920

Don Tovey said:

Having said that, when I follow him on a run with him 2up & me one up I can just about keep up with him on my standard 750.
It must be the quick action throttle that makes mine go quick.

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Assuming a 150 lb passenger and the old rule of thumb for acceleration of 1 hp per 7 lbs this seems to be in the ball park and supports your dyno report.

What we are too quick to dismiss is that generally the 920 torque increases across the rpm range making for a much more trackable engine.

Thanks to al for the info.
Don, I would say that 61 rwhp is a terrific result for just the 920 mod. And if his bike still pulls away from yours when he is two up while you are solo, that is also very good. The passenger changes the power to weight ratio a lot, obviously dependant on size of the passenger.
The dyno results I have read of for 750s seem to be averaging around 45 hp except combats which are a little higher, maybe 47-49. The 850s with a free flowing exhaust are about the same as the Combat, which is what NVT stated as well.

So a jump to 61 on the back tire is quite a lot.

Shrapnel, Im all over the torque increase. I think I mentioned somewhere in the thread that many high performance mods boost the top end at the expense of midrange and bottom end whereas the 920 mod should give increased power all the way.
Really the increased torque is the same as saying increased horsepower at lower rpm, torque being a calculation derived from horsepower and rpm.

If we use Steve Maney's figure of ten horsepower loss from crank to rearwheel, the Dons friend's 920 is making 71 hp at the crank.

Glen

worntorn said:

If we use Steve Maney's figure of ten horsepower loss from crank to rearwheel, the Dons friend's 920 is making 71 hp at the crank.

Glen

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Power loss through the drive line is a function of many things including RPM, primary and final chain drive conditions, sprocket sizes, gear box speed, gear box lubricant, etc....

Typical efficiency numbers for industrial chain drives are generalizations for lower speed applications.

From an internet source "One of Mr Jack Williams ' design note books for the 7R and E45 states that a drip fed primary chain running at high chain speeds is probably no more than 90% efficient and lower with incorrect lubrication."

This loss must be multiplied by the power loss of the rear chain (say 98% eff) which must then be multiplied by the gearbox losses (say 98% eff), which must then be multiplied by the tire loss (say 99% eff). You can play around with the numbers as you see fit.

So 90% X 98% X 98% X 99% = 86% efficient or 14% loss at full speed. Around town motoring at lower rpm will be considerably less.

So at stock rpm conditon of around 50 RWHP, a swag at drive line loss is probably maxing out at around 10 hp at full tilt. Once you start increasing peak rpm, the loss increases.

Dances your drama confused me because I'd only extended your own calculations for torque-power of 750, 850 and 920's non-race engine then added the full race data for comparison. In public road life torque rules over hp as the pull up to thrilling speeds fast is way more important pleasure than hanging on for top end that is just plain stupid most the times.

Ancient accepted engine motto, There is no substitute for Displacement. As reported its felt from idle to top end, it also ups the CR ratio a bit w/o increasing the chance of piston-head clash and makes the over size Norton ports more appropriate sized for mixture velocity packing in, which I'd think adds to throttle response sense too.

I'm still waiting feed back of how difficult to kick a 920 off and how well the drive train can tolerate the extra grunt. Also curious about the ability or avoidance to spin tire on up shifts or just throttle snaps in lower gears or leans.

Hi, it's Reggie here (referred to in Don's post). Yes I do have a 920, but it has additional modifications other than just a big bore kit, that are listed below.

When it ran 61 rwhp, it also had a Steve Maney stage 2 head, runs 9.8:1 pistons, 34mm MK2 Concentrics and a 2-1-2 exhaust system and a PW3 cam.

I also used to have a Norvil 920(in the 1980s) as did another friend of mine for whom I built the engine, and both ran 4S cams.
I found by just putting a Norvil 920 kit straight on to an otherwise fairly standard bike plus a 4S cam, (I'm not sure of the C.R.), that there was a nice increase in torque but that the engine got a bit breathless over 5500rpm, so definately a more relaxing and powerful engine than standard.

With all of the above modifications when it ran 61rwhp, the engine has even more torque all over the rev range than the "Norvil" 920, and with the 2-1-2 exhaust on, over 4000rpm, the engine note changes and it pulls hard right up to 7000rpm, although the dyno readout suggested that max bhp was achieved at 6000rpm and max torque of 56lb/ft at 5500rpm. I'm no engineer (I work for our UK health service), and I'm sure somebody who knew what they were doing would get more power. I do keep meaning to take it on a dyno where they will advise me if and where it's running too rich or lean. If and when I do, I'll let you know.

Don wrote;

Having said that, when I follow him on a run with him 2up & me one up I can just about keep up with him on my standard 750.

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Don, I'll ditch the bitch, and if you like we can have a quick run side by side up the old A1 ( a straightish quiet road in the UK near to where we live) north of Wetherby if you like and see what the difference is :twisted:

oooh , I think Don may be in a bit of trouble here!!!


