Speed anomaly

At the recently held Isle of Man Classic TT races, several 4 valve Molnar Nortons participated, together with two 4 valve G50's.
Dyno tests reveal the 4 valve engines deliver appreciably more rear wheel horsepower than their 2 valve counter parts, yet through the Sulby speed trap they recorded slower top speeds. In all instances the aero part of the machines were identical, fairings etc, and with Michael Dunlop the rider of one of the 4 valve Nortons, rider ability to negotiate the Quarry bends prior to Sulby is without question.
There appears to be no reason for the speed discrepancy, certainly on accelleration the 4 valve engines excel, but to date all attempts to overcome this top speed dilemma have so far proved fruitless.

To add an even more curious detail, repeatedly the fastest timed single cylinder through the Sulby trap was a Royal Enfield Bullet.
All the above applicable to the Classic Senior TT class.


Perhaps from within the Forum membership there will be someone who can throw some light on the reason for the above speed discrepancy.

Is the dyno testing / hp numbers done on the same dyno ?
Without seeing said machines and dyno charts, any insights are going to have to come from someone in that circle. ?

Give/loan/hire/contract one of those 4 valve machines to the Enfield guy (name is on the tip of the tongue),
he obviously has the magic touch. !

Velo race chief Harold Willis comes to mind here, he had funny/appropriate nicknames for everything = willicisms,
and his one for the dyno that kept giving false hopes was Heenan Froude and Ananias...

One (faint) possibility - are the 4 valve machines reaching the full rpms expected of them ?
And are they geared the same as the 2 valve.
Is the carb intake area clear and unobstructed, and free from air flow eddies or swirlbacks ?

Do you know offhand the lap times for the varous bikes ?
Speed isn't everything.

Curious. And curiouser...

A 2 valve Ducati converted roadster came 3rd in the 350 race with an average lap of over97 mph, reliability and speed are needed on the IOM. those Nortons do sound very crisp though. I had a wonderfull week with my 3 bikes and two sons.

Bob, the same peculiarity was observed in the Junior Classic TT. As you say, the Doug Snow 350 Ducati was repeatedly the fastest 350 through the Sulby speed trap (after the MV's had broken down), closely followed by Chris Swallow on an Aermacchi. It must be said these two machines were fitted with slim fairings, and riders who were really well tucked in, so possibly in the 350 class the singles were the more aerodynamic, but in the Senior Classic the Molnar Nortons were to all outside appearances identical, both 2 and 4 valvers.

This anomaly was first brought to my attention last year by a friend riding in the Junior Classic on a 350 Ducati. He said he found he could overhaul K4 Honda's down the long straights that had blasted by him on accelleration through the bends prior. Unfortunately there are very many corners around the TT course where the K4's make good, and the opportunities for the Ducati were somewhat fewer.

The K4's will make better than 44 RWHP, with both Aermacchi and Ducati some four or five less. Very good 2 valve Nortons show 58 to 60 RWHP, while the 4 valvers have 63 to 64 RWHP, with one notorious super tuner claiming close to 70!
I am unable to give details for the shape of the power curves for the 2 and 4 valve machines, and it is possible that the 4 valve engines ability to rev is not co inciding with the power peak, which may be at a somewhat lower engine speed than that at which the 2 valve engines run.

The eventual fastest single and first placed machine in it's class was a 2 valve Craven Summerfield Norton ridded by Jamie Coward.
The Royal Enfield Bullet retired at the end of lap two with a broken coil wire.

Lap times of the 4 valve v's 2 valve manxs ?
If the 4 valves have stonger acceleration, they could still come out ahead, even with less top speed. (?)

In the 1950s, guzzi developed a short stroke version of their trusty ole long stroke laydown single.
While the short stroke had more hp, on some circuits the longstroke could beat it to the flag.
Without trying them against each other, it wasn't obvious which circuits suited which bike,
although the faster circuits with longer straights were usually short stroke territory.

Doug Snows fairing is a bit special and not something you can buy, The Island needs a motor with a good spread of power. Would have been interesting to see how the Enfield finished if it had kept going.

Hi Ron

Easy enough to find the lap times and average speed on line. (Rohan)

But do you know if the speed trap speeds are posted anywhere?

I think the 250 Eldee went through at about 96 mph last year and lapped at 83 average. So Bill must have had it wide open everywhere

John

Lap times of the 4 valve v's 2 valve manxs ?
If the 4 valves have stonger acceleration, they could still come out ahead, even with less top speed. (?)

Click to expand...

Rohan, I am more interested in the reason behind the 2 valve machines apparent ability to run to a higher top speed than overall lap times.

I kept fairly comprehensive notes following the riders progress through the race. The 2 valve Craven Summerfield Norton ridden by Jamie Coward was consistently the fastest Norton at Sulby, but the 4 valvers were recording the fastest lap times, although to my knowledge all 4 valve Nortons failed to finish except one ridden by Ivan Lintin, but the speeds it reached were never comparable to the quick machines.

