| COMPRESSION RATIO/BOOST PSI GUIDE |
| ENGINE TYPE 2.2L N/A 2.2L Turbo 2.5L N/A 2.5L Turbo |
| RATIO 9.5:1 8.1:1 9.0:1 8.0:1 |
| YEAR 1984 1984 1985 1985 1986 1986 1987 1987 1987 |
| Engine/Trans TI/Man TI/Auto TI/Man TI/Auto TI/Man TI/Auto TI/Man TI/Auto TII/Man |
| Max Boost 7 7 7 7 7 9 7 9 9 |
| Peak/Spike Boost 7 7 9 9 9 11 9 11 11 |
| Over-Boost 11 11 11.75 14 14 14.25 14 14.25 14 |
| Turbocharged Engine Boost Control |
| How the boost is controlled by the ECU is somewhat complicated, but i will try to explain it here as i understand it. Much of this information comes from a specification book for the sensors and logic modules (not the factory Service Manuals FSM'S.) Maximum boost for your car depends on the year and type of engine and transmission you have. - The first turbo engine Chrysler released in 1984, had a mechanically controlled boost limit of 7 PSI. - 1985 and up vehicles had Computer-controlled wastegates, but MAX boost for 1985 was still set at 7psi. However, a PEAK boost feature that, under certain conditions, would allow more than the 7 PSI MAX limit, up to 9PSI. - PEAK boost - controlled by a TIMER in the computer, would allow for 10 cumulative seconds of PEAK boost through Wide-Open-Throttle application(s). For every second not using PEAK boost, another second would add to the TIMER, up to 10 seconds. (NOTE: The Mopar Performance and most aftermarket performance computer modules for these vehicles SHOULD remove the entire TIMER, and allow for unlimited use of PEAK boost.) - 1987+ TII, and TIII had a MAX boost of 9psi, w/ 11PSI PEAK boost limits. - OVERBOOST - Overboost is the term used to describe the action(s) the computer takes when its sensors detect more boost than its fuel system was capable of handling. (I THINK) spark is turned off to the different cylinders to limit engine speed and reduce boost, until it falls below the OVERBOOST limit. OVERBOOST shutdown settings were set at either 11PSI (2.2L TI) or 14 PSI(2.2L TII, 2.2L TIII, 2.2L VNT, and 2.5 TI) |
| **NOTE: I have seen compression ratio guides for these engines that vary in parameters. SOME 2.2L n/a's were rated at a factory 8.5:1, ETC.... |