Car Tunes


I ’m helping my son finish dropping a 440 in his Dart Sport. New everything. All is great, except for little vacuum. We used a MP aluminum manifold—P4529118, and a MP cam P4120235 with 284° duration and 0484˝ lift. Vacuum at idle is around 10 inches, by advancing the timing considerably off the “mark” initially had it at 8 ahead with no vacuum at 750 RPM in neutral. There is no indication of too much advance when cranking, it starts good and throttle response seems good. Now I would guess the timing is probably 20 degrees advance with vacuum off at 850 rpm.

Almost certainly you’ll need to modify the advance curve. You need about 15° before TDC at crank/idle and 33 to 35° at 3,000. How quickly it needs to advance is a function of detonation/C.R. You can’t guess on this!
You need at least 12 to 15° of vacuum advance on top of this. That curve also needs to be custom tailored—there’s a hex adjustment (for spring pressure) accessible thru the hose nipple. See “It Sucks” in our February, 2010 issue for lots more on why vacuum advance is so important.
That vacuum amplifier stuff was all emissions‑related.
Anybody can slap together parts. Tuning is the secret. The devil is in the details.

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