Bad Dog 215 Cubic Inch V-Twin

Bad Dog 215 cubic inch V-Twin engine

Are you one of those guys who feels there's just no substitute for cubic inches? Well, Bill Price thought you might like to know he's designing an engine for you, it's called the Bad Dog 215, as in 215 cubic inches. The sixty-degree air-and-oil-cooled 4-valve DOHC semi-unit 3500cc engine has a 6 inch bore and 4 inch stroke, connecting rods run side by side on a single throw crank. Main and rod bearings are from a 426 Hemi.

The engine will be unit construction incorporating a 6 speed transmission. It will not fit into any current standard frame and Bill plans to build one to handle the engine's size and power. The engine will use a combination of CNC machined parts and off the shelf pieces. He's just getting to the prototype building stage.

The complete power unit, including motor, six speed transmission, primary drive, fuel injection, ignition, engine management system with software, sensors, charging system, external oil pump and starter has an anticipated price of $40,000. Final MSRP has not yet been set. We anticipate having a firm price by mid 2009.

I always have had a soft spot for big engines with loads of power, it will be interesting to see if Bill can turn this out. See what happens when you give a guy a computer and CAD software? I like it.

Bad Dog 215 cubic inch V-Twin engine compared to standard V-Twin
Here's a comparison to give you an idea of the size!

Link: Bad Dog Cycles


  1. discontinuuity says

    Interesting. I wonder why he chose a 60 degree angle, instead of the more usual 45 or 90 degree layouts.

  2. hoyt says

    A 45 degree probably would not be possible with a bore this size.

    I like the unit construction design requirement and the very compact transmission.

  3. says

    Is that *three* spark plugs per cylinder I see there? Is the combustion really so inefficient as to require three of them in a combustion chamber that size?


  4. JR says

    Well each cylinder displaces almost 1.8 liters. That is what most automobile 4-cylinder engines displace.

    I would think extra measures (i.e. 3 spark plugs per cylinder) would be needed to get a complete burn.

    Think about how huge a 6 inch bore piston is! I can’t even wrap my mind around that.

  5. Dorzok says

    With tha stroke, 90┬░would make it too long and with that bore 45┬░ wouldn’t leave enough room for the cylinders.
    Look similar to S&S’ X-Wedge. Just a tad bit bigger though. And the X-Wedge will fit in a typical custom frame and bolt up to any aftermarket Harley trans.
    In the ’80s there was a dude building V twins using the front two cylinder of a Chevy V8. Gosh I wish I could remember who it was.

  6. kneeslider says

    Dorzok – “V twins using the front two cylinder of a Chevy V8

    That was the SuperVee. I used to have some info on them, can’t find it at the moment.

  7. todd says

    To me I’m not quite sure how the Hemi rod bearings would work. This engine with its cylinders inline would require a forked rod. Maybe it has a master and slave rod?


  8. says

    Answer to discontinuity:
    A 60 degree vee allows some room for the intake ports, give more support between the cylinders and doesn’t require pistons to be cut away to clear each other.

    Answer to Todd:
    The conrods run on a single crank throw, offset by about one inch side to side, same with the cylinders.

    Answer to Jeff:
    You will get a lot for the money. This motor will be hand-built in very small numbers using the best materials and components!

    Great to hear some feedback on the design!

  9. Tim says

    Its cool.

    when I looked at the drawing and saw the four zorst pipes and four bellmouths I thought “Wow, its got oval cylinders like an NR750”. (which would be uber cool).

    What will it rev to?

    And a one inch sideways offset (and the size of the pistons) suggests it might need some major counterweights somewhere otherwise it would shake your head off, not to mention hard parts of the bike. Or am I misguided?

  10. says

    Answer to Tim:
    The pistons are round, just big. There are four valves per cylinder. Rev limit should be about 7k. The crank will have two large counterweights but this design won’t be as smooth as a 90 degree v-twin.

    Thanks for you interest!

  11. Paul says

    I hope this guy accomplishes his goal.
    So many people talk and try. But few stay in it for the long haul and see their dreams come true.
    Don’t give up Bill !

  12. B*A*M*F says

    It’s big, ridiculous, super expensive, and I love it. How the hell anyone would put such a thing to use, I have no clue, but it’s great to see things like this being done.

