273 advise needed

I think I would start with pulling the heads and the pan. You need to inspect the valves for seat recession and general condition, and you want to inspect and measure the bores. At that point you will have a much firmer base for making decisions.

When I rebuilt my Commando back in the early 90s at 125K miles, it probably only needed an .010 bore, but we went .030 because those were the pistons we could get. I didn't use Egge — at the time, I could get TRW hypereutetic pistons. From everything I've heard, you lose compression with the Egge pistons. If you want max HP, you should retain as much compression as possible.

You couldn't get a mechanical cam with the original profiles off the shelf at that time, so we went with a hydraulic Crower cam with a bit more lift. The original specs on this engine were pretty aggressive for a small displacement street motor. If you want +30HP you are going to have to do something different, not just refresh it. An alternative approach would be to try to maximize the low to middle torque — the stock cam is designed for max torque at 4000rpm, which is not really practical or useful on the street, at least not if you have an automatic transmission. BTW the HP peak was 5200 rpm — again, you will never see that in 3rd gear on the street, and hardly ever in 2nd gear for that matter.

My conclusion is that this engine was designed primarily to support their racing program, either D class drag racing or Trans-Am/B Production road racing. It really wants a 4 speed to take advantage of that high revving.

Anyway, in my latest refresh I had the heads mildly ported, which probably exacerbated the "no low end torque" problem... oh, well, I am not taking up any stop light challenges, since any average EV would dust it.