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Motorcycle News, Editorials, Product Reviews and Bike Reviews

  • December 20, 2013
  • Gabe Ets-Hokin
  • Surj Gish and

BTR GP: A dream becomes real



“I always wanted a roadrace-worthy Harley with a big-Twin motor.”

If anyone but Curt Winter told me that, I’d smirk and say something like, “good luck with that.” What American sportbiker wouldn’t want the torque of a Big Twin built into the handling of a roadracer? Too bad the heft and girth of the “Big Twin”—a moniker applied to the non-Sportster Harley-Davidson engines as well as their aftermarket clones—powerplant makes packaging a motorcycle with a sporty wheelbase almost impossible, right? Wrong—and you can’t tell a man he’ll never build his dream when he’s standing right next to it.

The 45-year-old San Leandro native has always loved motorsports; his dad, Frank Winter was a mechanic, machinist, “street hooligan” and the go-to guy for tuning work in his circle of riding buddies. “My dad rode an old rigid-frame Triumph with a Panhead motor in it,” Winter said—in the Winter family, you built what you wanted. “When I was a kid, I didn’t have money, but I had time and tools and my dad. He never gave me stuff, instead he gave me tools, parts…the stuff to build it.” When Curt was 10, he took the grinder and welding torch to his Mustang minibike, converting the rigid frame to a swinger with some pieces of flatbar and the springs from the saddle. He traded in the Mustang for a Yamaha JT2, which he rode and raced as a teen. After high school Curt went to work for the family business, Mar-Len Supply—which he helps run with other family members to this day.

Sharing space in the time-worn but tidy shop is Winter’s full-time business, BTRmoto. Over the past few years, he’s fabricated frames and other parts for over 40 projects—mostly hill climbers, where his 200-horsepower, nitro-fuelled Harley-engine racers do quite well. Curt’s racing career started when he was a teenager, and now he and teammate Jamie Perry attend hillclimbs all over the country with his family in tow.

Still, he’s always loved riding pavement, but like his father, likes the authoritative thump of the Big Twin. Back in the early ’90s he built his first Big Twin streetfighter, a bike so clean and well-built it caught the eye of Battle2Win and Thunder Press founder Reg Kittrelle. Since then, he’s been doing custom projects—a notable client is Arlen Ness, with Curt’s work featured on a Discovery Channel program—mostly with a sportbike slant.



When Winter decided he wanted a competitive roadracer, he knew what he had to do. His very compact and neatly packaged streetfighter still put 59.25 inches between the axles—okay for the street, but not ideal for racetrack-level handling. “It makes a shorter swingarm, with too much pivot angle.” He put an $800 Twin Cam 88 motor—pulled from a bagger and sold on eBay—up on his bench and thought, “what’s the minimum I need?” Stripped to the basics, with the primary case and transmission it was still about four inches too long, so Curt knew what he had to do—build his own transmission case.

High-end builders like Ecosse and Confederate have built such units, but they don’t sell them to working stiffs unless we buy an entire motorcycle—big bucks. But Curt’s been building his own stuff all his life, so “I took a gearset, blocked it up behind the motor and then built a case to keep it there…I don’t have any CAD stuff or CNC, it’s all manual. Super-basic.” Sounds easy, right?

And it works. I wasn’t able to ride the bike on a racetrack and instead just got a quick spin on the lightly trafficked roads near Curt’s Hayward shop. The bike is small and light—Curt says 405 pounds with a gallon of gas in the hand-formed aluminum gas tank (“I only make them for myself, says Curt”)—and the wheelbase is 55.25 inches, two inches shorter than he could build with a Sportster motor. The front end is late-model GSX-R1000, with the attendant bad-ass brakes. Carbon-fiber wheels shaved 25 pounds. The bike is easy to ride, even with tall gearing, thanks to the unbelievable torque the bone-stock (aside from carb and exhaust) Twin Cam 88 motor makes—115 foot-pounds, seemingly right off idle.

Curt rubber-mounted the big mill, but vibration is noticeable, contrasting with the crisp, modern feel of the chassis. It’s rough and vintage feeling, but Oh My God does it pull hard in the midrange. Put him on a technical course like Sonoma Raceway and Curt (who just recently had his first trackday) says he gobbles up B-group riders on Ducati Panigales and Japanese superbikes like potato chips.

