended octane in most cases.


To a point that is true. However, the latest gen ECUs are very much more aware of what goes on with the engine than any previous, all except maybe the standalone aftermarket units. Continued use of too low an octane level of gas can cause the ECU to go into a version of "limp mode", which it sometimes won't correct until reset. On VVT-type motors that means no cam advance, on most all others the ECU switches to a very low output fuel/ignition map, and sometimes the engine will run about 2/3 the Hp. Reseting a newer computer is much harder, it's not the simple "disconnect the battery" anymore. Most ECUs now have a small internal backup battery. 
All this because you wanted to scrimp a few bucks on gas. My advise is, if you can't afford the gas, don't buy the car......


----------



## Blank (Aug 21, 2003)

one tank of 87 once in a while is no big deal , the knock sensor will retard timing to compensate, and you will get neither the performance nor gas milage you usually do... keep it at 91 or better if you can, but dont be scared if it is a tankful of lower ctane gas... just dont run 87 exclusively... you wont get your $$$ worth in terms of performance, and if your knock sensor evewr goes, you could have problems...


----------



## IreiMember (Feb 3, 2005)

always try to stay with what oem specs are and what they reccomend. the rating on fuels is nothing other than a ping rating. absolutely nothing will ever happen if you use 87 it may not burn as clean as 91 obviously. but as far as power gains lol please... thats like saying puting in 110 octane in a car with a compresson ratio of 9:1 is gonna make it faster LOL .


as far as your specific problem goes it could be many things and to many for me or anyone else on this forum to speculate on. it sucks any way u slice it especially for a new car. 

gl 


Irei


----------



## Zac (Mar 10, 2004)

IreiMember said:


> always try to stay with what oem specs are and what they reccomend. the rating on fuels is nothing other than a ping rating. absolutely nothing will ever happen if you use 87 it may not burn as clean as 91 obviously. but as far as power gains lol please... thats like saying puting in 110 octane in a car with a compresson ratio of 9:1 is gonna make it faster LOL .
> 
> 
> as far as your specific problem goes it could be many things and to many for me or anyone else on this forum to speculate on. it sucks any way u slice it especially for a new car.
> ...


Is your argument saying that you will get the same power on 87 as 91 or that 91+ will make more power. A 350Z will NOT make the same power on 87 as it will on 91, the ECM will retard the timing.


----------



## Blank (Aug 21, 2003)

NickZac said:


> Is your argument saying that you will get the same power on 87 as 91 or that 91+ will make more power. A 350Z will NOT make the same power on 87 as it will on 91, the ECM will retard the timing.


yea, just cxause you lose power by going down on octane rating(because of retardation by the knock sensor) isnt the same as saying you will gain power by going up...


----------



## JAMESZ (Mar 12, 2004)

IreiMember said:


> always try to stay with what oem specs are and what they reccomend. the rating on fuels is nothing other than a ping rating. absolutely nothing will ever happen if you use 87 it may not burn as clean as 91 obviously. but as far as power gains lol please... thats like saying puting in 110 octane in a car with a compresson ratio of 9:1 is gonna make it faster LOL .
> 
> 
> as far as your specific problem goes it could be many things and to many for me or anyone else on this forum to speculate on. it sucks any way u slice it especially for a new car.
> ...


Do you know anything? From reading your posts I can assume that you don't. A 350Z will NOT make the same power on 87 if anything the ecu will pull timing and go into limp mode. If you don't know what your talking about don't give incorrect information that could cause problems for other users.


----------



## Zen31ZR (Mar 24, 2004)

IreiMember said:


> always try to stay with what oem specs are and what they reccomend. the rating on fuels is nothing other than a ping rating. absolutely nothing will ever happen if you use 87 it may not burn as clean as 91 obviously. but as far as power gains lol please... thats like saying puting in 110 octane in a car with a compresson ratio of 9:1 is gonna make it faster


 If its a turbocharged car, it will........  Why have _race gas_, then, by your way of thinking.....


