I know I've been posting a lot lately with all sorts of questions, but I'm learning as much as possible. Currently running an. 1981 c3 original motor with some mods :

Bored.. 30 over
Keith black flat top pistons
Blue Racer Crane Cam WG-1173
• .050 Duration: 224° Intake; 234° Exhaust
• Advertised Duration: 298° Intake; 304° Exhaust
• Cam Lift: .290 Intake; .300 Exhaust
• Valve Lift: .465 Intake; .488 Exhaust
• Lobe Center: 107° Intake; 117° Exhaust
Polished and ported original heads
Super comp full length headers
2 1/2 exhaust
Flowmaster delta 40's
New dizzy, wires, plugs
Rebuilt & modified quadrajet E4ME
Currently have the timing at 12*

With the cam and additional stuff on here can I increase the timing for any more performance? Anyone have something similar that has advanced the timing to maybe 14 or 16?

slowly getting this thing running like I feel it should. Yesterday adjusted the spring fire the secondaries opening rate, maybe tonight I can warm it up and get the dwell dialed in... So close

 

Here is a good article on timing.

http://forums.corvetteforum.com/c3-t...long-post.html

Scott

 

You'll have to use the butt dyno and a good ear
Keep bumping the timing up until it pings under a light load and then back off until it stops. Keep a record of your changes, air temp, engine temp and gas used.

 

Advance your initial timing some but limit your total to 36*. Do you have a curve kit in the distributor?

 

No recurve that I'm aware of. It's an 81 so to my limited knowledge timing is advanced by the computer

 

I read the article as well as all the papers mentioned in it. Each paper deals with vacuum advanced dizzys. Would the same hold true for my 1981 dizzy? Is computer controlled so I'm wondering if the setup would be the same. After reading this article I believe this would be the correct way to set it up :
1) disconnect my 4 wire adapter from the dizzy
2) using a tape, measure the balancer, then mark my balance at 36* clockwise from the timing mark already engraved on the surface. This would give me my 36* total timing mark
3) set my initial timing (currently 12*)
4) get engine revving to 2500-3000 ram or until the timing mark no longer advances. This would be the limit of centrifugal advance.
5) adjust dizzy until the 36* mask lines up with the "0" on the timing mark indicator. When at the limit of centrifugal advance.
(this would put me at 36* total timing, all in
6) verify timing is at factory spec (or my 12* as set now) when the engine is at idle
7) reattach the wire for the dizzy, test drive and listen for pinging. Any pinging, reduce timing by 2* until is gone
8)verify idle and dwell and call it a day?

I guess I'm asking if the computer controlled dizzy will handle the 36* total timing when all in without damaging the engine?

 

I'm not for sure on the 81 but when you take the cap and rotor off are their springs and weights?

 

Email Lars @ V8fastcars@msn.com Ask him about your 81. He will fix you up. I'm not sure on that one.

 

I know how to set timing and advance curve on a non-computer controlled distributor, but I know nothing about the computer controlled ones. Could someone clue us all in on just exactly what the computer controls? Does the computer just replace the vacuum canister? Is there a knock sensor that retards timing when detonation is sensed? Is the conventional mechanical advance still in place? Is there a chip available that will alter how the computer controls timing, for better performance? That sort of thing.

Scott

 

I don't believe there is a knock sensor. I know the computer controls the advance but I'm not sure how much etc. From my reading it simply operates on a predetermined curve. There is a chip from hypertech that alters the curve but I haven't gotten it. I just want to be sure that if I dial in 36* total timing with the dizzy unplugged the computer won't advance it so far that I cause damage. I guess I could start at 36* and retard as needed if there's pinging. sure would be nice to be able to dial in 36 though. I doing it tomorrow before work and I'll update then. I'm still pen for input if anyone has experience with setting these ccc dizzys

 

So this morning I measured the harmonic balancer so I could mark the 36* mark and set y timing so that I would be at 36* and "all in around 2500-3000 rpm. So I unplugged the 4 pin, plugged in my tach so I could read it while making adjustments and hooked up the timing light. I had turn the dizzy a tad to get it to 36* as I already had base timing set somewhere in the neighborhood of 12-14*. Well I get it set at 36* all in, plug in the dizzy and checked the timing. My 36* mark is damn near at te "0" on the timing indicator with the 4 plug reconnected!!! How is that possible?!? I ran it down the road and I can't hear any pinging or anything like that? Am I missing something here? I posted a short video of a little run with it so I could try to gauge how it's performing.

