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Discussion Starter #1 (Edited)
I have a newly rebuilt stock 289 4V with a c4. I degreed in the new cam myself. Here are the specs (measured):

Intake:
Lift (at lifter) ----------------- 0.0282 inches
Lift (x 1.6) --------------------- 0.4512 inches
Duration @ 0.050 ----------------- 203 degrees
Centerline ----------------------- 109 degrees
Exhaust:
Lift (at lifter) ----------------- 0.2975 inches
Lift (x 1.6) --------------------- 0.476 inches
Duration @ 0.050 ----------------- 215 degrees
Centerline ----------------------- 116 degrees

Lobe Separation ------------------ 112 degrees

Don't know for sure what the exact cam was installed by the builder (thats another story) but the closest match I could find was a generic Summit cam, pn# SUM-3600.

The builder also installed a new 3 piece timing set. I verified that it was installed properly (crank key at 12o'clk, crank gear mark at 12'oclk, cam gear mark at 6o'clk.

I also installed a new harmonic balancer with timing marks up to 50 degrees. I verified that 0 degrees is at TDC.

Valvetrain is stock with exception of compcams 1.6 roller rockers. Pushrods are all 6.8" long.

Okay, now that all that is out of the way here is the rub: The engine will not idle smooth at all unless the timing is at least 15 degrees. At 15 degrees engine vacuum is 15"hg. Even with this much timing vacuum at idle is not very steady and pulses up and down periodically. Idle rpm also changes with the changing vacuum. If I put the timing at 8-10 degrees the idle is so rough and low that the engine seems to want to die.

On another note, the engine is extremely sensitive to the idle mixture screws (before the rebuild with the stock cam the engine was relatively insensitive to idle screw adjustment). I have to set them at about 1/2 a turn for best performance. Any more than that the idle speed goes way down and is very rough. Less than that and the idle speed goes down a little, but the engine will die immediately after being revved. I have an AFR gauge and it reads around 12-13 with the optimal idle adjustment.

Anyway, the reason for this thread is that the engine seems to run best at 24 degrees initial timing. When timed there it runs very smooth and the idle speed is very easy to adjust to the proper rpm. Engine vac is very steady at 16"hg. Also, if I don't have the engine timed at 24 the temperature will slowly rise until it pegs the needle if I let it idle for more than 15 minutes. I verified that the temp is 225 degrees when pegged with a temp gun. If I put the timing at 24 degrees the temperature stabilizes at 185-190 degrees.

Sorry for the huge post but I would really like to have your guys' opinions on what might be going on. The compression is 100psi all around so I can't decide if all these issues are just because the rings haven't seated yet (I only have about 50 miles on this rebuild) or there is some other issue. Any help is greatly appreciated!
 

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I would go with it and not worry. As the rings seat it you will probably need to back off the timing. If it likes 24* initial and there is no pre-ignition, go with it. Just be very vigilant about listening to it and adjusting as needed. No racing crazy stuff till it's broken in. I am at 17* initial and it likes it.
 

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Im around 20-22 on my 390. When I first checked it after I got the car I was like "Holy cow wtf" was that guy thinking.
So i turned it down. Then spent the next week wondering why i couldnt get it to idle, hard brakes due to not enough vaccum etc.
 

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Discussion Starter #4
Thanks for sharing your experiences. Reading that makes me feel a bit better. I however have owned this car for many years and it has always happily ran at 10BTDC before the rebuild. I have no experience with changing cams before this so I have no clue what timing changes are normal for a given cam change.
 

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Yep, just make sure that you limit your distributor so you're not exceeding 40* all-in.

My 289 likes 20* of initial and has, at one time, just run with it locked out at 25* and was happy about it. I just let it do its thing.
 

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Different cams can make a huge difference. My 390 is at 47* total, and it likes it. I have ran cams wanting anywhere from 34* to 36* to 44* to 47*. I understand my stock iron heads have less efficient combustion, thus the higher timing advance.
 

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It appears you have been very diligent and thorough in your cam install. With the cam change, did you check your PR geometry? Also, assuming your running hydraulic lifters, if the adjustment (lifter) is too tight you can loose vacuum or visa-versa.
Do you know the mechanical "built-in" advance for the distributor?
I agree with others, engines will tell you if they are happy with certain settings. I've run as much as 40º total with good results. So, just be vigilant for noises while under a load and continue the good break-in sequence.
 

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Discussion Starter #8
It appears you have been very diligent and thorough in your cam install. With the cam change, did you check your PR geometry? Also, assuming your running hydraulic lifters, if the adjustment (lifter) is too tight you can loose vacuum or visa-versa.
Do you know the mechanical "built-in" advance for the distributor?
I agree with others, engines will tell you if they are happy with certain settings. I've run as much as 40º total with good results. So, just be vigilant for noises while under a load and continue the good break-in sequence.
I checked the valvetrain geometry (yes I have hydraulics). I actually found that there were 3 different pushrod lengths in the engine ranging from 6.81" to 6.9" before the rebuild. All were too long and causing the roller tips to ride on the edge of the valve stems so I replaced them all for 6.8" pushrods. I too suspected that I may have adjusted the rockers too tight so I backed all of them off a quarter turn, but it didn't seem to affect anything.

Currently with my timing at 24 my total timing with mechanical only is about 48. I only driven the car with the timing at 15 (too afraid to drive it with ~50 total timing). I also don't want to connect the vacuum advance for fear of too much total timing. However, when I rev the engine in park with the total timing up to 50 the engine seems okay with it. I don't really know what pinging sounds like but the engine seemed pretty smooth.
 

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Pinging sounds can be explained in a number of ways and be heard differently by any of us. Basically, it sounds like rattling marbles in a muffled can. Take a coffee can wrap in it a shop rag, add a few "marbles" and shake it around. You'll get an idea.
Usually shows up when under a load, such as not being in a low enough gear and "lugging" the engine, or traveling up hill in too low a gear.

"Marbles" are you old enough to know what marbles are? Just kidding!
 

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A couple of thoughts. A number of us have found harmonic balancers that have "shifted". They can rotate a bit and that throws your markings off. I doubt that's happened by your description but it's one way you can have a car that runs fine with some pretty wacky timing readings.

I once made the mistake of buying a Summit branded roller timing chain. It so happened I was not lax and rechecked the cam timing before I put everything back together. Though I had put it in "straight up" , it was way advanced. I put it in the retarded position (the gear had three slot choices) and it was still advanced a bit. After monkeying around with it for way too long, I ordered a Cloyes roller set like I should have to start with and the cam timed up perfectly the first try. Point being that you may have done the right things but been bitten by a similar issue anyway.

That was a long time ago, the cam have been retarded instead. One or the other, I can't remember.
 
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