Norton intake ports compared to Harley XR 750 (2013)

I just made some port molds of a Harley XR 750 intake racing D port.

The port is oval shaped and with a raised floor. Going very wide around the guide (wider than the valve)

45mm intake valve (36mm ex)

Floor is flat & D shaped
Roof has prominent ridge leading & following guide

Oval - 41.5 x 28mm at manifold, length is 3” from manifold to valve

¼ from seat 38mm front to back, 40.5 side to side
½ from seat 35 front to back, 42.5 side to side
1” from seat side to side maxes at 49mm
28mm top to bottom leading up to 26mm top to bottom 1” before guide

You can see in the photos that the floor has a raised more gradual curve than the Norton (28mm in port shown). And gets very wide around the guide with a more gradual radius at both the floor and roof curve.

The Harley has a 77mm Stroke and 79mm bore and can rev over 9000 and is reputed to make 100HP. The ML cam is approx close to Norton D+ and JS stage 3 but with more lift.

Look at the diff in the floor compared to the 28mm Nort port in the back (photo below). This raised floor method is what makes the Jim Comstock - Full auto head work.



top view with the Harley port on left. This shows just how for you can go with a pushrod twin.



photo of head

As a certain German soldier once said : 'very interesting' , ' I know nothing' and 'we will ask the questions' !

Not a surprise that a completely different engine, designed from the start as a racing engine, would have different ports than a Norton. Pushrod or OHC makes no difference, the same port shape can be inserted into either design if you are starting from scratch.

The Fullauto head still had to fit it's port into a casting that is 100% compatible with the stock casting, so it will never be as good as an engine designed from scratch as a racing engine. Comparing the Fullauto head to an xr750 head makes no more sense than comparing it to any other completely different engine, say a Northstar Cadillac, wow look the different engine has different ports!

Also, the designer of the ports for the Fullauto has already shown that a stock small-port Commando head can be ported to achieve performance similar to the Fullauto head when he tested Ken Canaga's Axtel-ported head and found it gave very close flow and velocity numbers to the Fullauto, and it was ported over 30 years ago!

I am glad that new high quality Norton heads are being made, but the owner of a standard 750 Commando head should not be made to feel that his casting is obsoleted by the Fullauto. Of course the Fullauto head is popular with the "throw money at it" crowd because they do not have to have any mechanical knowledge or porting ability to get "Axtell" flow numbers with it, but for those with a little ability and the brains, it is very possible that they could save themselves a few thousand dollars by learning how to refine their old Norton head as Axtell did.

Ron Woods dirt track racer built up with almost all stock engine parts except for the cam and valve springs made as much or more horsepower than probably almost all the current Norton "vintage" racers out there today that are built up with almost 100% aftermarket and much stronger components.

After watching Dave Roper run a 350 Harley Sprint with a well developed 750cc Norton in a roadrace, you can draw the conclusion that time spent on reliability and rider ability is just as good or better than money spent on exotic parts. A similar conclusion drawn to that while looking at Axtell's 30+ year porting job on a garden-variety Commando head running with the Fullauto offering on a flow bench.

beng said:

Not a surprise that a completely different engine, designed from the start as a racing engine, would have different ports than a Norton. Pushrod or OHC makes no difference, the same port shape can be inserted into either design if you are starting from scratch.

The Fullauto head still had to fit it's port into a casting that is 100% compatible with the stock casting, so it will never be as good as an engine designed from scratch as a racing engine. Comparing the Fullauto head to an xr750 head makes no more sense than comparing it to any other completely different engine, say a Northstar Cadillac, wow look the different engine has different ports!

Also, the designer of the ports for the Fullauto has already shown that a stock small-port Commando head can be ported to achieve performance similar to the Fullauto head when he tested Ken Canaga's Axtel-ported head and found it gave very close flow and velocity numbers to the Fullauto, and it was ported over 30 years ago!

I am glad that new high quality Norton heads are being made, but the owner of a standard 750 Commando head should not be made to feel that his casting is obsoleted by the Fullauto. Of course the Fullauto head is popular with the "throw money at it" crowd because they do not have to have any mechanical knowledge or porting ability to get "Axtell" flow numbers with it, but for those with a little ability and the brains, it is very possible that they could save themselves a few thousand dollars by learning how to refine their old Norton head as Axtell did.

Ron Woods dirt track racer built up with almost all stock engine parts except for the cam and valve springs made as much or more horsepower than probably almost all the current Norton "vintage" racers out there today that are built up with almost 100% aftermarket and much stronger components.

