81 HEI distributor

[Macgyver]

Hey all you 81 owners, i had a question about the OEM distributor. The one that I have has a 4pin female wiring harness that comes from the base that I htink plugs into the computer. Since i ditched all the computer stuff i had to unplug that harness in order for the distributor to fire. im wondering if im going to need a new one in order for her to run like a cherry. Is this the same type of wiring harness that is OEM or is this an aftermarket one? I thouhgt I had heard somewhere alongthe way that the 81 computer controlled distrib had a 7 pin connection.

 

[Jack]

I replied in detail to your PM. Suggest both reread thread below and to trust description by stingray6974 (mike).

http://www.corvetteactioncenter.com/forums/showthread.php?t=45997

 

[GerryLP]

Macgyver,

You seem to be talking about the inline-4 pin connector labeled A,B,C, and D. This is the connector that connects to the computer, and I guess it does make sense that it would not function if you have the computer disconnected.

The module inside the distributor should be a 7-pin type module. As far as how good its going to run I would say "not as good as it could".

What happens is that the advance timing was handled by the computer, and therefore, while missing the computer and having no mechanical advance it then won't have any predetermined advance timing. The initial timing its the only thing keeping it going (so to speak).

A non-computer distributor (usually a 4-pin type module inside) will serve well in this capacity. It contains the mechanical weights that will force an advance timing predetermined by the type of springs used.

By the way, as long as you are planning modifications, an MSD multispark unit will require the removal of the 4-pin type module inside the distributor and use a combination of pick-up harness and harness extension. The MSD box handles the switching that the module usually performs.

 

[Macgyver]

Well then I guess I need a new distributor. Son of *****.

So then what type of distrib do I need? Im guessing I need an HEI w/ vacuum advance.

Does the 81 have an electric tachometer? What type of distrib would I need to look for then? I really want to get it locally because I need to have someone to look at to be held accountable for refunds and that sort of thing. Dealing w/ SUmmit took too much patience and I cant wait on the mail anymore. Could I just rebuild mine and get a vacuum canister to add on for the advance.

 

[Macgyver]

Wait do I need a new ignition that is separate from the ECM as well or is a new one comping to come w/ a new distributor? Or should I get an MSD 6AL ignition box? I was under the impression that that would be over kill for something making less than 250 HP.

 

[bossvette]

If you are not using the computer any early HEI from a Chevy V-8 would work try your local boneyard Does your 81 have a large cap distributor with a red 10 gage wire and a smaller brown wire going to the coil? If so you have all the connections needed to make an early Hei work, the red 10 gage is the ign feed and the small brown is the tach signal. You will not need the computer connections.

 

[Jack]

If you know what you're looking at, the local junkyard is top choice for an early HEI ... expect to pay $30-$60. Aside from a yard, there's a local source nearly everywhere. Run on down to your local GM dealer's parts dept ... they can order you a brand new complete early-style 4-pin-module HEI GM P/N 1104067 ... expect to pay about $300.

Even if you could add a vac can to a 7-pin HEI ... you'd still have a 7-pin module that needs connection to a computer/ECM ... and you still wouldn't have a mechanical advance.

No, you don't need MSD or other ignition to work with early HEI ... but a box can be added per GerryLP's post. The early HEI is self-contained and needs only a power supply wire and, if electronic tach is used, a signal wire to tach.

The 81 has an electronic (aka electric) tach.
JACK:gap

 

[GerryLP]

.... Could I just rebuild mine and get a vacuum canister to add on for the advance.

The short answer is "no". The vacume cannister is for the momentary added ignition timing at part throttle (one camp of CAC members believe that its sensed by manifold pressure and the other camp believe that its sensed by the pressure drop across the throttle plates, but lets not quable over who's right, please ).

Even if you could add the cannister to the L81 distributor, the lack of mechanical weights would prevent the engine from functioning like it should on a daily driver. (Some drag race cars don't bother with it, because they run short periods of time at wide-open-throttle (WOT). These cars usually only need the initial timing all in. Next time at the track listen for the cars with a relatively high idle setting).

