Technical Ignition boxes - when is it needed?

You have the option of a built in rev limiter in the 6AL box which could be handy.

 

http://capacitordischargeignition.c... copied design throughout the 1960s and 1970s. A good read! Pete

 

You don't NEED an ignition box, but every street car I've put one on it made a noticeable improvement in idle quality and part throttle driveability. It's also nice to have a built in rev limiter and easy tach hookup.
I had an MSD 6AL with the RTR distributor on my 55 for years with a pretty similar spec sheet to your engine. The box finally gave up (operator error, didn't unhook the grounds when welding on the frame), so I tried running it on just the distributor alone. There was a noticeable decline in idle quality and part throttle response.
I replaced my dead MSD 6AL with the Summit Racing CDI box. I read it's the same guts as the 6AL. It certainly seems to perform the same.

 

I guess it depends on if you want to go fast, or be able to putt around town with the best idling engine?



(I was disillusioned 35 years ago when I put my truck with it's fancy new MSD box on the ignition scope, and the Multiple Sparks went away above about 2500 rpm)

 

I've been setting up points distributors for EFI conversions for this for years. The big thing is to make sure the timing curve is set up as if you are over-carbureting the engine since most of the throttle bodies are close to 1000 cfm. Find peak vacuum at idle via timing at 900 rpm. Whatever that timing setting is will be your base timing, typically 20+ BTDC but there are a LOT of factors. Once this is dialed in, you lay out the timing curve.

My rule of thumb on needing MSD or similar CD boxes is either when the combustion chamber is turbulent from irregular domed pistons, or the bore exceeds 4 1/8". It takes time to overcome these issues and sometimes the shorter spark duration (higher joule spark) combined with multiple sparks can do a better job igniting the fuel with enough time to complete the burn.

 

MSD related ,
I contacted MSD Development with concerns of product failure , in last 4 or so months I have experienced this , the Graphite burning off , 2 different style caps , with Box & Non ,
Stock & Performance .
Points cap 500 miles.
@ first Tec try to say there was a gap ,
I proved wrong by showing wear marks on button Tab . & if air gap Cratering / arking would of been present.
HEI mini 2 OEM 100 miles
I have used MSD since 80s.
Older parts made different then Newer ,
Is it Because of ""HOLLEY Corp "" ??
New cap / Rotor was delivered I notice a Green tag ,

In last few months MSD has included
A Rotor Tab Button gauge ,
To See the Green Tag in packaging tells me that they've been seeing having issues with product ,
The New ingredients recipe for making caps and rotors,

 

Following

 

At some point I am pretty sure MSD offshored a lot of stuff. Looking at the box is a dead giveaway; we had two genuine boxes separated by 5-6 years or so, the latest was made in China. Not a knockoff, but not a reliable either./