After watching Dave Roper run a 350 Harley Sprint with a well developed 750cc Norton in a roadrace, you can draw the conclusion that time spent on reliability and rider ability is just as good or better than money spent on exotic parts. A similar conclusion drawn to that while looking at Axtell's 30+ year porting job on a garden-variety Commando head running with the Fullauto offering on a flow bench.

Click to expand...

I'm not that technically advanced so for me to get performance I need to rely on the knowledge and engineering of others. I am however pretty good at wrangling the shit out of said engineering performances.
How bout you share exactly what we need to do with a stock head to get near axtell or fullauto performance? In terms that could be provided to a local engineering shop using an rh4 as s start point?

Btw, nice work Jim

Dkt26 said:

beng said:

How bout you share exactly what we need to do with a stock head to get near axtell or fullauto performance? In terms that could be provided to a local engineering shop using an rh4 as s start point?

Click to expand...

Click to expand...

Wrong starting point. RH10 as a core. RH4 does not have enough metal in the right spots.

Many times cheaper to have it done than to learn as you go. Many skills people have
were gained over a long period of time...meaning some of us dont have enough time
left to learn them!

Speaking of metal in the right spots....

When the race guys heard there was a new head being prepared for sale, the first thing they said was
Oooooo, can we get the inlet valve port raised 1/2" - to give more downdraft.

Saves all that welding and filling, to give more of that all important downdraft.

Dkt26 said:

How bout you share exactly what we need to do with a stock head to get near axtell or fullauto performance?

Click to expand...

For someone that bathes themselve in the righteousness of "FACTS......................Crickets. I hear hear crickets.

Axtel and the lads certainly knew their stuff but it blew up a lot. I don't know where beng is getting his "FACTS" on old race motors versus the new stuff out there but I am pretty sure Axtell & others were eclipsed a few years later. I know Kenny can wring the sh*t out of his motor weekend after weekend and not have to look into it till end of season and his is a very good motor.

No can do with flimsy OEM stuff.

Jim, excellent stuff there. I had a go at a very similar approach for a Norton head and CNC. The head would need to be welded up a lot for it to work and that brings in another set of challenges but not insurmountable.

Yes - Norton ports below.

Axtel and the lads certainly knew their stuff but it blew up a lot.

Click to expand...

Reliability, or lack of, was the problem with the #13 Norton ridden by David Aldana. That engine spent a lot of time in C.R. Axtell's shop. Nick Deligiannis was the tuner/crew chief/wrench and he and Gene Romero won a national championship with a Triumph that had a lot of Axtell mods. Considering all the above, I'd say the Norton basic design didn't make for a reliable high horsepower engine.

Dances with Shrapnel said:

I don't know where beng is getting his "FACTS" on old race motors versus the new stuff out there but I am pretty sure Axtell & others were eclipsed a few years later. I know Kenny can wring the sh*t out of his motor weekend after weekend and not have to look into it till end of season and his is a very good motor.
No can do with flimsy OEM stuff.

Click to expand...

You are not disputing anything I said, I am merely passing along information that is available to anyone that cares to look for it.

The 1975 Cycle World article "Dirt Track Limousine" states Wood and Axtell used 68' or 69' Commando cases to make 77 rear-wheel horsepower, they ran 43 races that year and DNF'd in three of them. Where was the Norton 750 that eclipsed those numbers " a few years later"? Or the AHRMA Norton with any better record of reliability? Facts that DWS infers but does not provide.......

If anything, "a few years later" Norton technology and power went away. Axtell quit making his parts and Wood quit racing and there was no equivalent parts until the last few years, it was 20+ years before vintage racers got back to Axtell power levels or eclipsed them. Fact.

The only other fact I mention is the flow and velocity charts put up on this very forum by the Fullauto port developer comparing the Fullauto and Axtell heads, which graphed almost identically to each other.

Wood and Axtell were racing for real, against XR750s and other state of the art competition with real AMA experts, they were not bored millionaires/playboys running a few races against each other in vintage events each year.

If someone wants to replicate Axtell's porting I would first read Smokey Yunicks book on building Chevrolet small blocks that has the word "secrets" in it's title, it has a good history of porting technology and what works in poppet valve ports and what does not. It has the exact ideas used by Axtell in his Norton ports. Also carefully read through the posts put up on this forum on Norton head flow by those successful in racing and making money selling Norton head work, and things are pretty well spelled out.

There is nothing magical about Axtell's porting, it was just smart and a product of experience. Axtell used stock sized valves in a regular Commando 750 head. He kept the port cross section uniform the length of the port, which was about 30.5mm at the manifold flange. He left the floor alone and as high as possible, kept it straight for as long as possible above the valve seat, and did make it bigger where it went round the valve guide, once again to keep the cross section uniform where the guide took up space in the port.

