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Old 03-07-2011, 07:18 PM   #1 (permalink)
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Timing Question- How much advance is too much?

I just got my carburated 302 going and am having some questions about the timing. First off i have a 302 with a comp 280 hr (roller) cam, AFR aluminum heads, duraspark ignition. Overall the motor has 9.6:1 compression. I read the article "Timing is everything" and have some questions. What is the most overall timing i can safely run? The article says it should be around 35 to 38. Currently it runs at 10 degrees initial and about 42 total. My distributor is out of a 85 mustang 5.0 with a 5 speed. I took the distributor apart and it has the mechanical advance limitors at 16L and 21L. Are they bigger than the article states (usually 10&13L or 15&18L)because of the roller cam? I'm just worried about running too much advance, however the motor runs really good where its at. What are your guys thoughts?
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Old 03-08-2011, 12:05 PM   #2 (permalink)
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Re: Timing Question- How much advance is too much?

I have never seen a 302/5.0 that liked more than 36 degrees total (disregarding the vacuum advance). Most make the most power with 34 or slightly less. The only way to know for sure is to tune it on a dyno. You need to have the advance plate modified for less mechanical advance so you can use a fair amount of initial advance. With the 16L slot in use you have 32 degrees of advance in the distributor and that doesn't leave enough for more than 2 - 4 degrees of initial advance which is not enough. Start by finding out how much timing advance your car likes and then have the distributor recurved to get the rate of advance correct for your engine.
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Old 03-08-2011, 01:24 PM   #3 (permalink)
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Re: Timing Question- How much advance is too much?

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Originally Posted by nick1964ford View Post
I just got my carburated 302 going and am having some questions about the timing. First off i have a 302 with a comp 280 hr (roller) cam, AFR aluminum heads, duraspark ignition. Overall the motor has 9.6:1 compression. I read the article "Timing is everything" and have some questions. What is the most overall timing i can safely run? The article says it should be around 35 to 38. Currently it runs at 10 degrees initial and about 42 total. My distributor is out of a 85 mustang 5.0 with a 5 speed. I took the distributor apart and it has the mechanical advance limitors at 16L and 21L. Are they bigger than the article states (usually 10&13L or 15&18L)because of the roller cam? I'm just worried about running too much advance, however the motor runs really good where its at. What are your guys thoughts?
42 sounds like way too much...at most maybe 38. I'd back it off to about 34 until you get it dyno tuned. Nothing worse than too much timing, I learned that the hard way





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Old 03-08-2011, 02:45 PM   #4 (permalink)
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Re: Timing Question- How much advance is too much?

As Paul said, disregarding the vacuum advance, your total shouldn't be that high. So, are you disconnecting the vac before checking it?
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Old 03-08-2011, 08:14 PM   #5 (permalink)
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Re: Timing Question- How much advance is too much?

The vacuum advance is disconnected. It runs good at 10 degrees initial and it sounds like I need to buy the 13L or 10L reluctor. Will any reluctors out of small blocks work or do I need one out of a duraspark distributor? Is it something Napa can order or is my best bet the junkyards? Thanks for the help!
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Old 03-08-2011, 08:44 PM   #6 (permalink)
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Re: Timing Question- How much advance is too much?

jonbar87 how how did you run it before it ended up that way. I only drove it a couple miles down the road at 42 overall so hopefully it didn't do any damage
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Old 03-08-2011, 10:17 PM   #7 (permalink)
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Re: Timing Question- How much advance is too much?

Weld the slot up and file it down to get the advance you want.

The article:
Duraspark_distributor_recurve_instructions_index

It's an excellent explanation of the work and improvements that can be made to the duraspark.

I've done it lots and it works well.

John
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Old 03-09-2011, 07:20 AM   #8 (permalink)
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Re: Timing Question- How much advance is too much?

Or, instead of welding the slot you can just slip a piece(s) of vacuum tubing over the post that is in the slot. I used to know how much tubing wall thicknes was needed to change 1* of timing, but it's been too long ago. Easy to calculate, though. The slot number is the number of distributor degrees, X2 gives you crank degrees. Measure the length of the slot minus the width of the post and you can divide to find how many thousandths of an inch of slot equals 1* advance. On my own car I needed a piece of vacuum tube covered with a piece of heatshrink tubing to get it dialed in just right.
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Old 03-09-2011, 08:06 AM   #9 (permalink)
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Re: Timing Question- How much advance is too much?

