ja1997max

Hi everyone,

I drive a 1997 and as you know it requires 91+ octane. From what I understand the 1998-1999 do not, but can run on regular without issues. My question: is it possible to convert my 1997 engine to run on regular fuel?

Any information would be greatly appreciated, thanks in advance

Jordan

skiboarder72

nope its the same exact engine they all take 91+

endus

iTrader: (1)

They all take the same.

You can run 87 in your car if you want...just don't expect the absolute best mileage or performance. There will be a slight hit...but if you really want to save the money there are zillions of people doing it.

BlueC

iTrader: (5)

Imo, seriously people, spend the extra $1 or $2 on premium. Its $28 to fill up on regular, and $31 on premium, thats with a 20 cents difference per gallon. (I dont fiull up on regular, never have, just did the calculations). So think about it this way, your losing roughly 20 hp on regular, look in the 4th gen FAQs. That $3 extra for 20hp back if you get premium. $0.15 per hp, pretty good gains eh?

So dont ruin your engines performance and gas milage just to save $2-3....

ja1997max

The reason I ask this question is because:

Fuel requirement type for 1997:
http://www.fueleconomy.gov/feg/noframes/13554.shtml

Fuel requirement type for 1998:
http://www.fueleconomy.gov/feg/noframes/14341.shtml

So if this is true, then there is absolutely no reason why someone with a 1998-1999 would need premium....? Unless the U.S. Department of Energy is wrong of course...

BlueC

iTrader: (5)

As your avatar says, read the FAQ.

98SterlingMax

Has anyone done a dyno comparison between using 87 vs. 91 octane and are there dyno graphs that we can look at that show the results. I ask this because I use nothing but 87 and my cars performance and mileage (~20 city ~30 hwy) is just fine. Heck, one time as an experiment I set the cruise at 66 (verified with my GPS, it was actually 69 cuz of my slightly oversize tires) and on level highway for 140 miles I got 40.4 MPG! Gotta love that auto overdrive...

Eric425

What makes you think you lose 20 hp? Prove it. Show us a dyno. Don't just make up numbers that you pull out your @ss. I usually use premium too, but once or twice I've used 89, but when I did, there no noticeable loss of power or gas mileage.

BlueC

iTrader: (5)

Read the FAQ for christ sakes. Im not pulling anything out of my @ss, maybe you should stop putting stuff in there.

BlueC

iTrader: (5)

http://www.dynospotracing.com/octane.htm

theres the link, guess where it was found... hmmm.... 4th gen FAQs!!!!

If you fill up with regular, the knock sensor will notice your using cheapo gas, so intead of damaging the engine, it retards the timing, hence the power loss.

ja1997max

Granted that the graph is correct, this still does not explain whether or not 98+ Maxima's require the premium fuel. There is nothing in the FAQ's other than basically saying all years are the same. True, if a car requires premium but gets regular octane then I am sure one will get a similar graph. However, if you will notice the links posted above from fueleconomy.gov (post #5) it gives us a different story, saying 1997 Maxima's premium is required whereas 1998+ can use regular without problems. If any body can clear this up, again it would be appreciated instead of referring me to FAQ's that do not explain my question.

Shift_my vq

blueC--- Eric You got son

dmplus

That dyno is a horrible comparison, it's two different cars not the same one! I've always used premium but i've driven my friends 95 who only uses 85 octane and theres certainly not a 11% loss of power. Who comes up with this crap?

hotshtsr20

i used 87 in my 99 once. it sucked. you could audibly hear the knock on throttle tip in. it felt a little more sluggish, not 20 whp sluggish, but not good either.

just use 91, its like $2-3 a tank. forcing your knock sensor into action sucks.

I30tMikeD

iTrader: (8)

You have to first understand why a higher octane is needed and what it does. fuel in the cylinder can spontaneously combust under pressure without a spark being present. The greater the pressure the greater the chance of combustion without spark...which is not a good thing. The engines cylinders are set up to fire in a sequence and if one cylinder fires out of turn it causes problems... which is called knock. Knock is not a good thing and excessive knock can put a hole in the side of a cylinder.

Ok, so we now know that fuel can combust under extreme pressure and cause knock. The VQ30DE, the engine in every 4th gen from 95-99 has a decently high compression ratio. 10:1 I believe. This means that there is a lot of pressure in each cylinder, at least compared to most cars on the road. With a higher compression ratio the more chance of fuel spontaneously combusting in the cylinder.

With out going into detail, gas that contains a higher octane level will not combust under pressure as easily as gas with a lower octane level. So that is why we need to use a higher octane gas.

