Thread: Rev Limiter Discussion

The daughter board doesn't send the tach signal. If it's not a wiring issue, I suggest trying another ECU to see if yours is fried.

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I've managed to turn the spark cut tach-jump issue into a feature!

Since I have control of the tach without the engine running, I have it setup so you can change the launch limit with the throttle and gear shift. Here's how it works:

1) Put shifter in any gear.
2) Turn on ignition (do not start). The tach will display the current launch limit.
3) Move throttle pedal until desired launch RPM is displayed on tach.
4) Shift to neutral. The new launch rev limit will be set.
5) Return throttle to idle.
6) Start engine.

Notes:
- To skip the process without changing the launch limit, just start engine normally.
- If the shifter is in neutral when the ignition is turned on, the tach does not move, and the launch limit cannot be changed.
- With an RT board, the change is permanent. With a basic board, the change lasts until the ignition is turned off.

Dave

That sounds super cool.

That doesn't sound like you've turned the problem into a feature exactly, just that you've found a new feature due to the problem. I assume the problem of the bouncing tach needle during spark cut still exists and is not a "feature" still?
=]

It depends on how you look at it. For a deaf person, the tach jump tells when they've hit the rev limit.

Dave

It would seem that maybe instead of cutting spark all together, if you initiate it maybe 180 degrees BTDC or something suitable then you could still have the spark event to keep the tach happy but the spark won't have anything to ignite?

I guess the stock rotor doesn't have that sort of angle sweep built into it does it? 180 degrees off is probably 0 degrees for the previous cylinder or something equally bad.

Interesting concept, but with a distributor, the best you can do is 90º out of phase (rotor 1/2 way between two plug wires). Then who knows which plug the spark might jump to. COP is another issue all together.

Dave

Yah I believe COP would solve the problem completely, but that damn distributor ruins everything.

The tach-jump issue is fixed. Works fine on B13 and S13 w/COP. I'm testing with an SR20DET swapped S13 in mostly stock configuration. Using spark cut only (no fuel cut), with the launch limit set at 2500rpm, it builds about 2psi boost without any timing retard.

Cheers,
Dave

So it's working on both COP and distributor cars? Your description is a little vague.
Care to explain how you fixed the issue?