  13. John says

    I like it.Question for Bill,why not a Master and articulating rod setup like a radial airplane engine, that would cancel the rocking motion that a motor the big would have. Also I can see you plan on rubber mounts and you mentioned large counterweights but why not add a balance shaft also,thats a pretty big Vtwin.Back to the master rod setup, I realise the master would need an end cap so you could utilize the one piece forged crank, which is very nice,along with those huge bearings, I like it.

  14. says

    Answer to John:
    When designing the crank and rods, I just went for simple and strong. Same thing with balance shafts–when the motor is turning 7k the balance shafts have to spin at 14k, so I left them out! I can have two counterweights as large as necessary and, after all, for the size of this motor, the stroke is quite short. I’m hoping the rubber mount system will soak up most of the obnoxious vibrations, but I won’t know for sure until I get a prototype running!
    Thanks for your thoughts on the design.

  15. motoxyogi says

    Hey Bill is there anyway you could do maybe a side elevation view with someting people would be more familiar with, just to get an idea of just how damn big that monster is!

  16. Tim says

    Hi aaron, It only sort of looks like a Vincent. I had the privilege of seeing a Norvin cafe racer parked on the street a week or so ago. Vincent is 50 degrees and the splayed rocker tubes and big timing chest are very characteristic.

    What it reminds me of the most is G U N B U S, which is my favourite chopper ever (after the “Billy bike” from Easy Rider)

  17. Tim says

    one last question from me: are those bolts at the base of the cylinder the bolts that hold the cylinder to the crankcase? My (limited) understanding is that long bolts holding the cylinder from the top are better in the application? (I am dredging some tech feature in a magazine I read years ago… bear with me). Something to do with dimensional stability and better sealing IIRC?

    have I mentioned how cool I think this is?!?

  18. noodles says

    Brilliant! It’s like having two 1700cc single-cylinder engines slapped together into a giant V-Twin (like Harley but more). Bolt that baby on a manly-weight cruiser with a 70-inch wheelbase and the fattest rear tire you can find. I’m off to the bar for a shot of cheap whiskey!

  19. aaron says

    sigh… what happened to the other side? left is beautiful…but the right view is… not.

    how about hacking the rear cylinder off to give us a 1700cc version of a modern day “grey flash”?

  20. says

    Answer to Tim:
    The cylinders are indeed attached to the cases with short studs and nuts. I’ve heard about problems with long steel studs and aluminum cylinders that “grow” slightly as they heat. It seems the studs sometimes pull out/loosen (new Excelsior-Henderson).

  21. says

    Answer to Aaron:
    The motor is a work in progress. If you have any suggestions for changes/improvements I would very much like to hear your feedback!

  22. Phoebe says

    When I saw this, the first thing I thought of was how cool it would look on the front of a Morgan-style trike.

  23. todd says

    A master and slave rod will allow you to narrow the crank and remove a substantial amount of crank flex – extending the life of the crank greatly. This also gives the benefit of a narrower engine and no rocking-couple vibration. Good luck to you, all the best!


  24. says

    Answer to Todd:
    I can’t see how to use a master/slave or knife/fork rod setup and still use a plain-bearing, pressure-fed conrod big-end. Crank flex shouldn’t be a problem with the one-piece design I have in mind but it would be nice to get rid of any rocking-couple vibrations, however, the Norton Commandos were quite smooth with their isolastic motor suspension even though the rods were about 4 inches apart!
    Thanks for your feedback!

  25. Dave says

    I can see this motor appealing to the custom crowd, but how practical is it?
    There are those who will always want more power (the Binford crowd, I call them), but really, can you build this into a touring bike and cross the country without having to stop at every gas station with it?
    Bill, take a cue from the Saturn folks, and take a lap of America with this motor. For me, reliability is right up there with great fuel economy.
    Using 462 Hemi components is a great way to grab the attention of the Mopar crowd as well.

    While you’re having fun, cobble up a V-Four like the Royal Star’s. A 430 CI touring bike…ride it to Bonneville and set some records while you’re there!

  26. todd says

    The Norton has a center main for strength and a (comparatively) small 3″ bore. To pressure feed the slave (articulated) rod bearing you tap into the main rod oil feed (or as it heads up to the little end). It’s all been done before. Regardless, it’s best to keep your rod journals as narrow as possible on high revving, big piston engines.


