G. Jay Nelson
Recruit
- Joined
- Jan 27, 2026
- Messages
- 1
I have a 1999 Silverton 392 that has the Crusader 7.4 XL (454 ci) Throttle Body Injection (TBI) engines. The engines are tired, but hull and interior of the boat are in excellent shape, so I have decided to repower the boat. The Crusader 7.4 XL was a 380-horsepower engine, but is obviously no longer manufactured. I have decided to replace these engines with new Mercruiser engines.
There are essentially two Mercruiser options available for repowering my boat: the 350 HP, 6.1 L MAG Stroker Bravo MPI, or the 375 or 425 HP, 8.2 L Horizon DTS ECT in either standard or high output configurations. The 350 HP, 6.1 L Stroker engine is designed as a direct replacement for the 7.4 L GM engine, and economically mates to former 7.4 applications (i.e., engine mounts, transmission/throttle connections, and console configurations, etc.) and can use the current transmissions. The 8.2L engines require the transmissions be replaced, have issues fitting into previous 7.4 L engine spaces, and require extensive console rebuilding to convert to the fly-by-wire system.
In short, the 350 HP, 6.1 L Stroker engine is a much more cost-effective conversation than moving up to the 8.2 L engines. My concern is the boat’s performance with the lower HP engines. The low-end torque is greater on the 350 HP, 6.1 L Stroker than the old 7.4 L Crusader and the top end RPM is higher, but the HP is 30 HP less (combined 60 HP less). The Silverton 392 is 39.9 LWL and has a maximum weight of about 28,000 pounds. I typically cruise at 8.5 knots (displacement speed), but would like the occasional speed to outrun weather. Has anyone repowered a 39-foot cabin cruiser with the 350 HP, 6.1 L MAG Stroker Bravo engines that can offer me some insight as to the potential changes in performance?
There are essentially two Mercruiser options available for repowering my boat: the 350 HP, 6.1 L MAG Stroker Bravo MPI, or the 375 or 425 HP, 8.2 L Horizon DTS ECT in either standard or high output configurations. The 350 HP, 6.1 L Stroker engine is designed as a direct replacement for the 7.4 L GM engine, and economically mates to former 7.4 applications (i.e., engine mounts, transmission/throttle connections, and console configurations, etc.) and can use the current transmissions. The 8.2L engines require the transmissions be replaced, have issues fitting into previous 7.4 L engine spaces, and require extensive console rebuilding to convert to the fly-by-wire system.
In short, the 350 HP, 6.1 L Stroker engine is a much more cost-effective conversation than moving up to the 8.2 L engines. My concern is the boat’s performance with the lower HP engines. The low-end torque is greater on the 350 HP, 6.1 L Stroker than the old 7.4 L Crusader and the top end RPM is higher, but the HP is 30 HP less (combined 60 HP less). The Silverton 392 is 39.9 LWL and has a maximum weight of about 28,000 pounds. I typically cruise at 8.5 knots (displacement speed), but would like the occasional speed to outrun weather. Has anyone repowered a 39-foot cabin cruiser with the 350 HP, 6.1 L MAG Stroker Bravo engines that can offer me some insight as to the potential changes in performance?
