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Registered User
Join Date: Jan 2004
Location: Milwaukee, WI
Posts: 3,205
Crank fire vs Distributor for TP?

What are the pros/cons of using an HPV-1 system vs a distributor (JB racing)? Is one better than the next? Would be used on a turbocharged engine.

Jeremy C.
Why's he calling me meat? I'm the one driving a Porsche. (Bull Durham)
----Nothing is far away in this car!----
-1978 911 SC TURBO, Minerva Blue Targa 965 update.
-2008 550i M-Sport
Old 10-30-2016, 06:04 AM
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Tom_in_NH's Avatar
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Location: NH
Posts: 75
My take on it, is that the distributor-based twin-plug setup delivers more energy, due to CDI units firing the two coils. The other aspect that may be important to some, is the period-correct look of the distributor. However, changing your timing curve is a pain. There are those that use the MSD 6AL-2 that provides programmable curves with distributor based ignition. It requires removal of the advance mechanism and locking the rotor. However, I believe rotor-phasing can become an issue here. Regarding use on a turbo motor; you may be able to do the very critical boost-retard with one of the MSD units....but I'm not positive of that.

The HPV-1, in particular, is a bit limited with regard to programability. However, crank fire, in general, offers virtually limitless combinations of base timing, max advance, and the curve between those two points. It is more complex, and probably a bit more pricey than the distributor. For the non-technical among us, there are plenty of forum threads regarding this.

Regarding the more energy from a distributor-based setup; I'm not sure how much it's actually needed, unless your cylinder pressures are very high. Think 12:1 +++ compression or very high boost. Every contemporary car is running coil-on-plug.....

1983 911SC Coupe
2013 Honda F6B (another flat 6 !)

Last edited by Tom_in_NH; 10-30-2016 at 07:15 AM..
Old 10-30-2016, 06:44 AM
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Walt Fricke's Avatar
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Location: Boulder, Colorado
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I am dubious that the two coils, even CDI, of a twin plug distributor, are going to provide a better spark than the six coils of an HPV1 or similar crank fire system. Three coils ought to saturate better at high RPMs than one.

The HPV1 is certainly not as flexible in terms of adjusting the curve as Electromotive's EFI systems, but for a race motor that ought not to matter much. I assume you are running CIS, or something like it and not using electric fuel injectors? When I was running carbs on my NA race motor it worked great.
Old 10-30-2016, 10:43 PM
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Max Sluiter
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the energy is in the capacitor, not the coil.
1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
Old 10-31-2016, 06:58 PM
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Plays with cars's Avatar
Join Date: Nov 2001
Location: Southeast of Seattle
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Programmable seems the way to go. Especially on a boosted engine. I'd be looking one that use a MAP sensor as well so you can build a 3D ignition map to optimize on an off boost performance. Megajolt is a programmable unit based on the Ford EDIS components and it fits this bill. Its basically the ignition side of a Megasquirt system.
Mark B
'73 911S (long term ownership) '70 914-6 (long term project) '74 914-2.0 (sold)
Old 10-31-2016, 08:15 PM
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Any crank triggered system will always be more accurate than a distributed system. You have gear lash and any play in the gear assy to consider.

But if the gears are new and the lash is within the span of the rotor and cap contacts, you will be Ok and as accurate as a distributor based system can be. Accuracy is very important as is control and most crank triggered systems have a lot more ability to control the timing curve over a distributor system.

What also need to be considered is the power level you want. These engines have huge combustion chambers (90+cc) and in a Turbo application often fairly flat topped Pistons. No inductive system will be anything close as good as a CDI system in these applications. Coil saturation and the time to charge the coil will make no difference here. The time between firing events is long enough to fully charge any coil 1 or 6. It's the energy released that is important. Inductive will make the engine lazy and unresponsive. Many are using this sort of Ignition without the knowledge of how much better their engines would run if they had used CDI.

If the distributor is used only to distribute the spark, locked out and some sort of timing control used in conjunction with CDI units and coils, , then you have the simplest system using the better ignition type. For a turbo application, CDI is a must if you want any sort of performance.

If you use a distributor, and 6 spark plugs, use 1 CDI unit driving 1 coil. If you are running 12 plugs, use 2 CDI units and 2 coils, each powering 6 Plugs.
Old 10-31-2016, 08:31 PM
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