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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 mark parker » Sat Sep 19, 2015 4:44 am

Pretty much done with the porting and manifold making. Both done and within 1 or 2CFM of each other at most lifts. Turned up some washers and lifted the guides 4mm and they are in to stay. Flow at different lifts are all good. Hard to imagine that the port on the left of similar volume, with the same valve and carb flows so much worse than this great little XR styled port. At .436" the round port flows 158CFM. At .300" the oval port flows 170CFM, at .350" 185CFM at .410 193CFM at .450" 199CFM and .500" 204CFM.

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Left port now.

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Re: Norton intake ports compared to Harley XR 750

Postby acotrel » Sat Sep 19, 2015 1:20 pm

I have a couple of questions : Who has got the fastest road race 750cc Norton in America ? Is their bike setup to develop high horsepower at high revs, or a lot of midrange torque at moderate revs ? And how is their bike geared for most circuits - high or low ? I suggest that what happens in the inlet and exhausts of a four stroke motor happens under sonic conditions, so when you use a low velocity flow bench - what you see might not necessarily be what you get when the motor is operating.
When you widen the inlet port each side of the valve guide, you might be kidding yourself. A change of direction at that point might induce swirl and upset the standing wave and reduce the mass transfer in the port when the motor is revving fast.
As far as XR750s putting out 100 BHP - on whose Dyno ? As I understand it, most of the dynos which are inertia based give results which are all comparative to the Yamaha Vmax, and a nominal horsepower value for that motor is used to set the fiddle factor. When the 500cc Manx Norton turned out 50 BHP, it was probably measured on a Heenan and Froud test brake from first principles. Are you telling me that the XR750 turns out twice the horsepower of the Manx ?
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Re: Norton intake ports compared to Harley XR 750

Postby acotrel » Sat Sep 19, 2015 1:24 pm

I read some of the early posts about CR Axtell. Was he a road racer or was he on the dirt ovals. The motor requirements for the two types of racing are not the same.
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Re: Norton intake ports compared to Harley XR 750

Postby Dances with Shrapnel » Sat Sep 19, 2015 5:21 pm

Hats off to you mark parker. Nice work and documentation so far. I've really enjoyed this and it has given me impure thoughts for my Norton 750 USS rebuild.

As for Mr. acotrel.............

acotrel wrote:I have a couple of questions :


Uh oh!

acotrel wrote:Who has got the fastest road race 750cc Norton in America ?


I do, I do ..............well at least I thought I did until the last engine fragged on the dyno - it was ready. :lol:

acotrel wrote:Is their bike setup to develop high horsepower at high revs, or a lot of midrange torque at moderate revs ?


I hope I don't disappoint you acotrel as this has been covered for you several times before but the answer is yes to both - high hp at high revs and a lot of torque at mid range revs. The engine is a 75mm stroke with 12.6:1 compression ratio. It gives up virtually nothing for mid range and has an extra 1,500 to 2,000 rpm of additional torque and power.

acotrel wrote: And how is their bike geared for most circuits - high or low ?


Think about what you are asking here..................the bike is geared like any other race bike. Gear for the longest straight and then maybe tweak it a little if you think you can gain on infield turns. I am running a six speed with this 750. Keep in mind that this is no longer your garden variety long stroke Norton, gear accordingly.

acotrel wrote:I suggest that what happens in the inlet and exhausts of a four stroke motor happens under sonic conditions, so when you use a low velocity flow bench - what you see might not necessarily be what you get when the motor is operating.


Did you mean to say super sonic conditions as in sonic choke? I do agree that flowing a port at one pressure differential only is not the complete picture but it is one hell of a good start. Professor Gordon Blair (and others) made a case for flowing both the intake and the exhaust at multiple different (and considerably higher) differential pressures so that you could develop a map of the port behavior. Professor Blair also made the case for flowing the ports in reverse as this is what happens during overlap. All this data was then used to simulate the performance of the motor.

acotrel wrote:When you widen the inlet port each side of the valve guide, you might be kidding yourself. A change of direction at that point might induce swirl and upset the standing wave and reduce the mass transfer in the port when the motor is revving fast.


You might be kidding yourself if you think a fixed cross sectional port is going to behave well when you stick a valve stem and valve guide in the pathway which forms a constriction in cross sectional area. Furthermore, please explain or illustrate what a "standing wave" is and how it pertains to our beloved Nortons. You can use flip charts and wave your arms around if that helps.

acotrel wrote:As far as XR750s putting out 100 BHP - on whose Dyno ? As I understand it, most of the dynos which are inertia based give results which are all comparative to the Yamaha Vmax, and a nominal horsepower value for that motor is used to set the fiddle factor. When the 500cc Manx Norton turned out 50 BHP, it was probably measured on a Heenan and Froud test brake from first principles. Are you telling me that the XR750 turns out twice the horsepower of the Manx ?


