I have a 390 with , based on info from another post, low compresion pistons, bored .060. I have installed a CC XE262H cam kit. Valve Springs, roller T chain set, etc.
What should my ignition base timing be set to, and should I use ported or full vacume to the dizzy? I'm running a eldelbrock 600 cfm carb with eldelbrock performer intake, and Hedman headers. The heads and botom end are stock.
Once you modify, timing seems to be a trial and error thing. However, it's fairly widely accepted that max mech advance should not exceed 38 DegBTDC.
So, to be safe, set your max advance (no vacuum connected) to say 36 (34 if you're nervous) and then see what you have at idle. Next time, you can just use that idle spec.
To set 36 max mech advance without running the engine unloaded at high rpm, I just rotate the engine (with wrench on crank snout bolt) until my timing marks show 36. Then I hold the rotor CCW tightly, and rotate the dist CW until the coil sparks (I just hook a spark plug to the coil ouput with an old ignition wire and lay the plug on the intake for a ground). Make sure the rotor button is poiinting more or less to #1 cyl terminal on the dist (make a mark on dist housing before removing cap with black felt marker). You don't want to accidently time it for #5 or #8 which are on either side of #1.
Double check by letting go of the rotor, and then rotating it CCW again. Just before it stops, there should be a spark. Now you can check it with a timing light without having to let the engine race unloaded for any length of time. Using your light, just zip it up until the timing mark stops advancing, and read the timing.
Lock down the dist and road test the car. If it knocks, retard the timing a bit. I like to lug the engine up from about 1000 rpm in low gear and listen for "pings".
All this should get you in the range. As you have a vacuum advance unit, it will probably be enough. If you want to play with the intial timing, you can try advancing it a bit at a time, but don't forget, the dist advance end stops for max advance have to be adjusted each time to keep the total under 38 (or 36, whatever).
I wouldn't worry about the spring rates unless you get a situation where it knocks at a specific rpm.
EDIT: Check out this link.....you can see recommended initial timing based on cam duration at 0.050" But again, don't let the max mech advance go over 38 Deg....
Oh,, I forgot....when doing the above, make sure when you rotate the rotor button, you only go to the max of the mech advance. Don't force it so the vacuum advance moves.
Here's a couple of good links on timing for modified engines:
Inital timing is dependant on what your total mechanical timing advance is. Max timing should be no more than 38°. To determine your total mechanical advance, connect a timing light and disconnect the vacuum advance (they always say to plug it but for this test I never have). Start the engine, with the light aimed at the damper, rev the engine until the advance maxes out. This is your total mechanical advance. Adjust your timing until you have 38°, then check your initial timing and you have the number you should use with your present dist's advance curve.
I would recommend you recurve your dist, which is another whole ball of wax.
Using manifold vacuum is a cover up for a poor engine build. You engine if you used the right parts and tuned it properly should idle just fine without using max vacuum advance at idle. Vacuum advance is a gas mileage enhancer, not a crutch for poor engine building or tuning. Other wise use the ported vacuum.
I would recommend you recurve your dist, which is another whole ball of wax.
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Thats the best advice, cause ford used a lot of 16L and 21L combos in the 70's dizzys. I personally don't buy the sbc 36 total and prefer 42-44 but to each his own. There are several variables that can affect timing. I personally run about 20 inital, but i have modified the interior of my distributor. NO vac advance for me, i don't need 50-60 part throttle timing.
Faron Rhodes and Scott Johnston recurve distributors.
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Thats the best advice, cause ford used a lot of 16L and 21L combos in the 70's dizzys. I personally don't buy the sbc 36 total and prefer 42-44 but to each his own. There are several variables that can affect timing. I personally run about 20 inital, but i have modified the interior of my distributor. NO vac advance for me, i don't need 50-60 part throttle timing.
Faron Rhodes and Scott Johnston recurve distributors.
Unless you are running steep gears or a real light, as in Mustang light, rig; more than 38° is asking for a burn piston or two. To tell the truth I did run 44° total advance once but it was in a race car application with a 4.30 rear gear and I only ran the 44° in 1st, 2nd and 3rd gears. In 4th gear I dropped the timing back to 38° and this was back when we actually had gas with some real octane in it. I would never considered running more tha 38° on the street in any truck and usually cap the max timing at 36° to be on the safe side.
I have read talk about "the proper curved distributor" on this site. I have the CC XE262H cam kit installed, with Eldelbroc intake\600cfm carb and Hedman headers. Is the stock Duraspark and stock dizzy OK for my setup? (76 F250 4x4 390) If this is adequate, I'll let it stay. If a new performance ignition set up will make a seat of the pants difference, I'll buy it. This is a daily driver. I hate to say this...Adding the cam set up and headers did not add much "seat of the pants" power that I noticed. Now add the price of a mini starter, etc, etc. I'm a little disapointed in the bang for my buck. Now the thing will idle fine 99% of the time, then, it will die in traffic unless you keep tapping\pressing down on the gas pedal. Get it home, the idle is fine at 900 rpm. The wife drove it tonight, same thing, kept dying after a 10 mile in town trip. Bring it home, idles fine. GRRR I lubed the carb linkage and the dizzy advance mechanism tonight. We'll see...