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Originally Posted by bmcd66250 View Post
Or, instead of welding the slot you can just slip a piece(s) of vacuum tubing over the post that is in the slot. ... On my own car I needed a piece of vacuum tube covered with a piece of heatshrink tubing to get it dialed in just right.
That's my favorite method, and kits used to be available for this purpose with a variety of different sleeves to dial it in. Nick, too much advance is anything above the minimum necessary to get maximum torque. In the trade this is called Minimum Timing for Best Torque (MTBT). The most common methods to determine MTBT is by your MPH at the drag strip or dyno testing, although testing WOT above 3000 rpm from 30 to 70 mph on the highway may be an alternative if it can be done safely. We used a video camera once, and a guy's slick G-meter with timer another, to make it easy to get results as you're too busy driving to get good readings by watching.

Due to your engine mods, the burn rate will be different than stock, and usually a bit faster with a more efficient chamber, generally requiring less advance. The more efficient the burn control, the less advance you need, and the faster it should come-in. I would start on the lower side at perhaps 32BTC and work up from there. Generally a good starting place for a typical pump gas engine would be roughly 20 degrees mechanical advance (10L plate) and the rest initial of 12-16. If you get det before reaching MTBT, you need better fuel, or you'll effectively be running retarded to compensate and leaving a lot of power behind. FWIW.

David

PS: There are several "Timing is Everything" articles out there. Which did you read?
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Old 03-13-2011, 07:11 PM   #10 (permalink)
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Re: Timing Question- How much advance is too much?

Quote:
Originally Posted by nick1964ford View Post
jonbar87 how how did you run it before it ended up that way. I only drove it a couple miles down the road at 42 overall so hopefully it didn't do any damage
That was on a supercharged engine that I ran hard for about 3 months. You should be ok if you didn't do WOT pulls....
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Old 03-14-2011, 09:48 AM   #11 (permalink)
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Re: Timing Question- How much advance is too much?

I have a 302" code F engine (9:1-9.5:1) stock rebuilt 2bbl with a mild
com 31-218-2 street cam C4 trans
My distributor is 10 (20 mechanical advance) I set the initial after
road testing to 20 initial for a total of 40 degrees BTC
Vacuum disconnected and plugged.
I read on a dyno for that engine total advance is 38-42 degrees
I also wander if my harmonic balancer is accurate (hasn't slipped)
it looks fine but I don't know

Question is: is 40 total too much for this engine?
Thanks

Last edited by 68cougar29; 03-14-2011 at 10:11 AM.
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Old 03-20-2011, 02:59 AM   #12 (permalink)
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Re: Timing Question- How much advance is too much?

is this black soot on top of those pistons (photos above) symptom of too advanced timing, or is it just oil seeping through worn valve guides/leaking or no valve stem seals?

Last edited by 67gtman; 03-20-2011 at 03:31 AM.
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Old 03-27-2011, 03:42 PM   #13 (permalink)
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Re: Timing Question- How much advance is too much?

No, det does not generally cause carbon formation - except that your rings were damaged by det and may have been a result of that. If anything, det cleans carbon off. The carbon is from a secondary source (rings, guides, seals, etc.)

David
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Old 05-03-2014, 10:13 AM   #14 (permalink)
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Re: Timing Question- How much advance is too much?

Modified engines need a lot more initial advance than production engines do, but it is an area that little hard data is available for. One source is the Ford Off Highway Parts manual. For example, on page 11 of the 351C section(specs reproduced at enmac.us/automotive/) the initial timing is 27-31.5 ! The problem is that using high levels of initial advance can lead to serious damage unless provision is made to retard the timing during cranking.
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Old 05-03-2014, 11:32 AM   #15 (permalink)
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Re: Timing Question- How much advance is too much?

Be careful, as Ford usually specified advance as distributor degrees when spec'ed with distributor RPM. The distributor of course turns at half the crankshaft rate in both speed and angle. The Ford reference is saying:
  • 8.5-11° distributor advance at 1000 distributor RPM
Which coverts to crankshaft timing as:
  • 17-22° crankshaft advance at 2000 crankshaft RPM
Which means - with a total advance of 38°, the initial timing seen on the engine with a timing light would be 16°BTC to 21°BTC.

In any case, timing should be set for best torque (even at idle), as too much or too little timing at any specific load and RPM will lose efficiency, reducing both power and mileage. This is often determined with a vacuum gauge, as the best efficiency at a given load, RPM and throttle angle, is also found at the best vacuum level. Your point about timing retard during cranking is certainly still valid.

David
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Last edited by PSIG; 05-03-2014 at 12:10 PM.
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