Glen

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Looks like a two into one exhaust from Unity - correct?

Any thoughts or comments on the before and after (the two into one) performance of your bike?

Dances with Shrapnel wrote;

Looks like a two into one exhaust from Unity - correct?

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These were made for me by Paul Bryant proprietor of Viking Exhausts, New Zealand.

Dances with Shrapnel wrote;

Any thoughts or comments on the before and after (the two into one) performance of your bike?

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With these pipes on, the exhaust note is quieter, possibly more refined is the way I'd describe it, but definately different.
As I recall, the difference performance wise was as felt by the "seat of my pants," slightly less power up to 4,000rpm with the 2-1-2, but then the exhaust note changes and it really pulls strongly up to 7000 rpm if desired. In effect, it's moved the power slightly up the rev range, but then you seem to get more than the standard open 2 into 2.

Nice Victory 2-1. Maybe I'll do mine with longer headers for lower rpm power boost. There are some tricks header builder do with partitions and angle of merge that help power some they say.

All these HP numbers are to me are more about bragging rights, in the end does the upgrade make it more usable and fun? That said it is a benchmark to gauge the thing by!

Back in the late 70s and early 80s we used to run 920s on the moto-cross bikes but I cant remember the specs

Dave Coates in Reading i seem to remember built some pretty hot motors including Terry Goods and I recall some very special 950+ motors with Porsche pistons and very thin liners, any one else know how they were converted from the standard motors? they used to pull 2 of us round rather well i remember

I traded some machine work for a cast iron barrel bored out to 940. Ken Canga has it if brave enough to try its thin skinned volume. He knows what pistons fits. Strongest engines in the works are the 1007 cc's but ain't seen anything on power measures - just the plans for land speeders and road racers.

The iron cylinder hobot is referring to was sleeved and bored to 82 mm for 940 cc. The liners get pretty thin at that bore, and I don't recommend it, but HPI used to build them that way back in the '70s. I tried one in a Commando racer, but couldn't get good ring seal, and actually made less power than the 920 (actually only 917 cc), so stuck with the 81 mm bore. The largest displacement I've seen for Commandos back before Steve Maney started making the liter sized kits was a 960cc, using a stroker crank and big bore. I raced a 938 cc engine with a Dave Nourish 91 mm stroke crank and 81 mm bore, and it was quite reliable. Steve now makes a 93 mm crank for the 1007 cc kit, but you can also get it with the standard 750/850 flywheel width so it can be used in standard cases. With that and the normal 920 bore size of 81 mm, you get 958 cc. I think Steve had at least one customer racing succesfully with that combination.

Hi Ken


Norton Commando 960cc Engine

Bore 81mm stroke 93mm
Camshaft 7S
Factory settings 0.225 thou lift on inlet valve at T.D.C with 16 thou tappet clearance.
We ran 15 degrees advance on timing gears to give 200 thou lift on inlet valve at T.D.C now inlet opens 61deg. B.T.D.C closes 78deg. A.B.D.C exhaust opens 88deg.B.B.D.C closes 60deg. A.T.D.C all checked with 16 thou Tappet clearance
Running Tappet clearance 16 thou all round

Ignition was a Boyer Brandsden Mk 2.
I use an Interspan
Ignition timing 28 deg B.T.D.C

Crankshaft- 93mm Maney Lightweight
Connecting Rods- Carrilo
Crankcases- Maney
Pistons- JE modified, Weight 396grams each
Cylinder Barrels- STD Norton 850cc relined and bored 81mm

Still dont really know how it goes yet!!!!!

Hope to get out at Lydden

Hope the info helps

all the best Chris

Chris said:

Still dont really know how it goes yet!!!!!

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That is cruel.

Hi Steve/Hobot, 2 into 1 by Viking (Not Victory) Paul Bryant made my non blueing headers, best chrome job ever!!!
Looking at him making a custom exhaust system for bike #2 (yet to be named) once I have filled the mill with JS goodies and carbs, and RH10 head Kibble white (?) valve job based on comnoz specs.
When do we see Mrs Peel turn a wheel?
Regards Mike

Chris said:

Hi Ken


Norton Commando 960cc Engine

Bore 81mm stroke 93mm
Camshaft 7S
Factory settings 0.225 thou lift on inlet valve at T.D.C with 16 thou tappet clearance.
We ran 15 degrees advance on timing gears to give 200 thou lift on inlet valve at T.D.C now inlet opens 61deg. B.T.D.C closes 78deg. A.B.D.C exhaust opens 88deg.B.B.D.C closes 60deg. A.T.D.C all checked with 16 thou Tappet clearance
Running Tappet clearance 16 thou all round

Ignition was a Boyer Brandsden Mk 2.
I use an Interspan
Ignition timing 28 deg B.T.D.C

Crankshaft- 93mm Maney Lightweight
Connecting Rods- Carrilo
Crankcases- Maney
Pistons- JE modified, Weight 396grams each
Cylinder Barrels- STD Norton 850cc relined and bored 81mm

Still dont really know how it goes yet!!!!!

