What should I be targeting for a distributor curve for my stockish 67 Coronet 383?
Initial? Total? All in at what rpm?
It is a street car that we take down the track occasionally - my daughter drives it. Runs 15.0 in the quarter. Weighs 4000 lbs with me in it. Has the original 383 with 8.9:1 compression, Holley Street Dominator intake with a Holley 750 double pumper carb Cam is 0.474 lift and 233/240 duration (intake/exhaust) @ 0.050.
Suggestion on what to do with the distributor? Its a 1990 vintage Mopar Performance vacuum advance with Pertronix ignition.
I'm going to type this before looking at Dr. Charles because I'm curious how similar or different we think about this.
What should I be targeting for a distributor curve for my stockish 67 Coronet 383? It is a street car that we take down the track occasionallyIt sounds like you're willing to tweak everything.
I *think* 1990 was still a Chrysler built distributor - which has the better advance mechanism - and the big block versions - should have a curve similar to the factory curves for the 4 bbl big blocks.
I'd start with 4 bbl and 440 high performance factory curves and factory initial as reference.
Then take your timing light and tach and measure what is on the car now.
12.5* BTC at 600 rpm was the Plymouth initial recommended. It should start advancing a little above idle rpm.
With the cam change, I would expect it will be happier (more powerful) in gear if it was around 15 - 16* initial. The catch being whether it can be idled at 600 rpm - doubt it.
Around 1600 rpm the advance should slow down. The second (higher rpm portion) of the advance should be long and slow. This is critical when using vacuum advance.
Compared with the factory 383 4bbl timing, the MP distributor will probably have a quicker secondary curve - and look like it stops advancing around 3000 rpm. That's probably fine for what you're doing. A little higher might be better if the car was used for long trips.
Mopar Performance recommended 38* BTC for production head 383. I'd consider that max unless testing at the track suggests otherwise.
Attached are three images:
'67 383 4 bbl and 2 bbl timing specs. (Interesting to note the 2bbl combustion doesn't gain efficiency at higher rpms)
'67 440 Hi Performance engine timing curves. (Use the non-CAP for reference)
Mopar Performance timing recommedations from the instructions. (Notice they recommned setting the distributor based on timing at 2800 rpm - close to all in. We can discuss why they did this later, but it is a good reference point for your 'all in'. If you see your distributor is still advancing past 2800 rpm, then a litle less than 3** is probably safe. If you can, see what rpm advance appears to stop. Be careful of course).
