1. Home
  2. Engines
  3. Tillotson Engines
  4. Tillotson 212R Engine
  5. Tillotson 212R Exhaust
  6. RLV B91MO 1-5/16 Open Modified (Square Hole) Muffler
RLV B91MO 1-5/16 Open Modified (Square Hole) Muffler
4106 RLV B91MO 1-5/16" Mod/Open (Square Hole) Muffler
Write a Review

RLV B91MO 1-5/16 Open Modified (Square Hole) Muffler

Part Number: 4106
Online Price: $53.46
RLV B91MO 1-5/16" Open Modified Muffler – High Flow, Square Hole
Availability: In Stock.

Send to:

*We'll ask for shipping info at checkout

Description

RLV B91MO 1-5/16" Open Modified Muffler – Square Hole Design


The RLV B91MO Open Modified Muffler is designed for high-performance 4-cycle go-kart engines where class rules require mufflers, but minimal exhaust restriction is critical. Built with a square-hole baffle design, it delivers significantly higher flow than the standard RLV 4104 muffler—making it a favorite among racers in open and modified classes.


Crafted from durable steel and weighing just 0.9 lbs (409g), this muffler is ideal for limited modified, 14.5ci open modified, super stock, and other racing classes that allow open-style exhausts but still require a muffler. It’s also a solid choice for mini bikes, custom pit bikes, or small engine performance projects.


Note: This muffler is significantly louder than standard mufflers and may not comply with noise ordinances at all tracks. Check local rules before purchasing. If your class doesn’t require a muffler, running open exhaust may yield more power.


Muffler Specifications:

  • Mounting Inner Diameter: 1-5/16" (fits 1-5/16" OD header pipes)
  • Outside Diameter: 2.25"
  • Overall Length: 7"
  • Weight: ~0.9 lbs (409g)
  • Material: Steel
  • Includes: Worm gear clamp for support bracket
  • Mounting Bracket: Not included (available separately – 1-3/8" / 36mm recommended)


Key Features:

  • High-flow square-hole design for less restriction and more power
  • Compatible with open and modified go-kart racing classes
  • Lightweight but rugged – ideal for racing or custom engine builds
  • Louder exhaust note for aggressive sound (track legal status may vary)
  • Includes worm clamp for mounting support; safety wire recommended for racing
  • Great for mini bikes, pit bikes, and performance small engine projects


Fitment Notes:

  • Fits 1-5/16” OD 4-cycle header pipes
  • Commonly used in:
    • Limited Modified
    • 14.5ci Open Modified
    • Super Stock
    • Other muffler-required open kart classes
  • Also suitable for custom builds, minibikes, and DIY small engine projects

FAQ

Q1: What size exhaust header does this muffler fit?

A: The B91MO is designed to fit 1-5/16" OD 4-cycle exhaust header pipes.


Q2: How does this muffler compare to the RLV 4104?

A: The B91MO offers less restriction and higher flow than the RLV 4104. It’s louder, and better suited for open or modified engine classes where performance is a higher priority than noise reduction.


Q3: Is this muffler legal at all tracks?

A: No. Due to its louder sound output, the B91MO may not meet noise restrictions at certain tracks. Always check your local track or series rules before using it.


Q4: What racing classes is this muffler used in?

A: Commonly used in:

  • Limited Modified
  • 14.5ci Open Modified
  • Super Stock
  • Other open kart classes where a muffler is still required

It’s also popular for mini bikes and custom small engine builds.


Q5: Does this muffler need additional support?

A: Yes. Due to the weight being cantilevered on the header, we recommend a support bracket (not included) and safety wire to secure it—especially for racing applications.


Q6: What’s included with the muffler?

A: The B91MO comes with a worm gear clamp for support. The mounting bracket (1-3/8" / 36mm) is sold separately.

Related Items

Recently Viewed Items

Logo