Where to start
If you’ve just added one new part, like a new distributor, then you would think you only needed to tune the ignition and then you’d be OK. That’s only true if the part you change is similar to the old one. But if for example you install a camshaft with more duration, it’s guaranteed you have to adjust almost everything, on the carb and ignition. Every part is working together, and the first time you add a non-original part, 1) all variables need adjustment, some more than others and 2) you can’t read in any manual how many degrees ignition you need. And that’s where the advice on these pages come in handy…
So, if you want to do it totally right, be prepared to tune everything each time you change a part. In reality, and assuming the parts you add are not significantly different (bigger carb, longer duration camshaft) from the old part, you can do the next best thing and only tune according to the table:
| New part |
Ignition |
Carb |
| Headers |
Yes |
Yes |
| Ignition |
Yes |
No |
| carburetor |
No |
Yes |
| Camshaft |
Yes |
Yes |
| Intake |
No |
Yes |
| Heads |
No |
Yes |
| Pistons * |
No |
No |
| Blower/Turbo ** |
Yes |
Yes |
| Nitrous |
Yes |
No |
| * If compression is changed: Yes/Yes |
| ** Requires modifications to carburetor |
Again let us emphasize that ideally both ignition and carb should be adjusted, but adjusting the part with the No in the table above will not add significant power in most instances.
Sequence
So what do we tune first, the ignition or the carb? Well the ignition is the most critical, if that’s far from the correct tune, then tuning the carb wont be easy. The best sequence is:
Ignition (vacuum gauge) -> carb -> ignition (at the track) -> carb (at the track)
We need to get the ignition in the ballpark before tuning the carb. After the carb is tuned we will tune the ignition again, at the track, and then, still at the track, the carb. Theoretically we should then retune the ignition, and then the carb again, this can go on forever because the parts affect each other, but we’ve found no measurable increase in performance by going on after the ignition->carb->ignition->carb sequence
Warning on detonation
Detonation. Pre-ignition. Concepts that make engine tuners a little scared. This is the biggest risk for your engine. We won’t go into details on what happens when an engine detonates. But you should know about and how to avoid it. If an engine detonates it can break itself in 5 seconds. So if you have serious detonation, you must stop your engine immediately and remedy the cause. Sometimes detonation can be heard, it sounds like a super tuned popcorn machine, mostly under acceleration. But you can’t always depend on that. A noisy car can make it impossible to hear, and if you’re at the track with open headers, you can’t hear detonation. And from painful experience we know that in a boat where the engine is in the rear and the noise is carried backwards, detonation can’t be heard. This created a 502 cubic inch boat anchor… Detonation happens when you have
- Too lean Air/fuel mixture
- Too early ignition
- Faulty plug wires inducing spark in the wrong cylinder
- Too hot spark plugs
- Forced induction
There are a few simple tips on this, they are that every time you start tuning, if in doubt, make sure that you have richer mixture/later ignition/colder plugs than the other way around. It’s better to err on the side of caution than on the side of “oops, I need a new engine”.