Let's put the discussion of comparative dynos to the side for now. A post 1989 XR750 is stinking fast. We've competed against the XR750 and there is that big difference in raw power. I would say the 100 BHP is real though I have never done a dyno run on one. The 500 Manx Nortons of today are closer to 60 RWHP. A post 1989 XR750 redline according to the HD factory service manual is 9,200 rpm whereas a well sorted out Modern Manx Norton short stroke is 8,600 rpm so not only is the XR 750 sweeping 50% greater volume but it is capable of doing it at a greater rate of speed.

So (Manx 60rwhp) X (9200rpm/8600rpm) X (150% swept volume diff) = 96 RWHP for an XR750...................allow say 4 hp for friction loss and you have an easy 100 BHP
Last edited by Dances with Shrapnel on Sat Sep 19, 2015 7:02 pm, edited 1 time in total.
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Re: Norton intake ports compared to Harley XR 750

Postby lcrken » Sat Sep 19, 2015 5:24 pm

acotrel wrote:I read some of the early posts about CR Axtell. Was he a road racer or was he on the dirt ovals. The motor requirements for the two types of racing are not the same.


Axtell did engine work for both flat track dirt racers and road racers. His business partner, Mike Libby, was an AMA road racer (Yamaha 250 2-strokes), so they were well aware of the motor requirements of both types of racing. He also did camshaft development work for a well known car racing engine builder, and was the engine developer for the Yamaha factory flat track racing effort in the early '80s that used the Virago style V-twin engines. He was also an old time hot rodder, and in his younger days collected timing slips and records running his hot rod Ford at El Mirage.

FWIW, Axtell's dyno was a Heenan Froude water-brake dyno, not a modern inertial dyno, and was very carefully calibrated. The brake was driven directly from a shaft connected to a sprocket driven by chain from the transmission countershaft sprocket, so the measured numbers were essentially rear wheel horsepower, but without the loss from the rear tire included. Might be more accurate to call it "rear sprocket horsepower", but that's not an industry accepted term. Is that what you meant by "from first principles"?

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Re: Norton intake ports compared to Harley XR 750

Postby mark parker » Sat Sep 19, 2015 10:02 pm

The flow bench is showing up well what is and isn't working. I have a couple of heads with various amounts of fill on the port floor. And are otherwise big round ports that do not have one nice curve over onto the back of the valve and are not widened at the guide. They do not flow properly or efficiently except at low lifts, at higher lifts when lots of air starts moving things are so wrong the flow goes down in proportion to more lift. The absolute best of them flowed 155CFM at .300" and the same at .450" . The best flow was at .410" 162CFM. At .500" it was getting better again at 159CFM (which does not compare well to over 200CFM of the new ports at that lift). And for sure some weird stuff was going on in there. But it's the flow bench showing this up. Otherwise I would never know seeing the bike ran good and strong.

This XR styled port is so different, it runs clean curves and swapping it onto the bench shows a huge increase in the ease air has of passing through. I have no doubt that port shape is exceptional for flow.

What I do not know is exactly how that will translate on the bike. I use midrange power the most, I actually do not need more power, but am curious what this will do. I'm hoping it will not lose midrange and bottom end, just keep that good power coming for another 1,000 RPM or so, because the big motor runs out of breath around 6,500 and power drops off.

I should get it fixed up and on in the next few weeks and we'll see what it does.

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Re: Norton intake ports compared to Harley XR 750

Postby cjandme » Sat Sep 19, 2015 11:54 pm

mark parker wrote:....... I should get it fixed up and on in the next few weeks and we'll see what it does.......

Very much looking forward to hearing about how your bike runs after this modification. thanks for posting , Cj
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Re: Norton intake ports compared to Harley XR 750

Postby jseng1 » Wed Sep 23, 2015 11:27 am

mark parker wrote:Pretty much done with the porting and manifold making....

Left port.

Image


Congrats Mark

Thats one BSA, one Triumph and one Norton with these Harley XR 750 ports so far. Hopefully more to come.
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Re: Norton intake ports compared to Harley XR 750

Postby Rohan » Thu Sep 24, 2015 3:20 pm

I haven't been following closely, has anyone run these on a dyno to see how these perform ?

