IMSA with DPI do seem to favor GTE/GT3 engine sizes with adjustments to get them up to 600 or so bhp. Granted, the original Caddy LT4 was 6.2 liters, and just used the basic block and heads from the stock LT4. Then to make BOP easier, RCR/GM destroked the engine from 6.2 to 5.5 liters.
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