----------



## IreiMember (Feb 3, 2005)

lol james its obvious you dont know crap about engines. yeah ok i guess your right you will loose 1 hp if you choose 87 over 91 sorry i stand corrected. 



race fuel is for race engines (yes people in the business call these engines not motors)with high compression. hince the need for higher octane fuels..... as far as posting false information. james im not the one who picks eveyrones postings apart on this forum. sorry i live in the real world if that offends you sorry get a life. no need in feeding ppl full of bull crap


oh and for someone who is so quick to point out faults maybe you should read up about some of the things "you claim to know about" id really like to know what your background is with the Z car or any car for that matter


Irei


----------



## Zac (Mar 10, 2004)

BlankgazeX said:


> yea, just cxause you lose power by going down on octane rating(because of retardation by the knock sensor) isnt the same as saying you will gain power by going up...


This is true...I guess I worded that awkwardly. The car will not be making its full potential because of the knock sensor (I assume the Z has one) will retard timing. Dyno graphs will show this on Spec Vs which use 87 while dynoing. Their graphs look somewhat like a richtor scale.


----------



## JAMESZ (Mar 12, 2004)

IreiMember said:


> lol james its obvious you dont know crap about engines. yeah ok i guess your right you will loose 1 hp if you choose 87 over 91 sorry i stand corrected.
> 
> 
> 
> ...


I've built/building a Z31T, worked on Z32s, I have been around and worked on the 350Z; I have been around/in development of parts for the 350Z. I know all of the guys that design parts at Crawford, and many of my friends own 350Zs. If you think all you will lose is 1hp your dead wrong. The ecu will pull timing to the point where the car is not making any power; and just trying to avoid detonation. Now I have a life the thing is everything I have read that you posted is incorrect. Unless you know what your talking about don't post because I will continue to correct you so you don't cause problems for someone that reads your posts.


----------



## Spongerider (Nov 18, 2002)

BlankgazeX said:


> yea, just cxause you lose power by going down on octane rating(because of retardation by the knock sensor) isnt the same as saying you will gain power by going up...


BlankgazeX, you are wrong in this statement. I have to agree with the majority.


----------



## Zen31ZR (Mar 24, 2004)

IreiMember said:


> race fuel is for race engines


Wrong. Race fuel is useable on all engines. I noticed a definite difference between running 91 octane pump gas in my car, and running 104 race gas in it. NA engines are mostly the ones that don't require an increase in octane, unless you increase the compression ratio and/or the valve lift. Turbo engines, when you increase the boost, you effectively increase the compression ratio. 
I've also learned the problems of running low octane in a higher octane required engine. My motorcycle requires 91 octane. I attempted to run 85 in it, and the pinging was painfully obvious. I promptly drained the tank and put the proper grade of gas in it. And this was in a carburated 15 year old motorcycle. Modern engine electronic controls will cause massive loss of power when low octane fuel is sensed by the knock sensor and the 02 sensor. You can't argue with the facts, and those are. 
It used to be that running too low a grade of fuel, in older engines, simply caused the head gaskets to blow, due to knocking, and other major problems. Now, thanks to modern technology, we don't have those problems any more, the effects are simply seen as a loss of power as systems compensate for the low grade. So people no longer seem to see the severity of the situation , as they may have 20 years ago before modern electronics.


----------



## IreiMember (Feb 3, 2005)

lol ok james here we go. read the posts i write(and i mean the whole thing not just parts you like to pick out) 

ok perhaps if you dynod your car with 87 octane im sure you would see that 91 will surely put up better numbers. (not by a whole lot though)

now as far as your timing retarding, yes to some degree you will have some retarding but not to the extreme like your thinking and this is why.

lets assume for the sake of argument that our new 350z has a compression ratio of 9:1 putting in what the oem recommends which im sure is 91 is always the best solution. however its not a requirement. 

o2 sensors senses the fuel mixture and tells the ecu to change the fuel mixure if need be. (via exhaust)

knock sensor senses the vibration in the antifreez in your block, which then controls the timing to stop a knock if one should come about before something bad should happen

it would take a really low octane fuel to cause an engine to knock and retard its timing. this is a brand new engine keep in mind. so its effeciency is gonna be way high unless there are other problems that we dont know about. (an old tired 10 year old engine would probably prover otherwise)

i will agree if a knock does occur there will be substantial power lose of course. 


