80 HP at 8700RPM by Herb Becker

The first bronze seats I saw for Norton twins was in the early Dunstall big valve conversions. I suspect he chose that material for the reasons Dances mentioned above. I've also seen it in a lot of later big valve conversions. Maybe just a copycat phenomenon, or maybe they had a reason. Another reason given for bronze seats is because they help reduce valve bounce in race engines.

As Jim mentioned, they are also commonly used for their compatibility with titanium valves. I had titanium valves and beryllium-copper seats in my Rotax race bike, and was amazed at their durability. They never seemed to wear. The heads were done by Phil Darcy, but he later switched from beryllium-copper to a bronze alloy (AMPCO 45, maybe?) because of concerns over the safety aspects of machining beryllium alloys.

I've never used the tungsten alloy seats, but they look interesting, particularly the powdered metal ones from Dura-Bond

http://www.dura-bondbearing.com/Product ... alve-Seats

Always something new to be tried.

Ken

Article in classic bike feb 98 with a similar head apparently went very well
I also did this to 1340 evo about 91, cam carb , 9.5/1 & exhaust it flew
nothing like watching a 25 stone ''motorcycle club'' member poping wheelies for 200m on a Harley, the std cases eventually cracked, didn't finish one meeting when the std rotors collapsed over the calipers

Hello all, sorry been away for a bit.

Here is a dyno sheet with the runs of my Becker built 750cc short stroke Norton on the dyno. He may have got closer to 80hp on one run when he went to the dyno without me but my sheet shows a peak of 78hp.

The green line is the bike how I raced it last year. The motor was very good but didn't want to rev past 6700rpm. I played with making the jetting richer at the track but at the end of the year we went back to the dyno and in fact, when we dropped the jets from 280's to 220's in the twin 38mm Mikuni carbs, the dyno showed an immediate 4hp increase. Boring out the carbs to 39.5 mm gave about 1 more hp and a really fat mid-range, about 62 ft.-lbs (the blue line). The bike would now easily rev to 8500 as well and put out just under 75hp.
The red line is when we tried 44mm twin Mikuni carbs- it gave a higher peak, about 78hp but has a big hole at 7200 that you have to pass through, rendering it not a usable power curve on the track. We left the motor in the blue line configuration.

FYI, this is the bathtub head- which is not a welded up head, it was made from a lovely Fullauto 'blank' head which I got direct from Fullauto. It had no holes in it, and an unfinished, un-machined combustion chamber so Herb finished it to his own specs, leaving the bathtub shaped chamber. He also made the spark pug holes smaller (10mm) so we could run smaller plugs and actually moved the plug holes 1/8" over so they did not interfere with the big valves. He also moved the rocker spindle pivot point holes up 1/16", he thought that might work better.

-Doug

Hi Doug what sized headers are you using on the FA head and is it a 2 into 1 or 2 x separate pipes?
Regards mike

Hi Mike, pipes are 1 3/4" ID as seen in the video from when we dyno-ed it last year here. We did try a 2 into 1 pipe on it but it made less power without any sort of mid-range payoff. That is not to say that a 2 into 1 will always make less, it just did for this motor.
[video]http://www.youtube.com/watch?v=jgkLhxxJMGY[/video]

Thanks Doug, appreciate the feed back.
You and Herb have any idea why the TIO didnt work as well?
Regards Mike

The main reason that a 2 into 1 exhaust won't work to give better mid-range is when the tail-pipe diameter is too small. I suggest should be the same crossectional area as the total of the two header pipes feeding into it with no restriction whatsoever. To my mind the tail pipe must resonate at twice the rate of one of the header pipes. It is not simply there to carry the gases away.

Hey Mike; I don't really know why the two into one didn't work as well- Dyno Don there said it has to do with the resonating waves and the two into one didn't work with the waves as well as separate pipes. on this motor.
It is possible another design of 2 into 1 might have offered different results.
You have to turn off your brain a bit with the dyno as it often will give you the opposite result of what you expect. I never would have guessed that making the carbs 4 jet sizes leaner would give it 5 more hp and another 1500rpm of revs, but the dyno tells all.

Doug MacRae said:

I never would have guessed that making the carbs 4 jet sizes leaner would give it 5 more hp and another 1500rpm of revs, but the dyno tells all.

Click to expand...

Did the dyno have an Air/Fuel ratio or exhaust gas analyser to tell this ?
Seeing it was bogging down from being too rich might tell a lot...

Doug MacRae said:

Hey Mike; I don't really know why the two into one didn't work as well- Dyno Don there said it has to do with the resonating waves and the two into one didn't work with the waves as well as separate pipes. on this motor.
It is possible another design of 2 into 1 might have offered different results.
You have to turn off your brain a bit with the dyno as it often will give you the opposite result of what you expect. I never would have guessed that making the carbs 4 jet sizes leaner would give it 5 more hp and another 1500rpm of revs, but the dyno tells all.

