340 camshaft question, yea another one.
I have the cam out now. But when I installed it, in 2014, I remember it was dot to dot and it was at 106. Right at the cards spec.
The engine idled at 850 in park with 15 inches of vacuum and would just about stall in drive. Of course the magnum heads are closed chamber and with a zero deck and .038 head gasket the squish is near ideal.
The converter does suck and I might change it this spring if I can physically do it. I can get under it but I can't get back up.
If your T-port sync
is correct,and the idle timing is between 12 and 16 degrees,
AND the idle speed is in excess of 700ish; then something is wrong.The engine is likely pulling air in somewhere other than the carb. And that air has no fuel in it. So the engine is looking for an excuse to stall.A sudden decrease of airflow past the idle discharge ports might be all it takes.So even though the TC might seem to be the culprit, the reality is that it might just be the sudden drop in fuel supply,due to an already lean idle mixture.
So, I just can't stress this enough;that the T-port sync has to be correct, and the in-gear idle speed has to be low enough, so that the TC is not chomping at the bit. Then if it still wants to stall the TC is just too tight. I can see no reason why that that cam should not idle at 650 in gear with the correct idle-tune. I'm pretty sure I could get down to 600/650 in gear and happy to be there.
All too-often a fella might crank 20/25 degrees of idle-timing into it (for some unknown reason,lol),and then has to back the idle screw way out to get a slow enough idle speed. This puts the T-port sync so far out that the engine will do just what you describe, for lack of fuel flow when the airspeed drops.
The following test Assumes that the T-port sync and idle-timing are correct, and that the idle speed is about 750 in neutral, or a little less;
Jack up the rear and secure on jack stands. Warm up the engine. stick it in manual low, and let the tires spin up. As soon as the engine stabilizes, slowly start breaking the wheels to a stop. If the engine stalls, or wants to, buy a new TC. If the engine accepts this, put it into neutral. Apply the brakes hard, and put it in low. If the engine stalls or wants to, it's probably cuz the TC is too tight, and the airspeed drop through the carb was too abrupt. Lower the idle speed and try again.If lowering the idle speed doesn't work, crank in more idle-timing, and try again.. If it still stalls, buy a new TC.
But I'm still wondering why you chose an 850 idle-speed. The 15 inches of vacuum says to me that she could idle a lot slower. However, if that is the speed it took to prevent a stall when going into gear, with a correct T-port sync and idle-timing, then that is added proof that either the engine is pulling in dry air somewhere,or the TC is just too tight.
So once again we are at a crossroads; is it the idle tune, or is it the TC?
The idle-tune is by far the cheapest and easiest to prove.
If you put a smaller cam in there, it will have more idle torque, so it may pull that tight TC. But if you again try the same idle-tune that is currently in it, it is every bit as likely to stall.