The compression ratio in all 4th gen maxima's are the same. They all need to have 91+ octane to run the best. Now....if one chooses not to use 91+ octane the engine will not explode. We have knock sensors that detect knock in the engine. So if you choose to use 87 octane and you get some knock the ECU will retard the timming to fend off the knocking. This will save your engine damage but at the same time is will hurt fuel economy and performance.

So just use 93 and your car will love you. Why does fueleconomy.gov say that 98+ maxima's don't require a higher octane??? Got me...they have a lot of cars to keep track of and they are bound to make a mistake. There is no reason why a 98 maxima would not need to use 91+ octane. All 4th gen's have the exact same engine with the exact same compression ratio. They simply made a mistake.

ABK

Busted, now we got proof.

All 4th gens (I don't know about other gens) got 10:1 compresion so I think that premium is a must to limit the knock.

SteVTEC

1997: http://www.nissannews.com/nissan/199...ma/specs.shtml
Recommended Fuel
Premium unleaded

1998: http://www.nissannews.com/nissan/199...ma/specs.shtml
Recommended Fuel
Premium unleaded


Since when does the government get anything right?

SteVTEC

err, well actually......

What happens is that as the piston is compressing the air-fuel mixture, the pressure in the cylinder is rapidly increasing. When the spark plug fires and ignites the mixture at the top of the chamber, a pressure wave starts downward as the piston is still travelling upwards and compressing (remember that the A32 will fire the spark plug up to 40-45 degrees BTDC). What then happens is that now the air-fuel mixture near the piston can get squeezed both by the piston moving upwards, and the flame front moving downwards and doubly increase the pressure on the mixture. If that rate of pressure increase or overall pressure is too great, the mixture at the piston end can spontaneously ignite and now you have two flame fronts. One of them is travelling upwards, the other is travelling downwards. When they meet somewhere in the middle, that is the knock that you hear.

There are two solutions.

Choice 1: Use higher octane fuel (good)

Higher octane fuel can handle the squeeze a lot better since higher octane prevents combustion. It allows the mixture to handle higher temperatures and pressure before spontaneously combusting. Use of the higher octane fuel allows you to keep your more advanced ignition timing, and the more advanced ignition timing is good because that means that there is more energy from combustion available by the time the piston reaches TDC to thrust it hard downward with and this gives you more torque. Since you have more torque per unit fuel, your engine is now running more effiiciently, and it's also cost effective as long as you're still on pump gas.

Choice 2: Retard ignition timing (bad)

By retarding the ignition timing a few degrees you're now firing the spark plug later. What happens is that by that time (a few degrees later) more of the pressure ramp is over and done with and this puts less heat/pressure on the lower air-fuel mixture as the upper mixture near the spark plug is firing and expanding. You have uniform mixture light-off and only one flame front which is exactly what you want and no knocking. The tradeoff? Since you fired the spark plug later, now you have less power from the combustion cycle available to thrust the piston downward with by the time it reaches top dead center. This means you have less torque available and that the engine isn't operating as efficiently as it could.


The pressure ramp rate and overall pressure are both critical, and this is why factory boosted engines always have lower compression ratios. The lower compression ratio lowers both overall pressure and also the ramp rate which allows them to run higher boost still on pump gas while keeping the ignition timing reasonably advanced. On the otherhand, when you mod the crap out of those same engines and crank the boost up, if you run race gas (extremely high octane) that's the only way to keep the knocking in check because of the extreme pressures. It's either that or very retarded timing (or a combination of both).


Hopefully, that made sense.

98SterlingMax

Absolutely correct, I was wondering when someone would mention the flame front. Still, I get good results from 87. Oh, BTW if you look at the 1998 specs that you gave the link to you notice that you can get a 4 speed manual AND a 5 speed manual? I guess even Nissan makes mistakes... oh and I didn't realize that our engine took 8.625 quarts of oil with filter.
EDIT: Also, I know my SE will do more than 112...man, they GOTTA get a proofreader, there is also a spelling error in there.

Eric425

Whoa...guys. Owned? I don't think so. Look at the top of the dyno, near the graph. They're two different cars, AND THEY ARE NOT MAXIMAS!

mchne

iTrader: (3)

anyone who makes a fuss over the extra $2-$3 it costs to fill with 91+ instead of 87 shouldn't be driving, because you obviously aren't in the financial position to own a car.

I drive my car a LOT, I fill my tank once a week. $3 more a week for 93 octane at shell instead of 87. that's about $12 a month.

you can't afford $12 a month for the peace of mind that you're doing your part to ensure your car is running at it's best? maybe it's time to start riding a bicycle instead.

you gotta be f'ing kidding me. get over it, people.

