Using (3) Single Phase Transformers for 3 Phase 240/480

I have 3 1KVA Transformers. Acme T 2 53010 S model. I want to transform 240V 3 phase to 480V Three phase. I wired each transformer as 240/480, and then connected them as a delta wye with the 240 side as the delta and the 480 sides as the wye, grounded in the center. I ended up with 1,000 volts on the output. I rewired ea transformer as 240/240, delta wye and ended up with 440V on the output. I can drive a 3 phase 480V motor with it, but I would really like to have 480V.

Any idea what I am doing wrong? Was I wrong to assume I could use 3 480/240 transformers, with the 240v inputs used to get 480V out in a delta wye configuration.

To be specific on the transformer wiring, I connected h2 to h3 on each transformer. X2 to X3. Wired the H1 H4's in a wye. Wired the X1 X4's as a delta. Then put 240V 3 phase on the x side.