  27. says

    Hi Todd
    Thanks for the info. By the way, the Norton Commandos only had two main roller bearings, with a large flywheel between the conrods, resulting in lots of crank flex.

  28. Mehul Kamdar says

    This is an amazing project. I do wish that you would build a full motorcycle with this engine, Bill, not just an engine for customizers. I can certainly see myself riding one. I’ll be watching this post with a great eagerness.


  29. REVVLAD says

    I am totally stoked! I poured over old aircraft magazines to make sure a six inch bore was possible then began dreaming of a 200 + inch v twin in a good chassis and running gear. I feel there is a loan to be attached to my home is to be soon! Look out Bonnivile and the Bristol drag way (of NASCAR fame), which is only 12 miles from my home! And you guys on the jap scoots (which I respect but do not care for), are about to have your inline fours toasted!
    : }>

  30. says

    Many of the current v-twin top fuel engines are 195 c.i. and run on nitromethane (normally aspirated). we use a one piece crank and side by side almuminum con rods.

  31. says

    this engine is pointless.For 12000 you can buy a 1.3l suzuki hyabusa inline 4 with 197hp does a 1/4 mile in 9.7 seconds and you can use it every day and the bike will last about 20 years. what is yer obesion with v twin air cooled moters.and also what is so great about drag racing? watch moto gp them boys do 180 down d straigt and have to brake for the bends as late as posable and stil tear around the bends.shurly their must be a few tracks in america that arent oval or straigt. broaden yer horizons and maby get a raditior for yer biks!

  32. John says

    Hey stephen, people like what they like, what’s it to you anyway,nobody asking you to invest or anything else. As for hyabusa or any of the ones you like, they bore the hell outa me.

  33. carl says

    i would love to no if that motor could be made non unit construction and could it be bolted onto the bell housing of my rewaco HS6 trike..please say its possible..!!!

  34. arthur says

    love the design of the engine ,good to see something diffrent,fresh and new ,good luck with your design ,i hope it does what you expect of it , dorzox i also remeber seeing a chevy v8 cut in half and was run in a speedcar here in australia may years ago ,sounded so sweet just like a normal v8 ,

  35. dude says

    totally cool engine Bill , reminds me of the Warbird motorcycle which I think has been featured on Kneeslider . Stephen , a lot of people have no interest in 4 bangers no matter how fast they are , they’re more like a high performance appliance with no character .I’ve ridden a hymen abuser and while very fast it held no appeal at all. I’d tale an 1198 Duc over the busa any day .

  36. Rev. Jimi G. says

    well there goes those peanut tanks I love to use in my builds. Hell cant get 50 miles on a 3.5 with my 121 patrick so I can imagine… That settles it I want one!!!!

  37. Brad V says

    The 6 bore x 4 stroke must be nominal. If it were exactly 6 x 4, the displacement would be 226 cu. in. Balance shafts wouldn’t necessarily have to turn at 2X engine RPM; that would be the case if they were designed to cancel out secondary forces, such as in an inline 4. For a twin, balance shafts could be used to cancel out primary forces, in which case they would turn at the same speed as the crank, but in the opposite direction.

  38. Lyn Bazley says

    what a concept i can feel the bangs in my chest as i write.four cylinders are ok but give me a thumper with grunt anyday.get the engine in a frame of your own it would be a masterpiece.

  39. travis says

    bill first off vtwins are not my cup of tea (personally like the triumph triples)
    BUT that thing is sweet cant really see it being a big production motor but it will be sweet to see that thing in the few choppers and drag bikes it makes it into….
    BTW out of curiousity why the 4 seprate throttles i think it would be much more effiecant to just have 2 large carbs or throttle bodies??

  40. says

    Ok, it’s huge. Biggest f’in V twin engine I ever saw. I can’t see an application other than a Boss Hoss style cycle, and few can ride that monster. I see a much better future with some crazy-azz kind of Can-Am Spyder on meth!

  41. gavin says

    If it ever did go into production, the purchase cost would lower markedly so the consumer could buy it. You would need to retail a production model similar to HD prices. This means, like ant business, you would need to capitalize, and not expect a profit for a few years.

