The X3 M40i and X4 M40i carry the same B58 six as BMW's best sport sedans, then hide it behind a quiet exhaust and two plain slip-on tips. It is fast, and it sounds like a crossover. If you picked the M40i because you wanted the engine, you should get to hear it.
The Dinan Valved Cat-Back Exhaust with black tips replaces everything behind the catalytic converters on the BMW G01 X3 M40i and G02 X4 M40i. The factory center collector and resonator are gone, the split routing becomes one straighter 83mm pipe (80mm stock), and the rear exits through a true quad-tip layout with four 3.75 in. black ceramic tips. It keeps the factory valve, so the car still settles down when you do.
How the Dinan Valved Cat-Back Exhaust Keeps Sound Without Drone
Loud is easy. Livable is the hard part in an SUV you drive every day. Dinan uses a Helmholtz-equipped muffler that targets the frequencies behind interior drone, while the free-flowing single pipe gives the B58 a sharper, fuller voice. The factory valve stays in place, so low-speed cruising stays composed and the pipe opens up under hard acceleration. Want the valve open on demand? The system works with an optional aftermarket exhaust valve remote.
The quad tips are four separate working pathways, not Y-tips or dummy outlets. The whole system is brushed 100% T304 stainless steel, TIG welded, with no hydroformed pipe. At 53 pounds against the factory 60, it also takes 7 pounds off the rear of the car. Dinan measured up to 6 HP and 5 lb-ft at 6600 RPM.
Dinan Cat-Back Exhaust Install and Legal Status
This is a direct bolt-on that uses the factory mounting points. No cutting and no welding. It fits both pre-LCI and LCI cars. Because it starts after the catalytic converters, it does not affect vehicle emissions: Dinan rates it Emissions Code 5, legal for sale or use on emissions-controlled vehicles. Dinan part number D660-0099-BLK. Sold by AutoTecknic, an authorized Dinan dealer.
What's Included
- Dinan valved cat-back exhaust, brushed T304 stainless steel
- Four 3.75 in. (95mm) double-walled black ceramic-coated clamp-on tips
- Valve componentry
- Clamps, hangers and mounting hardware
Key Features
- Removes the factory center collector and resonator
- Single straight-through pipe, 83mm vs 80mm stock
- Helmholtz-equipped muffler to reduce drone frequencies
- Factory exhaust valve retained, compatible with an aftermarket valve remote
- True quad-tip layout with four individually working outlets
- Four 3.75 in. double-walled black ceramic-coated tips
- 100% T304 stainless steel, TIG welded, no hydroformed pipe
- 7 pounds lighter than stock (53 lb vs 60 lb)
- Dinan-measured gain of up to 6 HP and 5 lb-ft at 6600 RPM
- Emissions Code 5: does not affect vehicle emissions
Vehicle Fitment
Fits the following B58-powered BMW M40i models, pre-LCI and LCI:
- BMW X3 / G01 (2018-2024): X3 M40i
- BMW X4 / G02 (2019-2025): X4 M40i
Not for the F97 X3M, F98 X4M or the 2025 and newer G45 X3.
Installation Notes
Dinan rates the install at about 2.3 hours using the factory mounting locations. It is a full cat-back, so a lift and a second set of hands make it much easier. Most owners have a shop install it.
- Let the exhaust cool completely and raise the vehicle safely on a lift.
- Disconnect the factory exhaust valve and loosen the clamp behind the catalytic converters.
- Unhook the factory cat-back from its hangers and lower it out with a helper.
- Transfer or connect the valve componentry as shown in the Dinan instructions, then hang the Dinan system on the factory mounts.
- Align the sections and tips, tighten every clamp, then start the car and check for leaks and correct valve operation.