 

I also made a short video so you can see what I'm trying to figure out with the timing. I unplugged the 4 pin connector from the dizzy and made a mark on the harmonic balancer showing 36*. I then started the car (it was already warm) and proceeded to rev it to about 2500-3000 RPM as shown on the tach I plugged in. Once I did this I advanced the timing so the 36* would hit the "0" mark around 2500-3000 rpm. Locked the dizzy back down, turned off the car, reconnected the 4 pin and started again. Now when I checked the timing the 36* mark was nearly at "0" at idle?!? Any advice here? I posted a video showing the run I made afterwards, here's the video of what I am seeing when I checked the timing after advancing it to 36*...

 

Please note that none of the info in my timing articles is applicable to the ECM-controlled carbs built 1981 and newer. You cannot use the articles as written. Timing curve alterations to your car can only be accomplished using a re-burned chip for the ECM.

Lars

 

What your seeing is the computer is working in place of a vacuum advance. You have 3 timing systems. Initial, mechanical, vacuum (or in your case computer). What your seeing at idle dist plugged in is initial plus vacuum (computer). The three combined should not be over 53-54. In a conventional dist at idle you have initial plus vacuum at idle. Accelerate and vacuum drops off and mechanical climbs in as RPM increases. At 3000 RPM light throttle cruise you have initial plus full vac advance (or computer advance) plus all in mechanical. Should not exceed 53-54 combined. Check your initial with computer advance unplugged at idle. Subtract initial from your 36 all in (initial plus mechanical) number. This gives you the full mechanical advance number. Then subtract the initial from the number you read at idle with the computer plugged in. This gives you the computer full advance number. Add initial (read at idle unplugged dist) plus mechanical (calculated above) plus computer advance (calculated above) together. This number should not exceed 53-54 for all three. Do this and report back.
I hope this explanation is clear. I do not have a lot of experience with computer controlled timing but I do know timing curves and advance theory. If you are above 54 one or more of the three timing circuits needs limiting or adjustment.

EDIT:As Lars said when I was slowly typing with no vacuum can the vac or computer adjustment would be with a chip. You can adjust mech advance speed, not amount, with lighter springs to get "all in" @ 2500-3000.

 

Street racers technique,
Ping minus 2 degrees should get it real close to where you need to be.
Use the fuel grade you plan to run regularly.
Advance it distributor till it pings slightly under load back off 2 degrees.
Do not drive in advanced condition too long as ping is pre detonation and no good for engine.
Until you can get it on the right electronic monitor this will work
Marshal

 

Thanks for the response. I'll check everything over lunch. I actually brought my timing light etc to work just in case...
If I recall my initial with dizzy unplugged was 14*, subtracted from all in 36* gives me 22*
Plugged in I was reading 38* +- subtracted the 14* initial reading unplugged gives me 24*.
initial 14 + mechanical 22 + computer 24. Gives me 60. did I do this right? So I need to retard the timing?

 

Thanks Lars. I've read a lot of your stuff on carbs, timing etc. You're knowledge is more than welcome. I had a feeling there wasn't much I could do besides set initial timing on the ccc. So I guess the hypertech chip is next

 

I would go back to the 12 degrees factory OR leave it as is, softer springs to get all in @ 2500-3000 and rechip it to get 54. Do not know how involved it is to limit mechanical on those or adjust computer curve. It is rare to have initial plus full comp advance plus full mech advance but it will happen at a certain point. Stock mech is usually all in @ 4500-5000 so this keeps you under the magic 54 degrees because over that your usually WOT so computer advance backs off. Or, put an HEI in it then you can curve it with no issues.

 

All these measurements go out the window if the hormonic balancer slipped and threw off the timing marks.
The motor has a lot of work done to it and the butt dyno would work best unless you had a real dyno. With your advance being mapped by the ECU you're stuck with that unless you buy the Hypertec chip.
The only other choice is scrap the 81 dizzy and use old school hei.
Keep bumping it up until it cranks hard or pings. Then back off. You can feel it if it's running better or worse. It's that simple.

 

You definitely need to tighten up on the th350 kick down cable or check you throttle linkage. You are up shifting way to early IMO.

I certainly don't hear any pinging so you can go a few more degrees + on the timing