And what figures am I looking for? I am going to be setting this with the stock chip, I currently am in the stages of returning my after market chip for a diffrent one, but will be putting it back in soon. My mods are below, do I check it with the wire dissconnceted/ thanks

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86Z28, GM 350, Jet perf Q-jet & chip Dual snorkel air cleaner, Edelbrock performer intake, Edelbrock headers, Edelbrock cat-back, Off road pipe, MSD 6AL, Accel Super Coil, Taylor Spiro-pro wires, Rapid fire plugs, Jet fan switch, World class t-5, Hurst Short Throw Shifter, Ram Flywheel, Center force dual friction clutch,Aluminum drive shaft, BW disc rear 3.45's & a posi, PBR calipers, Earls braided brake lines, Polygrapite bushings all the way around, poly tranny mount & torque arm mount, Hotchkis lower control arms & panhard rod, Rancho limiter straps, KYB struts & shocks, Gm Wonderbar, Edelbrock strut tower brace, SSM sub frame connectors, Jamex lowering springs, Carbon metallic brake pads, Crossed drilled rotors, Mobil 1 Tranny fluid & motor oil, GM syntheic rear end oil, K&N, Grant stering wheel, 1,200 watt system, Jet Black Paint, 91 Z28 rims, 92 wing, Tinted windows.

 

This is all assuming you have the older large cap HEI system. If you have the newer small cap HEI without the coil in the cap then mechanical advance is determined by the computer and the only way to change your total advance is to have a custom chip burned.

Total timing is base timing plus mechanical advace.

Base is what you set the distributor at. Lets say 10 degrees. Mechanical advance is determined by the weights and cams. The springs only determine how quick the advance comes in. Stock ignition systems have a slow advance and usually don't get to full advance until after 4000 rpm. To check it, you need an advance timing light or a balancer that has degree tape or full marks on it. Bring the rpm up and set the advance light to zero. As the rpm keeps climbing, keep resetting the timing mark to zero. When the timing marks stop increasing, your advance light will display how much total advance you have.

Typical car setup is 10 degree base timing and 26 mechanical. This gives 36 degrees total timing. If you increase your base timing to 15 degrees then total timing is now 41. This isn't good. When you increase base timing, you should decrease the mechanical advance by changing the weights and cams.

Vacuum advance is only used in part throttle operation so I won't discuss how it works just to say you don't need to bother with it for now.

The best thing to do is determine how much base timing you can have and still be able to start the car. Then with all the car and engine specs, take the distributor to someone who has a recurve machine. They can accuratly set how much advance is required for your car.

The springs, as I mentioned above, determine how quickly the advance comes in. Heavy springs make a slow advance and light springs are quick. They can be mix and matched to alter the curve. It's best to have all the advance in before 3000 rpm.

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87 IROC-Z SuperPro ET Bracket Race Car
461 naturally aspirated Big Block

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87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

 

I though the computer took car of my advance, I though that was the reason for me dissconecting the 4 wire connector to check the timing? I do have the large cap hei but I don't have a vacunm controled dist, as far as I know there are no weights in the dist. Let me know if I am wrong. thanks

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86Z28, GM 350, Jet perf Q-jet & chip Dual snorkel air cleaner, Edelbrock performer intake, Edelbrock headers, Edelbrock cat-back, Off road pipe, MSD 6AL, Accel Super Coil, Taylor Spiro-pro wires, Rapid fire plugs, Jet fan switch, World class t-5, Hurst Short Throw Shifter, Ram Flywheel, Center force dual friction clutch,Aluminum drive shaft, BW disc rear 3.45's & a posi, PBR calipers, Earls braided brake lines, Polygrapite bushings all the way around, poly tranny mount & torque arm mount, Hotchkis lower control arms & panhard rod, Rancho limiter straps, KYB struts & shocks, Gm Wonderbar, Edelbrock strut tower brace, SSM sub frame connectors, Jamex lowering springs, Carbon metallic brake pads, Crossed drilled rotors, Mobil 1 Tranny fluid & motor oil, GM syntheic rear end oil, K&N, Grant stering wheel, 1,200 watt system, Jet Black Paint, 91 Z28 rims, 92 wing, Tinted windows.

 

BlackZ you're correct, Stephen was telling you how to change/check with the older style HEI.

He mentioned that the advance in our cars is controlled via EPROM.

 

And on the carbed cars there is a 4 wire connector correct? is it the only one near the dist? thanks

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86Z28, GM 350, Jet perf Q-jet & chip Dual snorkel air cleaner, Edelbrock performer intake, Edelbrock headers, Edelbrock cat-back, Off road pipe, MSD 6AL, Accel Super Coil, Taylor Spiro-pro wires, Rapid fire plugs, Jet fan switch, World class t-5, Hurst Short Throw Shifter, Ram Flywheel, Center force dual friction clutch,Aluminum drive shaft, BW disc rear 3.45's & a posi, PBR calipers, Earls braided brake lines, Polygrapite bushings all the way around, poly tranny mount & torque arm mount, Hotchkis lower control arms & panhard rod, Rancho limiter straps, KYB struts & shocks, Gm Wonderbar, Edelbrock strut tower brace, SSM sub frame connectors, Jamex lowering springs, Carbon metallic brake pads, Crossed drilled rotors, Mobil 1 Tranny fluid & motor oil, GM syntheic rear end oil, K&N, Grant stering wheel, 1,200 watt system, Jet Black Paint, 91 Z28 rims, 92 wing, Tinted windows.

 

Let's see if we can work through this. You have a factory CC carb & distributor setup. That means there is a flat four-wire connector coming up from the bottom of the distributor. In order to check the timing, that connector must be disconnected. You can then set the base or initial timing.

The advance is built into the chip, and uses engine speed, throttle position and vacuum to determine how much advance to give the engine. This can only happen when the four-wire connector is hooked up. If you try to use a timing light and watch the timing mark when the connector is hooked up, you will see the timing mark jump all over the place, regardless of engine speed. Even if that wasn't the case, trying to check the timing in the garage would be like doing it with the vacuum advance connected on a non-CC engine.

I'm afraid all you can do is set the base timing and trust the chip manufacturer for the rest. The old tuning rule applies: Set timing, make runs, record results. Adjust timing, make runs, record results. Repeat until the track shuts down. Set timing at the place where the engine ran the best. Hope atmospheric conditions didn't affect tests.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4. 2.93 limited slip. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 w/'87 LB9 block, ZZ3 cam and intake, World 305 heads, Hooker headers & y-pipe, 3" Catco cat & 3" cat-back).
57 Bel Air, my 1st car. 0.030 over 396, 9.7 CR forged TRWs, Weiand Action+, Edelbrock 1901 Q-Jet, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlock header mufflers, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, LT MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Best 15.1/95.5 @ 5800' Bandimere.