Granatelli Motor Sports 3.5 inch electric exhaust cutout kit
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3.5 Inch Exhaust Cutout Guide: Sizing, Electric vs. Manual, and How to Choose

By Joey Granatelli3 min read

3.5" vs. 3" or 4"? Electric or manual? How to choose a 3.5 inch exhaust cutout, where to mount it, what the law says, and every Granatelli Motor Sports 3.5" kit.

A 3.5 inch exhaust cutout gives you a quiet exhaust for the street and an open exhaust for the track. 3.5" tubing is typical of high-output builds that have outgrown 3" exhaust. Before you buy, you have three decisions to make: whether 3.5" is really your size, how you want to control the cutout, and whether you need a single or dual kit.

This guide walks through each one, then covers mounting, the legal picture and every 3.5" kit Granatelli Motor Sports makes.

3.5" vs. 3" or 4": Which Size Do You Need?

Measure the pipe you have

3.5" sits between the two most common large sizes, so measure carefully. Use calipers on the outside diameter of the pipe where the cutout will mount. Stepping a 3.5" system down to a 3" cutout adds a restriction, and stepping up to 4" means fabricating adapters.

Is a bigger cutout louder?

Not on its own. Your mufflers do most of the quieting. With the cutout closed, the exhaust sounds the same as before. With it open, exhaust exits before the mufflers, so any size gets much louder.

Measured a different size? See our 3 Inch Electric Exhaust Cutout Guide or 4 Inch Exhaust Cutout Guide.

Electric or Manual?

Every type bypasses the mufflers when open. The difference is how you open and close it.

Type How you control it What's in the kit Best for
Electric One-touch rocker switch in the cab Cutout with motor, switch, wiring harness, turndown, V-band clamp, gaskets, hardware Street/strip cars you want to open from the driver's seat
Manual By hand: remove the block-off plate Cutout with block-off plate only. No motor, wiring or vacuum pump Track days and budget builds where you open it before the run

Want wireless remote control with its own vacuum pump? Granatelli Motor Sports vacuum/pressure-controlled kits come in 2.5" and 3"; see the 2.5 Inch Exhaust Cutout Guide.

Single or Dual?

Match the kit to your exhaust layout. A true dual exhaust needs one cutout per side so both banks open together and the sound stays balanced; that's what the dual kits (part numbers ending in K or D) are for. A single exhaust, or a system downstream of a merge, needs only one cutout.

Weld-In vs. Slip-Fit, Stainless vs. Mild Steel

Option Best for Trade-offs
Weld-in / weld-on Permanent, leak-free installs; builders with welding access or a muffler shop Requires welding; harder to remove later
Slip-fit / clamp-on DIY installs and systems you may change later Clamped joints need periodic re-torquing
Stainless steel Daily drivers, wet climates, salted roads Higher price
Mild steel Budget builds and vehicles kept dry Will corrode without coating

Where to Mount a 3.5" Cutout

  • Keep your distance. Mount at least 18" from the cylinder head and any O2 sensor (Speedway Motors).
  • Always after the cats. Never install a cutout upstream of a catalytic converter.
  • After the crossover for sound. Mounting after the X-pipe or H-pipe gives the best tone.
  • Dump outward. Aim the turndown or opening toward the rocker panel, away from fuel, brake and transmission lines, so fumes don't collect under the car.
  • Plan for the control type. Keep electric wiring away from the pipe, and put manual cutouts where you can reach the block-off plate.

For step-by-step install notes and dyno results, see the 3 Inch Electric Exhaust Cutout Guide. The process is the same at 3.5".

Are 3.5" Exhaust Cutouts Legal?

Size doesn't change the law. SEMA describes U.S. exhaust noise rules as a 50-state patchwork, and many state statutes specifically name "cutout, bypass, or similar device." California Vehicle Code 27150, for example, prohibits cutouts on registered vehicles but exempts off-highway use at sanctioned racing events. In practice, keep the cutout closed on public roads, use it at sanctioned events, and check your own state's statute. This is general information, not legal advice.

Granatelli Motor Sports 3.5" Exhaust Cutout Kits

Type Material / install Single Dual
Electric Stainless steel, slip-fit 302535 302535D
Manual Stainless steel, clamp-on 305535 305535D

Electric kits carry a 90-day warranty with optional 1-, 2- or 3-year extended coverage, and every order over $100 ships free.

Frequently Asked Questions

What size exhaust cutout do I need?

Measure the outside diameter of your exhaust pipe where the cutout will mount, and buy that size.

Can I use a different size cutout on 3.5" pipe?

Only with adapters. A smaller cutout creates a restriction where you want flow, and a larger one adds fabrication and leak points. Matching the pipe is the better choice.

Which is easier to install, electric or manual?

The cutout itself installs the same way. Electric kits add a switch and wiring; manual kits need neither.

Will a cutout add horsepower?

Opening the cutout reduces backpressure. Gains depend on your engine, headers and tune.

Keep reading: Shop all Granatelli exhaust cutouts · What size exhaust cutout do I need? · Exhaust Cutout FAQ

Shop Granatelli Motor Sports

View the Granatelli 302535 3.5" Stainless Steel Slip-Fit Electric Exhaust Cutout Kit

View the Granatelli 305535 3.5" Stainless Steel Clamp-On Manual Exhaust Cutout Kit

Need help choosing a cutout for your build? Call 1-805-486-6644.

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