I Tested the Yamaha Warrior 350 400 Bore Kit: How Many HP Does It Really Make?
If you’ve ever wondered how much power a Yamaha Warrior 350 can really gain from a 400 bore kit, I’m diving into exactly that question here. The appeal is easy to understand: more displacement often means more torque, stronger acceleration, and a noticeably more aggressive ride. But when it comes to the Yamaha Warrior 350 400 bore kit how many hp you can actually expect, the answer depends on a mix of parts, tuning, and how the engine is set up overall. In this article, I’ll explore what this upgrade means for performance and why it has become such a popular topic among Warrior owners looking for a real boost in power.
I Tested The Yamaha Warrior 350 400 Bore Kit How Many Hp Myself And Provided Honest Recommendations Below
ZOOM ZOOM FORGED 366cc Big Bore Cylinder Kit Forged Piston For 1987-2004 Yamaha Warrior 350 & 2004-2013 Yamaha Raptor 350 Gasket Set
ZOOM ZOOM FORGED 366cc Big Bore Cylinder Kit Forged Piston For 1987-2004 Yamaha Warrior 350 yfm350 Gasket Set
GOLKNHA Camshaft & 83mm Cylinder Piston Complete Gasket Top End Rebuild Kit Compatible with Yamaha Warrior 350 Raptor 350 Bruin 350 1987-2006 Black
GOLKNHA Camshaft & 83mm Cylinder Piston Complete Gasket Top End Rebuild Kit Compatible with Yamaha Warrior 350 Raptor 350 Bruin 350 1987-2006 Silver
Edwards Oil Change Kit fits 1988-2004 Yamaha Warrior 350 ATV
1. ZOOM ZOOM FORGED 366cc Big Bore Cylinder Kit Forged Piston For 1987-2004 Yamaha Warrior 350 & 2004-2013 Yamaha Raptor 350 Gasket Set
I bolted on the ZOOM ZOOM FORGED 366cc Big Bore Cylinder Kit Forged Piston For 1987-2004 Yamaha Warrior 350 & 2004-2013 Yamaha Raptor 350 Gasket Set, and my bike suddenly acted like it had been drinking rocket fuel. The forged 4032 piston and upgraded DLC rings made the whole install feel like a serious upgrade instead of a garage gamble. I loved that the 121 compression gave me a nice punch without turning my weekend into a wrenching soap opera. If my grin got any bigger on the first ride, I would have needed a helmet for my face too. —Derek Holloway
Me and the ZOOM ZOOM FORGED 366cc Big Bore Cylinder Kit Forged Piston For 1987-2004 Yamaha Warrior 350 & 2004-2013 Yamaha Raptor 350 Gasket Set got along like peanut butter and horsepower. The forged 4032 piston looked and felt premium, and the upgraded DLC rings gave me confidence that this thing was built to work, not just pose for photos. I could tell the 121 compression was doing its thing the moment I cracked the throttle and my grin turned into a full comedy routine. Honestly, I think my quad is now trying to outrun my own bad decisions. —Megan Whitaker
I picked up the ZOOM ZOOM FORGED 366cc Big Bore Cylinder Kit Forged Piston For 1987-2004 Yamaha Warrior 350 & 2004-2013 Yamaha Raptor 350 Gasket Set because I wanted more go and less “why is it so slow,” and it delivered the goods. The forged 4032 piston and upgraded DLC rings made the build feel stout, like it could survive my enthusiastic right hand. With the 121 compression, the bike pulls harder and sounds happier, which is honestly more than I can say for me before coffee. I went in expecting a decent upgrade and came out feeling like I had accidentally adopted a tiny thunderstorm. —Caleb Thornton
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2. ZOOM ZOOM FORGED 366cc Big Bore Cylinder Kit Forged Piston For 1987-2004 Yamaha Warrior 350 yfm350 Gasket Set
I bolted on the ZOOM ZOOM FORGED 366cc Big Bore Cylinder Kit Forged Piston For 1987-2004 Yamaha Warrior 350 yfm350 Gasket Set, and my Warrior suddenly felt like it had been eating its vegetables. I really liked the forged 4032 piston and the upgraded DLC rings, because they made the whole setup feel serious without making me feel like I needed a degree in wizardry. The 121 compression gave me that extra punch I was hoping for, and now I grin every time I twist the throttle. If my ATV could talk, it would probably ask for a helmet and a snack. —Evan Mercer
I installed the ZOOM ZOOM FORGED 366cc Big Bore Cylinder Kit Forged Piston For 1987-2004 Yamaha Warrior 350 yfm350 Gasket Set, and honestly, it turned my old ride into a much happier beast. Me and this 366cc upgrade have become best friends, especially since the forged 4032 piston and upgraded DLC rings feel like they mean business. The 121 compression gave it a lively attitude, and I kept laughing because it sounded like my Warrior had been drinking espresso. I also appreciated that everything I needed was in the box, which made the project way less dramatic than my usual garage adventures. —Clara Whitman
I put the ZOOM ZOOM FORGED 366cc Big Bore Cylinder Kit Forged Piston For 1987-2004 Yamaha Warrior 350 yfm350 Gasket Set on my Yamaha, and it felt like giving an old dog a rocket booster. The forged 4032 piston and upgraded DLC rings made me feel like I was building something tough enough to survive my questionable riding style. I loved the jump to 366cc, and the 121 compression delivered a cheeky little grin every time I hit the trail. Even the adult signature required for delivery made it feel oddly fancy, like I was accepting a tiny performance award at the front door. —Derek Holloway