TRy richening the idle mixture. It seems "wrong" but when in gear at idle the air velocity through the carb is really low - the "burning eyes" syndrome is not too much fuel as most guys think - it's not enough - sparse mixture releases unburned hydrocarbons.
As to the base timing, I like to use a really light spring on one side of the distributor advance package that'll give an advance "bump" once the truck starts. Example - lets you crank at 15 degrees but idle at 20...
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TRy richening the idle mixture. It seems "wrong" but when in gear at idle the air velocity through the carb is really low - the "burning eyes" syndrome is not too much fuel as most guys think - it's not enough - sparse mixture releases unburned hydrocarbons.
As to the base timing, I like to use a really light spring on one side of the distributor advance package that'll give an advance "bump" once the truck starts. Example - lets you crank at 15 degrees but idle at 20...
Thanks guy's for the info.
My timing is set to 8 degrees advance at idle. Set it much more then it pings under acceleration. (regular 89 octane gas). Which dizzy spring and how do you replace it if this will solve my problem?
It seems funny, but a few day's ago I adjusted the fuel\air mix as per manufacturers instructions, by rpm. I was tired of the "burning eye's syndrome" as was mentioned. That's when the problem started. I guess I'll try the vacuum guage method or just make it rich again. Any info on the ignition question I asked? Specificaly, would replacing the stock dizzy with an aftermarket one make a difference? If so, which do you recommend?
[quote=Barry_R;8084949]TRy richening the idle mixture. It seems "wrong" but when in gear at idle the air velocity through the carb is really low - the "burning eyes" syndrome is not too much fuel as most guys think - it's not enough - sparse mixture releases unburned hydrocarbons.
OK, I enriched the carb. Idled fine. The truck was warm, the fumes almost burned your eyes in the garage. The wife and my young one went to taco hell, about 5 miles away. the truck died 3 times at a stop light about 3 miles away, a dude in a camaro laughed at my wife while she kept restarting it. The wife kept feathering the gas pedal to keep it running. She brings it home, idles fine, I drive a few miles in town, idles fine. I'll rebuild the carb this weekend to se if it fixes this problem.
PS: My young one told me.."Daddy, the truck kept dieing, mommy was mad when the man in the car laughed at her. She made the truck tires squeal real loud"
Ever wonder why these trucks won't behave when we build for race but in reality drive to Taco Hell and to get Groceries. We over carb over cam throw away the air cleaner, chuck the maniflods intake/exhaust and laugh at the heater stove. Then we replace the exhaust system with a dual exhaust system designed for a 800HP engine.
I know nobody is listening but what most of us want is everyday torque!
Ever wonder why these trucks won't behave when we build for race but in reality drive to Taco Hell and to get Groceries. We over carb over cam throw away the air cleaner, chuck the maniflods intake/exhaust and laugh at the heater stove. Then we replace the exhaust system with a dual exhaust system designed for a 800HP engine.
I know nobody is listening but what most of us want is everyday torque!
+1 What works on the race track is useless on the street.
Ever wonder why these trucks won't behave when we build for race but in reality drive to Taco Hell and to get Groceries. We over carb over cam throw away the air cleaner, chuck the maniflods intake/exhaust and laugh at the heater stove. Then we replace the exhaust system with a dual exhaust system designed for a 800HP engine.
I know nobody is listening but what most of us want is everyday torque!
That is a true statement! Although that is not the case here. Rebuilding the carb solved the stalling problem. I built his motor, (NOT the block with recipricating gear, this was purchased) based on advice from several people on this forum that understood I have a daily driver. I researched their advice. A mild cam, mini starter, performer intake, hedman headers, eldelbrok 600 carb, HD clutch\PP, dual exhaust with flowmasters does not make for a beast that cannot be driven like a stock engine. The POS heater stove has been replaced with an electric choke. All are mild improvements in my mind. I had a few technical issues, as FE's are not my forte. People like you here helped me out with those issues. Torque? I have plenty, I pulled the neighbors 25' boat today. No problem there. With that being said, after re-installing the carb, I laid posi 33" tall, 12" wide rubber tracks from my driveway past the neighbors house. Let me re-phrase that, I burnt my 33x16.5x12 tires on dry pavement. I dont EVER see me doing that again, well, on dirt mayby.
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+1 What works on the race track is useless on the street.[/quote]
That depends.: Circle track, I agree. Where can one hold 100 or more mph for any lengh of time on the streets or back roads? A mild street light to street light engine build\setup works well. Leave em in the dust from a stand still and back off and smile when they catch up. Plus, the engine just sounds so cool...
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Now the thing will idle fine 99% of the time, then, it will die in traffic unless you keep tapping\pressing down on the gas pedal. Get it home, the idle is fine at 900 rpm. The wife drove it tonight, same thing, kept dying after a 10 mile in town trip. Bring it home, idles fine. GRRR I lubed the carb linkage and the dizzy advance mechanism tonight. We'll see...
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Let me re-phrase that, I burnt my 33x16.5x12 tires on dry pavement. I dont EVER see me doing that again, well, on dirt mayby.
Circle track, I agree. Where can one hold 100 or more mph for any lengh of time on the streets or back roads? A mild street light to street light engine build\setup works well. Leave em in the dust from a stand still and back off and smile when they catch up.
Plus, the engine just sounds so cool...