Higher Octane fuels in low compresson engines will not produce more power _PERIOD!_

im looking at all data as we speak and will post some more precise data as time permits.

Irei


----------



## JAMESZ (Mar 12, 2004)

10.3:1 is the compression on the 03-05 VQ35DE found in the 350Z (minus the 05 track and 35th anniversary). The engine doesn't exactly have "low" compression. In every thread you have come back saying you will have proof. The fact is you do not. You continue to post B.S. that could cause problems for other users. In fact thus far you have not posted one piece of useful information. So sit back for awhile and absorb some knowledge before you start posting. That way you won't post the wrong information.

I have noticed you know nothing about the engine managment on any car. And since you know NOTHING about Zs and especially the 350Z please stop trying to act like you know everything. The engine will pull timing and ALOT more then you are letting on. You act like it won't effect anything when in reality it DOES. Please you have NO experience with the car. I'm sick of telling you over and over again your wrong. 

And 100 octane will help on the 350Z it cost to much to be practical, but dynos have shown a 7rwhp gain from running 100 octane gas. Also low octane has caused pinging in the Z33. Performance gains aren't exact, but people have slips showing a .3 second difference between 91 and 100 octane in the 1/4 mile.


----------



## Blank (Aug 21, 2003)

Spongerider said:


> BlankgazeX, you are wrong in this statement. I have to agree with the majority.


how so? what i said is pure fact...?


----------



## Blank (Aug 21, 2003)

NickZac said:


> This is true...I guess I worded that awkwardly. The car will not be making its full potential because of the knock sensor (I assume the Z has one) will retard timing. Dyno graphs will show this on Spec Vs which use 87 while dynoing. Their graphs look somewhat like a richtor scale.


not to mention what would happen if the knock sensor crapped put... major engine knock and leading to fuct pistons...


----------



## Zen31ZR (Mar 24, 2004)

BlankgazeX said:


> not to mention what would happen if the knock sensor crapped put... major engine knock and leading to fuct pistons...


Blown head gaskets, too. Depends on the engine. Some engines, such as the 4G63, simply melt the pistons before the headgasket goes. I have personal experience with that.....


----------



## Spongerider (Nov 18, 2002)

IreiMember said:


> lol ok james here we go. read the posts i write(and i mean the whole thing not just parts you like to pick out)
> 
> ok perhaps if you dynod your car with 87 octane im sure you would see that 91 will surely put up better numbers. (not by a whole lot though)
> 
> ...


We are talking about the Z33, right? The ECU from the factory is tuned to 91 octane and the Z33 compression is 10.3:1 (*fact*) not 9:1. Have you noticed that it is very hard to make power on these cars? The reason is that Nissan has tuned the Z33 to it's optimal and why it's important to put in high octane gas. Anything less will drop your HP considerably and I'm not talking 5 hps (there is a reason the variable timing is used in this car). You won't find a dyno comparisions of octane difference because it's a waste of money and know one in there right mind would subject a $30+K Z to that kind of abuse.

_Originally Posted by *IreiMember*_
_"Higher Octane fuels in low compresson engines will not produce more power PERIOD!"_

I hate to say it but this statement puts you in the *John*.. A Z32 has a compression of *8.5:1* and when this car came out the octane rating in Cali was 92 and when they switched over to 91 octane people with JWT ECU's went into safety boost. What does that tell you?? If you have some knowledge of how a car works this is telling you octane does count.

If you do have data please post it I do have a open mind?


----------



## Spongerider (Nov 18, 2002)

BlankgazeX said:


> how so? what i said is pure fact...?


