Total Degrees Advance for CCC '81 Distributor
Thread Starter
Race Director
Joined: Jul 2004
Posts: 12,710
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From: Scottsdale Arizona
Total Degrees Advance for CCC '81 Distributor
Last question of the day for me. I did some fiddling and wrencing yesterday. As posted elsewhere, I've got an odd combination of symptoms, none of which are too severe, but i want them to go away. I'm fairly sure that timing is the culprit, but since my initial timing appears to be about 85 degrees of advance, I think that my balancer may have slipped just a little 
Having said that, 85 degrees of initial timing would probably account for a slightly rough idle.
My question is, what is the total advance of the computer controlled distributor? Also, what parameters are needed to get full advance? I know that the computer has sensors for manifold pressure and rpm, but I can't think of how else I'd simulate a load on the engine.
I presume that for best performance, I still want 36 dgrees of total advance, but since I'm not sure how much is total and how to convince the car to advance, am I reduced to doing it by ear with detonation? There must be a better way.
Having said that, 85 degrees of initial timing would probably account for a slightly rough idle.
My question is, what is the total advance of the computer controlled distributor? Also, what parameters are needed to get full advance? I know that the computer has sensors for manifold pressure and rpm, but I can't think of how else I'd simulate a load on the engine.
I presume that for best performance, I still want 36 dgrees of total advance, but since I'm not sure how much is total and how to convince the car to advance, am I reduced to doing it by ear with detonation? There must be a better way.
Thread Starter
Race Director
Joined: Jul 2004
Posts: 12,710
Likes: 329
From: Scottsdale Arizona
OK. Maybe an easier question to start. What kind of contorsionist tool is required to loosen and tighten the distributor hold down nut. I can't believe how awkward it was to get at.
Safety Car
Joined: Dec 2004
Posts: 4,071
Likes: 0
From: San Diego CA
LoL!! You need a distributor wrench from Kragen. It's about $9 and it's just a weird shaped wrench. Sort of S shaped I think.
What's funny is I just got one of those yesterday, along with a timing light.
What's funny is I just got one of those yesterday, along with a timing light.
Safety Car
Joined: Jul 2001
Posts: 3,921
Likes: 2
From: York PA
I was always able to get a normal open ended box wrench on mine , 9/16". To set the timing you need to unplug the 4 wire plug coming out of the distributor and set timing to 6 degrees. You can advance this to about 10 degrees and it will run a little better. Then reconnect the connector. Don't plug/unplug the distributor connect with the ignition on it freaks the computer out 
. With the ditributor plugged in I remember seeing the advance close to 20 and it's capable of getting near 40. You should really replace the balancer, if it it slipping it might soon come apart. Also your timing being off could explain it running rough.
. With the ditributor plugged in I remember seeing the advance close to 20 and it's capable of getting near 40. You should really replace the balancer, if it it slipping it might soon come apart. Also your timing being off could explain it running rough.
Melting Slicks
Joined: Jul 2002
Posts: 3,000
Likes: 22
From: Boulder Creek California
With a normal wrench you just need patience, or you may need to remove some shielding for clearance.
6*, 12*? Unless you are doing an ultra-NCRS restoration, there's no reason to time it to factory smog-spec. You should be able to set it by ear, listen for the best quality idle not necessarily the fastest. If you are not comfortable doing that, get a Top dead center Finder and re-mark your balancer. ...or replace it.
-Chris
6*, 12*? Unless you are doing an ultra-NCRS restoration, there's no reason to time it to factory smog-spec. You should be able to set it by ear, listen for the best quality idle not necessarily the fastest. If you are not comfortable doing that, get a Top dead center Finder and re-mark your balancer. ...or replace it.
-Chris
Safety Car
Joined: May 2001
Posts: 3,758
Likes: 3
From: Surrey
As Stickboy said. Stock is 6BTDC (with that connector unplugged). I've advanced mine to 11BTDC & it's vastly improved low end throttle response & there's no pinging. Apparently you can safely go to 13BTDC.
A spanner (wrench) for the dist hold down can be simply made out of a normal open ended one, a large vise (securely bolted down) & a large hammer. I like making service tools this way
A spanner (wrench) for the dist hold down can be simply made out of a normal open ended one, a large vise (securely bolted down) & a large hammer. I like making service tools this way
Instructor
Joined: Jun 2000
Posts: 128
Likes: 0
From: Friendswood Texas
Not trying to hijack the thread but have some questions.