The chassis is remarkable. The GSX-R suspension is compliant, not harsh, and the Ducati 999 shock and linkage do a good job in back. Curt’s hill climbers make more than 200 hp, so he knows how to build a frame to handle big numbers, and the giant aluminum swingarm (also built by Curt) should be icing on the rigidity cake. The brakes are four-piston radial-mount calipers and massive soup-plate floating rotors. They’re fine, believe me.

My only concern with this motor would be vibration, though Curt does say the vibes lessen at higher rpm. Even at low speeds, the buzz and rumble from the V-Twin made my eyeballs jiggle and blur my vision, but Curt says it can be tuned out (at least partially) with blueprinting and other touches In the Big Twin world, stock is just the starting point.


Curt wants to keep developing the BTR GP, as it has plenty of potential. He says he can save more weight with a trellis-style steel swingarm and going to a magneto ignition, which would save 15 pounds and add some power, thanks to reduced drag on the crank. But it wouldn’t stop there—an array of hot rod Big Twin clones will fit in his frame, including the fearsome Ultima T-VO, a 127 cubic-inch monster that “out of the box” makes 140 hp and 145 ft.-lbs. of torque (covered with a three-year warranty). And then you add the turbocharger, which could net over 200 hp. Suddenly, the bike goes from a quaint (but good-handling) VW Microbus to a McLaren supercar. Needless to say, several enthusiastic roadracers—retired champ Michael Ernest and Pacific Track Time’s Ken Kesey among them—want to help develop the bike and make it a contender.

An air-cooled, long-stroke pushrod motor may create questions about reliability, but Curt has that handled. His bike has an upgraded oil pump—a common weak point—and he’s not worried about the press-fit crank twisting under extreme loads, as roadracing doesn’t create the stresses a drag bike or hill climber might experience. Another moto-journalist rode the bike all day at a track day, bouncing the poor thing off the rev limiter until it started leaking oil, but there’s no reason to ride the bike that way; power drops off well before redline. One thing building your own bike teaches you is to respect machinery.

But what’s this all about, really? Curt says he would like to use it to showcase his transmission design and ultimately develop a production Big Twin sport-tourer (he’s already built bikes like that for clients). It’s also a rolling business card for a talented fabricator and race bike builder, but even though Curt admits that now, with a busy family and professional life it’s easier to just buy the things he wants rather than make them, sometimes there’s stuff you just can’t buy. “I’ve always wanted a track-worthy Harley and this is the best.”

Gabe Ets-Hokin is the Editor of City Bike magazine, and a frequent freelance contributor to


  1. Norm G. says:

    I know they make right hand drive, but did he get creative and use an existing set of BST’s but mount them backwards…?

  2. DB says:

    Regardless of what I or anyone else thinks about this bike (I like it by the way), Mr. Winter has built HIS dream machine. Not to many of us can say that.

  3. ryan says:

    More like motorcycle “weekly”

  4. Blue says:

    I can admire the hard work that has gone into this unit, only a dedicated craftsman could see this project through the minds eye. Congrats on making it happen.

  5. Chase says:

    Admirable custom wor which is always a good thing. This is a fantastic creation with no real commercial value as the target market is very very small.

    That new Buell with the Rotax motor is a superior bike in every way and is also a relatively small pool of buyers.

    Please build me a KTM 500 Vtwin 2 stroke motor with EFI in a Britten copy carbon fiber chassis.I’ll be waiting.

  6. Vrooom says:

    Nice looking bike, and hell of a job fitting it together. I question the reliability of a Harley motor in that environment, as the leaking oil part of the story pointed out. As the article also says, on a very tight track it’s probably tough to beat, add some straights and fast corners though and it’s likely in some trouble.

  7. tla says:

    I hope there’s going to be pics of the transmission/case in the next issue of CityBike….props to Mr. Winter on his creation.

  8. todder says:

    Wonder how it would compete against a vrod powered ROEHR:

  9. PatrickD says:

    Without doubt this is a showcase for this guys capabilities, but he’s going out of his way using a Harley motor. Hell, even an air cooled desmo motor would give this guy so much more to work with. Imagine the dry weight of a bike that had this much invested in?
    Apply the same to a TL1000 motor or almost any real-world big twin.

  10. Sasha says:

    Hi All
    I like the approach and building something different is what he has accomplished, no argument there.
    The numbers quoted are very questionable regarding HP/Torque, 115ftlb from a 88 cube twin cam with carb and exhaust mods is only likely if the dyno tuner has been smoking some powerful drugs. I just sold a 2010 Wide Glide with a 113ci SE motor that I built it made 127HP/117ftlb.Pipe and carb mods changes on a stock TC88 65-70HP if all is really well and perhaps 80ftlb of torque. The same Wide Glide as a 96CI engine with super trap 2-1 SE211 cams high flow air filter and SE race tuner made 92HP and 93ftlb.
    For something different I got of the HD and got a ZX14R with Ivans tune and a full Akrapovic 4-1 exhaust. AT 54 I am hoping the ZX will scare a few years out of me.

