Hi All,
I'll keep it short and sweet. What recommendations do you have for ignition timing and or modifications using a '78 Duraspark and the following setup? The intent here is to pull a house....or maybe two!

General
466 cid, balanced
9.5:1 compression

Intake
Stock manifold (will be installing Edelbrock Performer)
D3VE A2A heads- gasket matched, light porting, slightly oversized S/S valves
600cfm Holley 4160 list 80457, 66 main jets, 30cc accelerator pump

Cam ADV
Duration 270 Int 280 Exh
Lift Int .490, Exh .516

Exhaust
Hedman Elite headers, 1 3/4 tubes
2 1/4" from collectors into single 3" Flowmaster
Single 3" tailpipe

Drivetrain
Stock C6
Dana 70 Locker 4.10

Ignition
'78 Duraspark
Mallory canister type coil
Champion spark plugs
Motorsport 8mm plug wires

Did I miss anything?
Thanks in advance for your thoughts!

-FSH

 

I would disconnect the vacuum advance, and plug it off. Then advance the timing a couple of degrees and then take it out for a road test.

Find a good long hill and bear down on it in high gear going up, and try to listen for any pinging. Keep advancing the timing a little bit till it starts to ping, and then back off the timing a little bit. This will be the best setting for power.

Then hook the vacuum advance hose back up. It will probably ping like crazy, so see if it's adjustable(allen wrench up in the hose nipple). Try to turn the vaccum advance down till the pinging goes away.

I personally like advancing the timing without the vacuum can hooked up, which makes the initial timing fairly high. I was running about 14 degrees on a 302 I built. It had great low end take off like this. But I found if I hooked the vacuum advance back up, I had to set it way down to around 2-4 degrees to keep it from pinging. It ran like a dog then, so I set it back up and left the vacuum off. But if you can adjust the vacuum, leave it in if you can. It will help gas mileage.

PS Also make sure if you leave the timing way up, that you test it for starting on a hot day. Get the engine warm, and then shut it off. Let it sit for about a minute, and then try to crank it over. If the starter struggles too much, then turn the timing back a little bit till it cranks the engine over without too much trouble.

 

Excellent, I'll work that angle. At one time I did remove vacuum advanced timing and the ping went away. However, total time dropped from 36-38 or so down to about 25. Poor performance was the result. Also, dropping the initial timing to 4 eliminates ping when vacuum advance is used. That math comes out good...looks like I get about 10 degrees advance....setting at 4 with vacuum puts the timing to 14 or so at idle/low speed and no ping.

On the vacuum diaphram, what direction turn increases/decreases the timing?

Thanks,
FSH

 

Not sure about that. What I would do is hook the timing light up, and move the vacuum line from a ported source to one that has vacuum at idle(manifold vacuum). With the timing light, you should see the timing jump way up when the dist is hooked to a manifold source, and then you should be able to adjust the screw and keep putting the vacuum line back on to see what difference it makes.