Ok show me the *fact*, I'm waiting? But if your word is fact then you really need to go to the 300zxclub because that kind of baby talk belongs there.


----------



## Zac (Mar 10, 2004)

♣Zen31ZR♣ said:


> Blown head gaskets, too. Depends on the engine. Some engines, such as the 4G63, simply melt the pistons before the headgasket goes. I have personal experience with that.....


I've seen it!!! (crap, my buddy was pulling bad knock on his heavily modded 4G63 with 93 octane).


----------



## Blank (Aug 21, 2003)

Spongerider said:


> Ok show me the *fact*, I'm waiting? But if your word is fact then you really need to go to the 300zxclub because that kind of baby talk belongs there.


ok idiot, run 87 in your car, but dont tell other peole to, because you are too ignorant to realize IF THE KNOCK SENSOR FAILS A 350Z WILL BECOME SERIOUSLY FUCKED UP WITH 87 OCTANE GAS! and like i said, you lose power with lower octane BECAUSE of the sensor, is that what you are disputing? or are you disputing my statement you WILL NOT gain power from higher octane?

its a high performance car, use high performance gas... god i went through with this shit in the qr section with spec V's, some dumb ass is gonna have 100 people fuck up thier cars to save 30 cents at the pump...

in the end, if your car says 91, run 91, 87 will hurt it, 100 wont help it, use what is recomended...


----------



## Zen31ZR (Mar 24, 2004)

BlankgazeX said:


> ok idiot, run 87 in your car, but dont tell other peole to, because you are too ignorant to realize IF THE KNOCK SENSOR FAILS A 350Z WILL BECOME SERIOUSLY FUCKED UP WITH 87 OCTANE GAS! and like i said, you lose power with lower octane BECAUSE of the sensor, is that what you are disputing? or are you disputing my statement you WILL NOT gain power from higher octane?
> 
> its a high performance car, use high performance gas... god i went through with this shit in the qr section with spec V's, some dumb ass is gonna have 100 people fuck up thier cars to save 30 cents at the pump...
> 
> in the end, if your car says 91, run 91, 87 will hurt it, 100 wont help it, use what is recomended...


We've already shown that 100 octane will help it..... 
You'd lose power in a car running 87 octane that should be running 91 octane, knock sensor or no. Why? Because the knock is incomplete combustion..... The typical engine only uses 33% of the energy contained in a given amount of fuel. When improper octane levels cause knock, that means far less is used. 
Knock is improper flamefront propegation in the combustion chamber. Typical knock can be best explained as _too fast_ of such propegation, instead of uniting as a single "wave" and creating the powerful push on the piston, it splits up, "echoing" off the walls of the combustion chamber and charging the middle, where one or more meet and cause a reverberation effect. All of this is supersonic and takes place in milliseconds, your brain registers it as a high frequncy tapping sound....... 
Anyway, what I'm trying to say , is that you would lose power whether the knock sensor heard that noise or not. Knock sensors are designed to hear that certain frequency of where 90% of all knock occurs. However, it can happen at a much lower or higher frequency, especially if the car has any modifications that affect airflow. Air density affects knock frequency. It's possible to have knock the the sensor will not even notice, especially in older vehicles.


----------



## Zen31ZR (Mar 24, 2004)

And I should perhaps point out that Irei is incorrect as to how the knock sensor hears the sound. It is not listening to the sound of the antifreeze. Not on gasoline cars anyway, that is reserved for the newer diesels. No, it is listening to the sound of the engine block itself. The metal is of a known composition and will conduct sound almost always in the same way. Composition of antifreeze can change, and could change how much or how little of that particular knocking sound is actually heard by the sensor. Go ahead, pull the knock sensor on any car, it is not in a water jacket...


