High RPM Power Loss

[MK1_Oz]

At the last Classic Adelaide event I again noticed that on a slight incline at over 7000 rpm the car would not pull. To rectify this from prior events I had port matched the inlet manifold and given it a clean up. Didn't notice any difference.

I am suspecting that maybe the ignition system is breaking down at high rpm and I am seeing the misfires as just reduced power. Could that be the case? Are the MSD systems worth looking at as something that will ensure a better spark at high revs? Couldn't find any past threads on the topic...

I have also thought that maybe the coil is not able to draw sufficient current due to the ignition switch (10A rated) and Delphi bulkhead connector (20A rated) that it goes through. To measure the amps drawn by the coil I could just run a multimeter inline in the coil power feed. My multimeter is rated to 10A only so marginal?

[Miniliteman]

What is your current ignition system?
Standard? Electronic?

[MK1_Oz]

Sierra electronic dizzy with Bosch FIM024 (??) amplifier and matching Bosch coil. Also, twin Weber 45's with (I think) 38 or 40mm chokes.

[Danny M]

Take it to a dyno with someone that knows what they're doing like Mike Dale and connect an engine analyser like the old Bosch or Sun ones and see if it's dropping out, then start playing with plug gaps and close them down and see what it does

[Miniliteman]

Is it this distributor?
If yes, that has a "built-in" spark-retard at high revs because of how the reluctor-sensor inside is working;
that may cause loss of power.
Check several of these on my distributor-tester and all had this phenomena.

I've always used the Lumenition Performance ignition (black module).

[MK1_Oz]

looks the same although mine does not have the vac advance. Is the "built-in" bit inside the distributor or the exterior module? Never heard of that before.

Yes could do with a good dyno session again.

[wayovermyhead]

I have seen and installed quite a few MSD's over the years, and seen almost as many failures! Like a lot of that mass consumer stuff that comes out of the US, it's pretty unreliable (compared to Bosch stuff anyway). Iv'e also heard first hand from the blokes who distribute it here just how much of it gets sent back. It's just one of those things that's been round for donkeys years, used to be good once and just has market presence it doesn't deserve.... that's my opinion anyway.

Also, you only get multiple sparks below about 3500rpm, after that there is no time for the multiple spark and it turns off so you won't have that benefit at high RPM. And further more, with a GOOD inductive setup, you will likely get MORE spark energy at higher RPM than the MSD as although the spark is pretty fat, it is also very quick whereas a good inductive setup while producing a lighter spark will still output more total energy due to the increased dwell time.

I agree with getting it on the dyno, as otherwise it's a very speculative solution that just involves more money where it perhaps aint needed. Whatever you do, keep it simple and reliable lest you add it to the list of issues we read about after the next rally.

Llewellyn

[Miniliteman]

The reluctor-sensor gives a positive-0-negative pulse when the 4 little coils pass the magnets inside the distributor. When this signal goes "through zero" that's when the amplifier stops the current through the coil and you will get a spark. To get rid of unwanted voltage spikes on the sensor-signal there is an RC-filter iun the amplifier. But this will mean a phase-shift of the signal. AT low rpm this phase-shift is small but at high rpm it will give a small retard of the spark as there is only a few milliseconds between each spark.

With an active (3-wire) sensor like the Lumenition optoswitch you do not need that much of filtering so no phase-shift.

Tried a MSD-6AL system back to back with the Lumenition Performance system on a 2 litre Pinto (224 bhp on the dyno) and we could not see a difference.
As said, the MSD amp only gives multiple sparks at lower revs but if for some reason the spark is being blown out by the mixture it will not give an new spark but a inductive system probably will if there still is enough energy left in the coil.

Leon.