Ole sparky....
 

If the original, stock Bosch system is working, keep it! If the Bosch CDI goes belly-up, consider the MSD 6A or 6AL units. They work well, are easy to install and can be bought for about 1/2 the cost of repairing a Bosch unit. You can pocket the extra $$$ or use them to buy a set of Magnacor (or other quality) wires.

WOW thanks for a the advise, and i didnt realize it was such a complicated subject...but yes my ignition probably works fine but it is an 83 and do not know if it has been replaced or its the original, so i think i may be doing myself a favor by replacing it soon before it leaves me stranded on the freeway...and i did not want to pay the big money its costs for a new bosch, i was looking for a possible cheaper alternative...thks again....and anymore info you guys may have... Damian

Damian,

I would take Fred's advice, "If the original, stock Bosch system is working, keep it!". My understanding is that the stock units can last indefintely, so why replace it if it's working? If you do replace it with another CD unit, hang on to the old one in case the new one quits on you.

Switching out the stock Bosch CDI always bring a lot of opinions and some are quite passionate on the subject.
The Bosch unit it good but they do fail over time. You have a unit rebuilt if you want to stay stock. Some never have a problem with Permatunes and other will have nothing but problems. Permatunes seem to have a considerably higher failure rate than Bosch or MSD.
Many owners, including myself, have swap a Bosch for an MSD 6A or AL and feel our motors perform better. Even though, as Loren states, there is no definative technical data to support the claim, my perception is that my SC starts faster, idles better, has smoother acceleration, and picked up a couple MPGs. I had already replaced the plugs wires last year and a new cap and rotor in the spring before I installed the MSD in August. And like many, I plan to keep the Bosch unit just in case I need it.

your unit might last another 10 years - it will give some warning as it goes bad

I'd keep it and save the $$ for something worthwhile, e.g. you could send the money to me...

Oft-used phrase:

"If it ain't broke, don't fix it."

MHO,
Sherwood

Actually Damian, if you have a working Bosch CDI you want to replace, I'll pay you $100.00 for it and you can apply that towards the MSD...

Sounds familiar...
 

I've had 2 PermaDoom units fail on me. I'd recommend the stock Bosch unit. Buy a good used unit here on the used parts forum...

I would go Bosch, NOT Permatune. I created a thread and listed some pros and cons of the Permatune and Bosch unit:
http://forums.pelicanparts.com/porsche-911-technical-forum/242720-bosch-cdi-unit-some-questions.html

thks for all the info and especially the info on the bosch units, think i probably go with a msd and will diff. hang on to my used unit....

what about a Crane Hi 6 Fire Ball ignition unit.
Just fitted one to my 2.4MFI and it works great. Nothing wrong with my Bosch CDI just tucked it away in the parts pile. Looked at both the MSD and Crane units. Went with the Crane unit because it has the internal and adjustable rev limiter. No plug in modules to mess about with.
The unit limits revs very softly too.

It also says the actual pulse time is shorter with the multi-spark systems which leads to worse combustion.

Just to add this in. My car had no records or indication of servicing the stock Bosch ignition system so I thought I would go ahead and replace the rotor, cap, and plugs. I noticed a much improved smoothness to the motor and better running condition. I dont want to say power because people on this board just roll their eyes way someone says they felt more power but I can say it had a bit more spunk. Whatever that means you to, I think the power people might be feeling with MSD etc. might just be the same as a refreshed ignition system.

Permatune is unreliable junk. Against board advice I had one installed (I gave it a chance) when my 24year old Bosch finally died, and within 3k miles it was dropping out when hot. Replaced it with a used Bosch and haven't had a problem since. Can't speak of the MSD on a 911 but use them all the time on my domestics and they rock.

Permatune is not an option if you intend on having a safe, reliable car. However, it did seem to run slightly better with the Permatune vs. Bosch .

rjp