Widening the port into 2 channels like that is to get more flow around the valve stem,
without enlarging the port height-wise. (?).

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Re: Norton intake ports compared to Harley XR 750

Postby Rohan » Thu Sep 24, 2015 3:31 pm

acotrel wrote:As far as XR750s putting out 100 BHP - on whose Dyno ? As I understand it, most of the dynos which are inertia based give results which are all comparative to the Yamaha Vmax, and a nominal horsepower value for that motor is used to set the fiddle factor. When the 500cc Manx Norton turned out 50 BHP, it was probably measured on a Heenan and Froud test brake from first principles. Are you telling me that the XR750 turns out twice the horsepower of the Manx ?


That statement about v-max's is a little misleading ?

Inertial dynos have been around since before the v-max, AND before computers.
A chap who does/did the fairground races with an ole little Injun Scout has a little early one for home/workshop use,
and he describes somewhere how he runs up the bike in his garage, and can use a stopwatch to judge performance.
As 1920s road bikes, Scouts put out about 10 hp, enough for 60 mph on road, so every little bit extra helps.
(think Burt Munro, same bike starting point).

Some folks have run their engine on both types of dyno, so relative measurements are easily compared.
Intertial dynos are rather more convenient for fully assembled bikes too.
Its not rocket science, and absolute numbers are not everything.

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Re: Norton intake ports compared to Harley XR 750

Postby Rohan » Mon Sep 28, 2015 4:11 pm

Rohan wrote:I haven't been following closely, has anyone run these on a dyno to see how these perform ?


Are folks avoiding answering this question ??

If such ports are the flavor of the month, but no-one has actually tested them to see how they stack up...

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Re: Norton intake ports compared to Harley XR 750

Postby Dances with Shrapnel » Mon Sep 28, 2015 4:56 pm

Hold your horses Rohan, while you were at Elba, on September 19th, 2015
mark parker wrote:I should get it fixed up and on in the next few weeks and we'll see what it does.


The indicated increase in flow rate is impressive and as I understand it, there is little to no compromise on port velocity so all is good there. Any time you can increase valve flow coefficient without decreasing port velocity you are definitely going in the right direction (within reason) for these engines.

This has all been proven out before by the HD XR750 performance.
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Re: Norton intake ports compared to Harley XR 750

Postby mark parker » Sat Oct 31, 2015 9:39 pm

I had to do a bit to the head to make it usable. I made some alloy washers to add to the inlet spring seats and lift them 4mm, These are glued in with JBweld and also hold the valve guide. The valves I use are shortened jaguar valves 44.6mm and the stems are reduced down near the head, it was pointless having valve guide further into the port that would never touch the valve stem. I shortened the guides at the top just enough to give good clearance for the valve lift I'm using. Replaced two valve seats and did a final flow test. 195.3 and 196.7CFM at .410".

It's been running about two weeks and seems good. It responds to throttle slightly differently, it responds best rolling on the throttle. Bottom end and midrange performance have stayed good.
I haven't data logged it yet but the power seems to build better into higher RPM. The carbs sit a little closer to the head than before.

Image

So its just been riding to work and back, to get things sorted.

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Re: Norton intake ports compared to Harley XR 750

Postby Bernhard » Tue Nov 03, 2015 7:18 am

mark parker wrote:Pretty much done with the porting and manifold making. Both done and within 1 or 2CFM of each other at most lifts. Turned up some washers and lifted the guides 4mm and they are in to stay. Flow at different lifts are all good. Hard to imagine that the port on the left of similar volume, with the same valve and carb flows so much worse than this great little XR styled port. At .436" the round port flows 158CFM. At .300" the oval port flows 170CFM, at .350" 185CFM at .410 193CFM at .450" 199CFM and .500" 204CFM. ]


Impressive as these figures are, do you have some gas flow figures for a standard Commando port head, so we can compare the two :?:

Would also like full info on standard ports, dia, if you have used 32mm to 30mm manifolds e.t.c.

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Re: Norton intake ports compared to Harley XR 750

Postby Paddy_SP » Tue Nov 03, 2015 7:41 am

lcrken wrote:
acotrel wrote:FWIW, Axtell's dyno was a Heenan Froude water-brake dyno, not a modern inertial dyno

Ken


Ken - do you happen to know what model of dyno it was? I have a DPX2 in bits which I keep promising myself I'll sort out one day. I used to work on them for a living (at the British Internal Combustion Engine Research Institute), many years ago. After that I moved on to a much bigger H&F 'butterfly brake' which we used for F1 engines.

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