I have seen some discussion regarding these 3 things, but with no explanation as to "why?". What are the concerns?
I know pinging is possible with a chip and 91 octane or less fuel. Is pinging necessarily bad? or basically just annoying?
I live in Colorado where I am constantly at high altitude and cannot get above 91 octane fuel. Should I be concerned when chipping my 2.7T 6spd?
Thank you for any input,
Eric.

 

Pinging is bad. It is jarring to the motor, but more importantly, causes something-er-other to heat up and can cause serious damage. Small amount of ping are okay, large amount are not.

More octane makes fuel burn slower. This allows you to spark earlier and generate more power through the early (important) part of the power stroke. Octane reduces volatility.

At altitude, the reduced air pressure and therefore reduced amount of oxygen in the cylinder charge reduces the burn rate. Thus, 91 octane can work as well as 92 or 93 sometimes at high altitudes. I think this is why you get lower octanes available at altitudes.

Problem is, a turbocharger (or any kind of supercharger) can compensate for altitude by packing in the air and fuel. This essentially returns conditions to sea level conditions. Thus, your 91 octane isn't enough for a 92 octane engine any more.

Now, on top of that, some chip manfacturers get their power (not so much on computer controlled turbos, like Audis) from changing the fuel mixture profiles in the chips. Apparently engine chips have several profiles for different altitudes. Some chip upgrade companies change all the profiles (esp. sea level) to be the one which puts in the most fuel. Thus, you no longer have any altitude adjustment in your computer and your car can therefore run poorly at altitudes the chip company didn't test at.

I'm not ascribing these problems to any particular companies.

If it were me, and I had a 2.7T in Denver, I would wait for an altitude compensated or "no ping" chip. Or request one. Basically, they can just not retune for 92 Octane. www.giacusa.com has these for the 1.8T engine, perhaps they can make one for the 2.7T.

 

Pinging, pre-ignition and detonation are basically uncontrolled combustion. These are very bad for engines, especially turbo or supercharged engines. If they become severe enough they can put a hole in the piston. I have examples of this if you want to see. : ( Or they will pound the area of the piston ring lands and cause a ring to fail. Typically when either of these failures occur you are looking at some substantial cash to fix the motor. Basically you have nice chunks of metal floating in your oil pan.

By using higher octane these become less of an issue has the actual rate at which higher octane fuels combust is slower. This in turn allows you to have higher boost levels and hence more power.

Higher boost also increases the temperature of the incoming air/fuel charge. This also leads to detonation as well. That is why there are charge air coolers (aka intercoolers) that cool the incoming air reducing the thermal loading on the engine. Heat is the ENEMY of turbo motors. An issue that you run into a higher altitude is that most turbos are not referenced to absolute pressure. Typically all this means is that you will not make as much HP as you would at sea level. Fortunately turbo cars suffer less due to increases in altitude than do normally aspirated cars.

This is a very quick and dirty explanation of it. If you want a more detailed explanation including the thermodynamics behind it I will be glad to supply them.

 

I had a late '80s turbo Volvo that had been massaged to run higher than stock boost. It ran fine at my sea-level Oregon home on premium gas.

On my annual August climbing trips to Wyoming, I always had to stop for gas in Salt Lake. There the premium gas was lower octane than in Oregon (Federal law sets the permissable octane in "Premium" gas based on the average altitude of the state!) and my poor car could barely make it up the mountain past Park City. It would knock dreadfully (no knock sensors then) at anthing near full boost. I'd creep up the mountain in the right lane at about half throttle.

I'd be careful about overboost if I lived at high altitude.

 

Most modern, computer controlled engines have knock sensors that retard the timing when necessary to prevent knocking, or pinging. This is particularly true with turbo engines. Does it not work properly in chipped engines? Why are we talking about knocking, and how does it overcome the compensating systems?

 

Yes, modern systems won't let knock happen--or won't let it happen very much. But I would want to know if a chip were so aggressive that it frequently had to hold itself back at altitude. That would be fine if I lived at sea level and rarely went high. But if you live at altitude, why pay for a chip that gives boost on the one hand, and takes it away on the other? Note: I am not claiming that any particular chip has this problem, merely that I would want to be sure of the altitude/octane flexibility before I bought. My experience with the archaic Volvo is cited merely to demonstrate that the propensity to knock--whether controlled or not--can exist with lower-octane gas found in high altitude states. (This is not to say that turbos are bad at altitude; in fact properly set up they deal with altitude _better_ than normal engines which merely lose power at the rate of 1% for every 300 feet. )

 

Does that Octane Booster stuff help?

 

Yes

 

Yes, knock sensors should retard your timing or reduce boost and prevent damaging detonation (pinging) with low octane gas. This is great for a person who lives at sea level usually and so buys a normal chip, then goes to altitude once in a while.

But if I lived at altitude, I would demand a "no ping" chip instead of relying on the systems which were designed as backup to work full time.

Besides, the backup plan in the ECU may be to reduce boost to almost nothing or nothing (in fact, the manual says as much). So you may find that your car with a chip performs worse at altitude than if it didn't have a chip. That's fine unless you happen to spend a lot of time at altitude.

I think is about what Ed Slaughter said also.

 

Thanks for all of the info.
I was wondering if anyone in Colorado with a "chipped" Audi could provide some feedback. Is it a "special" chip or a standard chip from one of the chip makers?
Is there pinging? Any other concerns?
I know Boulder Audi Tuning "chips" Audis, I'll ask them as well. I'll also talk to some of the chip sellers (APR, Garrett, etc...), but real world info is appreciated. Thanks again for all of the help,
Eric.<ul><li><a href="http://www.fastaudi.com">Boulder Audi Tuning</a></li></ul>