HEI Ignition question

[cmegga]

This may be a really dumb question, but one thing I never really understood.

I have an 81 , with a semi recent rebuild. I added a MSD 6a ignition and unhooked the stock computer .

I want to get a new distributor cap, wires , etc a whole toon up kit. All the product list for HEI or non-HEI ignitions, how would I tell which I have ???

 

[LEEJANDZ]

cmegga -- This may be a really dumb question, but one thing I never really understood.
All the product list for HEI or non-HEI ignitions, how would I tell which I have ???

HEI = high energy ignition

I believe came standard in the mid 70's.
I know my 79 is HEI.

As long as your 81 has the stock set up, you have HEI.

 

[cmegga]

Sorry, but Im still confused here.

Its still the stock distributor, but no running threw the computer they had on the 81.

Is there something I can look at or check for to be sure before I order parts ?

 

[page62]

You have HEI.

 

[Dave L.]

cmegga - how can you use the stock distributor on an 81 corvette and not utilize the computer? They work hand in hand. Are you using the stock carb also without the computer? I am surprised the car will even run. Enlighten me please...

Thanks.....Dave

 

[cmegga]

I have stock distributor, no computer hooked up.

The carb is a Edelbrock performer, with performer intake manofold and MSD 6A ignition. From there Im not sure how exactly my mechanic put her togher.

I had a whole engine rebuild with new pistons, cam , RPM heads. He tought the computer would hold it back, restrict the fuel, airflow, etc. so we lost it in the rebuild.

Was this the right move ?? Should I look at replacing the whole distrbutor , upposed to just the cap and toon up kit ??

 

[mvftw]

HEI = No Points

 

[Dave L.]

cmegga - I can go along with the carb and intake. I'd really like to know how you are going to set the timing and control the advance without the computer. I would think you are going to need a pre '81 distr. with vacum advance to make your set-up work properly.

Dave

 

[cmegga]

Burglar


your hitting the nail on the head here. Thats exactly what he did now that I recall , he did swap it to an older style dist. Sorry I had lost tract with all the work done.

Would that still be an HEI set up ??

 

[Dave L.]

yes HEI

 

[Jack]

Burglar


your hitting the nail on the head here. Thats exactly what he did now that I recall , he did swap it to an older style dist. Sorry I had lost tract with all the work done.

Would that still be an HEI set up ??

If you have a large distributor cap that contains (or once contained) the ignition coil ... then you have HEI. If I'm not mistaken the later HEI (like 81) are same as earlier ones ... EXCEPT ... they do not have a vacuum advance (the 'puter replaced the vac advance) ... but I recall they retained the mechanical (centrifugal) advance. An MSD 6 box can be used with any HEI ... it simply bypasses that ignition module inside distributor. Thus the hei's pickup still functions as the trigger .... and any advance (mech/vac) remains functional, and rotor & cap still "distributes" the spark.

I have a "conventional/earlier" ( not 81/82) GM HEI triggering MSD 6 box ... module is bypassed ... it has both vac & mech advance. You do not have to have a MSD distributor ... nor a points dist ... to use a MSD 6 box ... it works with HEI ... just bypass or eliminate HEI's on-board ignition module. A "gutted" HEI retaining both vac & mech advance is a fine distributor to use w/ MSD 6 ... if that's what you have then I wouldn't change a thing but tune up (cap & rotor).

BTW, configuration is similar if using Crane Hi6 box & HEI.
JACK:gap

 

[Dave L.]

Jack - No go. I just rebuilt my dist last week. No weights under the rotor,hence no mechanical advance. It's computer controlled.

Dave

 

[Jack]

Jack - No go. I just rebuilt my dist last week. No weights under the rotor,hence no mechanical advance. It's computer controlled.

Dave

Hmmm ... a buddy's 81 had no vac but did have mech. Does yours have ignition coil in top of dist cap ... does yours have no vac advance also?
JACK:gap

 

[Dave L.]

Jack - It has the coil in the cap like any regular HEI and no vacum advance. I pulled my 1981 shop manual and it states.....
"The EST (electronic spark timing) distributor has neither a centrifugal nor a vacum advance,since advance information is sent out by the ECM."

Dave

 

[cmegga]

If its any help.
Guys if this help, this is what Im looking at.

This obvisuly is not mine, but a pic I pulled off Jegs. Same style cap, same vacume thing on the side with a hose coming out of it.

 

[rpounds]

The HEI on Corvettes started in 1975. Your '81 is HEI.

Ron

 

[Jack]

If its any help.
Guys if this help, this is what Im looking at.

This obvisuly is not mine, but a pic I pulled off Jegs. Same style cap, same vacume thing on the side with a hose coming out of it.

That jegs pic is not a GM HEI ... it may be for a ford.
http://store.summitracing.com/global/images/prod/large/acc-8122.jpg
above is link to GM HEI cap & rotor pic
http://store.summitracing.com/global/images/prod/large/acc-9107.jpg
above is link to GM HEI distributor pic having both mech & vac advance
http://store.summitracing.com/global/images/prod/large/sum-850001r.jpg
above is link also to HEI distributor pic having both mech & vac advance

If your cap & rotor does not look like above ... you do not have GM HEI.

If your distributor looks quite similar to the one in the jegs pic ... it may be an Accel distributor ... some of the Accel distributors for chevy used Ford Caps ... some used Chrysler caps. Suggest you closely inspect distributor for ID/PN stampings-tags. With those numbers/some good pics of yours ... I can help identify it.
JACK:gap

 

[cmegga]

Jack

Ill take a pic this weekend. The distributor is almost exact to the pics you posted, but no coil in the middle. It has a Plug connection dead in the center of the cap.


Thanks guys for all you help so far.

 

[Jack]

Jack Ill take a pic this weekend. The distributor is almost exact to the pics you posted, but no coil in the middle. It has a Plug connection dead in the center of the cap. Thanks guys for all you help so far.

Yours may be an HEI that has aftermarket remote-coil conversion coil-cover on distributor cap ... mine does ... enables use of firewall-mounted coil with big-cap HEI ... 9 terminals instead of big-caps' normal 8. Coil-cover is a square cover about 3 1/2"x3 1/2" mounted to center of cap with two small screws .... OE-type HEI coil-cover has no terminal ... if remote-coil conversion that cover will have one terminal. GM also made a much later version of HEI that has a smaller cap and no coil in cap ... 9 terminals ... AFAIK, those did not come with a vacuum advance can. Post a pic.
JACK:gap

 

[page62]

Not HEI. You can tell if it has a coil wire going to the centre of the cap.