Team Camaro Tech banner
Cancel
Create thread New Garage Forums

MSD 6a vs. HEI

Jump to Latest
1 - 9 of 9 Posts
#2 ·
I've only started reading about different types of ignition systems; so I hope someone will correct me if I'm wrong. There are two basic types of set-ups available: inductive ignition and CD (capacitive discharge) ignition. HEI operates on the inductive system which requires that the coil ramp battery/alternator power to create the spark. As you can imagine, higher RPMs will give the coil less time to di it's job in this situation. The CD ignition uses capacitors to provide an initial step-up in power before hitting the coil. This step-up happens very quickly, allowing multiple sparks at lower RPMs. As is the case with inductive ignitions, higher RPMs give the capacitors less time to charge; however unlike inductive ignitions, it isn't very detrimental to the performance of the system. Instead, the system drops is the multiple-spark advantage, yielding to a single spark around 3000 RPM. It is my understanding that MSD pioneered and remains the leader in CD ignition systems.

What does all that mean? If you're looking for ultimate performance at high RPMs, go with a CD ignition system. It will also help ignite the mixture in forced-induction engines (super- or turbocharged). If you have a more pedestrian engine, the HEI system will work well for the application and probably be the better alternative. In a CD system, a separate ignition box is needed in addition to the distributor and coil. Conversely, in an inductive ignition system, you only need the distributor and coil. Having more components only mean there are more things that can go wrong. If you've been following my saga of ignition problems, you'll realize that I've had to replace the distributor, the coil and now the ignition box. It's not cheap. Furthermore, there are high performance HEI modules available that will offer increased performance and hooter spark to a 7000 maximum RPM. Needless to say, since my cars are more street-performance oriented, my next build will be using an HEI system.

Here is a link to a magazine article for your topic: http://www.chevyhiperformance.com/techarticles/45618_inductive_cd_ignitions_basics/index.html
 
#4 ·
The biggest single improvement you can make to an old car is an electronic ignition. It sucked keeping a set of plugs clean with points. An HEI is the most reliable distributor made. If it fits in your car you're done. The MSD is more hardcore but on a street motor you won't notice a difference. Save your money for other things.
 
#5 ·
Reliability and the availability of HEI parts was the decision maker for me (I have a street mobile). HEI preforms well enough. MSD boxes haven't impressed me much. The fact that the multispark feature poops out at moderate RPM kind of defeats the purpose IMHO. Search the archives for people with MSD problems and that'll be another reason to consider HEI. <flame suit on>
 
Save
Reply Quote Like Like
#6 ·
I've had my share of problems with my MSD set-up; however it looks like they made some improvements in their electronics with the 6AL-2. I'm runnig the CD ignition because I've got a little too much compression for the street. Like I said, my next build will run HEI and a more tame compression.



dnult said:
Reliability and the availability of HEI parts was the decision maker for me (I have a street mobile). HEI preforms well enough. MSD boxes haven't impressed me much. The fact that the multispark feature poops out at moderate RPM kind of defeats the purpose IMHO. Search the archives for people with MSD problems and that'll be another reason to consider HEI. <flame suit on>
Click to expand...
Multiple sparks at lower RPM should also help with fuel economy and throttle response by ensuring more complete combustion. Then again, if you rally need a CD ignition, you might not be too concerned about fuel economy. I'm getting single-digit mpg...
 
#9 ·
Well when i had points and added an msd 6al box it starrted quicker and idled better. The last couple years since i've had a pro billet distributor its been eating a cap a year, not to mention the 5 year old 6al box that died. If an hei would fit in my z28 i'd give up a litlle high rpm performance just to have the reliability and ease of not having to mail order parts. Honestly every year the car gets closer to factory gm parts just for reliabilty. I'm not trying to knock msd but hei parts can be had anywhere.
 
1 - 9 of 9 Posts
About this Discussion
8 Replies
6 Participants
Last post:
Dave69Z
Team Camaro Tech
posts
2.4M
members
90K
Since
1998
A forum community dedicated to 1st generation Chevy Camaros owners and enthusiasts. Come join the discussion about performance, builds, restoration, modifications, classifieds, troubleshooting, reviews, and more!
Full Forum Listing
Explore Our Forums
Bench Racing Engine Body Shop Performance Brakes, Suspension & Steering