# Which type of gas is best?



## Grimwolfsburg (Apr 13, 2018)

So I have a 2017 mk6 jetta 1.4T And I've been putting 91 Octane since the beginning. I was talking to a buddy of mine and he says that I should be running E85...what IS the difference of E85 and 91 octane? I never really know anything about that subject AND on top of that, which brand is best for a Dub? Shell, chevron, arch, 76.. etc?
Ive been using 76.


----------



## Chockomon (Aug 20, 2005)

If you’re not tuned then all you need is 87










Just today on 87 octane 400 mile trip averaging ~75mph


----------



## Grimwolfsburg (Apr 13, 2018)

It is tuned, and before I did use 87 but it started to have that knock noise in the engine and mechanic said to run 91 but is it a huge difference from E85?


----------



## Chockomon (Aug 20, 2005)

Grimwolfsburg said:


> It is tuned, and before I did use 87 but it started to have that knock noise in the engine and mechanic said to run 91 but is it a huge difference from E85?


If it’s tuned then you need to contact whoever the tuner is. The tune is designed for a specific octane rating 


Sent from my iPhone using Tapatalk


----------



## jsrd001 (Nov 3, 2016)

Grimwolfsburg said:


> It is tuned, and before I did use 87 but it started to have that knock noise in the engine and mechanic said to run 91 but is it a huge difference from E85?


I'm sorry, how can one know what knock noise is but not the type of fuel he should be using?


----------



## Grimwolfsburg (Apr 13, 2018)

That's why I'm asking because I DONT KNOW man. I had the knock noise before even tunning it due to ECU problems


----------



## Chockomon (Aug 20, 2005)

jsrd001 said:


> I'm sorry, how can one know what knock noise is but not the type of fuel he should be using?


Because the fuel required is dependent on the tune.



Grimwolfsburg said:


> That's why I'm asking because I DONT KNOW man. I had the knock noise before even tunning it due to ECU problems


If you had knock beforehand, you may have another issue (IE maybe timing is off).

Before tune, you should have been able to run 87 octane and make 150hp all day without any issues as per VW. Now that it is tuned, you need to run whatever the tuner recommended for that tune. You will NOT get any additional performance from a higher octane (or E85) as the car isn't tuned for it. If your engine is still knocking at the recommended octane rating, then you have another issue (likely timing).

Likely you have Unitronic (because that's all that's really out there for an NA 1.4T). If you have stage 1, you need 91 octane. If you have stage 1+, then you must use 93 octane.

Can you post of video of your engine knock?

And sorry I missed your question about E85 vs 91. Yes, they are different fuels entirely and it's not easy to determine what it really is. E85 can be anywhere from 51% to 85% ethanol and 49% to 15% gas/hydrocarbon. Typically it has a pretty high octane >100, however its energy per volume is lower than gasoline and as such, you need to burn more of it and you'll typically see lower fuel economy.


----------

