Is an ECU really required for carbs, or are you better spending the cash on extra fine tuning. If so is there a recognised 'best' ECU for this purpose?

[Edited on 9/10/07 by scootz]

you could have a distributor, with mechanical ignition and carbs, no ecu needed

I think the ECU on carb engines mainly manages ignition timing - I'll stand to be corrected though.

I'd have thought the cash would be better spent on cams, induction and fine tuning.

I'm trying to get rid of the one I've still got on my Haldane, I've fitted distributor and points from a cortina, replaced the diabolical electronic choke control from the carb, fitted a capillary type temp gauge etc, there might be other bits need sorting but nothing major I'm sure.

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Originally posted by HAL 1
I'm trying to get rid of the one I've still got on my Haldane, I've fitted distributor and points from a cortina, replaced the diabolical electronic choke control from the carb, fitted a capillary type temp gauge etc, there might be other bits need sorting but nothing major I'm sure.

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I do indeed have a distributor. Just trying to work out if it's worth buying an ECU...

Even the best mechanical distributors are limited to changing the ignition advance accoding to engine speed with , possibly additional advance created by high vacuum when the throttle is closed on overrun or idle.

The point of proper electronic ignition is to allow another input, say a throttle pot to allow the ignition advanced to be set according to the load as well as engine speed, this allows a fair bit more power out of the engine all other things being equal.

The most basic types of electronic ignition simply reduces the current at the points in the distributor. The idea is to reduce the rate of wear on the points. The next level is the Aldon/ Pertronix Ignitor, Lumenition etc. These dispense with points and use either magnetic or optical sensors to determine the point of spark using the mechanism of the distributor to provide advance with the limitiation of engine speed as the only control. They do dispense with points therefore minimise servicing requirements they also allow an amplifier that optimises the coil output and therefore gives a fatter spark.

Megajolt and the like use a crank sensor to determine the top dead centre using electronics to vary the timing of the spark. The electronics have input from a Throttle Position Sesnsor or, if you are using a turbo or supercharger a Manifold Actual Pressure sensor to give the electronics information as to when to spark.

In your tintop there is likely to be a much more complicated ECU that will also have water temperature sensors, knock sensors, air temp sensors etc. that works with fueling information from the Lamda sensor and airflow sensor to figure out when to spark to burn as much fuel as effectively as possible to minimise emissions.

So a proper electronic ignition is invariably better than a points set up and a decent mappable system like megajolt, when set up properly will give significant additional power!

caber

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Originally posted by Fatgadget

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Originally posted by HAL 1
I'm trying to get rid of the one I've still got on my Haldane, I've fitted distributor and points from a cortina, replaced the diabolical electronic choke control from the carb, fitted a capillary type temp gauge etc, there might be other bits need sorting but nothing major I'm sure.

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Next step replace your indicators with semaphores and your headlights with acetylene fueled lamps!

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Distributors suffer what is called "spark scatter", you never know exactly when the spark is going to happen but it is probably within a couple of degrees either side of where it is set.

ECUs control electronic ignition much more accurately. This allows more ignition advance without going too far (you have to back off a distributor to take account of scatter)

ECUs can be mapped so you can advance the timing more where the engine will take it and less where it won't, giving an engine that is happier are more engine speeds yet more torquey across the whole range.

ECUs don't get wet contacts in bad weather either.

As previously mentioned, the dizzy has limitations....I think one of the best mods to a kit car is changing to something like Megajolt......Install is not do difficult, but you have a car with more mid range pickup, much smoother running, better Throttle response, better reliability, smother tickover, etc, etc.....
Well worth the change.....

I went form a dizzy on a 2ltr cvh to Megajolt,
and it has been fantastic :-)

PJ...

The benefits of a mapped ignition system are even greater if you modify the engine with different cams etc.