Manual Exhaust Cutout Guide: How They Work, Manual vs. Electric, and How to Choose

A manual exhaust cutout is the simplest way to get an open exhaust when you want it: a branch off your exhaust with a block-off plate. Leave the plate on and the car drives like normal. Take it off, and the exhaust exits before the mufflers. No motor, no wiring, no vacuum lines, and nothing electrical to fail.

This guide explains how manual cutouts work, when one makes more sense than an electric or vacuum kit, how to pick the size and style, and where to mount it. It ends with every manual cutout kit Granatelli Motor Sports makes.

How a Manual Exhaust Cutout Works

The cutout is a short branch on your exhaust pipe that ends in a flange. A block-off plate seals that flange for normal driving, so exhaust flows through the mufflers as usual. When you remove the plate, exhaust takes the shorter path out of the branch instead, which raises volume and reduces restriction. Reinstall the plate, and you're back to stock-quiet.

Manual vs. Electric vs. Vacuum Cutouts

All three bypass the mufflers when open. The difference is how you open and close them, and what that costs.

When a manual cutout is the right choice

• Track and drag-strip cars where you open the exhaust in the pits before you run.
• Budget builds where the money is better spent elsewhere.
• Cars in strict areas where you want no temptation to open the exhaust on the street.
• Builds where you want to avoid extra wiring under the car.

If you want to open and close the exhaust while driving, choose an electric or vacuum kit instead. Not sure yet? A manual kit can be upgraded to electric later.

Choosing a Size

Match the cutout to your exhaust tubing, not to your engine. Measure the outside diameter of the pipe where the cutout will mount, ideally with calipers. Granatelli Motor Sports makes manual cutouts in 2.25", 2.5", 3", 3.5" and 4". For help deciding between sizes, see the size guides: 2.25", 2.5", 3", 3.5", 4".

Clamp-On vs. Weld-On, Stainless vs. Mild Steel

Where to Mount a Manual Cutout

• Somewhere you can reach. You'll remove the block-off plate by hand, so pick a spot you can get to with the car on ramps or jack stands.
• 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.
• Point it outward. Aim the opening toward the outside of the car, away from fuel, brake and transmission lines, so fumes don't collect underneath.
• After the crossover for sound. Mounting after the X-pipe or H-pipe gives the best tone.

Using It at the Track

• Let it cool first. The cutout and plate get very hot. Wait for the exhaust to cool, or wear heat-resistant gloves, before you remove or reinstall the plate.
• Keep the hardware together. Bring the tools you need and keep the plate and its fasteners in a bag so nothing gets lost in the pits.
• Reinstall before you leave. Put the plate back on before you drive home on public roads.

Are Manual Exhaust Cutouts Legal?

Manual or electric, the law treats them the same. 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 block-off plate installed on public roads, open the cutout only at sanctioned events, and check your own state's statute. This is general information, not legal advice.

Granatelli Motor Sports Manual Exhaust Cutout Kits

Every kit comes with a block-off plate. Dual kits (part numbers ending in D) include a cutout for each side of a true dual exhaust. You can also browse the mild steel manual exhaust cutouts collection.

Frequently Asked Questions

What is a manual exhaust cutout?

A branch off your exhaust sealed by a block-off plate. Remove the plate to open the exhaust before the mufflers; reinstall it to close it.

Is a manual or electric cutout better?

Manual is cheaper and has nothing to fail. Electric lets you open and close it from the driver's seat. Choose manual if you only open the exhaust at the track.

Does a manual cutout need a motor or wiring?

No. Granatelli Motor Sports manual kits come with a block-off plate only: no electric motor, no wiring and no vacuum pump kit.

Can I install one myself?

Clamp-on kits are a reasonable DIY job with basic hand tools and a way to cut the pipe. Weld-on kits need welding equipment or a muffler shop.

Will it add horsepower?

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

Can I upgrade to electric later?

Yes. A Granatelli Motor Sports manual kit can be upgraded to electric, so you can start with the block-off plate and add a motor when you're ready. Motor-only parts are available, including the 2.25" 307522W, 3" 307530W and 3.5" 307535W. Call us at 1-805-486-6644 with your part number and we'll confirm everything your size needs.

Keep reading: Shop all Granatelli exhaust cutouts · Electronic or manual exhaust cutout? · Exhaust Cutout FAQ

Shop Granatelli Motor Sports

View the Granatelli 305530 3" Stainless Steel Clamp-On Manual Exhaust Cutout Kit

View the Granatelli 305525D Dual 2.5" Stainless Steel Clamp-On Manual Exhaust Cutout Kit

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