Board index Flathead Power-Technical Questions, Answers, and Suggestions Sporties Looking for a Set of ThunderHeads /Iron Sportster

Looking for a Set of ThunderHeads /Iron Sportster


Post Sun Jul 13, 2014 4:29 am

Posts: 2
asphaltgambler wrote:
XLR - My engine is BIG for an old skool iron motor - 3.5" X 4-13/16

What I want to do is convert the thunder heads into dual intake / custom ports. Since these are aluminum you could do just about modification you'd want.

Thses are the only aftermarket head ever offered for the iron sportster. So I want as set. Any leads?

UI have extensive fabrication /welding skills and have access to one of the best machine shops in the country. They are a complete facility with a flowbench.

Well this comes back 8 years after the original post. Thunderheads on a 93" engine is a no go. The valves are way too small for a 90 plus inch engine. These heads were designed for 1000 cc's, not 1500. There is no room for bigger valves due to the shape and size of the combustion chamber. XR 750 heads would be worse, as they are even smaller, and designed for an engine of less than half the displacement of a 93 incher. The best option is to get your iron heads done by someone like Dan Baisley. In an aftermarkey head, Alan Sputhe's alloy heads were designed for an 80 inch motor. They easily produced 100 hp with his barrels and cylinders, and they are set up for dual carbs, and right side dual exhaust if I remember correctly. No XR or Thunderheads are going to do the job. Sputhe heads may be easier to find as well. If you do find a use for Thunderheads on a smaller motor, there are two three you need to know that many guys apparently don't. You need to degree your flywheels and make new timing marks at 25 and 28 degrees, and you need to get or make a small bushing to modify the mechanical advance unit so you only get 25 degrees total advance instead of 40. The rocker arms have to be cut and welded to different angles if you don't get them with the heads, and absolute maximum lift at the cam lobes is .450. Do not try to exceed. Andrews X cams do the job very well.

Posts: 2
I just found this forum, I hope some body still paying attention to this Thunder head stuff.
I bought a set in late 1980 after my 79 sporty came apart with 4000 miles on it. The Crank pin nut came off because the factory decided to use locktite instead of the screw on locking thingamajig they used for years, luckily didnt damage the cases.
Prior to falling apart my stock 79 sporty ( pipes & lectron carb ) would outrun my 74 CB 750 with similar modifications by 4 - 6 bike lengths up to 100mph then the Honda would pull ahead. I had 4 or 5 buddies each with sportys & mine was the quickest - I don't know why.
After installing Thunderheads & Thundercams made by Sifton, back in the 80's this was one of the quickest HDs around, Easily beat Honda Triumph, Norton, & depending on the rider I would pull a Kaw 1000, It would barely run on pump gas but ran like a bear on 110. I'm guessing a gain of 30+HP,It would pull to 7500 RPM before you knew it , probably why I've had to rebuild the bottom end 5 or 6 times. Recently (2 or 3 years) ago rebuilt it again S&S rods & crank pin, and true spin balance job. I probably only have 200 miles since, I can't believe I used to ride it 20,000 miles a year . Thunderheads made the Iron head a real performer 25 years ago, probably not so hot by todays standards Still runs like bandit starts with one KICK!

Posts: 1
I wonder of all the people $#!+ talking shovesters etc.... how many have actually built one.
ill decide for myself if it was worth it.
2014-08-17 22.39.32.jpg

Posts: 2
Location: Pittsburgh PA
Just bought a nice '80 Sporty with Thunder Heads. I realize that your post is old, but just wondering if you found a set and what your experience has been. Thanks.

Posts: 2
I have a set of Thunderheads on a running complete bike.
I will not part out the bike. let me know if you're interested

Posts: 2
Location: Pittsburgh PA
If it is better than mine, I would be interested. How about a picture and price. Thanks.


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