# 2008 2.5L - 87 or 89 fuel?



## alwaysdutch (Oct 19, 2011)

What fuel type do the '08 engines use for best performance? Something told me that the '08 engines run best on 89.


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## jaja123 (Jan 17, 2011)

I do 93oct all the time


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## [email protected] (Sep 2, 2011)

the best performance is on 93.

even on 93 these cars are still knock limited.


-Jeffrey Atwood


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## LampyB (Apr 2, 2007)

yeah they run noticeably better on 91/93 instead of 87/89. i've noticed a slight decrease in power when running 87/89. i didn't really notice a change in mpg's though, but the power loss was pretty prominent on the highway.


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## ArminT (Mar 8, 2010)

Maybe it was placebo affect but i felt like everything with the car ran better with 93. including shifting was smoother. but thats 93 octane for ya.... i use 87 90% of the time anyways for now.


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## halbwissen (Jul 20, 2001)

Check this thread out, specifically the European Car link in the first post. 

http://forums.vwvortex.com/showthread.php?t=5470571


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## PhAyzoN (Nov 29, 2010)

93, or the highest available wherever you stop to fill up.


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## TylerO28 (Jul 7, 2008)

Always always always 93... Or 92 if its not available
Besides on 12 gallons think about it, what is 2 bucks?


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## Apexxx (Nov 10, 2011)

Octane does go by the engine, but also by the driver. My mom would be fine in a Passat 1.8t on reg or plus, but that would suck for us guys. 

Well, mom now has a 2.5 JSW and I tell her 89, all the way.

89 keeps engines set for 87 from retarding timing, running how it should, at a minimum. 

My wife drives an Opel Astra, speced in USA for dino oil and 87. Well, we were going w/89 but the engine absolutely screams on 93.

See, higher octane burns more slowly so it drives the piston more smoothly. It also needs more detergents because of the slower burning, so don't believe the hype.

I use 2cycle oil in my gas at 500:1. It's cheap and works great. Use extra the first treatment to coat the fuel system. It's a great fuel treatment for about $.02c a gallon. I premix some Techron in because I have DI.

Once a year I do a Seafoam intake cleaning in spring.


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## madbikes (Dec 30, 2010)

I'd love to put 93, but only 91 is readily available here. For this particular car I put 91 since the first tank. I guess I'll try some 93 depending on how much will it be at the track (going to Thunderhill Raceway on Monday morning in Willows, CA).


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## bjohns86 (Nov 7, 2011)

Apexxx, as well as some others...you should cite some references here that are not from other forums or company websites because your claims are erroneous. Octane rating does not lead to more power and a naturally aspirated engine that has factory settings (i.e.- 2.5L Jetta) will not benefit from running 93 ROM octane fuel versus, say, 89 ROM rated fuel. The increased presence of octane (or its isomers) in fuel decrease gasoline's tendency to auto-ignite (detonation). An increase in octane content is ideal for supercharged engines or those running high compression ratios, maybe 9.5-10:1 or higher. If you run gas with too low of an octane content, however, the fuel/air mixture will auto-ignite, causing the tell-tale knock sound, which the computer actually "hears" and adjusts the timing accordingly to avoid this, but it can only vary the timing so much so you may still come away with piston dome/crown damage regardless.
Higher octane levels do not lead to smoother combustion, nor does it make gasoline burn faster or slower, but it does require more input energy to start the combustion process, which may be what you are calling slower. Also, detergent content does not correlate to octane content, so I am unsure where this hype is you speak of?
Also, using a the fuel/oil mix you speak of does nothing for you or your engine. There is no such thing as "coating your fuel system"! I am not saying that you shouldn't do what you are doing as the dilution factor you are using can't do any harm, but it will also do no good.
Most importantly, however, is that I am not trying to put you down or call you out offensively, I just don't think ideas like these should be allowed to go without being challenged.

Oh, and no, magnets on your fuel lines don't increase fuel mileage or power!! C'mon people! Good luck!

