Raising the rev limit on stock ECU

[fax0815]

Hi,

I´ve got 2 build 4AGE engines, one in an AE86 the other one in an AE82, with 272° 8,5mm cams running on stock ECU, with the ignition slightly advanced, AE86 cat model (bigger injectors) and higher fuel pressure.

1st engine has been dynoed at 139hp (stock intake and exhaust) the 2nd one will be dynoed next week.

Since the engine is now pulling right to the end of the rev range (~200-300rpm before the limiter), it whould be necessary to raise the revlimit since there is to little time between the end of the powerband and the rev limit, making it awkward to shift quick and stay in the power band. Probably 8000rpm whould be good, as the engine can take it.

I´ve taked to the oldshool 90´s rallye boys, and they were doing some magic back in the days in darkrooms, playing with the crystals on the ECU to "reprogram" the ECU.

Now my question, ist there anyone out there who can still do this?

Are there any other options? Due to regulation of the rallye series and budget stand alone is not possible.

Any piggyback solution avaliable?

[Ivan141]

Much has been discussed about this specific topic before.. there is nothing magic about messing with the crystal oscillators that the CPU clock works with. It's basically making the ECU timing and calculations inaccurate with the side effect of it reading a lower value for RPM.
No data about which crystals to use is known to me, though I would expect you need to make the clock slightly faster (so it reads less pulses per time unit).
Possible other side effects this might introduce are at your own risk (you'll have to discover that for yourself I guess, I wouldnt know).

[gon]

yes, raising the clock of the main ECU will give you a higher rev limit but will also mess everything else on the ECU.
I would not advise this modification unless you monitor your engine very carefully using a wideband lambda sensor and a knock detection device.

If you still want to go ahead, open you ECU check what the crystal speed is , go to an electronics shop a buy the one just above and give it a go.

Read the following topic carefully:
http://www.aeu86.org/forum/showthread.php?tid=11968


The image above is not from a 4AG ecu, I think its 4afe ....
having said that , the crystal on the 4AG ECU looks about the same but longer, it is located in the very corner of the ECU (opposite side from connector). It is laying down and it has a protector cover that must also be removed for replacement.
The cover reads 4NDK71: