First up, your looking to end up with the right ignition graph. Here is one for a bike engine.
Two ways. The best is to have it done on a Sun distributor dyno, where the whole advance curve can be checked and modified by a specailist. The ideal distributor is something with the overrun vac retard used on some mid 70's Fords, especially import 2.6/2.8 V6's and maybee some of the early US Durasparks had it.
They allow you to tailor make a normal conservative turbo curve under 100% load, and then go to large advance under part throttle.
Key curve for an 8:1 compression engine with 9 psi boost on the gage under wide open throttle load should be
idle, 15 (no load)
1000, 18 (advance sees a huge drop in vacum)
1500, 20
2000, 22
2500, 28
3000, 28
3500, 28
4000, 28
Under no load (when the vacum retard sees 20 " hg or -10 psi on the gage when off throttle into corners, or coasting to lights, or pumping the brakes),
idle, 15
1000, 18
1500, 24
2000, 30
2500, 34
3000, 40
3500, 40
4000, 40
This gives you great economy part throttle (lots of advance before detonation always is), and then really safe (detonation free) performance wide open throttle.
if you don'y have the 300 bucks to get one tailormade, then just do like
Does10's has done, sacrifice a little fuel economy, and but make up a real safe fixed distributor. First up, you need to interigate the existing distrubutor for the current advance curve.
Find the TDC and 6 and 12 BDC marks, and locate new 28 and 30 and 32 and 34, 36 degree marks. You do this by grabbing a $1 360 degree protractor, and lay it out over a spare crank pully and front cover. An old engine is best. Identify TDC, 6 BTDC , and 12 BTDC on it, then find where 28, 30, 32, 34, 36, and 38 BTDC are. Then clean the surface with prepsol, and lay out either
a) retro reflective tape 1/8 or 3mm wide on it (from signs companies or graphic artists).
or b) just painting 'whiteout' works best. Place a big ***8 for 38, or **8 for 28 on the white with a fine tip black felt pen. Transfer this to the pully on your car.
There are aftermarket kits, but I've not used them
You can see them real good with a timing light at night.
Stock advance curve can then be ploted by reving your engine in neutral with the advance curved hooked up at
idle,
1000,
1500,
2000,
2500,
3000,
3500,
4000 rpm.
Do it twice to be sure the ignition is in good shape.
Un hook the advance, and try it at
idle,
1000,
1500,
2000,
2500,
3000,
3500,
4000 rpm
Plot it.
Again, the ideal advance curve is to have heaps of initial timing, up to 18 to 25 degrees will start if your compression is 7:1, but more likely 15 to 18 degrees will be fine for 8:1.
The key is to use stiffer springs from the Ford supplier to bring it back to the
idle, 15 (no load)
1000, 18 (advance sees a huge drop in vacum)
1500, 20
2000, 22
2500, 28
3000, 28
3500, 28
4000, 28
curve I've suggested
Rekit the mechanical advance. Stock ones after many years can be quite unreliable. Bush wear (no plotical jokes please) and siezed of galling plates and springs can create spark scatter problems. With the the vac advance removed and the hole plugged with a plate or rtv, you'd be pretty close with a good distirbutor with stock springs, and by setting up 15 to 18 degrees static. The key is to have the advance come in hard and fast, with full boost at 2500 rpm and 28 degrees.
That should avoid the big bang, and is the single esiest way to save cash.
Placing a restricton on the stock ignition bsaeplate can do just as good a job, but you really have to prove you've got close to the ideal curve
before and
after you've done the work on it.
Remember, everyone else talk about other kinds of BS, but the only thing yo've got to get right is the amount of advance at each rpm. This one!
If you ignition is safe, you engine is safe.
