New Batch in Production…More Pipes Available Fall 2021

All Fat Boy 4 Exhaust Systems come with a FREE jet kit (for stock carburetor)included with instruction packet

DRI offers a LIFETIME WARRANTY against defects in materials and workmanship on all Fat Boy 4 systems sold. Warranty is for original purchaser only and is non-transferable. Each system is supplied with warranty registration card that must be read, signed and returned to DRI.

Optional Accessories
See Below

Other Required modifications:
Pro Flow Air Cleaner with K&N Air Filter, Carburetor Re-Jetting.On DRI Retail direct sales jets for stock OEM carburetors are supplied at no charge.
Larger C/S sprocket advisable in hard pack terrain or on with 18" tires.

Performance: 25% HP Gain peak; 21 bike length gain in a 300 yard acceleration run, average. Outstanding throttle response and excellent midrange pull.
Fat Boy 4 4-Stroke Power Exhausts are a proprietary product of Duncan Racing International, Inc. DRI is the sole manufacture and developer of this product. DRI has designed this product to be the top ATV 4-Stroke exhaust on the market.


Fat Boy 4 Features

-CNC Bent 304 stainless steel headers, mid-pipes and tail sections. Standard finish; brite finish.
-CNC machined stainless steel header flanges.
-Custom designed .100" wall aluminum extrusion muffler body. Standard finish satin. Polished by special order.
-Front and Rear End Caps CNC machined from 6061 billet aluminum.
-Muffler mounts CNC machined from single piece of 6061 billet aluminum. Attached to muffler body by heli-arc weld.
-O-Ring Seal at tail pipe to muffler joint.
-All mufflers completely rebuild able and repack able.
-Stainless muffler cores.
-Optional (at additional cost) Bolt On Turndown; redirects exhaust fumes and noise toward the ground. Also required for use with spark arrestor. Attaches with 4 stainless screws (supplied) and has O-Ring seal.
-All systems are individually marked with their own serial number.
-Complete DRI Technical phone support for installation and carburetor jetting questions.


Fat Boy 4 HQ Muffler Features

-25% More Packing than Standard Fat Boy 4 Muffler
-Core and Packing are Specially Designed to Reduce Noise
-20%-30% Lighter than Stock Exhaust (varies with model)
-99-97dB Noise Output, 2-3dB Quieter than Standard Fat Boy 4 (varies with model)
-Comes with Turndown and Spark Arresting Screen