80 HP at 8700RPM by Herb Becker

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Brooking 850 said:
My torque is low 60"s with a long stroke motor with only 0.040" over from a standard bore , 10:1 , mild cam , RH10 head with standard Vv's, the torque allows me to pull a tall 1st gear in a TTI close ratio 5 speed.
This a race motor.
80 HP at 8700RPM by Herb Becker

Regards Mike
Click to expand...
And to assist the Nortoneer in envisioning the transformation from a bone stock ’74 850 with an RH10 head to Brooking 850’s race bike, here is a dyno chart of a stock bike (thought it would be nice to have the comparisons on the same page, even though this graph is posted elsewhere on the site).
 

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  • 80 HP at 8700RPM by Herb Becker
    Stock 850 Dyno Chart - compressed.jpg
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Brooking 850, I've added your data to the table where the lower and upper limits denote start and end of +50 ft-lbs torque.

Description_______________Lower rpm_______Upper rpm________Range rpm
Long stroke race Norton_____4,350___________6,550____________2,200
NRE _______________________4,800___________7,500____________2,700
Brookings 850_______________3,750___________7,150___________3,400
Doug's Short Stroke_________4,400___________7,800____________3,400
1007cc_____________________3,700___________Well Past red line___+?


Some comparisons:

The stroke ratio (Brooking 850 versus Doug): 89/80.4 = 111%
The apparent redline ratio: 8,600/7,150 = 120% (per dyno pull end points Doug versus Brooking 850)
The apparent displacement ratio: 828/748 = 111% (114% @ 0.040 overbore)
Max power ratio (Doug versus Brooking 850): 87/71 = 122%

Many other factors enter into this including crankshaft rotational mass, compression ratio, combustion chamber performance, quality and nature of porting and valve seats, quality and nature of intake and exhaust tuning....etc.
 
Thanks for posting the curves. I have the same question - are you using the heavy crank ? I think my 850 has peak torque at around 6000 RPM. I usually try to change up at just below 7000 RPM.
 
If you are referring to an 89mm stroke Norton, max torque at around 6,000 rpm sounds a little high Alan; do you have a dyno sheet you can consult? 850 Brooking peaks at around 4,900 rpm and WZ507 peaks at around 4,600 rpm

Another short stroke I have data on peaks at around 6,400 rpm but it was a much more aggressive build for more power. Doug's peak torque looks to be around 5,950 rpm - more like a +60 ft-lbs torque plateau with a 1,400 rpm range from 4,900 rpm through to 6,300 rpm; quite remarkable.
 
Dances, yes a standard weight crank, longer rods and lighter pistons, lighter Vv gear, although not the rockers.
Standard length manifolds and 32 mm Premiers . And using standard size Vv.s
As you van see probably some wiggle room for improvement.
2 into 1 we built in NZ as a copy of he Maney system. Likes drink!

I have a RCR crank mounted ignition, which has a built in rev. limiter of 7500 RPM , I am looking at 7000 rpm often when I race it, although it is making its peak power close to the rev limit, it has plenty of torque up there to.
Very easy bike to ride, tractable engine great p/t through the rev range, it allows you to make mistakes and not lose to much ground as a result!

Regards Mike
 
Mike and his Norton go very very well, I can't come close on my BMW and my mate Adrian who has a very fast 1050 tuned up BMW told me that " Mikes Norton has some punch out the corners"
At the last meeting my mate cleaned up all the Nortons.
Best I can do it beat some Maney powered one with the usual 6 speed box, still any time you pass a Norton on a Bavarian Tractor is a good day. :lol:
 
72Combat said:
Mike and his Norton go very very well, I can't come close on my BMW and my mate Adrian who has a very fast 1050 tuned up BMW told me that " Mikes Norton has some punch out the corners"
At the last meeting my mate cleaned up all the Nortons.
Best I can do it beat some Maney powered one with the usual 6 speed box, still any time you pass a Norton on a Bavarian Tractor is a good day. :lol:
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I was reading an old bike mag article about Bavarian Tractor racing, he was getting 75hp at 10500 rpm ,I take you still have a few RPM's to go yet
 
