HD XR 750 & Full Auto port conversion

Dan Kyle are you the Dan that build the DuDa with Homer Knapp ?

regards Eldert

Hudriwudri said:

Yo fellas,




Trivia besides I hope I made my point and explained comprehensively what I saw first hand in the INCA paddocks.

Good evening to you all

Christian

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Hi Christian

we run the Inca series to for a couple of years with our Ducati

Regards Eldert

Eldert said:

Dan Kyle are you the Dan that would the DuDa with Homer Knapp ?

regards Eldert

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Yes

" I very much believe that with factory optimized no effort spared equipment 90-100 horses would be possible [XR 750]. Equally I believe knowing the commando.heads a lil that with a big bore engine 75-85 horses should/could be possible ..."

You can get more out of the Norton if you're willing to weld up the head and start over. That's what the "Narley ports" CD is all about. And with the Sifton 480 cam (JS4 with better ramps), solid cranks, heavy cases, there's no reason you can't get the same (or nearly) HP as the XR750. All the specs are there to by copied from the XR 750 but no one has stepped up (so far).

How do you weld up the inside of an inlet port so you can re-shape it ?

@Eldert
No sarcasm intended!
If you race INCA you should consider porting the Ducati head and reangling the valves in case it hasnt been done yet as the old bevel heads (at least the 900 and 750 as well as 450 heads Ive seen) have a real nasty short turn and the valve sizes are as on round head Guzzis also rather smallish.
Most probably easier to do on a non desmo head though, as I do not know how much reangling is possible before running into prob's with the desmo (will know eventually as I have a pair of DS1100 heads on the roster)

@acotrel
Sorry but either I'm feeling mocked about that question or you did not read all my posts about "in port welding"
In case nothing works one could still do it with a mini torch but I (imho) would be hesitant for long term heat input in particular on the port floors close to the seat ring bores. Everything else I pretty much explained already.
Regarding port area, that subject is a matter of converging opinion as there are as well other means of achieving the needed air speeds as well as Mixture trajectory.
Also one has to consider the cam lift regarding piston movement to gas harmonic coupling, without the desire to get too esoteric.

@jseng1

Jim I'm not quite sure if one could still squeeze 45mm intake valves in the head as I think one would even with reangling see light all around the port surface cutting through in installing such big valves.
But I admit very very interesting topic on which which I also pondered since I welded up a domihead to bathtub chamber a while ago.

@WZ507

Ah ok understood so we are talking bout the Er650 engine, right?
Have a friend that works a lot on them, to my knowledge one can overbore them about 2mm's and he also has some custom cam grind of his own with added lift and enhanced duration.
Would need to ask him about power figures but I think for road racing they are well above 90horses.
Will enquire now as I'm curious myself.


Kind regards

Christian

Hudriwudri said:

Jim I'm not quite sure if one could still squeeze 45mm intake valves in the head as I think one would even with reangling see light all around the port surface cutting through in installing such big valves.
But I admit very very interesting topic on which which I also pondered since I welded up a domihead to bathtub chamber a while ago.

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There are at least two people (Klaus Morning and Herb Becker) who have managed to fit 44 mm intakes into the Commando head (with re-angling, of course), and there are a lot of Steve Maney (and others') heads out there with 43 mm intake valves, but I don't know of anyone who has managed 45 mm. I've had enough trouble trying to avoid valve interference with just the 43 mm valves that I'm really doubtful whether one could make 45 mm valves work with any sort of performance cam, even if they could fit them into the head. But you never know. There are some pretty inventive folks out there playing with Norton engines.

Ken

43 or 44mm in valves would do. You would want to weld up the guide bores, move the valves away from each other and go to a 79 to 81mm bore. Photos below show the roughing in of the raised ports and filled in guide bores for re-angled boring. You may not be able to exactly copy the XR 750 but you can get very close.


