# Fuel additive



## Classic XE (May 2, 2002)

Which additive is best? Gas treatment, fuel injector cleaner, etc.


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## James (Apr 29, 2002)

tried octane booster this weekend... the one with the black horse on it. went up the mountains with three people and luggage in my car and a/c on. held 65 no problem. heat was fine car didn't sound like it was dying. 

injector cleaners shouldn't be used... i've used them, they help a bit.


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## dschrier (May 6, 2002)

I always use the STP fuel system cleaner complete. You're only supposed to use it every 6000 miles or so, and I haven't used it for maybe 10,000. When I first got my car, 90 sentra, I was getting 25mpg, now I get around 36 since I've started using fuel cleaners. They can probably be harmfull if you use them extensively, but once in a while they can't hurt, especially on a car that is really old anyways.


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## Subculture (Apr 30, 2002)

> tried octane booster this weekend... the one with the black horse on it.


Unless you have really high cylinder pressures (from high boost or high compression) you don't need octane boost. 



> I always use the STP fuel system cleaner complete.


There's a Nissan Tech Bulletin that advises against using fuel injector cleaners.


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## dschrier (May 6, 2002)

Well I have a 90 b12 which isn't on that list, so I guess I'm all set


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## Subculture (Apr 30, 2002)

It's your money.


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## dschrier (May 6, 2002)

Well what does a true fuel injector cleaning do differently than fuel additives. From what I understand most places just soak your fuel injectors in solvent which is all the fuel additives are, and they are 5 fold cheaper than a cleaning.


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## James (Apr 29, 2002)

Subculture said:


> *
> Unless you have really high cylinder pressures (from high boost or high compression) you don't need octane boost.
> 
> 
> There's a Nissan Tech Bulletin that advises against using fuel injector cleaners. *


I know... just wanted to try it. It felt very good tho but feelings are feelings.


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## Subculture (Apr 30, 2002)

> Well what does a true fuel injector cleaning do differently than fuel additives.


If you were to send your injectors to a place like RC Engineering, they would take your injectors apart, sonic clean them, reassemble them, flow test them, balance them (too make sure they are all flowing the same) and them send them back to you.



> I know... just wanted to try it. It felt very good tho but feelings are feelings.


Also, using too high an octane level can cause your car too _loose_ HP.


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## James (Apr 29, 2002)

Subculture said:


> *
> If you were to send your injectors to a place like RC Engineering, they would take your injectors apart, sonic clean them, reassemble them, flow test them, balance them (too make sure they are all flowing the same) and them send them back to you.
> 
> 
> Also, using too high an octane level can cause your car too loose HP. *


Explain that.


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## barnoun (May 7, 2002)

I think losing hp in that situation has something to do with the combustion occuring too slow because of the high octane, but not sure. Care to give a detailed explanation Subculture?


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## James (Apr 29, 2002)

well barnoun... don't know what subculture will say... but MY logic is that since our car has a knock sensor and my ignition is advanced and I'm climbing up hill with the a/c on with three people in the car, the car will retard the timing at the first glimpse of any pinging/detonation which i know happens sometimes when going up hills regardless when the load on the engine is high... therefore the octane prevents that from happening and allows more power in the uphill climb....

does that sound like a reasonable answer?


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## barnoun (May 7, 2002)

It's reasonable in that situation. In a straight, or when detonation is unlikely though, I think you'd still lose a little power(because the timing might not be advanced enough to allow complete ignition of the slow burning high octane fuel).


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## James (Apr 29, 2002)

IC. Well, how much do those boosters add to the rating of the gas? Adding 2 points to 91 CA gas wouldn't hurt that bad...


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## dschrier (May 6, 2002)

Probably not since in NH we have 93 octane and I put that in my 90 b12.


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## Subculture (Apr 30, 2002)

> Explain that.


Sure.
The following is an excerpt from the GASOLINE FAQ
6.13 Can higher octane fuels give me more power?
<snip>
If you are already using the proper octane fuel, you will not obtain more
power from higher octane fuels. The engine will be already operating at 
optimum settings, and a higher octane should have no effect on the management
system. Your driveability and fuel economy will remain the same. The higher 
octane fuel costs more, so you are just throwing money away. If you are 
already using a fuel with an octane rating slightly below the optimum, then 
using a higher octane fuel will cause the engine management system to move to
the optimum settings, possibly resulting in both increased power and improved
fuel economy. You may be able to change octanes between seasons ( reduce 
octane in winter ) to obtain the most cost-effective fuel without loss of 
driveability.


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## James (Apr 29, 2002)

Interesting... but you said you could lose hp by using high octane... how is that? 

sorry for asking so many questions, i'm just not familiar with fuel and it's effects on combustion.


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## Subculture (Apr 30, 2002)

> but you said you could lose hp by using high octane... how is that?


For the last 45 minutes I've been trying to find a web link that would give a detailed explanation. I haven't been able to find a link to the site I was looking for.

However, I do have an message from Zak Nilsson that was posted to the SoCal-SERCA mailing list that gives a pretty good explanation:

"...my understanding of how gas works in 
relation to how much power you make is this: Simplified, higher octane 
gas will actually cause you to lose power, not gain power. Octane = 
headroom for detonation basically. The only way you'll make more power by 
adjusting octane is by reducing it so you run leaner. But that increases 
your chances for detonation too. Increasing the octane is something you 
would do only if you're already at the detonation threshold. If you're 
near detonation, you can go up to say, 100 octane which will allow you to 
bump your timing further, or on turbo cars increase your boost level, 
which will, yes, give you more power.

So it's not the higher octane that gives you the power, it's the ability 
to get more aggressive with your mix that does it. You can almost think 
of it as your compression ratio. In a typical FMAX SE-R for example, on a 
stock 9.5:1 compression engine, you can do maybe 250 HP at the wheels 
without water injection... maybe 260 or so, and then you start running 
into detonation (on 92 pump gas). If you go lower compression, say 8.5:1, 
you will lose about 5-10 HP or so because of your lower compression 
ratio, but you will be able to go up to 15 psi at the same time without 
detonating, getting you into the 300 HP range.

Octane is like that, a safeguard, not a power adder. If you're not 
already detonating at 92 octane, you won't gain anything by going up to 
100 octane and in fact you'll lose some power. Anybody who knows better 
than I do about this, feel free to correct me.

I need some boost to test this theory. "


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## dschrier (May 6, 2002)

Octane makes it harder for the fuel to burn as I understand, so if you are pining or detonating at 87 octane you might lose power at 89 or 91 octane since the fuel will take more to burn. My car on the other hand pings at 87 and 89 octane fuel so I just use 93 octane and the pinging is gone.


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## James (Apr 29, 2002)

Sounds logical. Slower burn means less power because fuel is not combusted but is still injected. Screws up the a/f ratio which already signifies a loss in power.


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## Subculture (Apr 30, 2002)

> My car on the other hand pings at 87 and 89 octane fuel so I just use 93 octane and the pinging is gone.


Yeah, you don't want to let your engine detonate for any length of time as this can lead to spun bearings.


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## James (Apr 29, 2002)

dschrier said:


> *Octane makes it harder for the fuel to burn as I understand, so if you are pining or detonating at 87 octane you might lose power at 89 or 91 octane since the fuel will take more to burn. My car on the other hand pings at 87 and 89 octane fuel so I just use 93 octane and the pinging is gone. *


I was thinking about this when I read it before... but in this case you should be gaining power from going to higher octane because your engine is already past the verge of pinging/detonation so the octane helps control combustion.


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