My pecs are slow to grow in spite of the fact that I do a lot of straight arm flyes every workout. I also do floor dips between benches to get a stretch (3 x 15) and I get a good pump.
We do not have any cables at the gym I train at, so please do not recommend any cable crossovers or anything like that.
What you call a good pump is superficial. What you get from floor dips and straight arm pullovers is only a skin deep burn. A real pump comes from heavy work.
Forget straight arm flyes. They will wreck your elbows. Dips between benches are only good if they are made progressively heavier. (i.e., having a disc or weight attached to the body).
Try alternating the Neck Press (Supine Barbell Press lowering weight to the neck) and parallel bar dips (elbows out, chin on chest, feet forward. Grip 30-34” wide).
Perform enough sets and reps to congest the area and keep raising the resistance whenever possible to ensure growth.