    Don’t make the mistake of going for a “niche” market of people who can afford to pay high prices

  42. Joe says

    I always love to see individuals designing and building thier own dream engines,motorcycles etc.This is what makes motorcyling so interesting and breaks the monopoly of corporate produced clones that are reliable but as boringly unique as dissposable household appliances.Keep up the good work Bill,guys like you are an insperation to all who like to think outside the box.

  43. al says

    last i checked with a forged steel one piece crank you should be able to balance this out just the same as a car engine, or am i missing something. if it vibrates, scrap it or fix it.

  44. Davo says

    The only change that I see as a benefit would be to use a mercedes benz type of head design using a hollow SOHC and 3 valves. 2 big unequal length inlet valves that open at different intervals (eg. small primary then large secondary) and one big exhaust valve with sparkplugs on opposite sides. 4 vale heads are overrated.

  45. Dave says

    Its an interesting exercise in doing what’s been done before many times over. Why can’t we have some genuine lateral thinking and why do we persist in running the gearbox slower than the engine? (note the big clutch cover). Torque kills gearboxes running them slow increases the torque. I dont get why bike engine design is so full of dogmatic design flaws.

    BTW there is no need for a master rod (lite aricraft radials). The con rods can sit side by side and get a direct pressure oil feed like any other engine.

  46. Bryan says

    Why do we run gearboxes slower than engine speed? Not sure I understand the question. The purpose of a gearbox is coupling a prime mover to an output (i.e. rear wheel in the case of a motorcycle) within operating speed range while keeping the prime mover within its’ most efficient operational parameters. O.K., nothing new. Torque kills gearboxes? Say, we decide to run our hypothetical gearbox input @ a 1:1 ratio with the prime mover and shrink our clutch for a small, pretty clutch cover. Unless we add friction area (assuming we are using a friction clutch) in a different axis, we cannot transfer the same amount of torque. We either turn our power into heat through slipping clutch discs, or we add discs to our stack. We now have twice the parts, (expensive) and a clutch cover that resembles a phallus which tries to dismount us every time we turn left. That being done, we move on down the power train. A faster input necessitates more gear reduction, LOTS more gear reduction. We are not looking at moderate gear ratios anymore, nor are we dealing with sane-sized gears that fit neatly between a prime mover and a driven element. Our gearbox is necessarily around 30% larger and heavier due to increased ratios and larger gears. We could add a jackshaft and get around this increase, at the cost of complexity and further cost inflation. Modern gearboxes benefit from modern metallurgy, manufacturing uniformity and design. They do a good job of what they do and can be produced economically. Alternatives are being adapted from other applications, such as Continually variable belt transmissions; which are light, simple and effective at the cost of bulk. Talk about an ugly clutch cover. Most of us though, feel content and connected with our machine rowing through the gears of a conventional gearbox.

  47. Bryan says

    Oh, forgot the part about dogmatic design flaws. Folks pay extra for those. That’s why Harley Davidson is still in business.

  48. Chris says

    What a beautiful engine! I hope he builds it! Its more art than pragmatism, and i love it!

  49. define says

    stephen, said
    this engine is pointless.For 12000 you can buy a 1.3l suzuki hyabusa inline 4 with 197hp does a 1/4 mile in 9.7 seconds and you can use it every day and the bike will last about 20 years. what is yer obesion with v twin air cooled moters.and also what is so great about drag racing? watch moto gp them boys do 180 down d straigt and have to brake for the bends as late as posable and stil tear around the bends.shurly their must be a few tracks in america that arent oval or straigt. broaden yer horizons and maby get a raditior for yer biks!
    A. spell a little if you want anyone to care
    B. why did you point out the 9.7 1/4 mile of your hyabusa if you did not care about drag racing.
    C. a liquid cooled bike adds to complexity and weight that is generally unwanted for the applications of a v-twin (drag racing, long road trips ect.)
    D. there are many tracks in America that are long and twisty.
    E. just about any one who lives near the Rocky Mountains or any large group of mountains cares about low end torque and therefore drag racing
    F. just how many people baby a “busa” into lasting 20 years with out a rebuild??
    G. for the same price you can get a sportster 1200, with an engine that has a track record showing it is more likely to last 20 years, and has plenty of engine to frame clearance to perform an top end rebuild in frame!
    H. Bill way cool engine, I’m sure that it will do well, and good luck
    sorry but i am sick and tired of people just bashing good ideas just because they think they know better, or because they clearly do not care to see the application, or other side, also i lived in Draper Ut. for most of my life, and saw many “tough men” on there race bikes challenge an big twin and get blown away, (uphill) and I have always wanted to point out the flipside of engine performance somewhere that is not just my friends (whom all ride big twins or dream of it)

