blown 944

I was using it with the control box then with msd. I'm not positive it is the exact coil you have. I have been using it for 7 years now.

The reality is though that I'm looking forward to Josh's developments this year. I prefer to use his stuff whenever possible.

URG8RB8

You might have missed my point, I too will ultize all of Josh's developments, however to optomize his control circuit/coding the optimal coil must be determined. I am just curious how this coil rates compared to the MSD unit. I do know that Accell has bought the rights from Jacobs and now use the Ultra coils design but repackage/rebrand it. They now call it the Accell Ultra Coil, Ha!

Rogue_Ant

While a capacitive discharge might be successful at igniting the air/fuel mixture - it does not have the benefit of a lengthy spark duration. The capacitors discharge a significantly high voltage across the coil primary, which induces a large voltage on the secondary. However, because the voltage is so high (both primary and secondary), there is little energy remaining to sustain the spark duration.

Yep, the MSD Blaster is definitely the best bang-for-buck ignition improvement that can be made.

If the Jacobs coil was designed to be used with a CDI type system, then it follows that the coil is going to be poorly suited for inductive operation (i.e. not using a CDI box). Generally a coil that is designed for CDI operation will have very low primary (and secondary) resistance, and a very low inductance. This allows the coil to step-up the primary voltage in order to fire the plug, but does not delay the energy through the coil (inductance). This works well for a CDI system, but using this coil on an inductive ignition, it will perform poorly as the inductance is the energy storage potential of the coil - without the inductance, the coil cannot build very much energy on its own.

Rogue_Ant

Ha - funny!
Well, if one believes the published specifications of the Jacobs/Accel Ultra coil; it should be a fast-charging, but low inductance coil. At peak DME amperage:

1/2 * 0.003 * 9^2 = 122mJ

It will charge very fast due to the fact it has fairly low inductance & resistance; but, because it has low inductance, the peak energy potential is not very impressive.

This is a coil that is really meant to be used in a CDI type system. And in that application, I'm sure it performs just fine.

eman930

This is good stuff, I ran the MSD Digital 6 plus on my 924s, it was a great ignition, I'd be interested to try the DME setup

URG8RB8

Thanks Josh! Pretty much explains everything right there! I will order the MSD coil tonight. Coming back on March 1'st, can't wait to start wrenching on the CA car again.

URG8RB8

Josh:

Just noticed there is a red model 8261 as well as the blue 8253, I assume the specs for the blue unit are better for our application?

Rogue_Ant

Yes, the blue version is a much better option for our application. (The red version is not an option at all for use without a CDI box)

The red version is purely a CDI-type coil. According to the specs is has extremely low resistance and inductance. Similar to the Accel/Jacobs coil, the red version is designed to purely act as a step-up transformer, it has very little inductance, or storage potential.

In-fact, I would be surprised if that could would work at all without a CDI box. It's energy storage potential is only ~5% that of the blue version.

eman930

What about the whole Mult Spark thing that MSD does? Says the do it at low rpm
Up to 3500, Does it truly have any gain in performance? The biggest difference I noticed in my MSD digital 6 plus setup, Was Better Throttle response and less bogging in taller gears, Am I crazy our is this normal with a ignition upgrade?

Rogue_Ant

The multiple spark discharge is done to try to mask the fact that capacitive ignition typically has an extremely short spark duration...

For example, Electromotive has stated that their ignition system (wasted-spark, inductive style ignition) will provide up to 2mS of spark duration. This is over 30° of crank rotation at 3000rpm. By contrast, capacitive ignitions might only provide 0.2mS of spark duration; this is only ~3° of crank rotation at the same 3000rpm. So by doing three strikes, they are attempting to add spark "duration".

refresh951

Good read:

http://www.gill.co.uk/products/digit...n/1_whyuse.asp

URG8RB8

Josh:

What are your recommended spark plugs and gaps with this coil setup. Need to order those as well while I am at it. Thanks for the red versus blue explanation as well!

Rogue_Ant

Lol - a lot of what they have to say will sound very familiar to anyone who has read this thread

One more note, with a sufficiently fast coil-charge time (or less cylinders per coil), mutli-strike can be done with inductive ignition a well. In-fact, this capability was built into the Ford EDIS wasted-spark module used on early 90's Fords.

Rogue_Ant

For a street car, NGK BPR7ES plugs (stock number 5534). If the car is never going to see over 17psi of boost, then the Bosch Supers work well too (one step colder than factory, stock #7995).

A large gap is not as important with an inductive ignition (compared to a CDI). This is because we want to use the ignition energy for spark duration, not just a large gap. With the HVC-II coil, I would start with stock gap, and then adjust if necessary (or desired).

URG8RB8

Suppose I have to ask another question now.
How about with E-85 at 20-22 psi on the street? Assuming the same NGK's but want to verify.