Stock Distrib. vs. HEI Distributor

[Macgyver]

After all the adjustments made to the carb Im figuring that I would need to adjust the timing. Ill let you know now that I know jack about the distributor except the concept of it. Here are my questions.

What is the stock distributor that comes on a 81'? Is a good one or should I replace it? If its good what can I do to improve it? Can you use a recurve kit on it?

Whats the difference between the stock distributor and an HEI distributor? Is there much to be gained by using this modification since they do seem to be somewhat expensive?

I was getting Feet/Gallon and after the carb rebuild Im now getting about 10miles pergallon. Will these changes maybe bump that up about 3-4MPG?

One last question, wheres the computer diagnostic hook up?

Thanks in advance for your imput.

Steve'O

 

[MaineShark]

Whats the difference between the stock distributor and an HEI distributor? Is there much to be gained by using this modification since they do seem to be somewhat expensive?

Your stock distributor is an HEI distributor.

Joe

 

[aerie1761]

Distrubutor

Your stock Dist. Is an HEI dist. controlled by the computer for timing. Its a good dist. if you want the computer to conrol it . I removed mine and put in one for a 1980 vette. with mechanical advance what a big difference. Your diagnostic plug is located in the center console.

 

[Macgyver]

Thanks. Someone told me it was HEI but I wanted to make sure. Is it one w/ a vacuum advance right?

Advancing the timing so that it fires earlier in the combustion cycle is done w/ a timing gun right? Its just a matter of turning it left and right am I right? How difficult is this?

And the diagnostic plug, is it at the bottom w/ all the stereo and electircal wires?

 

[gooney0]

Yes adjusting the timing is just a matter of turning the distributor. The timing light is for mesauring the timing. (which is good to know of course )

-Gööney0

 

[Macgyver]

Thanks a lot I appreciate it.

Steve'O

 

[aerie1761]

macgyver

The diagnostic plug is in the center console. If you plan on doing a lot of troubleshooting on your 81 vette I would invest in a shop manaul. There is a weath of info in there especially on the electrical side. Jim

 

[Jack]

Someone told me it was HEI but I wanted to make sure. Is it one w/ a vacuum advance right

If I recall ... the 81 HEI does not have vacuum advance. That's probably why aerie1761 swapped in an HEI from a 80 model. To optimize performance, tunability, mileage ... You want & need both vacuum and mechanical (centrifugal) advances for the typical street performance sbc/BBC carburated motor. Large cap HEI with both advances & 4-pin module is desired distributor ... they were used on many different models & years of chevy cars & trucks ... same distributor is currently supplied with GMPP crate motors (those that come with distributor). I have a brand new one I'll sell ... email me if interested.
JACK:gap

 

[aerie1761]

Jack

The 1981 vette was the first year of computer control. Not only did it control the carb but also timing.The HEI dist. on the 81 vette not only had vacuum advance but also centrifigal advance.The magnetic pick up was controlled by vacuum advance while the timer core provided centrifigal advance. I chose to change to a 1980 HEI because it was not computer controlled and I can set the timing for better performance.My engine performs much better.I still have a large cap HEI only its not computer controlled.The four pin plug was for the computer connection to the electronic module in the dist.

 

[81 VetteMan]

Jack,

I think you are correct, the 81 HEI does not have vacuum advance. (At least mine didn't)

Now Aeriel1761,

Hit it on the Nail, but I think he mis-stated it to have vacuum advance.

My warning ,remember that if you switch the distributor to the non computer controlled unit, I think it will upset the fuel mixture since the computer is still controlling the Fuel Mixture. . (Can someone confirm my thought process on this.)

I am currently switching out the Carb on mine,to take the computer out of the picture all together. I have already switched out the distributor.

 

[aerie1761]

vetteman

Again I would invest in a shop manaul. It clearly states that the correct dist. for an 81 vette has both vacuum advance as well as centrifgal advance and I can tell you it does because I replaced it. If yours doesnt maybe someone changed the dist. Now you are correct about the carb . Neither my carb or dist. is computer controlled.If you look at the electrical section in the shop manaul it has nice pics of the dist. and tells you exactly how it works.

 

[Macgyver]

Thanks for all the information here.

Ive been looking for the shop manual but on amazon.com all I get is the one for C-3s, like 67-82 Corvettes. Theres one for an 81 specifically right? Can you point me in the right direction to obtain one of theses.

Hopefully Ill get the timing set and get an advanced curve kit and set it all up w/ my guy tomorrow.

 

[aerie1761]

macgyver

There is three 81 shop manauls for auction on ebay right now.Or any of the corvette supply houses ecklers, mid america etc will have them but you can get a better deal on ebay.Just punch in 1981 corvette in the search box and it will take you to all the 81 stuff.