Ignition timing for my non-stock 3.0
 

I'm nearing the end of my rebuild and am starting to gather info on setting my ignition timing with the changes I've made. Some advice would be appreciated! :)

Here's my specs.

- Stock 1983 SC 3.0 distributor, has not been recurved.
- JE 95mm slant-nose style pistons 9.5:1 CR. My actual measured CR is 9.6:1 on the smallest head, a bit less on a couple heads which had a tad larger CC.
- 964 cams by Dougherty timed to as close to 1.26 as I can muster (will know how close I get tomorrow!)
- I'll be using 91 octane non-ethanol gas most the time.
- Stock CIS
- I don't think it matters, but exhaust will be backdated SSI's and 2-1 '74 stock muffler.

I should add that I'd like to err on the conservative side. I want this engine to last a long time and not be prone to detonation, so I'll gladly give up a little extra punch of power for longevity/play it safe.

I'd think total advance should be around 28 before you'll get pinging-knocking-
It may even be a bit less but I'd start there.
A couple degrees less that perfect won't rob you of much.
I have a 3.0 with about the same compression but Euro pistons
not tapered dome and run 25.

not an expert but the only way I know of to set timing (curve) on a modified engine is on a dyno.

you could dyno the engine with the stock dist and figure out max timing then maybe talk to a distributor expert.

Stock timing is generally set at around 4000rpm to 36-38 degs as I recall. I'm able to run 28 degs on my 3.0L - 9.5:1 CR only because I have twin plugs.

Thanks for the info guys.

So, let me just walk through this and see if it makes sense.

I'll set my distributor at idle to 5 deg BTDC. (this is stock setting for '83 3.0)

Mark the pulley at regular intervals, then run the engine at 2000rpm, 3k, etc. and use the timing light to monitor the advance amount at each of those rpm's.

Note at which rpm the advance tops out.

Listen for pinging/knocking/detonation. Audible detection is the only way to identify these conditions.

I can then adjust the total advance by dialing back the distributor, but that also affects the timing at idle, in effect retarding it.

The only way to adjust total advance is to recurve the distributor.

I've got this paranoia that I'm going to destroy my engine, break ring lands if there's detonation. So I'm trying to eliminate as much potential for that.

Jameel
Two things: You will not hear any pinging/knocking etc. those are load induced situations.
If you set timing at 5 deg for idle you might be close to the desired total advance. As I said it should be around 35-38 deg total. Just push the throttle up to around 4000 and you will see the advance stop. Turn the distributor until you get around 35 that should make you comfortable. Yes your idle will change, it will advance not retard.

Recurving your distributor changes how fast or slow you get total advance not what the total advance will be, that is determined by how far you twist the distributor.

You should also have marks on the pulley. Top dead center, 5 deg, and then, if I remember about an inch away the mark for total, 35-38.

Good luck

I think you are 10 deg too advanced there. No CIS engines came with that much advance stock.

Well I then stand corrected. I've only run weber's on my 2.4L, 2.7L and now the 3.0L

Thanks Kent. I can always dial back the idle adjustment screw if it goes up. That won't affect total advance if I understand correctly.

Correct

some things to consider about timing.

when you have a lot of advance there is a negative (power wise).
when combustion begins at 38 degrees BTD that force is already trying to push the piston back down BEFORE it even reaches TDC. this REDUCES power.

there is a point where adding timing stops increasing power, this can be long before detonation starts. so if you time the engine based on hearing detonation, you could be adding timing that the engine does not need.

one of the factors effecting the need for more timing is piston shape. piston shape effects how long it takes the fuel to completely ignite. bad shapes = slower burn times = more advance needed. this is why people dual plug their engines. (hi compressions, bad piston/combustion chamber and low octane fuels. it also allows for less advance).

with a custom engine I would take it to a dyno and figure out max advance and perhaps some optimum timing at various RPMS's. then I would send the dist off and have it recurved.

this is also the advantage of electronic ignition. it can have the ideal curve programed.

Stock distributor is recurved and no vacuum. I run 35d at 6000 rpm. Been awhile since setting, but most of the advance is there by 4000 rpm. Over 75,000 kms set at this and zero issues. Engine pulls strong.

Your distributor has less advance than most. Those of us who race 3.0 SC motors find the advance of 26-30 degrees to give best power. 26-28 degrees will be safe with that fuel and compression ratio. Unless you recurve it you have to use 10 degrees or more at idle to get enough advance.

You should consider rebuilding the distributor yourself. It's not that hard and you can see how the advance works and even modify it yourself. As I recall, you can just move the stops on the counterweights to allow them to move further.

-Andy

My 3.0 is about 9.5 compression with:
Max Moritz 3.2 liter pistons and cylinders, 2) 964 cams, 3) Raceware hardware, balanced rods, Carrera oil pump. New parts included: intake valve sleeves, rod bearings and rods balanced, and rocker arms. CIS and early exhaust.

John Walker set the total advance to 29 degrees. Runs very well and never pings.

Thanks Bob. Sounds like a good number to shoot for.

Thanks Andy. I did rebuild my distributor, but didn't change weights or anything. Just shimmed out the play and replaced the springs, plus a thorough cleaning.

If you use one of our CDI+ units you can dial in any advance you like. Just saying'.

It's tempting, along with the other nice bits you make.