Your local speed shop should have available the stock Accel Distributor or probably the MSD distributor (more $$$ for this one), or like Bosvette says, get one from the junk yard. A 1979 or 1980 Federal model GM car should have the one that you need.

Then, just upgrade the distributor with a Mr Gasket or Moroso timing advance kit.

Does the 81 have an electric tachometer?

Yes! But the tach signal is taken from the distributor rotor cap.

should I get an MSD 6AL ignition box?

No! You don't need to. The distributor that you'll need comes with the 4-pin module inside. This module does all the switching for the functioning of the coil. The MSD6AL box could be later an improvement if you want a more smooth idle and a little help on gas milage. I recommend that you get the car going with the new distributor (or used) and then later consider additional upgrades (like a high performance module).

 

[Macgyver]

Man o man! Yall got nothing but answers. Gerry and Jack to the rescue again. Thank you very much.

 

[JapanL81]

Ok, so i know this is an old topic but I got lost in the message traffic, heres my question and setup.

Stock ECM
Holly 600
Stock Distributor( with the Wires coming from the back)
EGR Valve Blocked
Cruise control Gone.
Heater core bypassed


Most of my plugs under the hood are disconnected.

Since i replaced my Quadrajet with the holly and the Holly1460 is electric choke, will the stock distributor work still or do i have to replace the distributor so i can make adjustments for timing since the timing is adjusted by the ECM but its not attached to my Carb anymore.

I don't have a local Junkyard that has anything GM in it so finding a junk yard dis. is not an option if you guys have an aftermarket one i can pick up online or if the stock one will work.

 

[bill81vette]

Have you tried to start your vette??? I don't see why it shouldn't work.... it is still hooked up to the ECM,Yes???

 

[dougelam]

Ok, so i know this is an old topic but I got lost in the message traffic, heres my question and setup.

Stock ECM
Holly 600
Stock Distributor( with the Wires coming from the back)
EGR Valve Blocked
Cruise control Gone.
Heater core bypassed


Most of my plugs under the hood are disconnected.

Since i replaced my Quadrajet with the holly and the Holly1460 is electric choke, will the stock distributor work still or do i have to replace the distributor so i can make adjustments for timing since the timing is adjusted by the ECM but its not attached to my Carb anymore.

I don't have a local Junkyard that has anything GM in it so finding a junk yard dis. is not an option if you guys have an aftermarket one i can pick up online or if the stock one will work.

Run yes, good not so fast.
with out the TPS input you lose the proper timing like when you go to full throttle. It does not know you requested full power it just sees the pressure rise in the intake plenum and attempts to add fuel which you disabled. You put your ECM in limp mode and power timing is not in that program

 

[JapanL81]

I know the ECM has a "safe Mode" as you discribed as a Limp Mode i haven't started the car yet as I'm waiting for the carb adapter to fit the holly to my stock Intake. So my next question is if i replace my distributor which one should i do with and what modifications are nessary?

Oh and my brake pedal switch is on the fritz but i can't find the part anywhere online does anyone have suggestions?

And yes the distributor is still hooked up to the ECM but every other connector to the block has been either cut modified burnt to the block or some how destroyed( from the previous owner)
Im basically trying to fix the last guys terrible hack job and mistakes

Thanks,
Nate

 

[Antz81]

I know the ECM has a "safe Mode" as you discribed as a Limp Mode i haven't started the car yet as I'm waiting for the carb adapter to fit the holly to my stock Intake. So my next question is if i replace my distributor which one should i do with and what modifications are nessary?

If you do need to replace it just go back to a HEI with vacuum advance. As far as i know all you should have to do is get vacuum to it.
Although i did think that the ECM got its info for the timing from the distributor reference pulse, but the TPS may also effect it.
The ECM will also contol the torque converter lockup so don't pull it out if you do change the distributor.

Oh and my brake pedal switch is on the fritz but i can't find the part anywhere online does anyone have suggestions?

Lectric limited have them.

