Norton intake ports compared to Harley XR 750 (2013)

Snotzo said:

I take it you've never heard of Dick O'Brien?

Perhaps your liking for Aermacchi ports explains why your Triumphs were such abominations !

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I never met Dick O'Brien, but I did meet C.R. Axtell and I watched him port a XR head. I seem to recall it was a head destined for Dick O'Brien.

Snotzo said:

I take it you've never heard of Dick O'Brien?

Perhaps your liking for Aermacchi ports explains why your Triumphs were such abominations !

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My 500cc Triumph engine was only an abomination because it did not have a 6 speed CR gearbox behind it. Otherwise it was a real whiz. When you have got a motor which, when you slip the clutch to get it back on song, bites you - it makes life very difficult. It would be OK if the bends on race circuits were all sweepers. Unfortunately, when racing you often get balked or find yourself in a tight corner doing 70 MPH and have to change down into a gear you have not got. Nobody needs that sort of anxiety. These days with the Seeley 850, it doesn't matter what happens, I will come out on top. I'm not blowing my own trumpet, but that 500cc Triton taught me how to race. In historic racing these days, most of the kids are very inexperienced and are very tyre reliant. So as soon as it rains, they are stuffed, and many race tracks are slippery anyway.

Commando ports are better small than big because the motor has a very long stroke. The upper rev limit of most Commando engines is about 7000 RPM before they start destroying themselves, so you are looking for more midrange rather than top end power. With a very short stroke motor, it is normal to use a cam with a slower lift rate and longer duration, and the power band is moved upwards, so larger ports give better results. With ports, it is probably essential to maintain gas speeds at a relatively high level, or you lose power from the middle of the rev range and add to the top. There are probably plenty of old race-bikes around which have vastly over-ported inlet tracts. Might work well at a track like Daytona but make life miserable elsewhere. With my old 500cc Triton, I could choose where I would lose a race. Gear it high and thrash them at the ends of the straights but get thrashed on the slower parts of the circuit, - gear it low and thrash them on the tight parts of the circuit and get thrashed at the ends of the straights. There was never a happy medium.

Snotzo said:

I take it you've never heard of Dick O'Brien?
!

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Dick O'Brien's brother Jesse was the porting guru .

Eldert

I did some runs on a dyno yesterday with the ported A65 head on my BSA 883.

Did a few runs but was told 'don't worry about these numbers, it's way too lean.
So we didn't try different advance settings because it needs the larger mains first.



Ben took a photo of one of the graphs, maximum torque looks at about 5,400 and its pretty flat right across descending gradually, I think the graph is saying 110lbft max, converting from Newton-meters(I do not understand this particular reading for torque as it seems very high, it is a reading and curve, but I do not know how it is arrived at)(edit; I looked this up and it's a measurement at the roller so at the engine it's probably around 65lbft and 57.5lbft @ 7,317 where the run ends at 80HP.

The HP graph is still climbing. Probably why the run has less power than the first which was 85HP. Some runs were going to around 7600. And not sure where rpm went on the first run as we were trying to set it up. I don't think I want to rev it to 8.

Looking and sounding good.

Ken

Thanks for the thread Jim... I do remember reading in one of the comics over here an interview with Dick O Brian in which he said the best power on XR engines came from a batch of heads that the foundry had miscast with small inlet ports.. And the issue of camshaft flex has got me slightly puzzled... Any one ever held a Rolls Royce merlin Cam .. its hollow and the length of a walking stick
and weighs very little .. the OD of the lobed shaft is much greater than that found on Norton engines.. yes I know the revs are somewhat lower !!! Maybe this would be the way to go if the cases permit? Incidently which of the Norton Cams are worse from a flex point of view the original with the breather mid length or those fom 72 onwards. Pushrod flex is well known and I suppose it changes the actual cam lift and timing ,but wonder if stiff pushrods whether steel or carbon actually give rise to cam flex..

I remember a Dick O'Brien quote re; the Harley VR 1000 cylinder head; "The ports are too goddam big and the valves are too goddam small."

The latest XR750 "cobra head" port shape is what Mark has taken advantage of and I believe that shape came from someone other than O'Brien or Axtell. His name was mentioned somewhere on this forum and he is a genius who could think out of the box. But I also remember seeing Axtell ports that were leaning in that direction with the beginnings of an eyebrow shape in the port roof. When the 2 valve port downdraft angle is limited compared to modern 4 valve ports then the "cobrahead" is the best option. See my Full Auto porting video for a better explanation in the "technical links list" section at jsmotorsport.com

I have just finished porting a Norton racing head for a situation that requires more HP than previously available. The work that Mark has done is very helpful and encouraging in this new direction.