Brad


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## alwaysdutch (Oct 19, 2011)

Well, I appreciate all the replies. I did some testing by using all three types available.

I started with the 87, and the car ran great, maybe a bit rough but nothing to really worried about. I nearly drove the tank empty and added half a tank of 89. I did feel a difference in acceleration and the engine seems to ran a bit smoother. Next half tank was the 93. At first at felt better again but then it kind of worn off to the same effects as driving the 89.

So, overall I tend to believe in my mind that the 89 runs good for this engine, but I think I am going to add 87 in it one more time to see if my brain is not goofing with me on this.


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## zevion (Oct 23, 2009)

alwaysdutch said:


> Well, I appreciate all the replies. I did some testing by using all three types available.
> 
> I started with the 87, and the car ran great, maybe a bit rough but nothing to really worried about. I nearly drove the tank empty and added half a tank of 89. I did feel a difference in acceleration and the engine seems to ran a bit smoother. Next half tank was the 93. At first at felt better again but then it kind of worn off to the same effects as driving the 89.
> 
> So, overall I tend to believe in my mind that the 89 runs good for this engine, but I think I am going to add 87 in it one more time to see if my brain is not goofing with me on this.


93 as Jeff Atwood said. You can save all that guessing and trusting your brain and perception and take the advice of the expert. :thumbup:


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## halbwissen (Jul 20, 2001)

bjohns86 said:


> Apexxx, as well as some others...you should cite some references here that are not from other forums or company websites because your claims are erroneous. ... Brad


Here you go..



DriveVW4Life said:


> Check this thread out, specifically the European Car link in the first post.
> 
> http://forums.vwvortex.com/showthread.php?t=5470571


If you didn't click the link, here's the dyno graph from European Car showing gains with higher octane fuel on an otherwise stock engine.


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## bjohns86 (Nov 7, 2011)

I appreciate the "source", but there are several flaws with it in terms of data provided as well as a lack of explanation. I will just hit the obvious ones now, but looking at this thread and the one you provided as a link it won't matter because folks are too focused on it working than not. 

1-2 mpg increase in mileage from switching from 87 to 91 ROM gas? Not likely, unless they can prove that they drove the same route at the same speed with the same throttle openings. The chances of them duplicating their route identically is nearly impossible, unless it was done solely on the dyno and the process was computer-controlled and not an actual driver, 1-2 mpg falls within the margin of error, I'm sure so I wouldn't hold my breathe. Also, fuel in Europe is rather different than that of the same grade in the US because the EU has different requirements on the allowable oxygen amount in gasoline, so they will use different octane boosters than the US; the US likes to use alcohols suchs as ethanol, and sometimes methanol, whereas the EU uses more highly-branched alcohols such as tert-butyl alcohol and methyl tert-butyl ether (MTBE), in their super premium fuel, so this will change the burning characteristics, though I am skeptical that the driver would actually notice. Maybe a double-blind test is in order? 

They claim a performance increase of 5 hp and 12 ft-lbs, which is fine, but what is the sample size of each run? They said they repeated the 87 fuel run 5 times, but didn't mention the 91 run duplicates, if any. Access to the raw data would be helpful. You can't conclude anything if the sample size is too small.

I see that it looks like they installed a software on their test car for 91 octane fuel, oops! They didn't claim this in the article and you can see that is what the second chart is labelled as at the bottom. If this is the case than they are misleading the reader. This install would have, ata minimum, changed the timing of the engine, which would be appropriate for higher octane fuel.

The worst part about this article is their lack of explanation. How do they think the engine is able to monitor octane levels? The only possibility is with the oxygen-sensor or the knock sensor. Other than that, there is no way for the computer to know what you put in the tank and I am not even sure the O2 sensor can pick this up, especially a change from 87 to 91, let alone an 87 to 89!

Regardless, of how my post is accepted, I am not trying to shoot anyone down by trying this, but I myself, do not see the payoff financially or performance-wise with this practice. Thanks for reading.