  11. Jeremy in TX says:

    I have never understood the fascination with these “big twins”, but I like the bike nonetheless.

    • thoppa says:


      I love to see people have fun with projects and this bikes looks great…great job ! But I still don’t understand why some project builders decide to use these engines. Is it patriotism or romanticism or something ? Or are they just cheap ?

  12. Gary says:

    Errr … okay. What’s next? An R1 engine in a Lowrider frame?

  13. Bill Blenn says:

    I wish there were a video with good sound of this thing

  14. Joe Lewis says:

    The most HP I ever got out of nt Buell was 86 at 6800rpm. Big torque though. Fun bike. It was rough on motor mounts, exhaust studs and mounts.
    Harley gets a bad rap attimes but they warrantied every failure even after warranty expired.
    It hd chrome PM wheels and every thing polished. Wish I would have kept it.

  15. Rick_A says:

    The numbers may sound good, but the Twin Cam 88 is a slow revving mill. Actual chassis dyno numbers are not very impressive.

    It’s a cool exercise that has been tried many times before. The XL engine would appear to be much better suited. Spondon had a 54″ XL frame kit available ages ago. Knock Buell but that’s a bike anyone can purchase affordably that can easily be hotrodded if desired, and has an established history in racing.

    As cool as it is in that “built ’cause I can” kinda way, an XB12 is a well sorted bike anyone can buy. I’m an old school Bueller and have been riding a 100rwhp, 90ft-lb S1 for eleven years. It runs like a Ducati superbike that only revs to 7k.

    • goose says:

      As someone who owns both a big twin (Road Glide) and a Sportster (XR1200) I can tell you they feel completely different. If you want a big twin you want a big twin, a Sportster isn’t going to cut it. Same goes in the other direction, if you want a Sporster a big twin isn’t going to cut it. The slow revving nature of the big twin is, to me and many others, part of what I like about the bike.

      As to the bike, I can’t seem me ever being interested in the bike featured in the article but the sport tourer version would come down to A. can I afford it? and B. is it well sorted enough to take on long rides? If the answer to both was yes I’d get in line to buy one.

      No big company (Harley, Polaris, etc.) will build a bike like this but a talented an slightly crazy guy like Curt Winter might pull it off.


  16. Bud says:

    Has he experienced cooling issues on the rear cylinder? Seems like it could be a problem.

    • oregonlocal says:

      All trad Harleys have cooling issues with the rear cylinder. Maybe th Rube Goldberg water-cooled heads on the new Big Twins will ameliorate this issue but they add stupidly complex plumbing in order to do so.

      Harley could have finessed this problem by forgoing Jap chrome and fake cooling fin esthetics on the V-Rod engine thereby making it a much more attractive mill for customers but they stupidly did not.

  17. Buzz says:

    Great story Gabe.

    Changing my oil is about as far as my skills go. I can only dream about being able to do something like this.

  18. oregonlocal says:

    Better a Sportster engine with 1450cc Axtell cylinders.

  19. mickey says:

    Lets see some pics of his Big Twin Sport Tourers sometime Gabe.

  20. Gronde says:

    Sportster engine is a much better starting place to build a race bike, but there’s always those that just have to have a Big Twin under them. You will never see enough Big Twin race bikes built to support a racing series, but the one-off example shown here is pretty cool. Too bad it vibrates more than most paint shakers.

  21. reg kittrelle says:

    Good on ya, Curt!
    I can’t for a moment imagine criticizing any part of your effort. Your accomplishment is not so much with the result …as great as it is.. as it is the fact that you took your idea, and brought it to life. The majority of us never get past the idea point.

    • Norm G. says:

      re: “it is the fact that you took your idea, and brought it to life. The majority of us never get past the idea point.”


    • powermad says:

      Its much easier to sit at the keyboard and criticize this man’s creation or pontificate on how stupid HD is than to actually do something.
      Lots of people can tell you how you did it wrong.

  22. stinkywheels says:

    It’ll be neat to see a primary and trans that will be shorter than a Sporty. I LOVE Buells and would love to see a Big Un I could play with. Kinda Yamaha MT01(?).