We know now how to set the initial timimg (unplugged) conector.
With the connector plugged back to the dist. I imagine that with a timing light with an advance feature you could determine the maximum timing advance at any RPM. Do we know what it would be? Is this information available for different years?
My question too is what effects a change in timing on a CCC equiped car? Is it just a predefined curve programmed on the chip?
Thanks
Robby
We know now how to set the initial timimg (unplugged) conector.
With the connector plugged back to the dist. I imagine that with a timing light with an advance feature you could determine the maximum timing advance at any RPM. Do we know what it would be? Is this information available for different years?
My question too is what effects a change in timing on a CCC equiped car? Is it just a predefined curve programmed on the chip?
Thanks
Robby
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Thread Starter
Race Director
Joined: Jul 2004
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From: Scottsdale Arizona
Originally Posted by Robby79
Not trying to hijack the thread
Thanks
Robby
Thanks
Robby
Permission granted!
You have more clearly restated my original question. UK Paul and I have discussed this on a previous thread and I'm not sure that anyone has ever chimed in with the answer. What parameters affect the curve? How much advance and when does it come in? If you change the initial, what happens to the advance curve? Is it fixed or "sliding?"
Excellent questions.
That damn computerized HEI thing is annoying as hell.
Melting Slicks
Joined: Jul 2002
Posts: 3,000
Likes: 22
From: Boulder Creek California
Kalway, I agree, one less thing likely to fail. The electronic part replaces vacuum advance doesn't it?
If so, should be:
As low RPM as possible without pinging (target 2000 or 2500): 34-36 BTDC Achieved with a recurve kit from your favorite autoparts store. (in the shiny chrome section usually)
With vacuum (or elec) plugged in it should add ~18 max. No more than 54 total (electrical adds on top of 36 at highway cruise) or you will get "chugging" at cruise. You can check this value at idle too, if you have 15* at unplugged, plug it in, remeasure timing, and figure the difference.
At idle: suprise suprise, this is the least important one! Really it will be determined by getting 34-36 at higher rpm. 20ish is not abnormal.
So lars, did I forget anything?
Chris
If so, should be:
As low RPM as possible without pinging (target 2000 or 2500): 34-36 BTDC Achieved with a recurve kit from your favorite autoparts store. (in the shiny chrome section usually)
With vacuum (or elec) plugged in it should add ~18 max. No more than 54 total (electrical adds on top of 36 at highway cruise) or you will get "chugging" at cruise. You can check this value at idle too, if you have 15* at unplugged, plug it in, remeasure timing, and figure the difference.
At idle: suprise suprise, this is the least important one! Really it will be determined by getting 34-36 at higher rpm. 20ish is not abnormal.
So lars, did I forget anything?
Chris
Safety Car
Joined: Jul 2001
Posts: 3,921
Likes: 2
From: York PA
Originally Posted by tersian
No one has decoded the chip thus far. I am waiting for Paul to do it, he's the hardware guy! He's a PROM reader 
I think the system is a good setup, but without being able to tune it, you can't mod the car. I even spoke with a developer at GM and there is no information about it out there. My guess is because this is a one year only thing. The setup was used on some other GM cars, but not in '81. If you are really interested I believe it was super chip that said they could do a custom chip, but it was something like $300 each time. I finally gave up looking about 2 years ago and went EFIAs for the total timing, it's based on input from the TPS, MAP and also engine speed.
Safety Car
Joined: May 2001
Posts: 3,758
Likes: 3
From: Surrey
Originally Posted by Robby79
With the connector plugged back to the dist. I imagine that with a timing light with an advance feature you could determine the maximum timing advance at any RPM. Do we know what it would be? Is this information available for different years?
What I've found out is that it's as Stickboy said. It looks like a 3D graph & various inputs determine the advance at any given moment. People call it a primitive system, but look at it this way: at least the timing isn't programmed to full advance all the time & it's dependant on the anti knock sensor telling the ECM to retard it, as done in certain "performance" PROMs for much later cars.
When I do get time to look at it I'll have a bit of a head start as I have both the stock PROM & an aftermarket one, so a file compare will hopefully put me in the right area for the timing curve. Well, that's the plan......
There's just not enough hours in the day (at the moment I'm looking like the guy in Tersian's avatar
).