----------



## bridrive55 (Aug 26, 2004)

♣Zen31ZR♣ said:


> We've already shown that 100 octane will help it.....
> You'd lose power in a car running 87 octane that should be running 91 octane, knock sensor or no. Why? Because the knock is incomplete combustion..... The typical engine only uses 33% of the energy contained in a given amount of fuel. When improper octane levels cause knock, that means far less is used.
> Knock is improper flamefront propegation in the combustion chamber. Typical knock can be best explained as _too fast_ of such propegation, instead of uniting as a single "wave" and creating the powerful push on the piston, it splits up, "echoing" off the walls of the combustion chamber and charging the middle, where one or more meet and cause a reverberation effect. All of this is supersonic and takes place in milliseconds, your brain registers it as a high frequncy tapping sound.......
> Anyway, what I'm trying to say , is that you would lose power whether the knock sensor heard that noise or not. Knock sensors are designed to hear that certain frequency of where 90% of all knock occurs. However, it can happen at a much lower or higher frequency, especially if the car has any modifications that affect airflow. Air density affects knock frequency. It's possible to have knock the the sensor will not even notice, especially in older vehicles.


And also, conversely, noise that the knock sensor recognizes as knock that is really harmless engine noise. Subaru's have huge problems with overzealous knock sensors.
I see what they were saying above though. Running C107 race fuel in a 350Z will not increase power, because all that a higher octane rating does is increase an engine's knock tolerance threshold. With a stock or even slightly modified VQ35DE, this isn't a consideration, because it doesn't knock with 91. 91 octane will deter 100% of knock just as well as 107 octane will. 87 octane however, might make the engine knock, which would activate the knock sensor, which triggers the ECU to retard the timing.


----------



## Zen31ZR (Mar 24, 2004)

bridrive55 said:


> And also, conversely, noise that the knock sensor recognizes as knock that is really harmless engine noise. Subaru's have huge problems with overzealous knock sensors.
> I see what they were saying above though. Running C107 race fuel in a 350Z will not increase power, because all that a higher octane rating does is increase an engine's knock tolerance threshold. With a stock or even slightly modified VQ35DE, this isn't a consideration, because it doesn't knock with 91. 91 octane will deter 100% of knock just as well as 107 octane will. 87 octane however, might make the engine knock, which would activate the knock sensor, which triggers the ECU to retard the timing.


Actually the Subarus (the STi) are having problems because the EJ25 was designed to run on 95+ octane gas.... The 91 octane salad oil we have completely freaks out the ECU. This problem is solved with an ECU reflash, but then the STi is not longer 300 Hp....  The 350Z, as JamesZ has already said, responds better to 100 octane fuel. Engines are specified to run the octane they are to balance fuel economy, Horsepower, and warranty. Also, cars that require higher octane can be offputting to potential buyers, especially with the prices we pay for gas these days. At 10.5:1 compression ratio, I would say that 91 octane was barely adequate to control knock in the 350Z. The 91 ZR1 Corvette, at a 10.1 ratio, specified 91 octane. Half a point higher, it makes sense that more octane would be required. 
Something else you don't realize, almost all engines experience knock at some point. Could be one out of every 30 power cycles. Could be one out of 100. Knock sensors start to wake up when a threshold point is reached, which is about 1 out of every 10-20 power cycles. At 5000 rpm, you do the math.  What higher octane does, is create smoother more useable power for the engine. Higher octane of itself is not more powerful, higher octane actually _slows down_ combustion, makes it more useable by the engine. It lowers the chance of having knock in the threshold range of the sensor, and lowers knock in general, which means the engine can make power on _every_ stroke, not just _most_ of them......


----------



## Zen31ZR (Mar 24, 2004)

I'll put this into perspective for some of you. What do a 79 308 GT Ferrari, an 86 Porsche 911 Turbo, a 94 ZR1 Corvette, and a 2004 350Z have in common? They all require 91 octane gas.... Even with such disparate power applications. What I'm trying to say is, factory octane requirement is a generalization. Especially for modified vehicles, factory octane requirement goes right out the window. Octane requirement is also specified the same for all altitudes, which is hugely incorrect in a place like Colorado.....


