I had an 86 xr4ti, and another owner showed me the mod with the vacuum hose. Made it a much better car, but I was always afraid it was gonna blow up. It also seemed to delay the drop in boost that hit when the waste gate opened. Especially effective at altitude (lived in Boulder at the time). Whenever I took it in for service, I put it back to stock to avoid a warranty problem. Underrated car. Read an article once that said it looked like a geothermal event bubbling up through the tarmac. Lol. Sorry for the OT.