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Re: Spark Advance Curve
[Re: bronco9588]
#1289572
08/23/12 12:49 AM
08/23/12 12:49 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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Quote:
Quote:
It should still read the same on the strap
Not really familiar with "strap"
Quote:
I just run a basic 10+ year old 6-A MSD not even a rev limiter because of the reasons you started the post. Definately not a plug n play deal.........good luck.
The 6AL-2 Programmable is entirely a different beast than the other 6 boxes.
Ground strap
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Re: Spark Advance Curve
[Re: BradH]
#1289575
08/25/12 12:24 AM
08/25/12 12:24 AM
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Joined: Oct 2003
Posts: 7,506
Az
Crizila
master
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master
Joined: Oct 2003
Posts: 7,506
Az
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Quote:
Here's a "no 'tude" response to the OP's post:
- A stock 400 is low compression and may tolerate up to about 20 degrees initial timing, but verifying the hot-start behavior will be important to determine how much it'll accept and still start w/o hard cranking
- Total timing considering the low compression and open chamber design is probably limited to somewhere in the 34-36 degree range; California-spec pump fuel is an even lower octane than most of the country (my local pump swill is 93-octane w/ 10% ethanol blended) and that'll probably cap the max advance at 32-34
- Depending upon gearing & converter stall speed, the advance curve should probably start around 1200-1400 RPM and reach full advance out about 3000 RPM
- Vacuum advance should be limited to 8-10 degrees to play it safe; one responder above suggested as much as 16 degrees, but that much will likely cause pre-ignition issues under high-vacuum cruise conditions
- Carb & ignition tuning are tightly related, especially since big changes in the initial timing curve can result in significant idle speed changes and require associated mixture adjustments
The programmable box is a cool unit, but it seems like major overkill for the current application.
I suggested a vacuum advance of 16 degrees. I also suggested an initial of 12, not 20 degrees. I ran my suggested numbers in a low compression 400 in a 78 Newyorker ( a real heavyweight ) with no problems. Honestly, you have a lot of latitude with that motor, no matter what gas you use. Ran my Newyorker back and fourth from the midwest to the coast several times on regular. No problems.
Fastest 300
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