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 Some Q&A I thought I would share ...

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Male Number of posts : 1384
Age : 35
Location : Chelsea, AL
Drives : GG IX MR SE
Registration date : 2007-07-09

PostSubject: Some Q&A I thought I would share ...   Wed Mar 05, 2008 1:40 pm

I got these question in a PM on EvoM and though they might be useful for others ...


1. When adding such items that increase airflow such as a FMIC and IC Piping (or even a drop-in for that matter), are you able to lean out the A/F because there's more air available OR do you have to richen it up a bit because the mixture will be too lean with all the added air coming in? In other words, without a wideband, how would you pursue tuning something like this? The ECU will try to hit the AFR numbers in the cell, so would you prefer a lean mixture here because you can?

Question 1 is slightly loaded ... lets start with the FMIC. It wouldn't technically add airflow, but make better use of the airflow that you already have. In this case, your tuned AFR would go leaner because you have more O2 in the mix with the same metered air volume. You would lower the fuel map values to reach the same AFR target as before. This denser air should also allow you to run a little more timing.

With mods that actually result in more air flowing in to the MAF (intake filter for example), it's a little different. your fuel and timing maps are based on load % which uses airflow as part of it's calculation. therefore increasing flow metered by the MAF you increase the load %. This means you will get at least a slightly different AFR simply because you're partially in a different load cell. This could cause the AFR to shift either way (lean or rich) depending on the values in those cells in the map.

So, basically ... if you change the density of the air, you will likely go lean. If you change the volume of the air, it all depends on the fuel map.

2. I've read (from you) that its not necessarily the AFR map that matters but the curves that the map makes. Can you explain more?

The fuel map values are simply a calculation based on the standard 8-bit values that the ECU uses to determine fueling in open loop. 14.7 in the map does not mean that the ECU tries to reach 14.7. A target AFR of 14.7 does exist in closed loop operation, but it does not apply to WOT runs.

Basically, every value in the fuel/timing/vvt map is nothing more than a 0-255 value because thats all the ECU sees. What we see in ECUFlash is irrelevant. ECUFlash uses XML to format those 0-255 values in to something we can more easily understand.

So, when I say that the values don't matter I simply mean that you don't have to put 11.5 in the map to get an actual 11.5 AFR. If a 9.8 value in the map gives you the desired AFR, then leave it at 9.8. Try to not think of the AFR map as a target value and consider only that raising the values will take fuel away and lowering the values will add fuel back in.

3. Does an MBC bypass boost cut?

No. Boost cut is based on a maximum load % and a timer that gives an allowance for being over that load %. An MBC will still affect the load values you are running and therefore sill cause boost cut if those limits are exceeded.

Project Tuning - Performance EFI Tuning - Birmingham, AL
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Male Number of posts : 1873
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Registration date : 2007-07-09

PostSubject: Re: Some Q&A I thought I would share ...   Fri Jul 18, 2008 5:21 pm

4. will my evo be as fast as the veyron?

NO. unless you have joey's car its not possible.
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