U shaped pieced were chamferd at the weld so they can be re-surfaced. Project on hold till I can get the port floors properly welded near the valve seats. This won't be a full blown XR750 copy - that would require widening the ports and more welding. But its getting the same raised port floors.

Sorry, I did not red your posts about 'in port welding'. I thought that once the head was over-ported it is stuffed forever. I wonder about guys who buy race cams then use them with different exhaust systems without trying them in different positions to see what works best. The first race cams I used were E3134 Triumph which first came out in the kit for the 1953 Tiger 100. If you fitted them to the recommended timings and used the specified exhaust configuration, they were excellent in both 650 and 500 cc race Triumphs. But once you change the exhaust system or over-port the head, you are playing with an unknown. One thing which makes a big difference to a 650 Triumph is the balance factor. The fastest 650 I had, had weld added to the bob weights on the crank. It was only on about 8 to 1 comp., with methanol, but it was an extremely fast motor. - What balance factor do the Harleys use ? I think the steel plug in the crank of my 850 adds about a pound to the weight of the crank.
Your assumption that the extra power of the Harley 750 comes from better porting . . . ? When you hear about a horsepower figure from a dyno - , what does that mean ? If a felloe competitor has got a faster bike, is he going to tell you the truth about why it is fast ? Have you had your Commando motor on the same dyno as the Harley motor and done the tests yourself ?
I don't doubt that a dyno can provide good precision, but accuracy might be a problem.

As I understand it, when one of the first inertia dyno was made, the claimed horsepower of the Yamaha Vmax was used to calibrate the dyno. A fiddle factor was used to make it read the maker's specified value for horsepower . And since then every motor which is tested on that make of dyno gives a result for horsepower which contains the original errors..
If you are only looking for improvement using only one dyno, there is no problem. But there might be a problem when you compare results from different dynos.
In short, if you believe the claimed horsepower figures for the Harley 750, you might be led up the garden path. There are many reasons a Harley might be quicker than a Commando on the dirt. One is it's more uneven power delivery.

acotrel said:

I don't doubt that a dyno can provide good precision, but accuracy might be a problem.

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Dynojet repeatability is well within 1%.
Not only are you getting HP and Torque reading, (graphs, printed numbers) but you can also measure the rate of acceleration in time.
You can also run mock acceleration races, between bikes, which negates gear ratios.
It is a very accurate tool for jetting both carbs and fuel injection.
You can product straight flat lines for fuel A/F Ratios for any A/F ratio.
As well as using the dyno to determine what A/F ratio works best for that bike, with that bikes Ign timing on the fuel that bike is using.

acotrel said:

As I understand it, when one of the first inertia dyno was made, the claimed horsepower of the Yamaha Vmax was used to calibrate the dyno. A fiddle factor was used to make it read the maker's specified value for horsepower . And since then every motor which is tested on that make of dyno gives a result for horsepower which contains the original errors..
If you are only looking for improvement using only one dyno, there is no problem. But there might be a problem when you compare results from different dynos.
In short, if you believe the claimed horsepower figures for the Harley 750, you might be led up the garden path. There are many reasons a Harley might be quicker than a Commando on the dirt. One is it's more uneven power delivery.

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Al, most of the horsepower figures you see for the XR750 back in the '70s and '80s, either from the factory or quality tuners like Axtell, are from conventional brake dynos, not inertia dynos. The numbers are directly comparable to values for Norton engines run on similar dynos. In particular, Axtell did accurate dyno measurements on both Norton engines and XR750 engines. He did many dyno runs on the Norton engines he built for Ron Wood, and Mert Lawill used the same dyno for a lot of his XR750 engine development. IIRC, the best numbers for the Norton were 76 or 77 hp for the standard 750 and a few more for the 750 short stroke. I was at the shop once when Mert was running his XR750 on the dyno, doing some exhaust system testing, but I don't recall the exact hp numbers. My memory says it was around 95 hp, but my memory isn't what it used to be. Both measurements were power at the rear axle. The bikes were set up with a long chain from the transmission output sprocket to a sprocket mounted on a dummy axle connected to the dyno. This is a picture of Axtell with a Norton Atlas on the dyno back in the '60s.





