HD XR 750 & Full Auto port conversion

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This is a project to raise the port floor similar to the HD XR 750 and Fullauto ports (starting with a stock head). A tube has been welded to the port floor and remains to be shaped, ported and finished. This project is on hold until I find someone who can get inside the port floor near the valve seat to weld the other ends of the tubes - preferably a laser welder (who in the US can do this?).

Here's the chamfered and welded intake floor. Note that the guide has been welded for re-angling.


The exhaust side.



See profile of the proposed raised intake port floor comparisons.


To make HP the port is widened around the intake guide. Radical HD XR 750s with ML cams are widened throughout and raised to form the "cobra head shape". Late HD race ports are as wide as 48mm at the guide and claim 90 to 100 HP. I don't plan on widening more than 34mm around the guide for the street.

The exhaust port modifications. Also gets wider around the guide.
 
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madass140

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very good Jim, I had considered the same option but also with the same welding issues.
I'm sure someone will pipe up with laser welding help. I think thats the only way.
One of my concerns is heat transfer from the insert to the head
 
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Re your welding inlet port, the HD factory welded up the whole of the port and recut them for Carl Rayborns racing bike, I cannot remember where I read it as it was a long time ago, before he got the no 1 plate.
 
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This is a project to raise the port floor similar to the HD XR 750 and Full Auto ports (starting with a stock head).
Excuse my ignorance, Jim. What do you mean by "Full Auto ports"? CNC machining? Others may be wondering as well.

-Knut
 
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If you look at the FA ports compared to the XR 750 ports you'll see that the profile is similar. The height on the XR 750 is only about 26mm at the tight spot. But is is very wide and this is why they out flow just about any other 2 valve 4 stroke.



But notice the difference in width (HD XR 750 on left).


Yes I'm still looking for someone who can weld the insert near the valve seat (laser weld or other).
 

Burgs

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Hi Jim
Why not mill the ports out from the bottom (combustion side) so you have a clean area to weld easily, then re-machine the head to what you want.
5 axis machine the ports to the XR style on a Centroid A560 or similar head machining centre.

This way you will have a solid lump to start with

With the welding of the head controlling the temperature will be important, keep between specified heat ranges, age hardening might help post welding.

When I first bought my Manx in 1971 the head had seen better days from piston/valve failures, we welded it and machined the combustion and sealing faces back to as standard as we could, this was back in 1972 and I have never had any problems, although last 40 years it only seen the odd ride days.

Burgs
 
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Burgs
I'm going to stick with my plan. If I can get the inserts welded near the valve seats then all I have to do is port it and I've had good results with porting. If I can't get anyone to weld it for me I'm considering gas welding it (I can gas weld alum and I've done it to reinforce cases but its the last & desperate resort). The reinforced cases did age harden and held up in racing.
 

lcrken

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Looks like the simplest approach would be to get a Fullauto head and just port it to match the XR approach. You would probably still have to weld up around the outside of the intake port, if you wanted to open it up as large as the XR, but that should be a lot easier. Might not help for the exhaust ports, but looks like it might work for the intakes. The drawback, of course, is the cost of finding and buying a Fullauto head. And if it worked, you still couldn't do the same to a factory head.

If you're mostly interested in seeing if the idea works, you could just cast some port boxes in plaster, where you cast the stock ports in plaster, and then play with the shape on a flow bench to see what works. I think that's what HD did in developing the aluminum head XR750 ports. And plaster is really cheap:). On the other hand, if it worked well, you'd still have to figure out how to get those port shapes in a Commando head, so doing the plaster ports would add a lot of labor, and you'd need access to a flow bench. If you promise to use it to develop Norton heads, you can have my old Superflow SF 110.