Regarding sheer speed in the Senior Classic class, the fastest machine recorded at Sulby was the Paton ridden by Ian Lougher, at a speed of 146.8 mph, easily 10 mph faster than the best single. Fastest MV3 was ridden by Dean Harrisson at 144.3 mph.

Snotzo said:

Rohan, I am more interested in the reason behind the 2 valve machines apparent ability to run to a higher top speed than overall lap times.

Click to expand...

If the 4 valves overall do faster lap times than the 2 valvers, then maybe its in the nature of the beast.... ?

Rohan

You can find the lap times here

http://www.iomtt.com/Classic-TT/Results-2015.aspx

The 4 valves do faster laps when they stay in one piece. But seemly due to acceleration not ultimate top speed.

Dunlops best lap on a Molnar 4 valve was 108.6 mph.

Chris Swallow got 106.7 mph and first single home on Dave Kenahs 2 valve Manx.

Ron. It says Jamie Coward was on a Honda in the programme. Did he swap to a Manx ?

If he did then Chris was second single home. Chris was very pleased with the lap times anyway. Third year lucky to get a finish.

He's back home now in Wellington and they are off to Manfield in a few weeks then down to the Burt Munro with all the Velos.

Program was incorrect, Jamie Coward was riding a 2 valve Craven Summerfield Manx

The earlier question on top speed anomaly leaves several questions, as for the 2 v 4 valve heads, and this is just my opinion, a 4 valve cylinder head has twice the amount of spring poundage to overcome compared to a 2 valve head, all things being equal, say , spring rate of 95lbs on each one. This a lot for the engine to overcome, so, it’s swings and roundabouts really.
Don’t think that Norton themselves never made a 4 valve head and decided to drop it. :!:

Re, “This anomaly was first brought to my attention last year by a friend riding in the Junior Classic on a 350 Ducati. He said he found he could overhaul K4 Honda's down the long straights that had blasted by him on acceleration through the bends prior. Unfortunately there are very many corners around the TT course where the K4's make good, and the opportunities for the Ducati were somewhat fewer.”
You have not stated whether the 350 Ducati was a Desmo or non Desmo. :?:
I would be surprised if a 350 K4 could out accelerate a 350 Desmo. A long time ago there was a 25 lap production race in the UK mainland where a 250 Desmo cake-walked the 250 production class, beating a lot of the earlier Jap 2 stroke twins of the same vintage.
I myself have ridden a 250 Ducati , both a Desmo and non Desmo in the same afternoon at Brands Hatch with the Kirby –Camp racing school in the 1960s and was very surprised with the acceleration of the Desmo-it was better than my 500 single that I had rode there on.

Re; “Regarding sheer speed in the Senior Classic class, the fastest machine recorded at Sulby was MV3 was ridden by Dean Harrisson at 144.3 mph. “ Snotzo Posts: 123Joined: Tue Mar 12, 2013 3:47 am

The MV3 is a little slow compared with the 1967 speed trap figures when Agostini was riding, Hailwood clocked 154 mph and the MV3 not far beyond. Is Dean Harrisson’s MV3 ex-factory bike or a replica :?:
And yes , I am quoting from memory, I don't have the old weekly comics anymore.

delete.

Bernhard
The 350 Ducati was a Desmo. It goes very well, and is equipped with a very special fairing which must help it to make top speeds, nevertheless, the best K4 Honda's can accellerate past, having more than 44 rwhp to propell them along.

The speeds you mention for Hailwood and Agostini were timed past the Highlander, and most probably without the transponders used today, but stop watches no doubt. During this years Classic TT practice, one rider used a GPS satellite system locked into a mobile phone, and recorded his progress through the lap. Downloaded afterwards into special tracking software, he could follow his progress around the circuit, and could see the speeds he achieved. His Sulby speed was identical to that from the timers, but the GPS signal showed that speeds past the Highlander were higher than those measured at Sulby, by 2.5 mph. Speeds down Brandish were also higher than at Sulby.

The MV3 on which Dean Harrisson won the Senior Classic TT was a Kay Replica, and is reported to be making the same power as the original factory machine.

Bernhard said:

The earlier question on top speed anomaly leaves several questions, as for the 2 v 4 valve heads, and this is just my opinion, a 4 valve cylinder head has twice the amount of spring poundage to overcome compared to a 2 valve head, all things being equal, say , spring rate of 95lbs on each one. This a lot for the engine to overcome, so, it’s swings and roundabouts really.
Don’t think that Norton themselves never made a 4 valve head and decided to drop it. :!:

Click to expand...

The valves and springs in 4 valves are (much) smaller than in 2 valve engines, but there are twice as many of them = so it is swings and roundabouts.

Think we need to see the dyno charts for these jiggers to see what is happening. ?
The 4 valve with more hp did faster laps.....

