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  #1  
Old 04-11-2016, 10:17 PM
Yadkin Yadkin is offline
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Default Distributor tuning

I am experiencing rough running under load and recently, some knocking at about 3000 rpm. My newly rebuilt engine has about 9.7:1 compression ratio with the stock iron cylinder heads.

Cam is a Comp Roller 33-000-9. This is one step up from an OE or "towing" cam. Idle quality is good, 650 RPM. I measured valve lift and they are all identical.

I did a dry compression test and found 7 cylinders at 170psi, 1 at 180. Wet compression all at 180.

Initial timing is 10 degrees BTDC. Using that as my zero, I measure centrifugal timing to be as follows:

RPM OE Rec'd This setup
800 .5-1.5 2
1000 3.5-4.5 8
1600 5.75-7 19
2800 8.25-9.5 24
4000 10.75-12.75 24(max)

Vacuum advance at 1000 RPM

In Hg OE Rec'd This setup
8 2-5 0
10 4-7 3
15 5.5-8.5 4
20 5.5-8.5 4

Last edited by Yadkin : 04-11-2016 at 10:33 PM.
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Old 04-11-2016, 10:29 PM
Yadkin Yadkin is offline
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I run 93 Octane pump gas, E10. I have a FAST 1.0 fuel injection kit.

I did nothing to my mechanical advance from it's factory setup, except of course for putting 90,000 miles on it. It's obviously putting in too much advance, and too soon. The vacuum advance is adjustable so that's not a big deal, except no reason to adjust it until I have the mechanical dialed in.

Fordmuscle.com suggests using a total advance of 38-40 for peak power. Mustang 360 recommends no more than 34-36. I have 10+24=34.

Last edited by Yadkin : 04-11-2016 at 11:14 PM.
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Old 04-11-2016, 10:33 PM
Yadkin Yadkin is offline
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I also have a Crane XR-i points conversion module in the distributor. I marked my crankshaft damper at 45 degree increments, tested each plug wire with my timing light and am within a degree at each.

Do I just need to re-curve the distributor to be more like factory specs? If so, how much lower should I make the total advance?
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Old 04-11-2016, 11:15 PM
Yadkin Yadkin is offline
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I'm going to set my initial at 8 and see what happens.
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Old 04-12-2016, 01:32 AM
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Quote:
Originally Posted by Yadkin View Post
...Cam is a Comp Roller 33-000-9...
Steve, this is a race roller cam core. It is a custom grind into whatever duration you choose.

Consequently, I have no idea what cam you actually have. It could very well be that your duration will produce a lumpy idle. Let's see the cam card.

Your compression spread looks ok. Your compression ratio demands premium fuel (93 is good but don't go lower).

You can always dial back ignition timing and it will work to a degree, depending on your cam timing. I've discussed my way of timing the cam but yours is quite different.

At what rpm is your cam timing 'all in'? - Dave
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Old 04-12-2016, 11:08 AM
Yadkin Yadkin is offline
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Thanks for your input Dave.

Here is a photo of the cam card.
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File Type: jpg IMG_20160412_100528575_HDR.jpg (73.4 KB, 61 views)
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Old 04-12-2016, 11:11 AM
Yadkin Yadkin is offline
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I found out last night that I had my vacuum advance plugged in too low on the throttle body- oops. I was getting a signal below the throttle plates instead of on top. It's a rain day so I can't test it out.
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Old 04-12-2016, 04:18 PM
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Quote:
Originally Posted by Yadkin View Post
I found out last night that I had my vacuum advance plugged in too low on the throttle body- oops. I was getting a signal below the throttle plates instead of on top. It's a rain day so I can't test it out.
The vacuum advance SHOULD be hooked up to manifold vacuum, i.e. Below the throttle plates.
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Old 04-12-2016, 04:56 PM
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Quote:
Originally Posted by scumdog View Post
The vacuum advance SHOULD be hooked up to manifold vacuum, i.e. Below the throttle plates.
That's not what I read yesterday. And it makes sense to me; here's why.

Under the plate(s): At idle, manifold vacuum is high, so the vacuum advance would increase to it's maximum then decrease under load.

Over the plate(s): At idle, vacuum is zero, then increases with increased throttle opening.

I've been taught to disconnect the vacuum advance and plug it temporarily while setting initial (at idle) timing. If you then add in advance with vacuum, you lost that setting at idle.
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Old 04-12-2016, 05:51 PM
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I just came back from a 30 minute test drive. She's definitely running better. No matter how hard I mashed the throttle, no knocking. Idle quality is better; so is top end power. I couldn't even see any smoke while full throttle, where as before there was a big blue cloud back there. Still, though, not as smooth as I expect while cruising.

Could it be the cam? I figured for a bit of "lope" at low engine speed, but not cruising speed.
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