CDI Recommendation?

[Ovis]

Hi all,

Looking for some advice, info, and ultimately a recommendation on what CDI system to go with. I finally finished my motor build and am preparing to get it in the car and on the road this summer. This is an early 65/66 motor that has been hot rodded a little with bigger pistons/cylinders and a MOD S cam. Weber carbs.

Permatune, MSD? Any advice on products and models is greatly appreciated!

J

[kenzinger]

I used a rebuilt Bosch by ************. Pricey but has been extremely reliable.

Sent from my Pixel 9 Pro XL using Tapatalk

[boyt911sc]

If you want a 6-pin Bosch OEM CDI, I have a dozen units from my collection that are tested and guaranteed to work or money back, $390 shipped.

Tony

[Ovis]

Thanks Tony, I will keep that in mind as I do my research and shopping. Appreciate it!

Josh

Originally Posted by boyt911sc

If you want a 6-pin Bosch OEM CDI, I have a dozen units from my collection that are tested and guaranteed to work or money back, $390 shipped.

Tony

[tobluforu]

http://www.capacitordischargeignition.com/

https://www.systemsc.com/products.htm

I have not used any of the above, these came from bookmarks i had from people on this board.
https://forums.pelicanparts.com/porsche-911-technical-forum/1159060-cdi-dead.html

[ischmitz]

I would always go with the Bosch OEM. Once properly rebuilt they are good for many years.

[jbell959]

Give Bob Ashlock a call. He rebuilds them and also has his own high-performance upgrade with all new electronics.

[silverlock]

Been running a Pârts Klāssik CDI box for about 15k miles — across a bunch of rallies & long distance trips — with zero issues. Did a core swap and they turned it around within a week.

[doswald]

I have the MSD Streetfire in my ‘71, with points. Runs good!

dho

[jmz]

I have a couple of early style CDI boxes from classic retrofit that I purchased new and never used. …went with later style distributor and cd box.


Research and PM me if it’s something you are interested in.

[mysocal911]

Originally Posted by jbell959

Give Bob Ashlock a call. He rebuilds them and also has his own high-performance upgrade with all new electronics.

Really? Like how does a CDI spark become "high-performance"? Or is this the typical promotional hyperbole?

[mysocal911]

Originally Posted by silverlock

Been running a Pârts Klāssik CDI box for about 15k miles — across a bunch of rallies & long distance trips — with zero issues. Did a core swap and they turned it around within a week.

You do carry an OEM Bosch CDI as a backup, right?

[shoooo32]

I have 70k miles on a Parts Klassik CDI. It has a vintage look with printed circuit board internals and a rev limiter built in.

Whether you get one from PK or Classic Retrofit, why run 70s OEM when a modern solution is available...

[mysocal911]

Originally Posted by shoooo32

I have 70k miles on a Parts Klassik CDI. It has a vintage look with printed circuit board internals and a rev limiter built in.

Whether you get one from PK or Classic Retrofit, why run 70s OEM when a modern solution is available...

Bottom line: Both have exhibited poor reliability! Being "modern" has basically nothing to do with reliability.

Again, always carry a spare, especially a Bosch one! Many of the original 3-pin Bosch CDIs are still in use with over 50 years in service.
Some waste money having their 3-pin Bosch CDI unnecessarily rebuilt!

When it comes to "modern solution", you'll find the Parts Klassik CDI uses electrolytic capacitors. Not a reliable "modern solution" for reliability in a very HOT environment.
A design like that would NEVER be used by an OEM auto manufacturer!

[pmax]

Originally Posted by mysocal911

Bottom line: Both have exhibited poor reliability! Being "modern" has basically nothing to do with reliability.

Again, always carry a spare, especially a Bosch one! Many of the original 3-pin Bosch CDIs are still in use with over 50 years in service.
Some waste money having their 3-pin Bosch CDI unnecessarily rebuilt!

Amazing how long these things last.

But yes, everyone should have a spare (or two).

When it comes to "modern solution", you'll find the Parts Klassik CDI uses electrolytic capacitors. Not a reliable "modern solution" for reliability in a very HOT environment.
A design like that would NEVER be used by an OEM auto manufacturer!

In fairness, 50 yrs and counting is hard to top with modern electronics.

[mysocal911]

Parts Klassik CDI - "a modern solution", not.



As previously posted; "Always carry a Bosch CDI as a spare."

[ischmitz]

I agree with almost everything mysocal911 says; the “modern designs” are a poor solution in search of a problem. Their designs lack in reliability and add unnecessary complexity. If modern engine control units were designed and built to these standards I’d invest into a tow truck service because roadways would be littered with broken-down cars.

However, there is one exception. Bosch boxes do require rebuilding once the main capacitor is sufficiently aged and worn or shorted. Aside from over-voltage that is their dominant failure mode. In some boxes I get in the capacitor shows memory effects, severe leakage and becomes part ohmic once at temperature. This further accelerates aging and replacing the capacitor addresses that issue.

Interestingly 6-pin boxes have a significantly higher capacitor failure rate compared to the older 3-pin versions even though it’s the same part. My theory is that 6-pin boxes in later cars are exposed to higher average engine bay temperatures resulting in accelerated wear rates.

[wazzz]

I agree too. The PCB on the pic above looks like a DIY circuit or a prototype board. Seems it has been hand soldered despite most components are SMD.
PCB traces with right angles like these are not recommended in good PCB design.

[shoooo32]

My experience is strictly anecdotal - I've never opened a Bosch, Parts Klassik or Classic Retrofit CDI and have only a basic understanding of capacitors.

You guys clearly have more skin in the game than I do given you repair these units. No different than the OP, I just want reliability. "Just carry a spare" is not a great solution in my opinion. That means there's been a failure, and I'm likely now troubleshooting this issue in some remote area of the country.

Given the SMEs in the room, what would be your opinion on the "ultimate CDI" for an aircooled 911? Did the aftermarket get anything right or does a freshly rebuild Bosch unit leave nothing on the table as far as reliability upgrades are concerned?

[mysocal911]

Originally Posted by shoooo32

My experience is strictly anecdotal - I've never opened a Bosch, Parts Klassik or Classic Retrofit CDI and have only a basic understanding of capacitors.

You guys clearly have more skin in the game than I do given you repair these units. No different than the OP, I just want reliability. "Just carry a spare" is not a great solution in my opinion. That means there's been a failure, and I'm likely now troubleshooting this issue in some remote area of the country.

Given the SMEs in the room, what would be your opinion on the "ultimate CDI" for an aircooled 911? Did the aftermarket get anything right or does a freshly rebuild Bosch unit leave nothing on the table as far as reliability upgrades are concerned?

The implication referred to is when using a "modern solution" CDI, not a Bosch.