With today's knowledge of port flow and behavior it is common sense that someone should be able to replicate Axtell's ports or do even better if they spent a little time researching the subject.

Most spare old Norton engines laying around have histories of use in street bikes, not racers, and have lots of life left in them for a sensible vintage racing effort using a sensible redline of 6000rpm, at which Woods engine was pumping out 67hp at the rear wheel, enough for fun?

In the early days of vintage racing, when it was still actually historical, that is what was used, real vintage chassis and engines. There are plenty of the same parts vintage racers used in the 80s laying around to be used now by sensible riders interested in history and fun more than big numbers and their egos, the same parts that Wood and Axtell used, Norton cases, Hepolite pistons and stock rods and heads.

Vintage racing in the USA today is not historical or vintage at all. The types of bikes and their proportionate numbers have nothing to do with what was raced in the 1960s or 70s. It has decayed into a freak show of machines that no one in the 60s or 70s ever saw or could obtain. In the country that saw the majority of the world's motorcycle production flood into it, the machinery is certainly here, but the racing has been corrupted into a farce by bored hobbyists that have no personal history with the racing of that era and who have put their egos and selves over what it should be.

Wow, facts from Cycle World. All I can say is my grandmother's Norton makes 77 RWHP.

43 races and 3 DNF's - can anyone here say grenade?

To Jimc's comments, they were not far off the mark with some of their designs and had a few home runs (cylinder head valve/port orientation and flow capacity). A lot had to do with the quality of materials (cast steel crank cheeks instead of billet steel) and too thin crankcase walls and webbing.

The XR750 had stubby stiff cams and roller cam followers allowing for very high acceleration rates. The Norton on the otherhand has this long single cam which must do the job of both the intakes and exhaust valves. It really is not up to the task of very high valve acceleration rates.

To give credit to Axtell where it's due, he did not have access to the latest strengthened cases and through-bolted barells that we all do these days.

i remember an interview with him that went roughly like this: " First the barrells broke . When we fixed that, the cranks broke, when we fixed that, the cases broke. There's not much you can do when you get to that point"

His skill at extracting power exceeded the capacity of the motor to stay together.

These days we'd go to Steve Maney and buy some strengthened cases, maybe some outrigger bearing gearbox parts and alloy barrells that won't crack. He couldn't do that.

No doubt Axtell deserve much credit for the tenacity and technical know how to build successful Norton twin race engines as does Peter Zysltra and others at Harley Davidson design team for the development of the XR750 engine. The XR750 did not start as a success but evolved; just as the Nortons of today evolve with newer and better components, more technical know-how. The engines were not stuck in the past but evolved, moved on and matured, unlike others. :lol:

If I recall correctly, Axtell may have strengthened cases but no comparison to Steve Maney engine cases. Yes, you push any motor and a clear hierarchy of "what fails next" becomes apparent.

Keep in mind that all this port/valve/performance enhancements was neatly laid out decades before Axtell, Smokey & others applied them. In the US this was done by the National Advisory Committe for Aeronuatics (NACA) which was the predecessor to NASA. There are a series of professional papers that were declassified in (I am guessing here) early to mid fifties that presented the research and applied research on the poppett valve and flow. This was from a time where high performance enhancements to piston powered aircraft was a matter of national security.

So if I read about the FullAuto head here with little to no work it can flow as good as Axtell's best heads. By all measures, this is a good thing. I am saving my pennies. As time and resources permit, I still want to have a go at the oval port similar to that laid out for the HD XR750. Lots of constraints with OEM heads but maybe some opportunities with a FullAuto head.

Again, thanks to Jim Schmidtt for presenting this interesting and worthwhile comparison of port profiles.

Axtel / Wood , output .



Heres some antique XR 750 data . theyre past 100 now , on the same stroke ?
( might have to go to image shack to get them all to come up , ancient history .



Link for articals : brien-folly-t12060.html

I am pretty sure the XR750 port mold shown above is from a late model XR750. If you accept the article at face value, that 6-8 HP edge still exists today when comparing the later XR 750 to some of the best Norton race engines of the last few decades, the difference is that both engines are about 10 hp stronger. I am talking short stroke Norton now; you really hit a wall with the 89 mm stroke.

Too bad the short strokes came around too late; it would have been very interesting. Not sure if any made it to the dirt tracks.

Interesting second article there Matt. The last few paragraphs were enlightening where they tested a fairly wide span of port diameters. When each port diameter was tuned with appropriate pipes and inlets, they apparently all performed about the same. Not enough information in the article to tell wether they were referring to peak power only or overall power band characteristics.