 

[JapanL81]

If you do need to replace it just go back to a HEI with vacuum advance. As far as i know all you should have to do is get vacuum to it.
Although i did think that the ECM got its info for the timing from the distributor reference pulse, but the TPS may also effect it.
The ECM will also contol the torque converter lockup so don't pull it out if you do change the distributor.

Lectric limited have them.

Yea i planned on keeping the lockup controller on as the B&M controller is almost 200$ if i can keep the stock one it will save me some cash.

Just to get this straight.
- When i get my new distributor after i put it in i need to run a vacuum line from the carb to the Dizzy( thats the easy part)
- Where should i draw power? from the original power from the 7 pin plug from the back of the stock Dizzy?
- is the lock up convertor attached to the dizzy anywhere i don't want to accidentally take it when i replace the dizzy.
-from what i understand the HEI has 1 wire and a vacuum port so i should only have to run a power and the vacuum i just want to make sure i draw power from the right spot.

 

[Antz81]

Yea i planned on keeping the lockup controller on as the B&M controller is almost 200$ if i can keep the stock one it will save me some cash.

Just to get this straight.
- When i get my new distributor after i put it in i need to run a vacuum line from the carb to the Dizzy( thats the easy part)
- Where should i draw power? from the original power from the 7 pin plug from the back of the stock Dizzy?
- is the lock up convertor attached to the dizzy anywhere i don't want to accidentally take it when i replace the dizzy.
-from what i understand the HEI has 1 wire and a vacuum port so i should only have to run a power and the vacuum i just want to make sure i draw power from the right spot.

Power comes from the big pink wire. Its on its own single plug so you shouldn't miss it.
You will also have the output to the tach. (smaller white wire)
As far as i'm aware the lockup only runs from the speed sensor so you should be fine there.

 

[dougelam]

Antz81 is correct, the power is the same
as for the TCC control it is fed power all the time and the ECM supply's the ground when commanded. You can switch the solenoid on and off as you like with a switch. I don't believe the computer will function without a tach signal.

 

[JapanL81]

Yea, ill tap into the tach signal from the white wire like you said Antz, I will tackle this project this weekend, i will be designing new headlight assemblies (keeping the stock aside) for Japanese regulations there are a few changes and i might as well just make new assemblies while I'm ripping out the Vacuum lines up there.

This should be all the questions i have for a while i have to leave the car behind for about a month for vacation which is fine by the time i get back my parts should be waiting for me.

Thanks Guys for all info you have given
Nate

 

[dirtypants]

what distributor for 81 but with all smog and computer removed and Edelbrock carb and intake

as in postin title 81, std trans 4 spd..all smog stuff removed incl catalytic, now with Edelbrock Performer series, intake, carb, cam..computer to be disconnected..so what distributor to use..as the stock one was 1. controlled by computer, 2. no idea of advance when no computer, and 3. Lars says the stock OEM types in C3s prior to 81 had poor advance curves anyway..but could be made better with a kit of weights and springs..so i guess could do that with an HEI for late 70s..but why, if/.or..are some now made with the improved mech curve and vac also..ready to run with a modern curve both mech and vac, ....or...do I get a fully electronically adjustable dizzy like the MDS E Curve? will it fit..if so what tips for fitting and setting up.
and...are the distrib to oil pump gears compatible...i have heard that on some..(mustangs for ex) they are not..a drive gear change is needed to not chew up gears and of course then the engine..
anyway..what dizzy to buy and install and any tips for the install and set up..not a race car..not even high mod...but all that stuff is gone/done by prior owner but dizzy never set up to match..
so what next..thanks.
Nick
near spokane wa

 

[Tom Bryant]

Any pre-computor HEI will do the job but you need to remember that these things are pretty old and have other problems. A friend gave me a HEI that I was going to freshen up for a project. It needed a coil and after I checked it thoroughly it also needed new shaft bushings, shims, module, cap, rotor, weight and spring kit to dial it in, and a proper vacuum advance for the engine it was going in. After I priced everything from Summit I ended up just buying a new Mallory HEI, also from Summit. It was cheaper than the parts alone. It's set up for street performance. Just drop it in, set the timing and go.

Tom