[DUMB] Rev Limiter Setup Questions | AEM
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dann_1990
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Last seen: 5 years 9 months ago
Joined: 10/01/2014 - 09:08
[DUMB] Rev Limiter Setup Questions

Hi,

My questions are:

  1. For the main rev limiter what is the best way to setup the wizard?
  2. For the 2step rev limiter what is the best way to setup the wizard? I have understand if you would like drama leave it at 0 - Soft cut
  3. What does the wizard does? I read on the AEM manual, but I quite don't understand.
  4. If I set the retard ign on the main rev limiter, what will happen? Backfire?
  5. (Silly request) I would like my car to backfire(afterfire actually) when I downshift or upshift, IMO it looks sick, how can I tune the AEM to make this?

My current Setup

I have the 2step rev limiter set to:

  • Fuel: 12000
  • Ign: 5100
  • Ign retard: 4900

Main rev limiter set to:

  • Fuel: 8100 
  • Ign: 7900
  • Ign retard: 12000
AEM_NS
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Last seen: 13 hours 50 min ago
Joined: 06/06/2014 - 09:31
How to set the rev limiter is

How to set the rev limiter is largely subjective and really depends on your personal preference so there is no "best" way.  We can only suggest that you try a starting setting, test it, log it, and adjust as necessary.  The most important part of that process is the LOG part.  The more data you collect, the better chance you'll have of understanding what's happening.

The wizard sets the rev limiter M and C options.  The C options are a constant cut duty that's applied when you reach the limiter threshold.  Cut duty is how many coils/injector are not being fired in one cycle to control engine speed.  A lower cut duty cuts less cylinders per cycle thus giving you a "soft" feel to the limiter.  A higher cut duty cuts more cylinders per cycle thus giving you a "hard" feel to the limiter.  The M option is a multiplier that gets applied to the initial cut duty based on overshoot.  A lot of overshoot means more M duty gets applied.  

The retard limiter simply retards the timing.  In my experience, this really softens and slows how the rev limit hits assuming that the retard occurs before fuel/spark cut.  It's usually cutting spark before cutting fuel that results in the pops and bangs out the exhaust although some will retard the timing during 2 Step to produce an anti-lag effect on turbo applications.   

Like you mention, a "back fire" and "after fire" (sometimes called "after flame") aren't the same thing.  Without going into how to specifically do it, I think what you'd want to try and accomplish to get flames out the exhaust is a condition where you're adding a lot of fuel and retarding your ignition timing.  How you go about doing that is up to you.  Also, this is usually only done on "over run" or decel (off throttle).  Popping during upshift on some cars comes from cutting spark during a WOT shift (shift cut) that used with sequentially shifted transmissions.