To put this in perspective - Currently the 750 roadrace bike to beat here in the US is the Yama ridden by John E. It has an 80mm bore and a valve lift of .535" The 750 Nort can have a 77mm stroke and 79mm bore (or 75x80 with a reasonably thick wall 920 cylinder) and this would be close to ideal - allowing for big valves with Narley ports. The Sifton 480 cam with lightweight BSA lifters would give about .535" lift -and its possible to have them custom made with smoother ramps to reduce valve stress.

So there is more room if racers are willing to go further and move up the power band. But as Herb told me on the phone - "At some point you have to quit developing or you never get it on the track".
 
It would be tough to near impossible to get a pushrod Norton match the valve motion (valve time-area) of the Yamaha with its overhead cam. And there's that other detail of riding the bike as well as John Ellis does - not a little detail.
 
Dances with Shrapnel said:
It would be tough to near impossible to get a pushrod Norton match the valve motion (valve time-area) of the Yamaha with its overhead cam. And there's that other detail of riding the bike as well as John Ellis does - not a little detail.
Click to expand...

Yes - of course an overhead cam has an advantage - my point was to at least get as close as you can with lift/duration.

I didn't know about John's riding ability and that's the hardest thing to beat. And he has some kind of custom head (not an iron skull). As far as power goes it surprises me that the Yam twin is so competitive - as in leading because they were never a threat when I was racing. The talk was that you couldn't get enough HP from them. The only one that was running well was ridden by superstar Kenny Roberts. I remember talking to him at a dirt track race but I don't remember if it had the iron skull head or if it was something custom from the factory (probably custom). The only other one I came across that looked like it could be fast was at a Laguna Seca BOTT race in the mid 1980s - a Yam twin in a sleek bright Red trackmaster frame. I remember the rider telling me he had adjustable steering angle and he would steepen it up till it wobbled on the straights - then back off the steering angle till it straightened out. I was looking forward to dicing with him but he crashed out - disappointing.

I like what you posted above showing the power band ranges. That's a great comparison. But how much powerband spread do you think is needed with todays 5 & 6 speeds? And what's the practical upper RPM limit of your 1007?
 
Riding ability is a very subjective thing. If the bike does nothing for you, you can feel like an absolute dud and go backwards faster, the harder you try. Success is not always about the most horsepower, however If someone else has got loads of it and you come out of a corner side by side, they will certainly beat you down the straight in a 'point and squirt competition'. Of you have less top end but plenty of midrange, the only way you can compete is to set the bike up to tighten it's line in corners so you can get on the gas much earlier than the guys with all the top end. If you set up the bike with the top end, to tighten it's line, you can get the hi-side. The gearing of the bike is extremely important if you want to use the torque well. A good close box keeps you near peak torque, so race-changing produces max. acceleration.
Many Ducatis have been set up to be stable handling. They better suit circuits with big bends and lots of straights, where you can ride around the opposition without being super-brave.
If you are building a race bike, start with the gearbox. If you haven't got that, you will go nowhere fast. Then the steering geometry is next and after that the power and tyres. You can always back off.
 
jseng1 said:
Dances with Shrapnel said:
It would be tough to near impossible to get a pushrod Norton match the valve motion (valve time-area) of the Yamaha with its overhead cam. And there's that other detail of riding the bike as well as John Ellis does - not a little detail.
Click to expand...

Yes - of course an overhead cam has an advantage - my point was to at least get as close as you can with lift/duration.

