Crystal mod to increase rev limiter

[a_sesshoumaru]

I have a map ecu and i am very happy with it except it doesn`t increase the rev limiter, i could tune fueling to 8000rpm with the map ecu (i dont plan that high) i was searching a way to increase my rpm`s and found only one thread about the crystal mod, i would like to know how it is done, and what are the crystals that need to be changed, i have a pre 89 ecu, this is the thread i found http://www.supramania.com/forums/showthread.php?t=7786&highlight=clock+crystal
please lets talk about the crystal mod, not to talk about replacing the stock ECU with a Stand alone. thanks

 

[MKIIINA]

i was really interested in it back in the day but after some research results were mixed. sometimes it worked exactly as described and other times there was little or no change. this mod was ported over from the MR2 community iirc.

also there was some chatter about the crystal "reclocking" the ecu and basically tricking it that could have remifications on other operations (timing i think was the major reason but i'm not sure)

 

[gofastgeorge]

I had mine done by a guy in Florida, Keith Golden.
E-mail: keith.goldin.co75@statefarm.com

The price 2 years ago was $110.
Turn around, after he got it was less than a week.

Mine works Excellent !!
Rev limit is at 8500.
Lets me take full advantage of my long duration cams
and TODA inner-shim follower kit.

 

[figgie]

the question is (and I know the answer as this controls the ENTIRE timing of the ECU).

Increasing the timing of the ECU affects ALL the parameters.

In short what you are doing is telling the ecu is the following:

On an unmodified ECU, the rpm is based on the timing of the RPM signal to what is calibrated inside of the ECU.

So if the ecu has a base timing frequency of 6500 (EXAMPLE ONLY as I do not know the stock frequency!!!!) @ 6500 rpm. I am seeing exactly 1 pulse per hz and this induces Rev limiting. Anything below the 1 pulse per hz will not induce rev limiting!

Change the frequency to 7800hz. Well now the timing is faster measurements for all so you are tricking the "MAPS" because the length is now shortened for ALL parameters. Now to achieve a 1hz/1rpm, the timing crystal hz been raised to 7800hz.

The question is, since fuel pulse is a function of the timing, it will now also increase that 10ms FPIJ by 1.2 at base without any O2 control. This also affects timing and a slew of other parameters. Just because the ECU is still within the O2 % window and is able to control that does not mean is a bright idea

Anyway with the cost of a megasquirt, this crystal mod should be totally moot!