Mark, I know it's asking a lot, but could you please populate your earlier posts with actual images? This has been a very interesting thread, and it's great reference material. Please track your time involved, and send the bill to Photo-Shmuck-It!

Thanks,
Nathan

jseng1 said:

The latest XR750 "cobra head" port shape is what Mark has taken advantage of and I believe that shape came from someone other than O'Brien or Axtell. His name was mentioned somewhere on this forum and he is a genius who could think out of the box.

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The late Ken Augustine, working under contract for HD, circa 1981.

It wasn't asked but not everything tried on the dispassionate flow bench has an effect and much of what has an effect, effects negatively. After that, merely flow testing without changing anything adds nothing at all, but knowing what is possible rather than merely wanted, is crucial. There is more to dynamic gas flow in running engines than steady state measurements on a flow bench and more to steady state measurements themselves than the flow bench alone will reveal. Along with that, knowing what is necessary separates the winners from the wieners.

Beyond that, you will have specific failures like porting through to water passages or oil and having valve guides, seats or seal surfaces lose their support when that nasty gas flow impeding material is removed. After that, you will need to do ALL of your other work properly, learn tuning and buy that equipment or hire someone like Derek to do that plus ride it to the elevated potential that you will presumably or at least hopefully, by then, have.

Ken Augustine

Kenny emailed with me, also the guy who did the World's Straightest youknowwhat. He said when he got the Norton heads right his two race pilot could not stay in saddles on WOT in 1st/2nd. I think thats what interested HD and how to tell ya got it right.

Sorry guys,
To warm this old thread up but it's been too much of a temptation.
I be been welding up ports (although mostly classic 2v Yamahas and Guzzis) and combustion chambers for quite some years now and there are some tricks to go for those who want to try:
1. You need an xxl long ceramic (6-9) nozzle
2. One needs a modern Inverter machine set on very hard settings.(depending on location play with frequency but leave the pointed tip!)
3. One has to flood the port with argon or heli.
4. Better to use a fatter (you want/need that point for heat concentration and less heat distribution to not cook out the alloy with too much energy besides the weld) than spec'd tungsten (grey I prefer).

Second I wanted to remind you that in the mentioned XR years (when also Jerry Branch did the port work) that aermacchi was part of H&d which was one of the reasons why Paso, back than on aermacchi, as well raced the XRTT.
I would be amazed if there wouldn't have been a slight hint of cross dpt engineering, as to my knowledge Renzo brought with him his own Italian mechanics.
Btw there was also a twin version of the aermacchi called the Linto, I bet power could have been raised with today's knowledge of cam timing and more important valve lift and angled Dellorto PHF'e with 90degr speedway type float chambers

For the rest i wish you all a very nice weekend

Kind regards from Italy

Christian

Ps. Regarding the pseudo static characteristics of a flowbench there is one or two SAE papers on the subject by either Yamaha, Honda or even AMF, with perhaps to my memory even correction factors.
Nonetheless a flowbench is what it is, a tool nothing more, it depends mostly on the good logical reasoning and engineering experience of the user. Nothing more nothing less

PPS: forgot, the coefficient of disch/flow takes into account the area of the flow thus one can get a somewhat clear idea of air speeds that should not get beyond 0,5-0,62, 0,65 Mach according to ital scientific literature guide rules thus one will not find in my book a supersonic intake port.
Fluctuating manometer phaenomens on intake ports are usually a sign for turbulences and thus e.g. disattaching flow somewhere in the port.

I think Norton might have a better idea about what the optimum port shape might be, than most other people. The cylinder head on a Norton twin is far superior to that on a Triumph twin. There is little point in changing up a gear beyond the revs at which maximum torque occurs, you probably accelerate slower. A port shape which produces 80 BHP at the top of the usable rev range might also produce more mid-range, but not necessarily.
I don't believe much about Harleys. Their only road racer was the XR750TT and they did not know what to do with Aermacchi. - Americans don't seem to like being made to feel inferior.

acotrel said:

There is little point in changing up a gear beyond the revs at which maximum torque occurs, you probably accelerate slower.

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That would depend, on the torque curve, and on the transmission gearing, as when you upshift, the RPM is going to drop, and if it drops into a lower part of the torque curve, you are not going to accelerate as quickly.

Second I wanted to remind you that in the mentioned XR years (when also Jerry Branch did the port work) that aermacchi was part of H&d which was one of the reasons why Paso, back than on aermacchi, as well raced the XRTT.
I would be amazed if there wouldn't have been a slight hint of cross dpt engineering, as to my knowledge Renzo brought with him his own Italian mechanics.

