Ignition timing on propane small block

[evil66]

Has anyone got any recommendations for initial and total ignition timing on a 273 running on straight propane? Engine is a very mild build with a single plane street dominator inlet, 216@50 crane cam, 9.5:1 compression and has a single impco 425 mixer.

I have heard that they like a lot of initial and restricted total timing but would appreciate any suggestions.

 

[xLURKxDOGx]

I'm in on 19/20 initial and around 35/6 total. Been running good for a while now.


Jake

 

[evil66]

Thanks jake,what engine have you got / cam etc.
I am thinking of trying a locked distributor at say 25 degrees to start with to see how it likes that. The current distributor has about 24 degrees advance so i cant run much initial timing and it feels very soft off the line.

 

[BigBlockMopar]

I run straight propane on my '73 318 Dart.

With the recurved distributor I used to run until about a week ago I had the following numbers;
- 10° initial
- 32° init+mech
- 47° init+mech+vac adv.
At 24.5° init+vac adv. (Transmission in Drive @ 550rpm) produced highest engine-vacuum (20.7" Hg).

Use the lightest springs (or just one spring) in the distributor, just enough tension to keep the advance mechanism at bay during idle.
Advance should be 'all-in' at around 2400 rpm.
With vacuum advance, timing should not exceed 40-42 degrees.


Last week I installed a MegaSquirt and could now digitally enter the Spark advance curve, which really woke up low rpm drivability.

Here's the posting on my site where you can see the (ballpark) advance table which already woke up the engine nicely in just about all the RPM-ranges;
MegaSquirt MS3x ECU install in the Dart

 

[xLURKxDOGx]

Thanks jake,what engine have you got / cam etc.
I am thinking of trying a locked distributor at say 25 degrees to start with to see how it likes that. The current distributor has about 24 degrees advance so i cant run much initial timing and it feels very soft off the line.

No problem! I wouldnt like to get that much advance, maybe try welding it smaller? I tried mine higher and that curve fell off a cliff at around 4300. Ive got a .40 over 273 10.5/1 with a compcams hydraulic .454/.454 with 3.23 and a stock converter. Im going to over haul it with my magnum goes in next month and try a good mechanical/solid cam.

Jake