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Norton intake ports compared to Harley XR 750

Classic Norton Commando Motorcycles.

Re: Norton intake ports compared to Harley XR 750

Postby acotrel » Wed Apr 27, 2016 1:22 pm

My own 850 motor has standard inlet ports except tapered 2mm per side for the first 25mm to suit the 34mm carbs. It pulls like a train, however I use methanol fuel and a skinny two into one pipe.
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Re: Norton intake ports compared to Harley XR 750

Postby Dances with Shrapnel » Wed Apr 27, 2016 3:43 pm

acotrel wrote:If I was looking for a good inlet port design for a Commando, I wouldn't look at a Harley XR750. The best ever 350cc single in the 60s was the Aermacchi Ala D Oro which has tapered inlet ports.


So what power was this 350 Aermacchi single in the 60's making?

The later XR750's were reported at around 100 RWHP. So (350/750) X 100 RWHP= 47 RWHP. Aermacchi's are good but I highly doubt that good. :roll:

I respectfully refer you to the Blowing Smoke thread elsewhere on this forum. :lol:
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Re: Norton intake ports compared to Harley XR 750

Postby mark parker » Tue May 24, 2016 7:51 am

Something I tried with the Harley style oval port was an experiment to see just what a change to that shape port would do in an A65 BSA head using the same 30mm entry and std inlet valve size. I checked the flow on a std head from 67-69 era and also on a '71 as the porting is a bit different. The '71 flowed 111CFM @ 28"W the earlier head 109CFM bare without carb or bell on the port, both about 60cc port volume. More than stock lift wasn't making a difference.

Between the 30mm round entry and the valve I lifted the port floor and port roof and widened it turning the port smoothly down onto the back of the valve. Port volume still measures 60cc but the flow surprisingly is now 135CFM, if I put a little radius at the port entry 142CFM. I think this is pretty significant and would make the world of difference to a stock A65 and let it make extra power and pull higher RPM without any losses of power down low. It's pretty simple to do and doesn't go near breaking through anywhere, but requires the port floor to be filled and lifted.

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84cc port next to the 60cc port. 197CFM and 135CFM I should take a mould of a standard port for comparison.

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Re: Norton intake ports compared to Harley XR 750

Postby jseng1 » Tue May 24, 2016 12:44 pm

mark parker wrote:Something I tried with the Harley style oval port was an experiment to see just what a change to that shape port would do in an A65 BSA head using the same 30mm entry and std inlet valve size. I checked the flow on a std head from 67-69 era and also on a '71 as the porting is a bit different. The '71 flowed 111CFM @ 28"W the earlier head 109CFM bare without carb or bell on the port, both about 60cc port volume. More than stock lift wasn't making a difference.

Between the 30mm round entry and the valve I lifted the port floor and port roof and widened it turning the port smoothly down onto the back of the valve. Port volume still measures 60cc but the flow surprisingly is now 135CFM, if I put a little radius at the port entry 142CFM. I think this is pretty significant and would make the world of difference to a stock A65 and let it make extra power and pull higher RPM without any losses of power down low. It's pretty simple to do and doesn't go near breaking through anywhere, but requires the port floor to be filled and lifted.

Image

84cc port next to the 60cc port. 197CFM and 135CFM I should take a mould of a standard port for comparison.

Image


Thats a generous radius to the valve and a good eyebrow shape for the roof while preventing the guide area from getting too thin and cracking. And you've achieved significant creased flow with the same port volume.
How did you get in there to fill the port floor? Were you able to weld it? If so - please show us the welding tip.

What is the 197 CFM port about?
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Re: Norton intake ports compared to Harley XR 750

Postby mark parker » Wed May 25, 2016 12:55 am

The 197CFM port is the bigger BSA port I did before. Like it the floor of this little port is built up with JB weld. Its always worked fine for me but it would be much better if it was welded. Shaping the port is more difficult with two different materials as the JB sands away easier. I have a TIG but even with a stubby electrode I doubt the head of the torch would fit in there. I might investigate it though.

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Re: Norton intake ports compared to Harley XR 750

Postby mark parker » Fri Mar 17, 2017 6:28 am

I've finally been doing some data runs with the BSA with the Harley style port, I've only done a few runs just to experiment with jetting. With more air flow through the same carbs it seems to need smaller jets. It's making about 85HP on the data logger, which is the best it's ever been. The graphs show acceleration in first and second gear and show the exact differences between jet sizes. These are 230 black trace 240 red trace. I did try 220s which perform almost identical to 230s. I have a C/ratio 5speed in the A65 now which has excellent ratios.

The 1st and 2nd graphs equate to accelerating between 30MPH and 98-99MPH. It's just rolling on the throttle at 30MPH.

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Re: Norton intake ports compared to Harley XR 750

Postby jseng1 » Fri Mar 17, 2017 11:35 am

Congrats on your successful results Mark.

One thing I've been wanting to do is drill a couple conical shaped holes in the bottom of the port floor, install the valve temporarily and poor some molten aluminum into the port to build up the floor. The conical holes would lock the floor in place. You could even insert a temporary rubber floor, ram in some casting sand, remove the temp rubber, replace the valve and then pour in the molten alum. You might have to come 1/2 way each direction with the rubber pieces. Its just an idea and has to be worked out but it could lead you to a raised alum port floor and you could carve in the direction of KR 750 "cobra head" (Narley) ports from there.

Nascar ports below
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Last edited by jseng1 on Fri Mar 17, 2017 11:41 am, edited 2 times in total.
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Re: Norton intake ports compared to Harley XR 750

Postby xbacksideslider » Fri Mar 17, 2017 11:40 am

Mark - awesome work, thanks for the detailed report and pics. Thanks to Jim too, again.
We should all appreciate that it can be as if you are doing two jobs to put together this kind of post.
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