Rohan,
I agree that a view of the dyno charts for the 4 valve engines might tell more of the story. Unfortunately as yet I do not have access to any, so for the time being it remains a matter for some speculation, and perhaps a little inspired guess work.

One distinct possibility is for the 4 valve engines to make peak power lower in their engine speed range than the 2 valvers. If this is the case, attempting to attain the same revs in top gear as the 2 valvers might take them past their peak power and into a decline, thus not having sufficient power to pull the gear, although accelleration would be there in abundance.

There could also be a situation where dyno room power does not equate to that when out on a track, something quite a few people have discovered to their cost in the past.

No doubt Andy Molnar is as interested as anyone to solve this little problem. If he succeeds before next years IOM races, expect to see one of his machines break the 110 mph lap- to be the first ever by a 500 single cylinder machine- and a Sulby speed around the 140 plus mark.

Snotzo said:

The MV3 on which Dean Harrisson won the Senior Classic TT was a Kay Replica, and is reported to be making the same power as the original factory machine.

Click to expand...

So, the MV3 was made by Kay.

I take it that the frame was not made out of titanium like the original made at the Italian helicopter works at MV Augusta :?:

http://www.mv-agusta.co.uk/bikes.html

Looking through snaps on my camera, I found this, taken off a computer screen at the I.O.M. It shows the final paractice speeds through Sulby for the Classic Senior TT entries. With the exception of Jamie Coward and Keith Amor's mounts, all the other Nortons are Molnar 4 valve engined machines.



Interesting to consider is how much horse power is necessaryto provide for 1 mph increase. In the instance of the Paton's, which have rwhp between 74 and 76, they have an advantage over Jamie Coward's 2 valve Craven Summerfield Norton of better than 14 rwhp, but the speed difference between this machine and the fastest Paton is 8.4 mph, 1.6 rwhp. for each additional mile per hour.

Of course this is to illustrate one instance only, and that with respect to a timed speed, not taking into account any other issues such as accelleration, handling, etc.
On speed alone, the Craven Norton was certainly on competitive terms with Dean Harrisson's MV3, but just behind Jamie's Norton on speed was a Royal Enfield Bullet.
Steve Linsdell's Enfield Bullet will not develop anything like the same rwhp as any of the Norton''s on the screen, so how does it manage to run so fast in a straight line?

All machines carry transponders, so the timing is not subject to hand held stop watch operation, and the day on which the above speeds were recorded was the last day of practice for the class.

More than a few people are puzzled as to why the 4 valve Nortons are not capable of faster top speeds despite their superior dyno horsepower, not least of all Andy Molnar himself. If he can ever find the top speed to go along with the current accelleration, he must surely have all the necessary ingredients to ensure an overall Classic Senior TT winner - provided of course he can solve the fuel consumption issue that stopped Michael Dunlop on the last lap.

Maybe the 4 valves need higher revs to achieve that peak power, and maybe riders weren't able to keep the motor 'in the zone' for some reason ergo actually produced less power at that point?

Alternatively, as all the 4 valves DNF, maybe they just weren't running right?

It surely seems very mysterious, but at the end of the day, there has to be a sound reason for this anomaly.

A bit of background that some may find interesting.
For the 1961 TT, Stan Hailwood asked Bill Lacey to build an engine for Mike, as he was without suitable machinery.
Bill had long held ideas about a special engine, so he set about the job, which entailed making a one piece crank, used with a D type Jaguar conrod, special oil pump, and a forged piston he obtained from Mahle. Bill also had cams made to his own design. All this with the bore and stroke left standard.
Bill had intended it to be best at 7500 rpm, but was pleasantly surprised to find it made 66 bhp at 7900 rpm, and was safe to 8300. This was crankshaft power, measured on Bill's Heenan and Froude DPX1 dynamometer.

Through Mike, this was the last Senior TT won by a Norton motorcycle.

Mike was timed through the Sulby speed trap at 138.45 mph, the same speed as John Hartle on an MV. The next fastest single was Dickie Dale, also on a Norton, nearly 10 mph slower.

When this feat is considered, with respect to the list of speed trap times given previously, it is hard to see where the progress has been made with current Norton machines.
From my study of dyno tests reported in another post 'The Last Norton Dyno Book?' I find most 500cc Manx engines tested at approx 50 bhp at 7000 rpm, only one exception being better, an engine owned by George Leigh, a dealer of Southport, which made 52.5 bhp at 7500 rpm, this with a lot of special parts and George's Titanium conrod.
Engines typical of these kind of power outputs would undoubtedly account for most of the lesser speed machines in 1961, but the Lacey engine was undoubtedly something quite unusual.
After the TT, Bill stripped his special parts out of the motor and rebuilt it with standard items. The special parts were never used again.

Very much better tyres are available now than riders had in 1961, and the TT course is undoubtedly smoother and faster for today's racers.

Does any of this make the speed anomaly issue any clearer? To me it serves to confuse even further!