Hey guys I am in the middle of my 460 build and need to know what the ideal timing BTDC I should be shooting for. I know the vacuum advance bumps it up, but what should I initially set it at? 9.5:1 compression and 89 octane if that helps.

 

Is this a fresh build that has yet to be broken in?I run my freshly built 466 @ 12 deg initial and about 14 inches of vacuum.I broke it in with 10 degrees.With almost 11.1 compression,12 deg allows me to start the engine without the dreaded hot start problem.I also run 40 % 100 octane LL av-gas with 91 pump fuel to keep detonation away.I'd say you should be fine to start @ about 8-10 degrees and tune it from there.

 

I usually try for 12-14 to avoid the low timing over-heating problem.

 

yes, its a completely fresh build, a 466. I think the cam said it has 2 or 3 degrees built into it, so how do I get the additional 7 or 8 degrees to get there? should I change the timing at the timing chain, or use the distributor to do this?

 

Distributor. Best bet is to have the distributor's advance curve adjusted for your engine specifics. Then all you need to set is the base timing. Never seen an engine that didn't benefit from this. Nor one that was right to start with.

 

Dont confuse spark timing with valve timing. Cam specs would be in regards to valve timing.

 

So install the timing chain "straight up" meaning no advance at the timing chain? How should I go about installing the distributor? How many degrees of timing = one tooth on the cam gear that drives the distributor? Just count the number of teeth and divide by 360?

 

Propper way to set up cam timing is with degree wheel. Straight up is simple and will get the job done. Spark timing is set with timing light and cannot be "guessed". With piston #1 at TDC on compression stroke, drop dist in so rotor is pointing to fire #1. That will get you started and then use the light to get it tuned in

 

Ignition timing only determines when the coil fires in relation to the crankshaft.
The distributor may be driven off the camshaft but valve timing doesn't determine ignition timing.

You will be adjusting the distributor in relation the the marks on the crankshaft harmonic damper.
Find Top Dead Center on the compression stroke of the #1 cylinder (front of the passenger side) and seat the dizzy so the rotor is pointing at the #1 marked on the cap.
This is at about 1:00, as you are viewing it from the front of the truck.

Here is where it gets tricky on a fresh build.
You need to fire the engine and immediately hold it at 2000-2500 rpms for 20 minutes (or whatever your cam maker suggests)
You can, and may have to, change your ignition timing while breaking in your cam to avoid over heating the engine.

As for the regular adjustment procedure;

Highlight the mark on the damper that you want to use (8, 10, 12, 14... BTDC)
Disconnect and plug the vacuum advance from the distributor. (or unplug the SPOUT)
Set the curb idle speed and then adjust the ignition timing by rotating the distributor until the mark you chose lines up with the pointer as observed with the timing light.
Tighten the distributor hold down and reconnect the vacuum advance.
Reset the curb idle speed and test drive it to listen for knock under part and full throttle acceleration.

 

Ok, thanks guys. It makes perfect sense now.