Harley Davidson 4 Valve Big Twin Sportbike

Harley Davidson 4 valve big twin sportbike

Digging around in some old images I came across this bike and I have zero information about it but as you can see, there's something very interesting here. Housed in a custom sportbike frame is a Harley Davidson big twin, with 4 valve heads no less! There is some type of induction system with velocity stacks sticking up through the tank and beyond that, you know as much as I do, ... or do you?

How about some help from the most knowledgeable group of motorcycle enthusiasts anywhere, ... that would be you, ... and let's see if we can identify who built this, when, where and any other information you can find. (Updated: mystery solved - see below) For all I know, this is some famous custom I just never saw before or maybe it's a one off that never got much attention.

I enlarged the engine area to give you a better look but that's about as good as it gets.

Since we've talked about big twin sportbikes on a number of occasions and Curt Winter has been building his Big Twin Racers, this seems to fit right in.

OK guys, dig in your archives and let's get some answers.

UPDATE: Wow! That didn't take long. First comment from VMX1000 has the link. Here's all the info on this really sweet build.

1232cc, short stroke, 4-valve, (was an Evo Big Twin), Fueling heads, Cosworth 90mm Formula One pistons, 2 x Weber IDF 40mm twin-throat racing carbs and on and on. 310 pounds!! OK, I am truly impressed! My list of all time favorite builds just grew by one.

Harley Davidson 4 valve big twin sportbike


  1. ROHORN says

    That was in “Hot Bike” in ’95 I think, under the title “Spirit of Semtex” or some such thing.

    Quite the brutal piece of hardware!

  2. John says

    Yea,Hot Bike Mag July 1995. The owner is Patrick Hook an Englishman. 4valve short stroke Evo motor and the bike only weighs 310 lbs.One of the pictures with the article shows the skinny owner holding the bike both wheels about 4 in. off the ground.Said he had trouble keeping the front wheel down.

  3. jurneyman says

    It is now Dr.Hook and a man of letters, a very accommodating, modest, and all around nice person who saved me a lot of hours with his personal trials of R+D. If anyone wants to build something similar to this beast, I will be very happy to help where I can.jurneyman

  4. Randy says

    I’m pretty sure I took a ride with this guy back in 2002 from the Harley Davidson dealer in Farifield, CA, up to Lake Berryessa and ending at the fairgrounds in Napa Valley. The Hell’s Angels and plenty of other bike clubs were represented, but this truly impressive bike really stood apart from anything else there that day.

  5. says

    This bike also has a writeup and great pictures in the coffee table book: Extreme Streetfighter Motorcycles >The Ultimate Collection. by Frank Allmann, Simon Everett. ISBN 1-84193-035-0

    It shouldn’t be too hard to find….

  6. Rick_A says

    As mentioned there is a pretty in-depth write-up of this bike in a StreetFighters magazine issue from years back. I still have the mag. Very interesting build. Starting with an Evo motor, primary drive, and transmission vs. an XL motor was really making a challenge of it.

    My favorite part of the story is how the other racers initially laughed at him until he was so successful that he was forced into a higher class.

  7. carl says

    i would love to no or find out the wherabouts of the 4valve heads..i have a harly twin cam trike and id love the oppertunity to be..erm..UNIQUE..!!,oh and while im on i have a supercharger for a harly twin cam for sale if anyone is interested ok my e/mail is carl.leese@sky.com

  8. Jim barlow says

    I knew of Paddy Hook in the early 90’s. He worked for the Suzuki GP team when Schwantz won the 500 title. The bike has RGV500 wheels and suspension to help it round corners. Top bike, Top bloke!

  9. colin astley says

    i know paddy tbh havnt seen him for a few years now but all round good guy and writer on many subjects , moths and wolfs to name a couple !! but yer hell of a bike work or some was done in a town just down road from me and the susuki gp thing is spot on..


  10. Paddy Hook says

    Thanks for the kind comments chaps – Colin was kind enough to point me in the direction of this article!

    By the way – Randy, it wasn’t me or my bike on the Fairfield run, although I’m sure I’d have enjoyed it!

  11. Dan R says

    Sorry guys. Look at the pushrods. A big twin has crossed pushrods. Sportster pushrods are more parallel. At 1232cc it is a juiced sporty. But STILL an awesome bike!

  12. nobody says

    Dan R,

    Basic H-D engine recognition stuff worth learning:

    You might want to compare Sportster cam covers to BT cam covers. How many Sportsters have 2 lifters in the same lifter block – and at different angles from each other rather than parallel like Sportster pushrods? How many Sportsters have bolt on primary drives & transmissions (Hint: none)? Why is the oil pump behind the cam (BT style) rather than underneath them (Sportster style) ? Etc..

    And NO, BT pushrods don’t cross each other.

  13. John says

    RealityCzech 10.11.08 at 12:28 pm
    A simple “Duh?” would suffice. What’s the point
    Yea exactly,what is your point,show us what you’ve built lately.

  14. Adrian says

    setting the pace for lightweight & big bore thumpers of recent. the duc M1100 is 373 lbs (wet i think) in 2009. the buell 1125 is around 390 dry. i wonder if the M1100 could strip off 50-60 lbs for a track. awesomeness. and probably an inspiration for mr. buell. what a foolish move to remove the very good buell line. one of the best realizations of american engineering. considering the amount of bailout money given to those losers at gm, ford and other useless engineers. cripes. perhaps the chinese will bailout buell. i wouldnt be suprised.

  15. nick calvert says

    hi, i have some imformation on this bike. it was built by two brothers ay ivybridge at a company called welbro. sadly one of them died and the last time i went over there there was a lovely blade in the jig with an amazing frame being wrapped around it. the bike was featured in back street heroes magazine years ago as well. any more info email me and i will try and find the mag.. they also built an amazing fj1200 about 20 years ago for a chap named crow. those lovely big beam frame rails being one of there many styles.

  16. roy says

    ive been looking for a bike like this for some time. or with a tripple snowmobile engine fitted in a sportbike frame.

    when i saw the weight,,it was on,,,,
    my zook dl1000 weighs about 440lbs,,put a MERCH 125/125 in my bike,,youd fly. or the arct-cat 1000cc trip fitted to my frame.