Lots of different design philosophies were apparently batted about in the XR 750 R&D.

Exhaust valve size - seems to run in line with what Jim Comstock has mentioned in the past.

should hang the Journalists . Motorcyclist was about the only non hysterical one in the U.K. nothing but whine . :x
digressing slightly , but we'll take the Mans word for it . :wink:

Icrken - >
"
No new bikes for a while. Maybe it's time for some flat track eye candy. This is the factory flat track bike I bought from John Hately when Norton went bust and the team folded up.





Doesn't look much like a Commando, but the engine is a Commando short stroke 750. I bought it for the engine, and later sold the rest to another Norton crazy. It's now being restored by Bill Milburn, an ex-factory rider, in Texas. I used the engine in my PR, but it's parts are now spread out among other engines. The oiginal crank eventually cracked, as did the new spare that came with it. The cases went when one of the steel rods gave up at Park City. The head and cylinder are still in use on my 920, along with the Sifton 460 cam with BSA lifters.

The paint job was my own effort, not the race team's. I painted it, stuck silencers on the end of the TT pipes, and rode it around the neighborhood a few times before I pulled the engine."

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75 cross over Ex . in one end , & out the other . :? ( see the concurrent I.o.M. machine , picture in next post .
intake & exhaust lengths / dimeters may be of intrest ? . if not law written in stone . :idea:
incidently , Fulllauto quotes increased meat for development / machineing in his castings .i.e. big port capeability .

Say Matt, you made it to the first annual Park City road race? I made to the last Park City annual; what a blast that was.

my missguided activities were circa 1980 . T100R Triton . the one in the ' Bonnie Book ' shown in the 55 I.o.M. ( ridgid )

BIKE ABOVE is KEN's & quotes . Old Perry had said ' Thats Lowes old bike ' one day , in passing .
such things should not get lost . Like the 7 blown cosworths free for the asking . Intuition
beats rationality . Though , in development , finding the faint train of logic through the dim mass of information
would save a lot of f ups . Easy to be wise in hindsight . A spiral of evolved logic -> in development .

Compromise was for the Japs . The British at that stage were chaotic , tragically . A honed Commando
with Rev Limiter and three bearing trans could have soldiered on indefinately . Bar Costs .

At least Poore tryed , crankcases progressively stiffened and parts uprated . But wouldve needed to be clarevoiant to
have put a bridge framed works replicer ? Like the Duke , into the market . IF the Govt. hadnt sunk N.V.T.
e.t.c. Et Al .

Still life in the old girl yet . A Mk III bottom end is the most developed of the production items , as is the gearbox .
( unless all printed matter is codswallop ) Therefore a ' Super Sports ' incarnation in our friends hands here , may be
anachronistic , but no less the better for it . Back in 75 a Rev Limiter wouldve seen it unburstable . At 7.000 .
7.500 for a balanced blueprinted 650 / 750 seems to have been atained in 1970 ( Dunstall ) . He who pays the piper,

Shouldve invested in Nortons here in Aus. in 1999 , when N.o.C. was a pile of rusty oily relics , only two at the meet
wernt an embarrisement , and one of them was a 61 Tri 650 . :wink: . All spit & polish now .and a price to go with it .

So hard to get reliable help these days , Wot Ho .



only reason said for Isolacking ( ) was WEIGHT . its a Race Bike . a ounce of handlings worth a pound of Horsepower .
I'll have BOTH , Please ! :x ( just the Pcture , hope theres some inspiration in it . Last of the pushrod J.P.N.s ,
ignore the presses tripewriteing , dunno how to edit it down to the picture ONLY . LAST WORKS 750 S.S. development .

Dances with Shrapnel said:

Too bad the short strokes came around too late; it would have been very interesting. Not sure if any made it to the dirt tracks.

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They did make it to the dirt track. The factory bike I had, that Matt posted pictures of above, had a well-massaged short stroke 750 engine, built by factory tuner Jim Messler. The Ron Wood bikes also used short stroke engines the last few years they were raced. Ron eventually used one-piece crankshafts that he had custom made by Moldex. The crankcases had welded reinforcements, and Ron had pistons custom made by Arias. The factory big valve heads had even larger valves installed by Axtell, along with his usual porting. The cams were Axtell. Ron still used his favorite Lucas racing mags, and either 34 mm or 36 mm Dellorto carbs, depending on whether they were running miles or shorter tracks. They managed to get over 80 rwhp on Axe's dyno, but the engines really were pretty fragile at that power level.

Ken