I'd also have to agree with OS engines. They are smooth, reliable, and inexpensive to rebuild. The Speed Tuned is no slouch by any means and is FAST. Regardless I've seen fast guys at my track using a bone stock TZ in whatever car they used to run and it'd keep up with anything. Don't forget to add in the NINJA as it's also a great motor for the price (same as the TZ) and FAST.