----------



## Zac (Mar 10, 2004)

Might as well also add, when fuel is reformulated (oxygenated), I have always been told to consider bumping up octane as it can cause pinging or premature burn, especially vehicles with excess carbon build up. I know that MD is reforumlated in winter months, and PA is not. Premium is generally 93 here, and 94-98 is readily available. I would imagine Cali is oxygenated. The STi may simply not be able to take reformulated 91 octane without having a serious reduction in timing.


----------



## Zen31ZR (Mar 24, 2004)

NickZac said:


> Might as well also add, when fuel is reformulated (oxygenated), I have always been told to consider bumping up octane as it can cause pinging or premature burn, especially vehicles with excess carbon build up. I know that MD is reforumlated in winter months, and PA is not. Premium is generally 93 here, and 94-98 is readily available. I would imagine Cali is oxygenated. The STi may simply not be able to take reformulated 91 octane without having a serious reduction in timing.


Aside from a few gas stations catering to the racers around here, the best we get is 91 octane. Kind of odd, since at higher altitude, we should get the higher octane stuff.


----------



## JAMESZ (Mar 12, 2004)

Spongerider said:


> We are talking about the Z33, right? The ECU from the factory is tuned to 91 octane and the Z33 compression is 10.3:1 (*fact*) not 9:1. Have you noticed that it is very hard to make power on these cars? The reason is that Nissan has tuned the Z33 to it's optimal and why it's important to put in high octane gas. Anything less will drop your HP considerably and I'm not talking 5 hps (there is a reason the variable timing is used in this car). You won't find a dyno comparisions of octane difference because it's a waste of money and know one in there right mind would subject a $30+K Z to that kind of abuse.
> 
> _Originally Posted by *IreiMember*_
> _"Higher Octane fuels in low compresson engines will not produce more power PERIOD!"_
> ...


Very good post. You put it in words better then I did.

I didn't point out the knock sensor Zen good point, the EJ25 has more problems then the knock sensor, the ecu is just a pain and it is hard to keep the pre 05 STis away from knock. In 05 they redid the ecu so now that is no longer a problem.


----------



## Zen31ZR (Mar 24, 2004)

Most cars have multiple spark and fuel maps stored in the ECU. Most cars run fairly conservative timing advance and injector pulse width depending on what the knock sensor and 02 sensor sees. Most cars also run a touch rich from the factory, turbo cars definitely do. This is to protect engine warranties, for no other reason. What happens when the knock sensor hears less knock, is that it lets the ECU advance timing until it once again hears threshold knock, within the fuel maps capabilities to do so..... If timing can not be retarded enough to combat knock, a lower value fuel/spark map is switched to. When less knock is heard, the ECU advances the timing til it gets threshold knock, or if it comes up on the out of range of a low end map, switches to a more aggressive one. This is why putting higher octane gas in a modern vehicle can have big results. Older vehicles with less advanced ECUs, or even no ECUs at all, don't really benefit from using higher octane gas, except to combat piston deposits, as was mentioned before.


----------



## Spongerider (Nov 18, 2002)

BlankgazeX said:


> ok idiot, run 87 in your car, but dont tell other peole to, because you are too ignorant to realize IF THE KNOCK SENSOR FAILS A 350Z WILL BECOME SERIOUSLY FUCKED UP WITH 87 OCTANE GAS! and like i said, you lose power with lower octane BECAUSE of the sensor, is that what you are disputing? or are you disputing my statement you WILL NOT gain power from higher octane?
> 
> its a high performance car, use high performance gas... god i went through with this shit in the qr section with spec V's, some dumb ass is gonna have 100 people fuck up thier cars to save 30 cents at the pump...
> 
> in the end, if your car says 91, run 91, 87 will hurt it, 100 wont help it, use what is recomended...


At first, I was wondering why you were talking to me but then I realized I responded to you thinking you were * IreiMember*. So please disregard my comment to you?

On a side note, please be mature enough to respond like an adult? You can disagree so long as we agree to be civil, ok?


----------



## Blank (Aug 21, 2003)

* * *


----------

