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Discussion Starter #1 (Edited by Moderator)
I wanted to create a place holder for this topic as I have mentioned it a few times but can't get to it all at once.

I had asked a while back if the mods would create a tuning forum to no avail. Subsequently, I routinely see mounds of disinformation, "close" information, and sometimes completely wrong information on this subject. I happen to have my own bit of information and decided it was time to get it out to those that are interested.

Now keep in mind that there are several "schools" when it comes to this subject. I will try in my subsequent posts to address as many as possible and explain the pros and cons as I see them.

Who am I and why should you listen to me? Well, I have tuned everything from 403 Olds engines to Fieros with Pontiac SC V6’s to Mustangs of all flavors to Crown VICs to Marauders to Sunbeam Alpines with V6 conversions to well; the Spyder both turboed and Supercharged. I am a big Ford Man and currently “Tune by Remote� around a dozen cars for friends all around the country. Most of which make between 385 – 600 RWHP. I don’t know everything but what I do know, I am willing to share.

Now what I don’t have is the time to sit down and write a 200 page post all at once so I think it makes the most sense to take it in steps. Should we ever get a Tuning Forum, we can separate it by topic instead of one very long post. I want to keep it simple and avoid “Engineer Speak� or lengthy chemical analysis discussions and the like. This post is for the masses and I want to keep it readable by all. So please keep your vast engineering degrees and backgrounds in your pockets. It is my sincere hope that this helps those that don’t know and those that do participate as constructively as possible. It is all about pulling the shades and letting some light in.

For now I’ll start by addressing AFR’s and we can go from there!


This area of tuning is one of the most fudged in the industry. There are many out there that will swear your target AFR should be 10:1 AFR to make safe power. While there are others out there that claim you need to run the same turbo setup at 12.8 to make best power. So what is up with that? Also what is this stoichiometirc value I keep hearing getting batted around.

Target AFR’s and Industry Speak

9.0:1 - No Power, Usually causes smoke and cylinder wash*
11.5:1 – Rich Best Power
12.5:1 – Safe Best Power
13.1:1 – Lean Best Power
14.7:1 – Stoich
15.2:1 – Lean Cruise

Note - Cylinder Wash refers to the fact that there is so much fuel entering the cylinder that it washes away the film of oil that coats the cylinder walls. NOT a good thing.

Ok so why do some people tune their cars for 11.5:1, some people 12.5:1, and others 13.1:1? Well the answer is complicated but “most� people just don’t KNOW which one to shoot for and simply follow good and bad advice from other people that don’t REALLY know or are mistaken.

I have always found the best and most reliable power for an FI engine to be produced at a 12.5:1 AFR. Now getting there can be a complicated process depending on the tuning method you employ. It is simple really. You will make best power with an FI engine at 12.5:1 but you must have enough control over fuel and spark to pull it off successfully. You must also have the appropriate IAT’s (Intake Air Temps) and PSI numbers to live in this region as well.

Simply put, tuners that adjust your AFR to an 11.5 value or less are most likely dealing with an issue of one sort or another. High IAT’s or Boost pressure, the inability to reduce spark by the required number of degrees (typically due to using a piggyback to manipulate a stock ECU) or the like.

To me, this is a shortcoming of your setup that needs to be addressed. If you are mucking with a stock ECU and can’t pull enough timing to run a 12.5:1 then you need an aftermarket ECU. Easy to say I guess, because money is money and I know we don’t all have as much as we’d like. But, at least don’t go out telling everyone you tuned your car to 11.5:1 to make best power with a turbo. You did it because you had to, not because it was a “best practice� or it made the most power for your setup. In reality you’re bragging that you are wasting gas and have a less then optimal setup the was rigged to work by someone that knew how (for financial, ease of production, or whatever other reasons as they may be).

Now NA setups typically perform best at a 13.1:1 AFR. That said, it is usually beneficial as well to run transitional areas of any fuel map that you create to scale down from a 14.7:1 in low load to 13.1 in medium load (non boost) to 12.5:1 under boost conditions.

Now keep in mind that all of this works in conjunction with Spark and Fuel Tuning, which will discuss later.


Stoich is generally rated at 14.7:1. It is the goal of most factory ECU’s to obtain this figure while in closed loop operation and thus the value we will focus on using for this topic.

It is defined as - Stoichiometric or Theoretical Combustion is the ideal combustion process during which a fuel is burned completely. A complete combustion is a process which burns all the carbon © to (CO2), all hydrogen (H) to (H2O) and all sulfur (S) to (SO2). If there are unburned components in the exhaust gas such as C, H2, CO the combustion process is uncompleted

Basically, Stoich is the AFR value that your car tries to keep while at idle, low load, and in cruise situations. This is when your 02 sensors are actively adjusting “fuel trims� (learned values) that the ECU uses in conjunction with a Fuel Map and readings from your MAF (and other sensors) to determine how much fuel to use in a given situation to reach this value.

In fact, the latter is what many people refer to as your car “learning�. It says ok, you are at this rpm, this load, with this MAF reading, at this temperature and last time I was here I adjusted the basemap value by this much to get it right so this is what I will do again. It then records the results over time and makes further adjustments until it gets the AFR it was requesting in the OEM program or tune.

You can read more about it on the Internet but I think this covers the highlights as we will need for tuning purposes.

Not a forum, but you got stickied. Please try to make this an information post. Please ask questions in another post - carl
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