OHV Volvo ignition options

[buzzboy]

I'm planning out my first adventure into the world of MS with a Volvo B18 that I'm building. I figured I could drop big money on side draft webers and have something less tunable than proper MS. The choice was easy.

I have been reading all the manuals for the past few weeks and I've got a few questions.

1) Microsquirt looks like it would be a good choice for me. I like the fact that it can be made weatherproof and that I can't mess up assembling it. Any reason I should look at a different MS?

2) I would like to stay away from adding a toothed wheel to the car so I want to go with distributor control. I read about people using the distributor to distribute the spark. What I don't understand is how a locked distributor will be able to change the advance more than a few degrees. The rotor is only lined up with the cap for a few degrees, not a full ~30° or however much final timing I will end up running. Otherwise, can I use the distributor only as a trigger to trigger a different ignition system?

[grom_e30]

the microsquirt is a good in the fact it is small pre built and has 2 on board vr conditioners, the downsides i have come up with from using one is you are limited to the amount of inputs and outputs it has, you only have 2 injector drivers so its batch injection or semi sequential on a 4 cylinder, also the connector comes out off the top of it not the side but it works.

i have not used a dizzy before but, the advance is in crank deg not cam deg so if your rota lines up for 10 cam deg you can double that.

if you are planning to use the dizzy as the rpm input you will have less accuracy on the spark timing vs using a crank mounted trigger wheel with a decent tooth count though, 4 pulses from the dizzy is equal to a signal to the ecu every 180 crank deg, if you had a 36-1 on the crank you would get a signal every 10 deg.

[buzzboy]

Darn. I was hoping to get away without rigging up a crank sensor. I guess I would be fine using only RPM as input if I go fuel only but if I want to to spark I need better resolution.

[DaveEFI]

The rotor arm usually has a wide enough contact to cope with any vacuum advance. It might be possible to find one which is the same - except with an even wider contact to use with a locked dizzy. But personally, I'd check to see if there is a trigger wheel kit for your engine, or if it is easy to fit one. The far more accurate timing has many advantages. If not, I'd start off fuel only. You can change to mapped ignition at a later date pretty easily.

A regards the MS itself, it should be fitted inside the car where being weatherproof doesn't matter. And I'd go for a standard MS2 (or3) with the V3 board. It is much easier to repair or modify etc if ever needed. Size surely isn't an issue? A good place is in the front passenger foot well, roughly where the pedals would go on a RHD. Usually plenty space there.