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Looking for a Set of ThunderHeads /Iron Sportster

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asphaltgambler

Posts: 7

Joined: Thu Oct 05, 2006 8:00 am

Location: Warrenton, Va.

Post Sat Oct 07, 2006 4:29 pm

Looking for a Set of ThunderHeads /Iron Sportster

I have a fairly bad-ass 93" iron sportster (street) that is at the end of it's HP potential in current form. It is 3.5' X 4-13/16", 12:5 to 1, Red-shift 550 grind, Super 'D' w/ two t-jets, etc. Zippers did most of the engine/trans.

My biggest limitation I think are the cylinder heads. They have the big XR valves, dual plugs, port work, etc. The ports can only be enlarged slightly due to the thin-wall design and do not flow nearly enough for the combination I have.

What I really would like to find is a set of Thunderheads in any condition to go to the next level.

For those who don't know these are basically aluminum copies of the stock iron head with better valve angles, combustion chamber and port size. They were manufactured by a small company in Texas back in the late 60's to 70's
There were quite a few sets sold over the years and I missed out on a set a while back.

So if anyone knows a better solution or the where-abouts of a set of these heads please let me know. I will even pay a substantial finders fee
Speed is just a question of money....................how fast do you want to spend?
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BREWSKI

Posts: 919

Joined: Sat Mar 27, 2004 1:01 am

Location: RENO,NV. U.S.A.

Post Sat Oct 07, 2006 4:46 pm

This subject comes up about once a year and I have to laugh!!!!!,the last bike I saw in an ad to have a set of THUNDERHEADS claimed over a 115 hp;BULLSHIT!!!. rOBISON iNDUSTRIES WERE BASED IN ca., and the Thunderheads were a piss-poor copy of XR-750 heads;the limiting factor being the single carb. Anyone who knows anything about HP Harleys KNOWS THE ONLY WAY FOR HIGH hp IS TO RUN TWO CARBS ON SEPARATE INDUICTION TRACTS. Owning 2 XR1000's and a custom based XR 1000,I know what I'm talking about. "A LITTLE KNOWLEDGE CAN BE A DANGEROUS THING" BREWSKI
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panic

Post Sat Oct 07, 2006 4:49 pm

Image
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asphaltgambler

Posts: 7

Joined: Thu Oct 05, 2006 8:00 am

Location: Warrenton, Va.

Post Sat Oct 07, 2006 5:14 pm

I've heard all the 'problems' from both sides on these heads. BUT being aluminum they can be welded/ modified to do what I want. I do not plan to just bolt them on.

So again, any one know where I can get a set of these?
Speed is just a question of money....................how fast do you want to spend?
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whryders

Posts: 11

Joined: Sat Sep 02, 2006 5:47 pm

Location: UK

Post Sun Oct 08, 2006 2:40 am

Thunderheads

I would agree with Brewski , forget about those heads , the company went bust owing money to pre-ordered customers (not me)
Why not go for a pair of Shovelheads (as in shovester) they must be very available over there . Trock Cycle made cylinders to suit the Sporty lower end and accomadate the shovel top , call them on 312 6834010 and also Carls Speed shop carried out this conversion , he was at 9411 Santa Fe Springs rd , Santa Fe Springs
Ca .90670 .both these contacts are over 20 years old so I don't know if they are still around.
You would probably need to get the heads ported , maybe by Branch ,I'v seen several bikes with these heads converted to single carb manifolds , one facing forward and the front going back
with this set-up you would still have piston availability and its a tried and tested conversion , plus its all Harley . Hope this helps out.
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asphaltgambler

Posts: 7

Joined: Thu Oct 05, 2006 8:00 am

Location: Warrenton, Va.

Post Sun Oct 08, 2006 9:18 am

The problem is the shovel valve/rocker arm geometry is all wrong for the sportster.
Speed is just a question of money....................how fast do you want to spend?
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xlr

Posts: 149

Joined: Thu Aug 05, 2004 12:01 am

Location: calif

Post Sun Oct 08, 2006 9:42 am

THUNDER HEADS

I HAVE DONE FEW CONV. WITH THUNDER HEADS. THERE NOT TO BAD FOR STOCK DISP. IF U USE A STROKER PISTONS COULD BE PROBLEM AS THEY R DIFFRENT. THANKS
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asphaltgambler

Posts: 7

Joined: Thu Oct 05, 2006 8:00 am

Location: Warrenton, Va.

Post Sun Oct 08, 2006 11:34 am

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.
Speed is just a question of money....................how fast do you want to spend?
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xlr

Posts: 149

Joined: Thu Aug 05, 2004 12:01 am

Location: calif

Post Sun Oct 08, 2006 12:19 pm

HEADS

HI I SENT U MY # IN UR MAIL BOX. THANKS
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BREWSKI

Posts: 919

Joined: Sat Mar 27, 2004 1:01 am

Location: RENO,NV. U.S.A.