I30tMikeD

iTrader: (8)

OK Mr. smarty pants.

ja1997max

Excellent, thank-you I39tMikeD and SteVTECH. I was not trying to be cheap but just interested (if there was a difference in fuel requirement) if it was technically feasible to convert engines. This highlights why it is important to have a number of 'reliable' sources available.

BlueC

iTrader: (5)

Maxima or not, it still proves my point, use regular, watch performance and gas milage drop. Not to mention I found the link for you when you said I had no proof. Face it, you lost.

SteVTEC

haha...I never noticed that. I trust Nissan info more than government data, but yeah, there's lots of errors on their spec pages too.

If you look in the 1999 specs, you'll see that they believe there was an "XE" model.

Also, and even more amusing on the overview page...



Mah 1999 Maximuh done got VEEEEETECH baby!

SteVTEC

Phatmax98

iTrader: (2)

Why does this graph look funny to me? The lines in it are broken...Don't flame..I just have never seen an acutal dyno and all the ones I have seen online never have had broken lines...is it modfied or something?

SteVTEC

well the one with the broken lines is the one that's on a lower octane than it should be and it's pulling timing. It could cause irregularities in the RPM ramp which the dyno may pickup and be programmed to ignore in order to keep the data consistent.

Quicksilver

iTrader: (1)

Look man, any car that lists premium fuel as it's primary fuel type will have this problem of losing HP and TQ when switching to a lower grade fuel. It's a fact. Some cars will actually gain HP/TQ when you up the fuel type to 91+ octane (for example, the 2004 Honda Accord V6). It looks pretty clear cut to me...

Folks, you may think you are saving money by using lower grade fuel, but in the long run, you will lose performance, and most likely suffer some kind of major mechanical failure related to knock/pinging/preignition. So, don't buy that candy bar and Coke at work from the vending machine, and put that money into your tank of gas.

SteVTEC

For the people that are too cheap to put the right kind of fuel in, that's what the knock sensor is for, so that you don't have any mechanical problems. It'll cut back timing and drop power (and mileage) to the point where it would have just been more cost effective to put the $0.20/gal more expensive fuel in anyways, all while being able to enjoy much better performance. But hey, it's their money.

Spaniard

iTrader: (1)

So I have a burning question:
As I have an aggressive program (via JWT ECU) so would I expect to see gains on 91 octane fuel if I added some race fuel? (e.g. like bringing it up to 95 octane?)

Like would some sensor determine that I have 95 octane going and advance the timing more? Or would it just ensure that the knock sensor stays way away from retarding the timing...

Tnx Id love to know as I am dynoing today...

Phatmax98

iTrader: (2)

I don't think it's the fact that people are cheap..more or less they are not technically intelligent and don't realize what happens when you use the lower octane...and most likely people don't care all that much since most people own their cars for what...maybe like 5 years and then sell it and get something else. So realistically "most" people do not care that they are putting cheap gas in their vehicles due to the fact that they will most likely sell it a few years down the road. Just my .02

SteVTEC

I think on really hot days, some of the guys with the JWT ECU have gotten slightly better track times with a little bit of race fuel because the timing is very aggressive. But it's colder out now, so I doubt it would have much of an effect. Dave B, I30tMikeD, and Nealoc187 would be good guys to ask.

Spaniard

iTrader: (1)

That makes sense... Thanks-

I30tMikeD

iTrader: (8)

I have the JWT/ECU as well. I am not $hiting you here, with all othe variables the same I saw at least a .2-.3 gain in the 1/4 from running a 96-97 octane level. I had a couple gallons of 93 then added one gallon of 104

I had been running 14.60's for months...then one day decided to add some race gas and ran 14.2's all day long and one 14.1. The wether was cold that day high 30's and low 40's throughout the afternoon and I did pull better 60' then usual but those factors don't account for running almost a 1/2 second faster. I say the race gas gave me at least a couple tenths.

There are a couple other things that might have been going on but all thing point to the race gas.

SteVTEC

that was in cold weather? oh cool...okay so then the JWT does like a little race gas even in cold weather too then.

Phatmax98

iTrader: (2)

I thought cold weather was better...maybe it's just me...but my car seems faster in the cold

SteVTEC

You're more likely to get knock and timing retard in hot weather than in cold weather.

VQuick

iTrader: (17)

My parents have a 2003 Accord (pretty nice car, for a Honda... ) and Honda says to use 87 octane. I don't know what the engine's compression is but it's a pretty high performance V6. They claim 240 HP, 212 TQ. Anyway, if the engine is "designed" to take regular fuel, would I really see a difference with 91 or 93 octane? In other words, is the knock sensor retarding timing by default? If so, that's pretty stupid.

Cal0205

My friend owns an accod, he says Honda looses HP when using 91+. The opposite effect of a Maxima