Camshaft question
a 750 edelbrock carb. The Dart has ridiculous toque and runs strong, but idles pretty rich.
That is a metering rod carb, right? ; make sure that the metering rods are staying down at idle, and also at low rpm/ modest throttle. That takes manifold vacuum; and if your idle-timing is retarded, or if the Vcan has been disconnected, good luck.
The stock convertor will also make this just a bit of a chore.
To see how much Part Throttle timing your engine wants , rev it up in Neutral/Park to just below your stall-rpm and hold the rpm there while;
You advance the timing a lil. Keep advancing, and dialing back the rpm, until additional timing produces NO additional rpm.
Now, put a light on it at the rpm that you were keeping it at. Subtract THREE degrees, and write it down. That is the Part Throttle timing that she will want, at that rpm.
Suppose your stall is 2400.
Choose 2200 for your target rpm.
Suppose your engine tops out there at 50 degrees.
How are you gonna get it?
Typically, your base-timing will be in the range of 14 to 20 degrees.
Typically your Power-Timing will be 36 degrees after say 3600.
That leaves about 20 degrees to be brought in by the centrifical system.
Typically, you bring it in at the rate of ~.8 degree per 100rpm, beginning around 1000rpm.
Thus, those 20 degrees will not be "all-in" until (20/.8)+ ( the start point of say 16*@1000)=3600
Therefore, at 2200; the centrifical will be; (2200 less 1000)/100, times .8degree,=9.6 degrees
So then, your all-in, before Vacuum advance will be 16 + 9.6= 25.6 degrees.
From the target of 50*, you are thus 24.4 degrees short, which HAS to come from the Vacuum Advance system.
Well, the Vcan is able to be modified out to 22* for sure ( I have done that), to possibly 24* ( Trailbeast has done that). Suppose you can get all 24. Then Badboom, yur in business.
But if your can only makes 20*, then you gotta get the rest from somewhere else. The easiest place is to just advance your base timing to 4* from 16 to 20* Badaboom. But hang on, if you do that, then your Power-Timing will also jump up 4 degrees to 40*, which, in a Mope, is practically guaranteed to cause detonation. So then, you gotta go back inside the D and limit the centrifical to 4* less, which would be 16*.
Badaboom, now you have a starter curve.
Now you get to fine tune it.
Happy HotRodding.
PS, someone mentioned to disconnect the Vcan until you get your PowerTiming bugged out. This is probably a good idea if this is your first tune.
Sometimes the engine will except 36* of Power-Timing at 3200 rpm, sometimes not until 3800, so you gotta hunt around to find the switch-point that your engine likes. Once you find it, write it down.
Sometimes you can/ sometimes you have to; swap some base-timing with the PowerTiming, either way to keep the combo, under load, from detonating. When you do that, you always gotta go back and re-engineer the Idle-Timing. And finally, Once the Power-Timing switch point is established, and the centrifical advance has been selected to establish the Idle-Timing, you still get to play with the "rate of advance" in-between those two points. Usually but not always, it sorta depends on your stall, you want to bring it "all-in" as fast as she will accept it without detonating. This will energize low rpm operation.
However;
Since WOT operation is NOT gonna be your primary mode of operation, at least it is not mine,lol, IMO, if you have choices to make, it is always better to bias them for your mode of operation, which typically, will be at 50% throttle or less. To help me with this, after I have selected the PowerTiming, I disable the secondaries, and do the rest of the timing-tuning on the Primaries only. This just takes the guess work out of it, and keeps your speeds down during testing. Your 3.23s and tires will get you about 60mph @3800 in SECOND gear, which is about where you can stop your Power Testing. Keep an eye out for JohnnyLaw.
It might help you to know that your engine, any engine, has exactly one perfect crank position that it wants peak cylinder pressure to occur at. This is said to be between ~25 and 28 degrees AFTER TDC. All your timing systems are designed to try and achieve that. Your job is to target that window and hit it as often as you can, and for as many load sttings as you can. Trying is about the best that you can do.
And finally; your WOT butt-dyno will not be able to tell the difference in the first two gears, if you are "bang-on", or up to three degrees short of optimum, so don't sweat the last three degrees. To actually find it, your dyno operator probably found it, and your top speed will point to it, but with 3.23s, that will be really really dangerous. The qtr-mile trapspeed is also a good guide.
Most of us just slap 34 to 36 degrees on it, and good enough........ especially with a stroker, lol. It will save you mucho time .
Somebody said to get your idle-engineered First before anything else. I agree, because if you don't, you will never be happy, and the car will spend too much time in the garage. I know it might sound daunting to get the tune into her, but when you finally do, you'll forgive her; I guarantee it.
Yknow, my wife complained everyday about being pregnant, but the truth is, as soon as she was healed up, she forgot all about it, and she went on to have more babies, lol. You'll forget all about the hassles too.
If it makes you feel better, I have a 367/4speed/with 3.55s. She will idle down to 550 in first gear, pulling herself around all day. and with the 750DP up top, will take WOT anytime, exploding in a noisome cloud of fury. And this, with 11/1 Scr and a 230/237/110 cam. Edit; and it does this with just 5* of advance.
I never begrudge her the time it took to make that happen.
You also will forget, lol.