Ken
 

WZ507

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If you're mostly interested in seeing if the idea works, you could just cast some port boxes in plaster, where you cast the stock ports in plaster, and then play with the shape on a flow bench to see what works. I think that's what HD did in developing the aluminum head XR750 ports. And plaster is really cheap:). On the other hand, if it worked well, you'd still have to figure out how to get those port shapes in a Commando head, so doing the plaster ports would add a lot of labor, and you'd need access to a flow bench. If you promise to use it to develop Norton heads, you can have my old Superflow SF 110. Ken
To the best of my knowledge, HD’s XR oval port was created by Ken Augustine, working under a contract with HD, circa 1981, where he provided 2 sets of aluminum heads and one set of plastic heads to the factory. Harley inquired if he could produce these heads for the factory at a rate of 10 sets/week, which he declined. Although the port was created in the 1981 time frame it was not made commercially available by HD until 1988.


Prior to the XR oval port introduction, the round port XR heads were done by CR Axtell (stamped and serial numbered) . Below are images providing a comparison of round (Axtell) and oval port (Augustine) XR IN and EX tracts.


Axtell stamp.JPG LR round oval compare.JPG LR round oval compare1.JPG
 
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Wake up Jim and take Ken up on his offer. Ken works a bit everyday in continuing the legacy and encouraging others to take it to the next level. It would be an insult to not accept his offer. You can get real comparative data and make this motor dream a reality. BTW, I would look forward to you sharing your findings .
 

WZ507

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Another option for experimenting with an XR oval port in a CDO head would be to simply hog out a sacrificial CDO port, transplant the XR port casting into it and fill voids at OD with epoxy. This undertaking would also reveal clearly where a shortage of metal exists. Once installed move the project to the flow bench for optimization, as you can cover a lot of ground efficiently with a little epoxy and Bondo. When airflow of the port is optimized to the desired goal, have it digitized and you’d be ready for a machining center, assuming you can metal-fill the port satisfactorily to provide the necessary material to machine.


LR XR transplant1.jpg LR XR transplant 2.jpg LR XR transplant 3.jpg LR XR transplant 4.jpg
 

lcrken

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Thanks for posting those port molds, Kurt. Really interesting to see the comparison between the round and oval port shapes. Do you have any data on the differences in flow rates between the two?

Ken
 
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I already have the port molds, specs and accurate measurements of the HD XR750 ports. I'm more interested in duplicating those ports than running flow bench tests. Ken - I would love to take you up on your offer but I can't make promises now with my present work load. I also have Axtell port molds courtesy of Ken Canaga. I have a similar copy of those Axtell ports in my current cafe racer.

I've already ported a Fullauto head and widened them as shown in the video below. That head was for a 500cc short stroke so I didn't go too wide.


Reangling the valves so they locate accurately on the tappet adjuster screw.

I've already worked out the compromise port shapes in Autocad so they will fit in the stock Norton heads. There are several stages (widths) depending on how much welding is involved and all of that is readily available in my "Narley port" CD. The current project is for my cafe racer and will only go to 34mm width around the guide which is 2mm wider than the FA head and doesn't need welding on the sides of the ports. I intend to perform the same porting and valve re-angling that I've already done with the FA head for the 500cc full race short stroke - except that the exhaust port floor will be closer to the profile of the XR 750. The only hang up is getting someone to (laser) weld the insert near the valve seats.

For a round port to compete with the "cobra head" shape that widens around the guide it would have to be steeper like you see on 4 valve motors. But because of vertical space restrictions limiting the angle the cobra shape offer more flow and you see the same shape in some Nascars.

 
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lcrken

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Really enjoyed your FA porting video, Jim. I don't recall seeing it before. Must have missed it back in 2018 when you posted it on the forum. Or else it's just another case of old guy memory lapse. It would be really interesting to see a flow chart comparison to the other FA heads that have been flow tested, but it doesn't sound like that's real likely.

Ken
 

Brooking 850

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Ken/Jim. I have had a FA head flowed here in NZ and it is currently on my race bike .
It came via Jim Comstock and has 1.5 mm larger intake Vv's and after a little more fettling I had it flowed while testing different carbs and bell mouths.
Currently running 34mm Mk 2 Amal smoothbores with JS manifolds , rubber boots and 60mm intake trumpets.
Ill dig out the flow charts and post if its of any use.
I dont have any dyno data as yet since this head has been on the bike.
Regards Mike
 

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