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Hall Effect Distributor - Home Reference

Practical Standalone Tuning

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Hi team, long time follower of HP Academy. Have purchased a few courses and am hoping to one day convert my weekender to EFI. Currently my motor is a Ford 250ci Crossflow (carby) that I have worked on over the last decade. Ignition wise, I have converted to a Hall Effect Distributor and run it off an MSD 6AL-2 Programmable. I use the MSD to adjust ignition timing based off both RPM and manifold vacuum (Using a Haltech GM 1-Bar MAP sensor) and this is the extent to which I use a laptop to tune.

I dont have a crank trigger so the only reference any hypothetical ECU would have on my motor is just the engine RPM based off the 6 teeth within the distributor (5v signal input). My question is, would it be possible to perhaps modify this distributor so that it provides an ECU a 'home' reference for cylinder #1 TDC as well as providing information for RPM? For example, perhaps cutting off the tooth that relates to cyl #1 (effectively making it a 5 + 1 tooth count?) - would this be enough to give an ECU an RPM and 'Home' reference signal?

I dont have a pic of my distributor but the screenshot attached is pretty much exactly what I have. Thanks for your help and love the site!


Attached Files

The answer is "it depends". Many modern ECUs can 720 sync (full sequential capability) using a single camshaft speed missing tooth wheel as you propose but some cant. Link, Motec, and most new Haltechs can use it. AEM, ECU master and older Haltechs are some that cant.

BTW, most would call this a 6-1 pattern, not 5+1.

Hi Adam, thanks for the reply mate appreciate it! Cheers for clarifying the tooth count. Yes the long-term plan is to do the conversion using a new Haltech ECU. Do you foresee any problem with using a single trigger source for both rpm and reference?

I understand that the majority with older motors such as this do use a crank trigger for the RPM signal - but that would still leave you with a similar issue where you have to run something off the cam (like distributor) for the home reference. IS cutting a tooth off for cyl1 a normal way of doing this?


It is a reasonable option but bear in mind it is crankshaft position that is important for spark timing.

With the system you propose your engine position information is coming from a distributor that is driven by a driving dog with lots of backlash - which is driven by a bevel gear set with lots of backlash - which is then driven by a cam chain or gear drive with back lash, before it is finally connected to the crankshaft. So it is not always a great indicator of crankshaft position. You will usually find with cam driven systems at certain RPM ranges there will be resonance from the valve train and torsoinal vibration of the crank that will cause all these backlash items to bounce around - and hence spark timing will bounce around too.

So a proper crank wheel connected directly to the crankshaft is always the best option, having said that, a 250 cross flow is hardly the pinnacle of performance engines, depending on how hot it is, 10 deg of timing scatter may not make a huge difference to the performance in this case. Obviously, the spark scatter will be no worse than the current MSD distributor based system - just not as good as it could be with a proper crank trigger driving things.

Hi Adam, late reply but thanks for getting back to me. Managed to get a bit more research in and also squeezed in a qtn in today's webinar that Andre covered. I think I know what direction I'm going to go in. Cheers!

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