460 total ignition timing advance?
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Junior User
Joined: Jun 2008
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From: wyoming
460 total ignition timing advance?
I decided to check the timing on my truck and have it set at 15 degrees with the vacuum advance disconnected of course. Oh ya Im also at 5k elevation. So I thought I would check the total advance. With the vac advance disconnected I have 27 deg at around 2700rpm, with the vac advance connected I have 53 deg same rpm. The truck doesnt ping but it does run rougher with the vac adv hooked up. Does anyone know what your total advance should be around? I was thinking somewhere in the 36 deg range sounded familiar. Any help would be appreciated.
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Junior User
Joined: Jun 2008
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From: wyoming
Thats where I figured I should be is in the 30s somewhere. So why is my vac adv moving it way farther than it should be. As far as I know its a stock electronic dist. From what Ive seen a vac adv either works or it dont. I thought maybe the weights and springs may be wrong but its only 27 total with just the mechanical adv. Ill try driving it with no vac adv and see what it does.
Hotshot
Joined: Dec 2003
Posts: 18,423
Likes: 9
From: iowa
there is something wrong in you dist based on your numbers the vac advance shouldnt be advancing your dist anywhere near 26 degrees by itself. see if you can find a vac pump to borrow hook it up, check your timing then apply vac without reving the motor and see exactly how much it is REALLY advancing the timing.
Post Fiend
Joined: Mar 2004
Posts: 6,056
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From: Union, Washington
Mechanical advance should never be more than 38° in by 2500 rpm. I prefer 34° to 36° in by 3200 rpm, because I tow with mt truck. I agree with monsterbaby, something is seriously wrong with your vacuum unit.
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Junior User
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From: wyoming
Bear, are you running a vac adv at all? If you dont run a vac adv Im assuming you need to play around with different springs and weights to acheive the desired 34-36 deg total. Do you loose off idle throttle response by running no vac adv, or does the different springs and weights compensate?
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Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
Bear, are you running a vac adv at all? If you dont run a vac adv Im assuming you need to play around with different springs and weights to acheive the desired 34-36 deg total. Do you loose off idle throttle response by running no vac adv, or does the different springs and weights compensate?
I used the shortest advance curve in the dist. which was 13°. So 26° advance with 10° initial gives me 36°. The vacuum advance unit is a non-adjustable unit and puts in around 15°, which is why I disconnect when towing, it makes the motor rattle and causes a slow overheat on long hills. If I could find a cheap adjustable one I would use it and limit it to about 10°. I would also prefer a 10° advance dist. like I had for my 390, but haven't found one for a 460. I also replaced the 4180 carb with a reworked Holley List 1850, 600 CFM vacuum secondary carb with dual stage power valve and a slightly heavier spring in the secondary vacuum unit and re-jetted both primary and secondary main jets. So throttle response is better than stock by a bunch.
Post Fiend
Joined: Oct 2003
Posts: 9,176
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From: Western Central NV
I do run a vacuum advance, but disconnect it when towing. The distributor, which I recurved with a Crane kit using two light springs with one fairly tight.
I used the shortest advance curve in the dist. which was 13°. So 26° advance with 10° initial gives me 36°. The vacuum advance unit is a non-adjustable unit and puts in around 15°, which is why I disconnect when towing, it makes the motor rattle and causes a slow overheat on long hills. If I could find a cheap adjustable one I would use it and limit it to about 10°. I would also prefer a 10° advance dist. like I had for my 390, but haven't found one for a 460. I also replaced the 4180 carb with a reworked Holley List 1850, 600 CFM vacuum secondary carb with dual stage power valve and a slightly heavier spring in the secondary vacuum unit and re-jetted both primary and secondary main jets. So throttle response is better than stock by a bunch.
I used the shortest advance curve in the dist. which was 13°. So 26° advance with 10° initial gives me 36°. The vacuum advance unit is a non-adjustable unit and puts in around 15°, which is why I disconnect when towing, it makes the motor rattle and causes a slow overheat on long hills. If I could find a cheap adjustable one I would use it and limit it to about 10°. I would also prefer a 10° advance dist. like I had for my 390, but haven't found one for a 460. I also replaced the 4180 carb with a reworked Holley List 1850, 600 CFM vacuum secondary carb with dual stage power valve and a slightly heavier spring in the secondary vacuum unit and re-jetted both primary and secondary main jets. So throttle response is better than stock by a bunch.
I bought a vacuum advance from NAPA that was ajustable. It wasn't cheap but no vacuum advance for stock 86 F250 460 is. You can almost buy a rebuilt dist. for a few dollars more. But my advance failed & I didn't want to change the whole distributor for only a failed advance. I can't remember what it cost. I think it was around 50 bucks.
Craig
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
Bear,
I bought a vacuum advance from NAPA that was ajustable. It wasn't cheap but no vacuum advance for stock 86 F250 460 is. You can almost buy a rebuilt dist. for a few dollars more. But my advance failed & I didn't want to change the whole distributor for only a failed advance. I can't remember what it cost. I think it was around 50 bucks.
Craig
I bought a vacuum advance from NAPA that was ajustable. It wasn't cheap but no vacuum advance for stock 86 F250 460 is. You can almost buy a rebuilt dist. for a few dollars more. But my advance failed & I didn't want to change the whole distributor for only a failed advance. I can't remember what it cost. I think it was around 50 bucks.
Craig
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
Did you turn it clockwise or counterclockwise? Clockwise shortens the curve and delays the advance.
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Junior User
Joined: Jun 2008
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From: wyoming
I turned it counterclockwise as far as it would go and it didnt make any difference, so then I turned it clockwise all the way and that advanced it even quicker. So I dont know if I have the wrong vac adv, and with so many different ones how do I know which one to get?
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
I wish you could still get the old style advance unit that the vacuum nipple unscrewed and you could shim or unshim the spring to change the curve and use spacers to adjust the amount of timing the unit could pull in. But alas the world made advances to vacuum advance units and made them worse.