914-4 2L race engine, 10.3:1 compression ratio and twin Weber's

Anyone have experience with the MSD systems on a Type IV? I'm thinking there may be benifits to having the higher spark voltages when compression ratio is relatively high. MSD claims plug gaps of .050 - .060" are possible, and that multiple sparks at lower RPM's improve throttle response. Thus, makes sense, but does anyone have real world experience that support these claims?

Yes and no

In your case the with the much higher than stock CR it very likely helps.
Stock or stockish CR would be debatable.

With that CR you definitely need high octane race gas and/or twinplug.

MSD are fairly bullet proof. I've used their coils in a pinch on several CDI cars when the Bosch or "better" aftermarket coils failed.
Only thing better would be crank fire; accuracy cannot be matched. Twin plugs at 10.3:1 are just about mandatory unless, as Mark intimated, you use fuel in the range of 100 +.

CDI and MSD are two different things:

CDI: Capacitive Discharge Ignition which is essentially an increase in spark voltage.
MSD: Multiple Spark Discharge which fires the spark plugs multiple times instead of once.

CDI setups will jump larger gaps, will more reliably fire at high compression ratios and at high RPM.
MSD setups only function at lower RPM and multiple sparks mean multiple opportunities to ignite the mixture, so this really is best for engines that experience erratic idle and low rpm misfires.

Mark,

I believe the msd is as you describe but also CDI according to what I have read from the msd website.

You're right, the 6AL does seem to have CDI built in.

Yep MSD is a CDI.

On our 1.8 FProd car (12.3:1 CR) CDI made zero power difference. It did crap out, though, while leading a race at Barber.

I rigged up a back up system I could switch back and forth between on the fly. The back up was a Bosch Blue Coil with no CDI.

We tested both systems on the chassis dyno and there was absolutely zero difference in torque or power.

We were using a Mallory distributor. Crank fire might be a different story.

We ditched the CDI and the attendant complications.

Len,

Very interesting.

Thanks for sharing; this is exactly the information that I was needing. There is no sense in duplicating what has been proven in the past, and saves me time and money!

As for crank fire set-up, I wish I could, but rules do not allow it.

Jim

MSD sells an affordable CDI system that also provides multiple spark. What I like about the electronic systems is they do not burn out the points as fast. What I don’t like is - what could be simpler than points?

Pay for shipping and I'll send you an MSD 6A, part number 6200 and a Mallory HyFire, part number 6852M.

0 miles on the Mallory, the MSD (a few hundred miles if that) might have had a ceramic resistor replaced inside when I used it on my Link ECU install 10 years ago. New resistor is like $5 and prints are available via a google search.

Thanks for the generous offer, but it sounds like I should pass on it. I respect Mr. Hoffmans's, as well as other's efforts, and will not pursue the CDI/MSD systems.


Thanks again,
Jim

Mike, sending you a PM

Len how much do you think camber design has to do with this?

I've always been on the fence with stock vs fancy ignitions for a /4.
For most apps with a T1 and T4 I've never seen any magical power difference between stock and CDI (etc.)
The only improvement I've seen has been the off idle issue that some engines have.

Where as the /6 uses a CDI from the factory, except for early stock engines and everyone uses a high output ignition system of some type.

I use a crankfire on my 180hp 2600cc T4 with aftermarket FI, 44X38mm valves... runs great.
But I've also built a similar spec carbed 2700cc T4, used a mallory with just a blue coil I didn't see any real difference ignition wise.

Mark, my thoughts center around the idea that there is a certain amount of 'spark' that is sufficient to ignite the mixture. Any upgrade in potential (CDI or MSD, etc) is essentially wasted after that. If 12,000 volts reliably ignites the mixture, adding 30,000 volts won't ignite it any better.

The Type 4, even at higher compression, seems to ignite pretty easily. I can't begin to approximate why because I don't know enough of the science.

Perhaps the 911 found success with the CDI because of the hemispherical combustion chamber. Perhaps Porsche simply opted to install it because it was 'safer' technology. Or perhaps it was more along the lines of trickling down from race success. Also 911 engines turn much higher RPM than typical Type 4.

The Type 4's basically flat top pistons and wedge-style combustion chamber may be much easier to ignite, and our redline is relatively low.

Len? You still reading this? What're your thoughts on combustion chamber shape, piston dome, and how difficult those different factors are to ignite?

Also, Len, what's your redline on that engine?

We all know the hemi chamber with dome pistons is a bitch for flame propagation, no doubt about that. I can definitely see the CDI helping in that design.

Our shift point was around 7800, but at Roebling Road I did stretch 3rd to 8100 or so.

One of the things that puzzles me about the multiple spark discharge concept when using a distributor is, how broad a crank angle can the rotor distribute spark in a given firing cycle. Without a special rotor, I don't think it could be as many as 20 crank degrees, which IRRC is what MSD advertised.

I agree, I was always dubious about jacobs ignition claims, basically it was just a multi spark CDI and at speed there's only time for a few sparks.
Evidence points that it likely it does help low speed issues, but once over say 3000rpm it has little, if any, effect.
I would think the hotter spark helps with the initial firing, probably more important on the /6 chamber, but little more

To me it's much like the sequential and batch firing of injectors arguement. At low rpms where watercooled cars can run it will make a difference in fuel economy, but little effect on car that normally runs at 3000+rpm.
Only so much can be achieved at higher piston/rotation speeds.

At the risk of this sounding like a dumb question:

I figured, like has been said above, once the charge is ignited, how does another spark help??? Nobody has been able to explain that to me. It seems like using a lighter against a fire that is already lit.

Another spark plug (with a lot more complication) or a multi-firing spark plug...
Once it fired, how is another spark going to help anything??? Please help me understand this.

I've asked this before, but have never heard a reasonable answer.

It seems to me like an efficient combustion chamber would solve it. Redundant spark is just expensive complicated wasteful extraneous complication. (We are talking 914s, not the most exotic race cars)

Agreed.
A crank fired C.O.P. ignition with smart technology firing continuously over 20 crank degrees might or might not benefit the flat-top two valve T4 chamber, I wouldn't bet a nickle that it would. But I'd bet the farm it would help a hemi with a domed piston, a lot. The bigger the dome the more helpful, obviously.

I'll accept that I will likely not benifit by going to a CDI/Multi-Spark system. However I do not understand the statement regarding high compression ratio and needing a twinplug head. Its a race engine in a race car, so running race fuel (adequate octane rating and probably leaded fuel) is not an issue other than the added expense.

How does having two spark plugs help the Type IV with higher CR's and/or lower anti-knock fuel?