Click to expand...

Doug, I suggest that every racer who has ever built a race bike has done this! Its so easy to think that the results of our tuning need bigger jets, and when it doesn't run right, our brain concludes we need bigger still, and before long, we've gone down a path of over rich mains and tried to compensate with over lean mid settings and all sorts of stuff!

Sounds like you found out in good time and sorted it.

That's some impressive power you're getting from your bike. Enjoy!

Dyno Don sadly doesn't have a gas analyzer but he is convenient and we try to use the same dyno so the results compare properly

Hi Doug thanks for that, I had something similar happen to me, original dyno results I posted on here all had a dip in the mid range on both my bikes, it turned out to be the crap mufflers I was attempting to use, after market peashooters. Std diameter headers. Also too rich
I am glad we made some gains on both bikes, spent a lot of time getting the TIO right on the race bike, and sorting the right peashooters for the road bike, also found the road bike was running way too rich on PWK flatslides. That was due to too small air cleaners.
Still running 32 mm Amal Premiers on the race bike with #300 mains. Loves a drink!
Regards Mike

Yes Herb is getting up there in the HP figures for Dougs bike. Some people don't think you can get 80 HP or more with a Norton short stroke but you can - but you have to do everything and there is a formula that's been worked out. I was working with Ron Wood for a short time and he told me that the people at the Norton factory didn't believe his 84HP claim. So they bought him a plane ticket and he flew over there with a motor to show them. Most people get about mid 60s HP with a race 750 long stroke. Ron W told me that the most he could get was 72 to 74HP and then you hit a brick wall until you went to the short stroke. The Ron W short stroke below (note the intake manifold length and Axtell decal).


Mike - later on I went to the K&N RC 2380 dual aircleaner for the PWKs - breathes much better than the small single pods. If the mid range is too rich you have to drop the needle or get smaller needle jets (I had to make them).

Surely the main reason to go short stroke is to move the usable rev range up a notch to get more horsepower ? Perhaps the way to go with the long stroke is always to look for more torque and increase the overall gearing to suit ? I question the usefulness of torque figures taken off inertia dynamometers. What you see might not necessarily be what you get.

Hi Jim, yes you sent me one eventually, remember I had to return the wrong K&N you sent intially, the right one is on there now.
Just used the info for others to be aware of.

Regards Mike

acotrel said:

Surely the main reason to go short stroke is to move the usable rev range up a notch to get more horsepower ?

Click to expand...

From first hand experience, one broadens the usable rev range. Perhaps stating "the main reason.......moving the usable rev range up" is misleading. The overall goal is to increase mass flow rate. Once you have done all you can with increasing volumetric efficiency, the only sensible thing to do is spin it faster. Bigger pistons allow bigger valves, usually a very good thing when you have less time to fill the swept volume. Funny how things work for you some times.

acotrel said:

Perhaps the way to go with the long stroke is always to look for more torque and increase the overall gearing to suit ? I question the usefulness of torque figures taken off inertia dynamometers. What you see might not necessarily be what you get.

Click to expand...

I say that torque figures from an inertial dynomometer are more representative of what you get for a performance vehicle. This was explained ad nauseam in another thread. The main thing is relative change as observed on any dyno is a very useful metric of changes to engine configuration. Keeping your work to one dynomometer simplifies things a bit.

I can understand how a brake and balance can measure twisting power. I find it difficult to understand how torque is measured when an acceleration is happening. Surely on an inertia dynamometer that is always the case ? If the torque output at the crankshaft is increased due to motor improvements, doesn't the acceleration of the flywheel in the dynamometer happen at a different rate, so that might change the torque input to the dyno flywheel from the crankshaft of the motor ?
In other words my question is - is the crank twisting energy required to accelerate the flywheel in the dyno linear across it's usable rev range ? - Perhaps that is the reason for the calibrated paddles which are attached to the flywheel in some inertia dynos .

Thanks for sharing all this Doug. I am pretty sure Herb fabricated your billet crank. Is the center bob weight removable? If it is, that would be a neat feature should someone want to change the balance factor or repurpose the crank to a different build.

Hi Alan, each time the owner goes back to the same dyno, despite what the actual out put reading may show, if the owner has made changes, it then compares apples to apples each time! Surely the right way to do things, especially for the A/F ratio being measured at the same point up the pipes.
Once again it gives a good data base to work from.
Regards Mike

Alan, we know you love your long stroke (as I do mine) but if your running a stock spec motor you'll be lucky if its putting out over 40 RWHP. So no matter how you look at it, and no matter what 'margin of error' is in the dyno reading, there ain't no way you'd keep an 80+RWHP Commando in sight for long!

You might catch a glimpse every few laps as he came past you though...!