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Ignition system quandry
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Posted by: John

OK, here's the deal. Working on planning out a turbo charged 2.5L OHC Ford 4 cylinder out of a Ranger. I can get low compression dished pistons on 5.2" rods for the extra stroke. .030 overbore and it approaches 2.7L of 4 cylinder fury!

Problem is that I want to use the 2.5L head. It's a "fast burn" design with high flow ports. It also has a stock camshaft with a fairly wide duration. This would be a good deal for a T3/T4 hybrid turbo.

Problem is that it has two spark plugs in the head. One for firing for combustion and the other for firing after combustion. It is there purely for emissions purposes to keep unburned fuel out of the exhaust. Emissions reasons is the sole purpose. Anyway, two options are to weld up one of the plug holes. That creates fun in the chamber and requires a good deal of work. The other option is run the second plug.

What I am wondering is how easy is it to fire TWO spark plugs at the same time? I know the control isn't the problem, the spark size is. But I would think that if you got a big fatty coil, it would have ample juice to spark two plugs at once.

Again though, that would create fun in the combustion chamber. Two ignition points would cause a really odd flame front. Then again, if the engine is boosted, would it really make that much of a difference? I dunno. Anybody got some insight?

Anyway, I was gonna play with a MegaSquirt II Sequencer for this project when it comes out. It allows for SFI AND ignition control. If I can, I'd program it to fire just like it does on the stock computer. Thing is though, I want to run at least 10 pounds of intercooled boost on it. 12-14 would be better and translate to about 350 horses most likely. Apparently MegaSquirt can control a boost controller and respond to it too. So if I overbuild the engine, it could see dual duty street/strip and turn the wick up to about 600 horses. The cool thing is that with 2.5+ liters of displacement it's a torque monster. The stock EFI engine puts out about 150 pound feet just south of 3,000 RPM. Better flowing head with a T3/T4 hybrid strapped on, it should make that right off idle and see something north of 275 lb. ft. over 3,000 RPM.

MegaSquirt is not emissions legal but, the vehicle this is planned for originally had a carb and an A.I.R. system. But if the engine is out of a 98 Ranger, that didn't have the A.I.R. system and was closed-loop on the emissions. A catalytic converter or two with a slightly rich tune should get the sniffer test far enough in line that it doesn't warrant a visual. Then again I know places that will forgo a visual inspection if they can get the sniffer to sync up well enough.

Anyhow, what do you think about firing two plugs on the same cylinder at the same time? Bad idea? OK idea? What?

Posted by: StoneFox

I think i would just put an old plug in the hole your not worry about it

but im lazy

Posted by: John

Quote:

Originally Posted by StoneFox


	I think i would just put an old plug in the hole your not worry about it but im lazy

Old plug would get caked in carbon, cause a hot spot. Since it's "cold" and the electrode ain't heating up either, it would quench whatever flame was immediately in the area surrounding it and cause problems.

Posted by: rodslinger

I'd say just use the recommended plug and go with it.... Plugs are cheap. A little trial and error can't hurt on a secondary plug setup.

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