Brad


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## thygreyt (Jun 7, 2009)

Brad, why do you talk or mention europe and its fuels when the 2.5 is only available in america?

And yes, the engine uses the knock sensors

sent from tapatalk


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## vento 95 GL (May 25, 1999)

bjohns86 said:


> I see that it looks like they installed a software on their test car for 91 octane fuel, oops! They didn't claim this in the article and you can see that is what the second chart is labelled as at the bottom. If this is the case than they are misleading the reader. This install would have, ata minimum, changed the timing of the engine, which would be appropriate for higher octane fuel.


 If you read carefully they added a neuspeed p-flo with the 91 octane. The test was done with stock software.


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## DerekH (Sep 4, 2010)

It's done with a knock sensor to my knowledge there is no such thing as an octane sensor. 

Also, why are you talking about oxygen in the fuel? There isn't any, gasoline is mostly carbon. Hence why you use a turbo, to add more oxygen. Same reason you use nos.


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## ArminT (Mar 8, 2010)

DerekH said:


> It's done with a knock sensor to my knowledge there is no such thing as an octane sensor.
> 
> Also, why are you talking about oxygen in the fuel? There isn't any, gasoline is mostly carbon. Hence why you use a turbo, to add more oxygen. Same reason you use nos.


 I use nos .


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## bjohns86 (Nov 7, 2011)

Thygreyt - I was commenting on Apexxx's post as he mentioned an Opel, which I do not believe is offered in the US. Being sold in Europe I was commenting on his post as the fact that he apparently lives in Europe may be a factor. In regards to your comment, why don't you explain to us all how the O2 sensor works, is it a heated or non-heated version, and how it will can determine the octane level of your gas. Then tell me how it can decipher between the engine running lean/rich from a mechanical/electronic problem and from a fuel that differs in 2-4 octane points! I am not aware of this being the case, but I am open to learning. Also, I never specifically mentioned the 2.5L engine in my second posting, though I did use it as an arbitrary example in the first one.

Vento 95 GL - If you look at the chart that plots the data for the intake vs. 91 octane you will see that it says 91 octane software. If you open the chart it is not there, but if you look at the thumbnail image of it in the article, you will see it. I don't know what they really used for software, but that image says "91 octane software". 

DerekH - Gasoline is composed of tons of oxygen-containing compounds. Most of them are alcohols and ethers to give you the "octane" rating. There is very little, if any, actual octane in gasoline. It may seem obvious but gasoline is combusted (if that is even a real word), ideally forming carbon dioxide and water. This is assuming perfect combustion which requires complete combustion and sufficient oxygen. Being that air is composed of roughly 21% oxygen by volume, you will find that this is not nearly enough to optimize the combustion of gasoline. So where do we get the extra oxygen required for optimization? This is why oxygen-containing additives such as methanol, ethanol, and ethers are beneficial, as well as forced induction and nitrous oxide. All of these methods add oxygen to the mix to promote "perfect" combustion. Also, you are right, there is no such thing as an octane sensor, though I never mentioned such an item, so... If you don't believe me, crack open your intro to chemistry book.

Brad


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## H3LVTCA (Oct 27, 2004)

I rock 93oct!


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## DerekH (Sep 4, 2010)

Gas, at least in canada only has a max of 10% added methanol. i don't know what they do in the states. And there isnt a whole lot oh oxygen in methanol. it wouldn't do a whole lot they add it because it burns cleaner than gas. less carbon. 

I'm not trying to pick a fight at all, i know how this stuff works. i only run 94oct because of that.


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## halbwissen (Jul 20, 2001)

Brad,

Where's your scientific data to dispute what European Car has provided?
None of what you've said up up to this point is a valid counter argument to what they've provided. 
Typical armchair forum expert. "Read a chemistry book" is what you suggested in an earlier post. Have you read any books on the engineering of the internal combustion engine?
Care to provide any real data to support your argument?


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## thygreyt (Jun 7, 2009)

he simply wont lose the argument... wont fight.


