Rogue_Ant

Lol.
E85 is harder to light-off. So I would probably start with a tighter gap, or factory (0.028") at the most.

URG8RB8

Thanks, will place order tonight!

Tom M'Guinn

Those plugs vaporize pistons. I opened my old Rx-7 motor and the pistons were 100% gone without a trace....

TurboTommy

Josh;
Thanks for this very thoughtful information.
I was coincidentally just recently wondering about spark energy and how it all works with regards to our stock ignition systems, and was researching and trying to compile info. And here you come with this!!
I would definitely be interested in a more efficient lighting off of the air/fuel mixture (at higher RPM). But, the thing is that maybe the stock 81mJ of energy might actually be enough to do the job? (with all good, fresh components, of course). If, in fact, more is better, then maybe an ignition timing change would be in order?

Rogue_Ant

Well, the stock system is definitely enough to do the job on a stock car. And we know it will work even with modified cars - however, that doesn't mean it is ideal, and at some point it is not acceptable at all (in-consistent ignition, misfiring, ect).

With a more powerful ignition, this should improve the flame-front. Faster combustion means we hit peak cylinder pressure earlier, which means that less ignition advance is needed. This results in a power increase since we are resisting the pistons upward movement less.

URG8RB8

That's Funny!!! Hopefully, non rotor heads will get the joke!

dnovak

I am in the same boat as Sid. majority of the time I have to have Josh explain these things three times before I might understand what the heck is going on but I am very lucky to have found two great guys living so darn close to me to help push these cars to the max!!

dnovak

User 52121

Ditto! Great stuff Joshua!

I already have the Rogue Tuner... maybe I'll think about picking up a better coil.

Based on actual conversations I've had with some of the other vendors - I'm pretty sure at least one of them doesn't understand things down to this level. PS - Reno I owe you a phone call.

URG8RB8

I am pretty sure 95% of the people on this forum don't understand the 944 down to this level, if not more!
Josh is a true marvel.

User 52121

True on both points.

I personally expect vendors to understand this stuff down to this level to be truly worthy of the respect that some of them get. At least then you know that the advice they give comes from a true fundamental understanding of what's going on.

KSira

Is there a way to calculate the best size of the coil? E.g. My coils (LS1 Style) has 185.6mJ energy and a spark duration of 1.2mS. Would there be any noticeable difference if changed to a coil with 250mJ and 2mS spark duration?

EDIT: Thank you for sharing. It is a pleasure to see a vendor with an engineers attitude, and that take great care and pride in doing research. Sometimes it seems to me that "tuners" don't even know the basic physical laws

MarkRobinson

Hey Josh, great thread, thanks for starting it.

FWIW, Back in '96, I added an MSD 6AL and Blaster coil to my Powerhaus 944T, car made 325/335 @ 15psi back then: good power for a 2.5l on pump gas. I noticed nothing by adding the MSD setup to my car & routinely took it to 7k during a variety of applications: strip, track, street, dyno, etc.

Later that year I was at SEMA & Crane Cams had their new CDI Combo the HI-6 and 91 & 92-series coils: 92 being the higher output. They had a display that showed a standard GM HEI igntion system lighting a spark plug, then a complete MSD6AL & Blaster setup lighting an adjacent spark plug, and finally their system lighting the last spark plug: wow. What a huge visual difference. The MSD's spark had about 2x the brightness of the HEI, and the Crane had about 2-4x the brightness over the MSD.

I bought a set & installed it & ran it for years...getting popped by it once; had to sit the rest of the afternoon out. I was running Nology wires at the time: I know I know, but I sold them through my retail store at the time so I had to support my product. Loved the ignition setup though.

Crane states 1200mj, 450v, and 7amps drawn at 10krpm. http://www.summitracing.com/parts/cr...6445/overview/

I saved a setup like this & will be running it on my boat...with an Mtune of course

refresh951

I will be interested in Joshua's comments. Seems like spark duration is the issue with a CDI setup. I think the spark would be brighter but have less duration. Seems CDI does have advantages in certain situations such as high oil content or very lean environments but that running an inductive setup should be better for our cars.

Rogue_Ant

I'm not aware of any "best way" to calculate best coil starting with just the energy output... Generally, I would opt for the coil with more energy and longer duration. That said, it can (and does) get more complicated, when you start considering other factors, such as does the coil make enough voltage? If the coil only makes 25kV, then it might not be able to actually jump the plug-gap. So, it doesn't matter how many mJ it has, if it can't use it.

Now, calculating the best/better coil option given coil charge time, and inductance lets me/us calculate what should be the best option, given the constraints.

The Crane rating is a little misleading... It does not produce 1200mJ per spark, rather it does 1200mJ per sequence. From what info I can fine, the energy per spark is around 150mJ. So a little more powerful than the MSD box.