  23. Philip says:

    I like the thought of big twin clone racing, kinda like Moto2 but with a big hulking engine to work around. Great story on Mr. Winter!

  24. Blake says:

    Very nice work.

    How does it actually perform on the race track?

    Re Gabe’s comment deriding the Buell X1: Neat things about the old Buell bikes were that you could actually purchase one for a very reasonable price, pass EPA emissions requirements, all with a 101 BHP engine that would achieve 50 mpg in cruising mode, and yet run respectable lap times at your local track. If you wanted, you could hot rod the engine up to 100 FT*LB/130 RWHP level with just bolt-on upgrades and some tuning.

    The big twin engine is a no go on the track, way too tall and difficult to get leaned over and then stood back up. The sportster mil, especially as improved through Buell, is a much better choice for an American air-cooled racing motorcycle.

  25. Marcus says:

    Wow, a nicely crafted supersporty big twin! This is what Eric Buell never gave us (Instead he lost track with engines from Rotax, a brand that produces engines for sleds, motorkites and probably also lawn-mowers). Impressive piece of work from that guy and impressively neat package!

    • Norm G. says:

      re: “Instead he lost track with engines from Rotax”

      some could argue (like me) that he’s FOUND track.

      get it, Laguna Seca, Road America…? and now Assen, Phil’s Isle, etc.

      see what I did there…? 🙂

    • Dave says:

      Rotax produced the engine for the Aprilia Mille and countless other motorcycles. Engines is all they do and the one they did for Buell was awesome.

    • Gary says:

      Lost track with Rotax engines!?? That’s the only way Eric could hope to start and keep winning races. HD themselves could not produce a consistent race winning engine as evidenced by their failed attempt a few years ago. I personally think that is why HD canned Buell. He did what HD couldn’t, but had to do it with an engine other than the heavy slugs that HD built.

  26. Magnus says:

    Now put a carbon fibre Hossak front end on it 🙂 I always knew one could build a perimeter frame around a big twin. Are you seeing this HD? If not HD how about Polaris/Indian?

  27. Joe Lewis says:

    I really like this bike. One of my favorites is my old Buell X1 lighting. Not very fast but handled well when it ran. This would be a fun bike on the street and I need one.

    • Gabe says:

      comparing this bike to an X1 is like comparing a Saturn V booster to a bottle rocket!

      • Blake says:

        How so? The 88″ big twin is no where near the 101 BHP of a stock Buell X1.

        • Gabe says:

          Did you actually read the story?

          • xlayn says:

            Touche, this bike is a beautiful example of incredible handicraft and the end result is impressive and very well put

          • todd says:

            I read it and nowhere did you mention the power of the motor. You did say “stock” twin cam 88. In that case, Blake is correct; a 67hp engine will never pull out of corners faster than a 101hp engine. The article only implies that Curt is a much better rider than the guys he passed on the Panigales and other super bikes.

            Curt does some excellent builds (follow him on Facebook) but he’s not trying to build a better Gixxer or Panigale just something different. In that, the bike exceeds.

          • bmidd says:

            Did you actually read the story? It’s stock except for carb and exhaust……

          • Gabe says:

            Todd, I wrote: “The bike is easy to ride, even with tall gearing, thanks to the unbelievable torque the bone-stock (aside from carb and exhaust) Twin Cam 88 motor makes—115 foot-pounds, seemingly right off idle.”

          • todd says:

            Gabe, yes, you did mention the torque. However, we were wondering how powerful it is to get a good understanding of the bike’s performance. You can easily crank out 115 foot-pounds of torque on a bicycle. Torque does not relate to performance without knowing what sort of power the torque can muster.

            That said, all the power in the world will still get beat by a good rider.

          • Norm G. says:

            re: “Torque does not relate to performance without knowing what sort of power the torque can muster.”

            HP=(torque*RPM)/5252. we know.

        • fast2win says:

          I agree. A stock xb 12 is probably faster. I do find several comments suspect though. A stock twin cam even with carb and exh. work making 115 ft lbs. 405 lbs is pretty light, unless he pulled the battery and starter, then maybe. And he could have made it shorter with a sporty, a xb is a 52 inch wheel base just sayin. That’s not to say I don’t think this bike is cool, I do.

    • Kagato says:

      …”when it ran” I hope you’re kidding us

      • Dave says:

        I have a friend with an x1. He has broken almost every major component in the engine at one time or another. Mostly under warranty but you know a great warranty service is like a great punter in the NFL, a fix for a problem your customers wish you didn’t have.