390 Ignition timing
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390 Ignition timing
Have a question for you guys. I am going to check the ignition timing on my 390, but someone has removed the valve cover tag that shows where it should be set. While looking around the web I see that some people set it at 6 degrees, while others set it between 12-14. Thanks
Laughing Gas
Joined: May 2007
Posts: 960
Likes: 10
From: Victoria (North Saanich)
First, I have been told by several guys that the timing on these old Fords is not always correct, so you could be showing 10 degrees on the harmonic balancer but it is really several degrees either way.
We originally set mine the old way, pushed it until it rattled, and then backed off till it stopped. Following this approach we set it at 12 degrees. This is not that easy with a stick, so I had doubts.
A local shop just got a dyno and the owner was telling me that he used to think he knew how to time an engine, but that the dyno had humbled him. I decided to drop the $130 and we put it on the dyno (my results are in my gallery). 14 Degrees turned out to be the best run on my engine.
Now I run about 10 to 1 compression, mostly stock heads and intake, and a pretty boring cam. Since I live at 3500 feet, advance and knock are a concern. I doubt that I actually have 14 degrees of advance.
Next up I'm thinking about aluminum heads and a hotter cam. The idea is that aluminum heads will allow more advance before pre-ignition sets in. What I'm curious about is if the dyno indicates more advance with aluminum heads. The experiment may not reveal useful data as I'll be changing valve sizes and cam at the same time.
We originally set mine the old way, pushed it until it rattled, and then backed off till it stopped. Following this approach we set it at 12 degrees. This is not that easy with a stick, so I had doubts.
A local shop just got a dyno and the owner was telling me that he used to think he knew how to time an engine, but that the dyno had humbled him. I decided to drop the $130 and we put it on the dyno (my results are in my gallery). 14 Degrees turned out to be the best run on my engine.
Now I run about 10 to 1 compression, mostly stock heads and intake, and a pretty boring cam. Since I live at 3500 feet, advance and knock are a concern. I doubt that I actually have 14 degrees of advance.
Next up I'm thinking about aluminum heads and a hotter cam. The idea is that aluminum heads will allow more advance before pre-ignition sets in. What I'm curious about is if the dyno indicates more advance with aluminum heads. The experiment may not reveal useful data as I'll be changing valve sizes and cam at the same time.
Posting Guru
Joined: Dec 2010
Posts: 1,240
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From: Chino Hills
I have a 352 that is stock, and it like 15+ initial and 36 total. I started it up this morning after I fixed my distributer, and it fired up on the first shot.
I imagine my truck has a stock low compression rebuild with about 8.5 compression.
So you 390 should like the same unless you have added lots of copmpression or cam. I live in SoCal about 100ft above sea level.
I imagine my truck has a stock low compression rebuild with about 8.5 compression.
So you 390 should like the same unless you have added lots of copmpression or cam. I live in SoCal about 100ft above sea level.
Fleet Mechanic
Joined: Nov 2010
Posts: 1,501
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From: Axtell, TX
the 390 came with either 9.5:1 or 10.5:1 CR so it won't be the same as an 8.5:1. I highly doubt he'll be able to run 15° or more bdtc. I'd say start at 10° and change as necessary from there depending on altitude, CR, and octane gas you are going to run.
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New User
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Thanks for the information. She is at 10 degrees when I checked, so I just left it be. The only reason why I wanted to check the timing is because she is very hard starting after I drive around, so now im guessing that the coil might be bad? Starts fine in the morning, but after warm up I have to crank with the gas to the floor for about 5-10 secs before she starts.
Post Fiend
Joined: Sep 2006
Posts: 14,325
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From: Island Southeast Alaska
Is the starter motor maybe dragging when the engine is warmed up? Do ya have stock manifolds or headers? Both can heat up a starter and if it is going south it will drag when hot but crank fine when cold. My .02
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The engine is completely stock with a new starter. She cranks over fine, but after I shut the engine off then go back to restart her, I have to crank with the pedal to the floor for 5-10secs. If I wait for a few hours then try, she will fire up with the turn of the key. I don't have any history on the motor as I just bought this truck with it running like this.
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Post Fiend
Joined: Sep 2006
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From: Island Southeast Alaska
My next guess and the thing that comes to mind is that it may be flooding. You are not pumping the throttle to start when hot but just holding it open, Right?
Take off the air filter housing and immediately after shutting the engine down look into the carb. Is there any fuel seeping in? Or a strong smell of gas? Is it wet inside?
What carb ya got and how old and what shape is it in?
Take off the air filter housing and immediately after shutting the engine down look into the carb. Is there any fuel seeping in? Or a strong smell of gas? Is it wet inside?
What carb ya got and how old and what shape is it in?
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My next guess and the thing that comes to mind is that it may be flooding. You are not pumping the throttle to start when hot but just holding it open, Right?
Take off the air filter housing and immediately after shutting the engine down look into the carb. Is there any fuel seeping in? Or a strong smell of gas? Is it wet inside?
What carb ya got and how old and what shape is it in?
Take off the air filter housing and immediately after shutting the engine down look into the carb. Is there any fuel seeping in? Or a strong smell of gas? Is it wet inside?
What carb ya got and how old and what shape is it in?
I rebuilt the carb (Motorcraft D5TE-ASA) a few days ago thinking that was the problem, but nothing has changed other than I can mash the throttle without her stalling. There isnt a strong gas smell after I shut her down, and I will check to see if there is gas seeping in after shut down. Oh, I forgot to mention that there is some minor popping from the exhaust while idling. Its not a constant popping, but more like a faint pop every 2-5 secs. Maybe it still is a carb issue.
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Where would I look to see what ignition system I have?
Post Fiend
Joined: Sep 2006
Posts: 14,325
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From: Island Southeast Alaska
That's a Duraspark II. A pretty dependable system. They generally work or they don't. Ya could try a new coil. And take the Module to like Autozone and have it tested. There are guy's here that can tell ya how to test the coil with a multi-meter.
How is the spark at the plugs when it is hard to start? Maybe check the spark when cold than hot and compare it. Spark should be blue and snap and jump a long way.
How is the spark at the plugs when it is hard to start? Maybe check the spark when cold than hot and compare it. Spark should be blue and snap and jump a long way.