Replacement Engine
I would like to replace my 1994 Nissan Maxima engine with one that requires less fuel but gives the same performance and power. Can you suggest one for me please.

The Nissan Maxima, which was due for a redesign the next year, saw no significant changes for 1994. The 1994 Nissan Maxima came in two trims: the GXE and the sportier SE. The SE was available with a five-speed manual or automatic transmission, and the GXE was available only with the four-speed manual. The GXE had a 3.0-liter, 160-horsepower V6, which was bumped up to 190 horses for the SE. The fuel economy is about 19/26 mpg for both engines. Drivers like the 1994 Nissan Maxima because it is a solid, dependable car that comes chock full of comfort amenities and is fun to drive. Many drivers find fault with the mechanical seatbelts.
I would like to replace my 1994 Nissan Maxima engine with one that requires less fuel but gives the same performance and power. Can you suggest one for me please.
makes a roaring sound when deriving and gets louder when the car goes faster
Can't seem to keep the lower pulley tight and then it thows the belts. Any ideas?
Air Conditioning
Automatic climate control front air conditioning
Airbags
Driver side front airbags
Audio System
Antenna Type: power · Single disc in-Dash CD · Premium Brand: Bose · AM/FM radio
Brakes
ABS: 4-wheel
Comfort Features
Steering wheel trim: leather
Convenience Features
Multi-function remote: keyless entry · Steering wheel: tilt-adjustable
Exterior Features
Paint: special factory paint
Lights
Exterior entry lights: security approach lamps
Mirrors
Exterior mirrors: heated
Roof
Moonroof: power
Seats
Front seat type: bucket · Upholstery: leather
Tires and Rims
Wheel type: aluminum alloy
Windows
Front wipers: intermittent
Airbags
Driver side front airbags
Audio System
Antenna Type: power · Single disc in-Dash CD · Premium Brand: Bose · AM/FM radio
Brakes
ABS: 4-wheel
Comfort Features
Steering wheel trim: leather
Convenience Features
Multi-function remote: trunk release · Steering wheel: tilt-adjustable
Drivetrain
Limited slip differential: front
Exterior Features
Paint: special factory paint
Lights
Exterior entry lights: security approach lamps
Mirrors
Exterior mirrors: power
Roof
Moonroof: power
Seats
Front seat type: bucket · Upholstery: cloth
Tires and Rims
Wheel type: aluminum alloy
Windows
Front wipers: intermittent