If you're building toward an ISR Series II catback on your BMW E36 or you've already got a Series II rear installed and need the matching mid section, the Series II Resonated Mid Section is the front-half piece that ties the system together. It's the modular component that splices into the factory exhaust ahead of the cat and connects to either the MBSE or EP Dual Series II rear sections to complete a full catback.
What It Is
The ISR Performance Series II Resonated Mid Section is the modular mid-pipe component of the Series II E36 exhaust family. It ships as a complete front-half subsystem with the flex downpipes and hanger bracket needed to splice into the factory exhaust ahead of the catalytic converter. The Series II designation refers to ISR's modular architecture, which lets you mix and match mid sections (Resonated or Non-Resonated) with rear sections (MBSE or EP Dual) to build the exhaust configuration you want without replacing the entire system later.
What It Does
This is a standalone resonated mid section sold for E36 owners running a Series II catback or building toward one. The resonator keeps cabin drone in check at cruising speeds, which is the difference between an exhaust that's livable on the highway and one that gets old fast on long drives. The included flex downpipes connect the mid section to the factory exhaust ahead of the catalytic converter, and the hanger bracket ties everything to the chassis.
On its own, this is not a complete exhaust system. It's the front half of a Series II catback and needs to be paired with a Series II rear section to function as a finished exhaust.
Why Resonated Over Non-Resonated
The resonator in this mid section is doing a specific job: managing the standing waves and frequencies that cause cabin drone, particularly at highway cruise RPM. A non-resonated system delivers more raw volume and a more aggressive tone but typically comes with significantly more in-cabin drone, which is fatiguing on daily-driven cars and any car that sees regular highway miles.
The Resonated configuration is the better pick if the E36 is daily driven, sees regular highway miles, or you just want a more refined tone without sacrificing aggression under throttle. ISR also offers a Non-Resonated Series II mid section that drops directly into the same modular system if you want maximum volume and don't mind the drone tradeoff.
Modular System Compatibility
This mid section is part of ISR's Series II ecosystem and pairs with either of the available Series II rear sections:
- Series II MBSE Rear (IS-S2RO-MBSE-E36) for a dual 2.5 inch tip configuration
- Series II EP Dual Rear (IS-S2RO-EPD-E36) for an alternate tip configuration
The mid section is also used as the front-half component of ISR's pre-packaged complete Series II catbacks (IS-S2MBSER-E36 for the MBSE Resonated catback, IS-S2EPDR-E36 for the EP Dual Resonated catback), so if you've already purchased one of those complete kits, you already have this mid section.
The Series II architecture is the value play here. Start with one rear configuration, swap to the other later, or change from Resonated to Non-Resonated as your build evolves. You're not locked into a single sound or tip style at purchase.
Fitment and Compatibility
This mid section fits the BMW E36 OBDII 6-cylinder chassis. Multiple critical fitment notes apply.
Manual transmission only. This mid section is designed exclusively for manual transmission E36s. It will not fit automatic transmission variants. This requirement propagates through the entire Series II E36 system, so any Series II catback build requires a manual chassis.
OEM front chassis brace must be removed. The front chassis brace interferes with proper mid section fitment. The brace will need to be removed for installation and will not be reinstalled. This is a hard requirement for any Series II E36 exhaust build.
Not compatible with OEM exhaust or non-Series II catbacks. This mid section is designed exclusively to interface with a Series II rear section. It will not bolt up to the factory rear exhaust or to non-Series II aftermarket rear sections. If you're not already running a Series II rear (or planning to install one), this is not the mid section for your build.
Mid section only. This is not a complete exhaust system on its own. A Series II rear section is required to complete the catback.
Who This Is For
This mid section fits a few common build profiles. If you've already installed a Series II MBSE or EP Dual rear section on your E36 and need to add or replace the mid section, this is the matching front half. If you're building a Series II catback piece by piece instead of buying a complete kit, the mid section is one of the two components you need (paired with a Series II rear). If you already have the Non-Resonated mid section installed and want to swap to a quieter cruise-friendly configuration, this is the drop-in replacement.
This is not the right part if you're running a non-Series II catback, if you have an automatic E36, or if you're looking for a complete exhaust system in a single purchase. For a complete Series II catback, the IS-S2MBSER-E36 or IS-S2EPDR-E36 complete kits are the better starting point.
What's in the Box
- 1x Resonated mid section
- 2x Flex downpipes
- 1x Exhaust hanger bracket
- 1x Gasket and hardware pack
Installation Notes
Professional installation is recommended. Mid section installation requires lifting the vehicle, removing the OEM front chassis brace (this brace will not be reinstalled), and splicing the flex downpipes into the factory exhaust ahead of the catalytic converter. The mid section then connects to the Series II rear section at the existing modular junction. All hardware and gaskets are included for the mid section connections, but factory exhaust hangers and bushings should be inspected and replaced if worn.
Off-Road and Competition Use
This exhaust is legal only for use in competition vehicles which may never be registered, licensed, or used on public streets or highways, and for use in other exempted vehicles. It is not 50-state street legal. Verify local emissions and noise regulations before purchasing if you intend to drive the vehicle on public roads.
Product Details
Brand: ISR Performance
Product: Series II Resonated Mid Section
Part Number: IS-S2RMD-E36
Vehicle Fitment: BMW E36 OBDII 6-cylinder (manual transmission only)
Type: Series II modular mid section
Configuration: Resonated
Material: Stainless steel
Architecture: Series II modular (front-half component, requires Series II rear)
Compatible Rear Sections: IS-S2RO-MBSE-E36 (MBSE), IS-S2RO-EPD-E36 (EP Dual)
Used In Complete Kits: IS-S2MBSER-E36 (MBSE Resonated catback), IS-S2EPDR-E36 (EP Dual Resonated catback)
Transmission Compatibility: Manual only (NOT compatible with automatic)
Required Modifications: OEM front chassis brace must be removed
OEM Compatibility: Not compatible with OEM rear exhaust or non-Series II catbacks
Sold: Individually as mid section component (not a complete exhaust)
Included: Mid section, flex downpipes, hanger bracket, gasket and hardware pack
Legality: Off-road and competition use only, not 50-state street legal
Key Benefits: Modular Series II architecture for flexible exhaust configuration, resonated design reduces cabin drone for daily driving, ships complete with flex downpipes and hardware, pairs with either MBSE or EP Dual Series II rear sections