Other XR750 tuners had also managed to get horsepower in the 90 - 95 hp range by the end of the '70s. The best top end number I've seen published is 107 hp for an engine built by Bill Werner and tested on Jerry Branch's dyno in the mid '80s. I think those numbers were taken at the crankshaft, but again, I'm not sure.

One thing to keep in mind when comparing the Commando engine to the XR750 is that racers were running the XR engines up to 9,200 rpm to make their numbers, where the standard stroke Norton stopped making more horsepower somewhere just over 7,000 rpm. That was before the days of the ultra short stroke engines we've seen being built just in the last few years, which have much higher redlines. If we can get the old Norton head to flow well enough, and the valve train to co-operate at those rpms, it should certainly be possible to hit some pretty good numbers. Interesting times to be watching some of the current development efforts.

Ken

@acotrel

My assumption regarding the horsepower claims comes from working with the HP potential of airflow figures regarding the flow area.
Having also seen in person some ported xr750 heads and having done myself a couple of 2valve Jawa Speedway heads for "non Hobby" use I would figure that considering the port architecture and the cam spec's on Harley's that one could achieve approximately aboutish 200cfm@25" on those with a max valve flow lift of approx 14mm"s so somebody decided and astute enough could very well arrive at 90-95horses quite likely around 7,5-8k rpm (shooting from the hip).
But hey that's just my ignorant assumption or better extrapolation, based also somewhat on DBD34, xs6/750, speedway head flow numbers and cam timings.
Regarding the hp figures to my limited knowledge both branch and axtell used a chain driven Heenan & froude type water brake, so comparability should be within limits given, although of course some minor deviations might have been inherent. (I will try to snap hopefully tomorrow a picture of my old chain dog dyno so one sees that tire slip is no issue)
Regarding the old V-max story: I mean I personally could not care less what it's calibrated on as long as reliability and most of all repeatability is given if the same Dyno is used repeatedly.
After all well it's nice to know what power and torque figures one has but after all a Dyno is just a tool as well as the flowbench.
Picking up the point of overported heads that is only true to a certain degree as one can easily rebuild wall thickness with epoxy metal or in case even with welding.
Although admittedly it's better to work the grinder attentively in order to not having to go to such lenghts.

Regarding the +80-85 Hp commando heads, I would love the idea even though I'm not owning a commando but to achieve those/such high numbers one has to enlarge one of the bottlenecks at the valve throat and in doing so I assume with heavy reangling one penetrates the port walls heavily.
Any other way I would not know how one could achieve the needed volumeflow (of course with suitable area therefore speed of gas). Perhaps with revving higher but I strongly suspect the engine would eventually run outta breath.

All the best and kind regards from italy

Christian

acotrel said:

As I understand it, when one of the first inertia dyno was made, the claimed horsepower of the Yamaha Vmax was used to calibrate the dyno. A fiddle factor was used to make it read the maker's specified value for horsepower . And since then every motor which is tested on that make of dyno gives a result for horsepower which contains the original errors..
If you are only looking for improvement using only one dyno, there is no problem. But there might be a problem when you compare results from different dynos.
In short, if you believe the claimed horsepower figures for the Harley 750, you might be led up the garden path. There are many reasons a Harley might be quicker than a Commando on the dirt. One is it's more uneven power delivery.

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You always ask people for proof, do have any on the dyno claim you made?
You do not state what dyno it is, or where you received this info.

I will say it again, I have first hand experience that HD XR 750 flat track motors in the last 10 years make 90 to 95 HP rear wheel SAE corrected.
End of story.
Please post the highest HP Norton Motor YOU have run on a dyno, not run on your butt dyno, as those are incredibly inaccurate.

