Standalone ECU for twin spark V8

I've fitted an M113 Mercedes engine into an old classic (or what remains of it) 1967 Triumph Spitfire. It's a normally aspirated engine, which originally had a plenum intake with a single electronically controlled throttle body. I am converting it to run a set of E90 M3 throttle bodies, which will be opened with a cable. The engine has twin spark plugs per cylinder with coli-on-plugs, which Mercedes originally fired independently I believe for emissions purposes. I will keep the twin sparks, but would be happy to fire them together.

I don't intend to make any significant changes to the internals of the engine, possibly cams in the future, but it'll be principally a road / trackday car and will have plenty of power and torque anyway for the chassis.

In short, for this engine and intended purpose, what ECU options do I have - I'm thinking the twin spark V8 bit limits my options?

Some Gen' 3 Chrysler engines also run dual plugs per cyinder.

Of hand, I expect(!) you can simply run them in parallel, like if batch firing compression & exhaust on other engines, but you may need to check the currents involved - if short there are options such as used for high current coils.

Alternatively, if you want to split the timing, you could actually batch fire then?

Sounds like an "interesting" project - I hope you're getting rid of the swing rear axle and fitting something both a lot stronger and better designed?

Thanks for the reply. It certainly is an "interesting" project. I've fabricated a twin wishbone setup for the rear, based on the geometry from the rotoflex GT6 and using an R160 Subaru LSD. I'm spaceframing the chassis, with a scuttle and rollover hoop incorporated. The mass of the engine and (E46 M3) gearbox are moved well behind the front axle and so it should be a very compact and stiff structure, with weight in the right place and just enough space for me to squeeze in to drive it!

In terms of the ECU, I'm happy to run wasted spark if needs be, but I'm going to need something capable of firing 16 plugs. Any advice on what will do this?

Techically, while you're looking at 16 spark plugs, with either option you're actually looking at 8 ignition events, which can be handled by any ECU that has the current rating required for two coils in parallel.

Using the SBC firing order (IIRC) as an example, you're looking at firing as a pair the coils as

2x#1

2x#8

2x#4

2x#3

2x#6

2x#5

2x#7

2x#2

If you're looking at the split timing, it's be more like

leading #1 (ignition/compression stroke)  & #6 (exhaust stroke)

trailing #1 & #6

leading #8 & #5

trailing #8 & #5

etc.

Gord's got you on a good path for the ECU so I'll just say I'm concerned by your mention of the R160.

They are extremely weak and I've blown several at 150 ft lbs of torque with street driving. Could you get a short R200 in there?

Thanks for the advice folks. I'll fire the plugs together for each cylinder, but I'm unsure as to what specification I need to check to identify whether an ECU has the capacity to fire both together?

Regarding the R160, it's one of the stronger ones with 4 spider gears and has a proper clutch pack LSD, so it's as good as they get. Aside from that, the car should weigh around 800kgs and will only run 205 section tyres, so it'll be very traction limited and so I don't think it'll ever really have to handle a great deal of torque.

Fingers crossed...

Can you identify exactly what the coils are, from that you can double up to determine the current draws, and check that against the current rating for the ignition side of the ECU, if it's powering/grounding it.

Oh, and if they use a separate igniter, or they're integral with the coils?

Plus any other useful information.

Despite some Googling I can't find much on these.

I've found a good page on the Haltech site though, which should help identify whether they gave an igniter, so I'll take it from there.

Thanks all.

Awesome James, best of luck with the project!

If they're smart coils then you could probably control it with an LPC8 ECU.

https://controls.is/shop/LPC8gen2

It appears they're dumb coils, but I see Haltech does a suitable ignitor module, so it would make sense to do everything via them.