Post Sun Oct 08, 2006 3:24 pm

I have to disagree,ALAN SPUTHE offered aluminum heads for the XL in the early '80's,I have the original magazine articles;these were twin carb heads for the 1000cc bikes. These heads are still on Sputhe's website the last time I checked,he later went on to build 80" XR based engines."A LITTLE KNOWLEDGE CAN BE A DANGEROUS THING" BREWSKI One of his 1400cc bikes was for sale @ HANFORD a couple of years ago.
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asphaltgambler

Posts: 7

Joined: Thu Oct 05, 2006 8:00 am

Location: Warrenton, Va.

Post Sun Oct 08, 2006 6:49 pm

Brewski - Thanks - I'll check that out and follow up

XLR - Thanks - I'll give you a shout Monday eastern time
Speed is just a question of money....................how fast do you want to spend?
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xlr

Posts: 149

Joined: Thu Aug 05, 2004 12:01 am

Location: calif

Post Mon Oct 09, 2006 12:48 pm

heads

yes i know alan very well. he is in grass valley cali. i have put two sets his heads on motors. some time ago. kinda hard to get. i have friend who has set will check see if he wants to sell. alans is for 2 carbs. like xr 750. ever thik of xr 1000 heads? i would check ur bolt pattern. i worked for tom sifton at one time. we talked about putting bsa gold star heads on a harley. at one time 1959 harley made 8 sets of alum heads {single carb} for there race dept. i only know of 2 sets left. i have 1 and friend of mine in fresno has other one. ever check with branch? seems like u can get ur cast iron heads to flow quite well. i have built a few strokers. problem with thunder heads is pistons have dome like xr 750. so u need there pistons. and rocker boxes. i tryed to get stroker pistons for thunder heads. best i could do is have them made j&e. but piston pin would go into oil ring.
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asphaltgambler

Posts: 7

Joined: Thu Oct 05, 2006 8:00 am

Location: Warrenton, Va.

Post Mon Oct 09, 2006 1:43 pm

XLR - I don't think I would go for XR heads from Sputhe or Harley. I don't have room for the exhaust on the left side and rearward-facing carbs on the right.

I'd like to see the race heads you're talking about. As far as the thuinder heads yes, it would have to be the complete deal and I could have pistons made to match the combustion chamber.

As far as my heads go they have been modified as far as you can safely take them. Main problem is the port size will not flow enough air to really let this thing breathe. The flow % numbers go south past 4500.


I left a message on your voice mail. Let me know.

Thanks!! :)
Speed is just a question of money....................how fast do you want to spend?
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panic

Post Wed Oct 11, 2006 10:14 pm

Haven't done it, but IMHO the geometry can be fixed without too much work. Sealing the tubes will be a little more work. The overhang can be potentially reduced to bring the levers inboard and closer to the tappets.
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asphaltgambler

Posts: 7

Joined: Thu Oct 05, 2006 8:00 am

Location: Warrenton, Va.

Post Thu Oct 12, 2006 6:32 am

Zippers told me ( a while ago) that it was not worth doing. If fact the ports are TOO big on a shovel head even with a large motor. Before some of the aftermarket heads came out they were actualy welding the floor of the intake and exhaust to increase flow. Somewhat like a "D" port

The other issue is the added height to the engine. I have a stock, but extensively modified '77 cradle and the engine is already .600" taller and just barely fits.
Speed is just a question of money....................how fast do you want to spend?
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BREWSKI

Posts: 919

Joined: Sat Mar 27, 2004 1:01 am

Location: RENO,NV. U.S.A.

Post Sun Jan 14, 2007 3:26 pm

Thunderheads use modified XL rocker arms,XL strokers have the wrist pin boss moved up into the oil ring land area. I repeat what I said earlier Thunderheads WERE a piss poor copy of the Round port (early) XR heads. Thunderheads NEVER delivered the HP potential that was advertise,if you really wanted to go with aluminum heads use either XR750 heads or STD dual carb heads,LAWWILL uses these on his STREET TRACKER bikes. Gary JOHNSON of drag racing fame modified a few sets of XR750 heads to use EVO XL cylinders. Like I always say"A LITTLE KNOWLEDGE CAN BE A DANGEROUS THING" brewski
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little stanley

Posts: 42

Joined: Wed Apr 19, 2006 4:48 am

Location: houston, texas

Post Thu Jan 25, 2007 9:35 am

asphalt:

Years ago Uncle Bob at Southern Motorcycle had a set of Thunderheads but I don't know if he still does. You can call them at 281-987-3324 - Houston.

-little stanley

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