Hudriwudri said:

Regarding the hp figures to my limited knowledge both branch and axtell used a chain driven Heenan & froude type water brake, so comparability should be within limits given, although of course some minor deviations might have been inherent.

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Yes, Axtell's dyno was a Heenan & Froude water brake, driven by a shaft to the dummy rear axle on the bike. This picture shows it with Axtell at work. I posted this picture and the previous one on the forum a while back, but they might have disappeared in the infamous Photobucket disaster. Both were taken from a '70s book on motorcycle tuning. I just ran accross a reference tody that mentioned Jerry Branch using a Clayton dyno back in 1973. It was also a "chassis" dyno, in that you could secure the bike chassis to it and drive the dyno by chain, similar to Axtell's. It was a pretty common dyno back in the day. The Kawasaki R&D shop in Southern California back in the '70s also used a Heenan & Froude. The hot setup for a brake dyno now seems to be the eddy current brake type, a bit more compact and easier to adapt to digital control. Both types can be extremely accurate.



Ken

Hudriwudri said:

@Eldert
No sarcasm intended!
If you race INCA you should consider porting the Ducati head and reangling the valves in case it hasnt been done yet as the old bevel heads (at least the 900 and 750 as well as 450 heads Ive seen) have a real nasty short turn and the valve sizes are as on round head Guzzis also rather smallish.
Most probably easier to do on a non desmo head though, as I do not know how much reangling is possible before running into prob's with the desmo (will know eventually as I have a pair of DS1100 heads on the roster)

Kind regards

Christian

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valves are re angled . relocated the rockerarm pivotpoints and used Ducati Pantah rockerarms . but by doing that the camshafts lobe centres where way of so we had to make new camshafts . and yes it is easyer to do the conversion with valve springs instead of a Desmo . plenty of room for the valve guide and to raise the floor and the roof of the port .

Regards Eldert

@Eldert
Ahaha i knew it I knew it
I bet you also had the combustion chamber rewelded an bathtub! I saw that you also raised the intake port. Cam profile something like the V2 300? Oh well I'm getting heavily off topic sorry.

@lcrken
Ah yes you're of course right, Branch had (it's not there anymore in the new location) a Clayton.
All the chain driven dynos don't need to respect the tire slippage, which is for repeatability very nice.
Those pictures are wonderful, would you be so kind and tell me the title of the book as I need to get it?
The big eddy current dynos (AVL) for the F2 guys supposedly also do such fancy thing as track simulation and simulation of drive train harmonics

All the best

Christian

Here's a picture of my brother with Jerry Branch, This was the 2006 Bub Speed trails at Bonneville. Really nice guy to talk to and he had a few stories to tell also.

Hudriwudri said:

Those pictures are wonderful, would you be so kind and tell me the title of the book as I need to get it?

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Hi Christian,

this is the cover of the book. It is a 224 page paperback book printed by the Peterson Publishing Company in 1967, I bought it back then for the magnificent sum of



Ken

I have got the impression that the 95 BHP XR750 s you are talking about are flat trackers. Running a bike on the dirt is very different to running it on bitumen. On the dirt you are balancing slide and drive. On the bitumen it is usually only drive with less emphasis on slide.. What is fast on the dirt can depend on how the power is delivered. With very smooth power delivery, there is less drive, so the bike can be slower. About port sizes - early two-valve Jawa speedway motors had large ports which were reduced in diameter by a couple of mm on later models. I think that was due to British speedway regulation. I don't know whether the bikes went faster or slower. But with speedway, knobby tyres give more grip and trials tyres give more slide. What looks faster probably does not depend on horsepower alone. A motor which is all top end is often slower than one which pulls hard in the midrange, but it all depends on the bike set-up and the way the power is delivered.
On a road race circuit a single cylinder motor is sometimes better than a twin, probably because of the way the tyre flexes.