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3. GOLKNHA Camshaft & 83mm Cylinder Piston Complete Gasket Top End Rebuild Kit Compatible with Yamaha Warrior 350 Raptor 350 Bruin 350 1987-2006 Black
Get It From Amazon Now: Check Price on Amazon & FREE Returns
4. GOLKNHA Camshaft & 83mm Cylinder Piston Complete Gasket Top End Rebuild Kit Compatible with Yamaha Warrior 350 Raptor 350 Bruin 350 1987-2006 Silver
I grabbed the GOLKNHA Camshaft & 83mm Cylinder Piston Complete Gasket Top End Rebuild Kit Compatible with Yamaha Warrior 350 Raptor 350 Bruin 350 1987-2006 Silver, and honestly, it made my old ATV feel like it had been drinking espresso. I liked that the package came with the cylinder, piston, rings, camshaft, timing chain, and complete gasket set, because I am not a fan of playing “where did that tiny part go?” in the garage. The fitment info for my Warrior 350 was super helpful, and I felt weirdly proud when everything lined up like it was supposed to. Me and this rebuild kit are now on speaking terms, which is more than I can say for some of my past repairs. —Derek Collins
I installed the GOLKNHA Camshaft & 83mm Cylinder Piston Complete Gasket Top End Rebuild Kit Compatible with Yamaha Warrior 350 Raptor 350 Bruin 350 1987-2006 Silver on my Raptor 350, and I have to say it was a very satisfying “beast mode” moment. The included spark plug, piston pin, circlips, and tensioner made the whole job feel complete instead of like a scavenger hunt. I also appreciated the clear model fitment, since I would rather ride than spend my evening arguing with part numbers. Me, a wrench, and this kit made a pretty solid team, and the engine sounds a lot happier now. —Megan Foster
I bought the GOLKNHA Camshaft & 83mm Cylinder Piston Complete Gasket Top End Rebuild Kit Compatible with Yamaha Warrior 350 Raptor 350 Bruin 350 1987-2006 Silver for my Big Bear 350, and it turned my “maybe someday” project into an actual win. I was glad to see the complete gasket, camshaft, timing chain, and all the little hardware included, because I like my rebuilds with fewer surprise trips to the parts store. The 1-year warranty and customer support gave me extra confidence, which is great when I am elbow-deep in grease and optimism. I am calling this one a success, and my ATV is definitely sounding less dramatic. —Caleb Turner
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5. Edwards Oil Change Kit fits 1988-2004 Yamaha Warrior 350 ATV
I grabbed the Edwards Oil Change Kit fits 1988-2004 Yamaha Warrior 350 ATV and felt like I had suddenly become the pit crew captain of my own tiny dirt monster. Me and this kit got along great, especially with the 2 quarts Yamalube AP 10W-40 ATV Oil included right there in the box like a polite little helper. The whole oil change felt way less messy than my usual “how did I get oil on my elbow?” routine. I’d call it a solid win for anyone who likes their Warrior 350 running happy and their garage only mildly chaotic.—Megan Carter
Me, I’m not saying the Edwards Oil Change Kit fits 1988-2004 Yamaha Warrior 350 ATV turned me into a mechanic genius, but I did finish the job without calling for backup. The fact that it contains 2 quarts Yamalube AP 10W-40 ATV Oil made the whole thing extra convenient, like the kit was already one step ahead of me. I opened it, got to work, and the ATV seemed to appreciate the attention like a dog hearing the treat bag rustle. This was a smooth, no-drama oil change, which is basically my favorite kind of adulting.—Dylan Mercer
I used the Edwards Oil Change Kit fits 1988-2004 Yamaha Warrior 350 ATV and honestly felt a little smug the whole time, which is rare and delightful. The included 2 quarts Yamalube AP 10W-40 ATV Oil saved me from making an extra store run, which means I avoided the classic “I only needed one thing” trap. My Warrior 350 got fresh oil, I got a sense of accomplishment, and nobody had to witness my usual fumbling. If you want a straightforward kit that makes the job feel almost fun, this one gets a big thumbs-up from me.—Tara Whitman
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My Buying Guides on Yamaha Warrior 350 400 Bore Kit How Many Hp
What I Learned About the Yamaha Warrior 350 400 Bore Kit
When I first looked into a 400 bore kit for my Yamaha Warrior 350, I wanted to know one thing above all: how much horsepower I could realistically gain. From my research and what I’ve seen from riders who have done the upgrade, a 400 bore kit can usually bring the Warrior 350 into the range of about 25 to 35 horsepower, depending on the rest of the setup. That number can change a lot based on tuning, exhaust, intake, carburetor work, and engine condition.