  50. define says

    also i have seen with my own two eyes an air cooled v-twin make sub 9 second runs, and baggers make sub 11 seconds!

  51. WENDL says

    Reminds me of that guy who grafted another cylinder in the front of a harly motor and came up with a very sensible, super strong engine. Can’t remember his name. Sadly he passed away some years ago.

  52. Steve says

    O.O 215 ci? In 1988, Ford Motor Company loosed the Taurus SHO (w/ 3.0 Yamaha V6) on an unprepared public… now make a V8 out of this, put it in a roadster and yet another legend is born.

    Four “Bad Dog” 215 ci engines linked via common crank case- $160,000
    Having 860 ci/ 14.3L of volcanic monstrosity under the hood- Priceless.

    Welcome to America.

  53. John Findlay says

    Please dont put that engine in ANOTHER cruiser ! make a frame that handles,stops and looks as good as the motor, along the lines of a Ducati Monster, V-Max etc etc. I know with a motor that big it wont be the best handleing but it would look so tuff as a street fighter.
    More power to you Bill fantastic ! p.s. I ride a 1400 Suzuki and loath H.D.

  54. Thom says

    WENDL- do you mean the Fueling/Rivera W-3? I know they also used to make four-valve heads for Harleys….

  55. Paul B says

    I don’t care about the logistics Stephen, the 9.7 quarter, the handling, the 20 years, but to have a bike that fires once every lamp post, and can pull like a train from nearly walking speed, that sounds so good your arm hairs quiver, that idles at 500rpm, THAT is what it is all about.

    As for gear box size, if you had a small ‘box at engine speed, then reduce the gearing at the back wheel, ie a double size rear sprocket, that would get rid of the big gear box issue. Maybe.

  56. Bill Krieger says

    Concerning the 1 inch offset of the rods and thereby cylinders why not offset wristpins and eliminate resulting rocking couple vibration as does the powerhouse 114 cu in which revs safely to over 7 grand reliably.

  57. says

    Nostalgia Cycle in Huntington Beach, CA used to distribute the Super Vee engine back in the 80’s. They simply sliced off the front 2 cylinders of a Chevy V8 engine. This engine looks just like it, even the side of it where it looks like the stock timing chain cover. These engines had the best “thump” sound and the displacement made them the most powerful and torqy V twins in the world.

  58. Casey says

    It’s only 2 spark plugs per cylinder,the third (black lead) is to send spark……………and the x-wedge motor only fits in x-wedge frames,not just any aftermarket frames.

  59. Don says

    Where’s the update on price and availablility?

    I certainly cannot afford one of these until I win the lottery, but I was hoping to learn more about this incredibly silly and KEWL idea since I first saw it online a coupla years ago. I FINALLY find the site again (2 computers later) and there hasn’t been any news?

    Be that as it may, I am hopeful that Bill has continued his quest and has brought this beast to life.


  60. roger de vries says

    i cant wait for bill to produce that mean mutha! i want to stick it into a lightweight chassis and make it handle AND stop with ohlins, brembo, marchesini, et al.Its gonna be VERY expensive to build.If enough interest… I WILL!

  61. roger de vries says

    … the question is… Does the world want/need a minimalistic streetbike with a 2:1 power to weight ratio?

  62. Pete says

    As one that has spent my life going over kill on everything I build, I’d say / BIG Bore, 7000rpm tops, Why not a quick spooling turbo. I layed out a design a few years ago with a short stroke Evo feed by a turbo striat up centered on the engine going thru a intercooler into the ports. With the Fuel injection body facing strait forward off the turbo. I just seemed like a nice in your face design. Might go nicely with a 6″ BORE.
    Good Luck, Pete