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## bjohns86 (Nov 7, 2011)

Oh boys! I am not going to exascerbate this situation as you apparently aren't open-minded enough to do some independent thinking/research, instead we will cruise forums and use them as our references as well as the word of a magazine writer as truth. That's fine, I have no problem with what you are doing! Also, I never claimed to be an "expert" of anything, though I feel that my having a PhD in organic chemistry gives me some familiarity of chemicals?! I can see that my posts are going to hit the wall regardless of what I say, as I asked Thegreyt a question about clarifying his statement about oxygen sensors and instead of answering it he just threw out "he simply wont lose the argument... wont fight." Anyway, it's all good!

Brad


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## halbwissen (Jul 20, 2001)

Brad,

I don't have a PhD and I can make a better argument for several reasons..

One, it's been proven by European Car - dyno and all. 
Two, Volkswagen suggests higher octane for maximum performance - it's in the user manual. 
Three, a reputable 2.5l software tuner has said in these forums on numerous occasions, that higher octane fuel will yield more horsepower {on stock software}.
All of these examples support my argument.

Why's it so hard to believe that VW programed the 2.5l to adapt to the fuel being used?


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## thygreyt (Jun 7, 2009)

Brad, no worries. I too understand chem, at least on some level, after 4 years of clases... Obviously not as much as others,but good enough. Which is why i'm not debating or contesting what you said.

What i said is that the engine adjusts timing based on the fuel, which is "sensed" by the oxigen sensors and the knock sensors. I have tested this firsthand. And if you are curious about it, read. I dont mean it offensively, but i just dont know enough to be able to explain it.

sent from tapatalk


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## vento 95 GL (May 25, 1999)

bjohns86 said:


> Vento 95 GL - If you look at the chart that plots the data for the intake vs. 91 octane you will see that it says 91 octane software. If you open the chart it is not there, but if you look at the thumbnail image of it in the article, you will see it. I don't know what they really used for software, but that image says "91 octane software".
> 
> 
> Brad


 Yes I see what you mean, but its just a typing error. a 2.5 with tuned 91 octane software makes more than 138whp. I'm sure European car tested with an automatic transmission to get those numbers as the manual usually gets closer to 150whp stock.


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## bjohns86 (Nov 7, 2011)

I appreciate all of your comments, though DriveVW4Life is having a hard time not getting defensive! Anyway, I could care less what folks do with their cars and what they believe, as long as it isn't a safety issue. My intention is to present a different, more concrete perspective to the octane argument and let readers decide whether they side with your views or mine; what ever they choose is fine with me. Though blindly believing in some magazine article written by someone with God knows what knowledge base is iffy. If people would actually look into the issue scientifically than I would be happy to list real, scientific references, though 99% of the viewers would not have access to them unless they wanted to purchase the texts/articles which is cost-prohibitive. Even Wikipedia has good information under the entries of "gasoline" and "octane rating". 
Lastly, if it is true that a "reputable" software vendor stated that significant power gains can be seen with upgrading to say 91 octane fuel alone on stock software, than I wonder about their business knowledge as that basically shoots his software offerings in the foot doesn't it? Why would I buy a software upgrade for higher octane fuel when I could just run it with stock programming and the engine will just compensate automatically? Do you see the business suicide here? And I am seriously interested in how an oxygen sensor can determine octane rating of the fuel? I also don't believe the oxygen sensor is able to convince the computer to vary the timing, that is often times the job of the knock sensor alone, but I am open to reliable information (references, people) showing me that an O2 sensor can do this. Thanks for reading and quit getting your undies in a bunch over someone challenging you!

Brad


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## thygreyt (Jun 7, 2009)

a sw tuner does more than adjust timing. AFR optimization is a BIG thing too... and stock sw can only do so much.


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## DerekH (Sep 4, 2010)

thygreyt said:


> a sw tuner does more than adjust timing. AFR optimization is a BIG thing too... and stock sw can only do so much.


 This, also stock software is only allowed to pull the timing a certain amount. Not enough to be completely optimized considering it isn't adjusting afr etc.


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