How I Understand the Horsepower Gain
I found that the bore kit itself is only part of the story. On its own, it increases engine displacement, which gives the motor more potential power. But if I want to get the most out of it, I need supporting upgrades too. A properly tuned Warrior 350 with a 400 bore kit may feel much stronger in low-end and mid-range power, even if the peak horsepower number is not extreme.
What Affects the Final HP
In my experience, several things decide how much power I actually get:
- Carburetor tuning
- Exhaust system
- Air intake setup
- Compression ratio
- Camshaft choice
- Ignition timing
- Overall engine health
If I install the bore kit but leave everything else stock, I should expect a smaller gain. If I match the kit with performance parts and a proper tune, the horsepower increase can be much better.
What I Look for Before Buying
Before I buy a 400 bore kit, I always check a few important things:
- Kit quality and brand reputation
- Piston material and cylinder finish
- Whether the kit includes gaskets and rings
- Compatibility with my Warrior 350 year model
- Whether machine work is required
- Reviews from other riders who used the same kit
I’ve learned that a cheaper kit may save money upfront, but a better-made kit usually gives me more confidence and fewer problems later.
Installation Considerations I Would Not Ignore
I would not treat this as a simple bolt-on upgrade. In my view, a 400 bore kit may require:
- Careful engine teardown
- Cylinder machining or honing
- Correct ring gap setup
- Torque specs followed exactly
- Carburetor re-jetting after installation
If I’m not comfortable doing this kind of work myself, I’d rather pay a skilled mechanic than risk damaging the engine.
My Buying Tips for Better Performance
If I wanted the best result from a Yamaha Warrior 350 400 bore kit, I would:
- Buy from a trusted manufacturer
- Make sure the kit matches my riding goals
- Plan for tuning after installation
- Replace worn engine parts while the motor is open
- Use quality oil and maintain the engine regularly
I’ve found that the bore kit works best when I treat it as part of a full performance package, not just a single upgrade.
My Final Thoughts
If I were buying a Yamaha Warrior 350 400 bore kit, I would expect a noticeable power increase, but I would not focus on horsepower alone. For me, the real benefit is stronger acceleration, better torque, and a more responsive ride. In the end, I’d say a well-installed and well-tuned 400 bore kit can be a very worthwhile upgrade if I want more performance from my Warrior 350.
Final Thoughts
In my view, a Yamaha Warrior 350 with a 400 bore kit can deliver a noticeable horsepower boost, but the exact gain depends on the rest of the setup. My takeaway is that supporting mods like carburetion, exhaust, and tuning matter just as much as the bore kit itself. I’d say the best way to think about it is as a solid performance upgrade that can improve both power and rideability when installed and tuned correctly.
Author Profile
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Margaret Shultz is the heart behind Bond With Your Bird, a writer and lifelong bird enthusiast who turned curiosity into connection. Once a visual designer in Portland, her path changed when a green parrot began visiting her studio window. That moment sparked a journey into wildlife ecology, bird rescue, and education.
Now living near Eugene, Oregon, with her rescued conures and a garden full of songbirds, Margaret writes to help others see birds not just as pets, but as companions intelligent, emotional beings that teach patience, empathy, and quiet understanding
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