how much can you modify the 2.5l TJ motor until you need to flash the ECU or get a jet (or equivalent) chip? I am planning a rebuild here soon, want to go bored .030, cam, ~10.5:1 compression. also is that too much compression for 87oct gas?
The stock compression is pretty much borderline for 87 octane, 9.2:1 for your TJ. You probably would want to get dished pistons and deck the block for better quench with lower compression.
I did a calculation for the same stroke as a 258 crank, .060 over, 16cc dished pistons (could go more depending on company, price, custom, etc), decked .010. If I recall, the quench was just a little worse than stock, with the compression at ~9.6:1.
There is one person on here with .030 over and stuff, another with .060 (I think), and I know of one other person doing some cam work and such to run premium/e85 on Jeepforum. The two guys here are pretty hard to get ahold of, but the other is in the middle of his machine work and willing to talk.
I have ZERO experience in building engines, I just like to study mechanics and such (planning to be a mechanical engineer), so I can't tell you to trust my word at all, I'll help figure stuff out if you need though!
good luck