Met him at Bonneville back in 2006, he was with the group my brother rode for. They shared a building with him and his business

@acotrel

I'm sorry to disagree with you but having, living and having raced in europe seen first hand aermacchi singles but their intake ports are nothing extraordinary nor the to my memory squish less combustion chamber (same story goes "imho" for guzzi or Ducati; nice or even brilliant mechanical parts, sad gas dynamics due to anachronistic port designs and low lift long duration cam profiles)
I could not care less about if some h&d afficionados feels inferior or not but and that is a big "but", the xr750 was under somewhat continuous development in terms of gas dynamics conducted by some of the most brilliant tuners (Branch, Axtell, Augustine) and I had the great luck during my visit to flowmetrics that I was able to have a good look at an oval port head.
Let me tell you: besides perhaps (big one) a full blown modern era ABSAF Goldstar (to remain on the pushrod topic) head or some Nascar heads I have rarely seen a pushrod head port design that seems so thought out in particular around the SSR.
For Norton's knowledge of all their ports etc I refrain for lack of knowledge to state a comment besides that the dommi heads I had the pleasure to weld and port were in my book inferior to BSA twins and nothing special.

Kind regards from Italy

Christian

Dan Kyle said:

That would depend, on the torque curve, and on the transmission gearing, as when you upshift, the RPM is going to drop, and if it drops into a lower part of the torque curve, you are not going to accelerate as quickly.

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With the Commando, the standard gearbox is useless for racing. The bike accelerates too slow. Even with the close box, it is always better to keep the motor revving very high. I always find it difficult to look at the tacho on short circuits, but on Winton I rarely ever let the revs drop below 5,500 RPM and I change up at 7,000 RPM. If you rely on throttle response, you will be slow My motor pulls strongly from 3000 RPM, right up and through the top, but I only use the top part of the rev range. 7,000 RPM is fast enough for any Commando motor. I really like the heavy crank - nothing stops it.
I learned a hard lesson from my 500cc short stroke Triton which had a very top end motor with oversize ports. My friend's 650cc Triumph motor with standard ports was much better - the gearing was radically different.

From what I have read on this forum, the 5 speed gearbox which is normally available for a Commands, has the top four gears the same ratios the same as in the normal 4 speed box , but with a low first gear ? If that is the situation, for racing you would be much better-off with the American 4-speed close ratio gear cluster, but with a standard Commando first gear to get you off the line in clutch starts (costs about $800).. Once you are rolling, you only ever use the top three gears. It is very rare to find a first-gear corner on a race circuit. I have bought a 6 speed TTI box, but it is probably over-kill. However when the Japanese wanted to get underpowered bikes going faster, they often simply fitted more gears with closer ratios.
If my 500cc Triton had a 6 speed close ratio gear box back when I was racing it, it would have been a world-beater. It did not matter how you geared it, - with the 4 speed close box, all the ratios were always together and either too high, or too low. It just needed more gears and I was too lousy to buy them.

acotrel said:

From what I have read on this forum, the 5 speed gearbox which is normally available for a Commands, has the top four gears the same ratios the same as in the normal 4 speed box , but with a low first gear ? If that is the situation, for racing you would be much better-off with the American 4-speed close ratio gear cluster, but with a standard Commando first gear to get you off the line in clutch starts (costs about $800).. Once you are rolling, you only ever use the top three gears. It is very rare to find a first-gear corner on a race circuit. I have bought a 6 speed TTI box, but it is probably over-kill. However when the Japanese wanted to get underpowered bikes going faster, they often simply fitted more gears with closer ratios.
If my 500cc Triton had a 6 speed close ratio gear box back when I was racing it, it would have been a world-beater. It did not matter how you geared it, - with the 4 speed close box, all the ratios were always together and either too high, or too low. It just needed more gears and I was too lousy to buy them.

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Once again you've managed to confuse me, Al. See below a table of all the 5-speed gearsets that I have data for that fit into the Commando case, as well as the standard Commando 4-speed for comparison. None of them have the same top four gears as the standard box, and none of them have a lower (larger numerically) first gear. If you are referring to the TTI 5-speeds, it's my understanding that they come in a variety of ratio sets, including close and wide, but I don't have the actual data handy.



Also, what is the "American 4-speed close ratio gear cluster"? I don't know of any American made gearsets for Commando boxes. Maybe you are referring to the close ratio 4-speed gearset that Norton made for the Daytona races to meet the requirement for a kick starter? That one had a 2.06 first gear, compared to the standard Commando's 2.56.

Ken