I didn't know about John's riding ability and that's the hardest thing to beat. And he has some kind of custom head (not an iron skull). As far as power goes it surprises me that the Yam twin is so competitive - as in leading because they were never a threat when I was racing. The talk was that you couldn't get enough HP from them. The only one that was running well was ridden by superstar Kenny Roberts. I remember talking to him at a dirt track race but I don't remember if it had the iron skull head or if it was something custom from the factory (probably custom). The only other one I came across that looked like it could be fast was at a Laguna Seca BOTT race in the mid 1980s - a Yam twin in a sleek bright Red trackmaster frame. I remember the rider telling me he had adjustable steering angle and he would steepen it up till it wobbled on the straights - then back off the steering angle till it straightened out. I was looking forward to dicing with him but he crashed out - disappointing.

I like what you posted above showing the power band ranges. That's a great comparison. But how much powerband spread do you think is needed with todays 5 & 6 speeds? And what's the practical upper RPM limit of your 1007?
Click to expand...

Yes Jim, rider ability really makes most of the difference and we have seen it time and again. Dave Roper is one that comes to mind here.

With the table of data, I was illustrating the broad torque capability of a shorter stroke engine. Periodically you hear the misconception that a shorter stroke engine is necessarily peaky but it is far from truth and quite the opposite. This is probably due, in part, to all the cams tailored for the long stroke that are readily available for a Norton big twin.

I would have liked to supplement the table with a column showing peak torque and at what rpm in order to approximate a curve but that would have been too much. Most everybody interested should get the drift. From a historical perspective, at times I lament about how Norton could have prevailed if they adopted a short stroke street version but reality comes crashing down as it would have been short lived by maybe a year or two. Too many other changes would have to have been made to do it right which clearly was not in the cards.

You are spot on about the modern five and six speeds. There is plenty of potential for moving the Norton torque further up the rpm range with a short stroke.

Any chance you or someone on the forum could post a dyno pull from a late model HDXR750 for comparison?
 
My 500cc short stroke Triumph motor was derived from a 650. It had a 63mm stroke billet crank, however still used the long conrods, so wrong angularity was probably the reason it had so little torque. Also the cams were of extremely long duration with reduced lift so much higher revs could be used. With megaphones fitted, the usable rev range was 5,500 RPM to 10,500 RPM. It had nothing below 5,500 RPM then it came on with a bang. It was simply an unrideable nasty piece of shit and I still carry injuries from it. It definitely needed a 6 speed box. You could choose where you wanted to lose a race. Gear it high and have enough to get down the straights in the lead group of riders, or gear it low and be able to ride it fast around the slow stuff, and then it would get sideways in corners while you were still going too fast to crash. These days I don't need that sort of adrenalin rush - the night before race meetings I would wake up in a cold sweat. However once at the meeting, as soon as the motor fired I was never going to crash ever again. I learned some very hard lessons.
 
A 75mm stroke 750cc Commando would not be all bad, however you'd need an excellent rider. Stopping it from being savage would be a major problem.
 
From my memory of XS Yamahas, the inlet ports are huge as standard. How would you get one to pull ?
 
Dances with Shrapnel said:
Any chance you or someone on the forum could post a dyno pull from a late model HDXR750 for comparison?
Click to expand...

No have, but its pretty evident that the XR 750 is still competitive in dirt tracking - the only thing beating them is the modern vertical twin Kawasaki. Note that the Yam vertical twin is not even in the picture. My pitch is for the Narley (hint) - we're getting closer.
 
Is the motor in a modern dirt track XR750, the same as in the XR750TT road racer in it's power characteristics ?
 
acotrel said:
Is the motor in a modern dirt track XR750, the same as in the XR750TT road racer in it's power characteristics ?
Click to expand...

I cannot say whether characteristics are exactly the same but I am looking at a class of motor so either late model will be a good start. There are reports of +95 (and higher) RWHP.

As for your nasty little 500 cc short stroke, I think you somewhat answered your own questions. A six speed would be indicated. Furthermore, my personal hunch is your 500 could have used some dyno time for development to find out exactly what the motor was telling you and what the motor wanted. This is really difficult to do by "seat of the pants".
 
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