Hope to get out at Lydden

Hope the info helps

all the best Chris

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Should be a real monster. I look forward to seeing how it works out. It certainly sounds like it has all the right ingredients to make serious horsepower.

Ken

Ugh MIke sorry forgot-fogged out on Pual's company name but i dealt with him during a period of significant illness w/o knowing that apparently he lost all control of products so not only did I have to about destroy new brass exhaust 'nuts', they are so blued even my buddy Wes has remarked about it and wondered if sign of timing or mixture off, nope all spot on and dark dry soot in pipes not even grey. OH yeah last week Wes helped me put a bend crease in RH pipe to keep it off contacting and cooking points area. Wes said man that pipe was heavy and it also took two of us to bend it once we trapped it in a trailer hitch structure. Took the bark off a number of tree forks as we escalated up the force and trapping attempts. There are handfulls of pissed off past buyers, mostly in UK it seems d/t mostly to the nice chrome cracking flaking off. I don't think Paul on purpose let this happen so glad he's getting rave reviews again.

Ms Peel engine is in Ken and Jim's hands right now for finishing touches. I don't have a real job no more, so money and time delays Peel project, used up on ofter vitals like home and car and dang ole Trixie Combat constant nickle and dime needs. Rode Trixie a bunch last few days, like today no more concerned about extra wear tear holding 19T in 90's or more a lot of the time now. Peel's 920 is similar to the hi rpm racers and if not putting on all the extra stuff could field her as natural inspired 38 mm QuikSilver carb, total loss ignition, trials bike under 300 lb. Every things I've studied or read implies she'd be good for 8000 routinely, if me or drive train could take it. Extra stuff adds like 35-40 lb but should allow about triple power of a base line Combat and take crashes and deer strikes in stride, though I might not. Hard stuff is done, just wires and cable and some welding and tubes and piston oil jets and plumbing to go to carry around the paint ball blunderbusses and Grizzy Bear pepper spray mines at each corner plus video cameras aimed at prey, rear tire and forks for those ain't ever seen the benefits of going so harsh and loose must straight steer like cars. Bike life this since '99 has been hard on me and bikes so i'm ambivalent to rush Peel, relaxed enjoying the process - in back of mind pensive I'm building my own special killer.

I know of at least 3 Drouin superpower related deaths. One a Salt Lake record holder that took a joy ride afterward and hit rough ungroomed surface.

Reggie said:

there was a nice increase in torque but that the engine got a bit breathless over 5500rpm, so definately a more relaxing and powerful engine than standard.

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Typical heavy big bore pistons can slow the RPM down and add tons of stress. Dave Watson had the same problem with his big motor not breathing or running well above 5500RPM (held back with heavy pistons). Then he went to 240 gram JS pistons and the useful RPM jumped to 7200.

For a race motor it makes sense to do that, however my plan is just to add some easy horsepower thru the normal rpm range used on the street and to do so with minimal cost and minimal effort, no rebalancing of crank for lighter pistons etc. I know the end result would pale in comparison to the power of one of these race motors, but then they are probably on the anemic side compared with the hot rodded 1360 Vincent motor Im building, which pales alongside a turbo Hyabusa. There is always something better out there!


I rarely take the Commando above 6000 rpm now and max power with the stock cam is at about 5800 from memory. At that point one can always shift to the higher gear! It s the Commando torque that most of us road riders enjoy, not max hp. Worth a try anyway.

Glen

worntorn said:

For a race motor it makes sense to do that, however my plan is just to add some easy horsepower thru the normal rpm range used on the street and to do so with minimal cost and minimal effort, no rebalancing of crank for lighter pistons etc.

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Street or race, anytime you can reduce reciprocating mass, it is a good thing. Naturally budget (time, money and pain in the ass factor) are always a consideration.

worntorn said:

I know the end result would pale in comparison to the power of one of these race motors, but then they are probably on the anemic side compared with the hot rodded 1360 Vincent motor Im building......

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OK, I'll bite. At the risk of starting a dick swinging contest, what power do you make or do you expect to make with the Vincent.

jseng1 said:

Typical heavy big bore pistons can slow the RPM down and add tons of stress. Dave Watson had the same problem with his big motor not breathing well above 5500RPM with heavy pistons. Then he went to 240 gram JS pistons and the useful RPM jumped to 7200.

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Jim, you are saying "not breathing well" figuratively, not literally?

My understanding is that the reduced reciprocating mass allows the engine to accelerate faster as a result of:
1.) less inertial mass of the "lighter" reciprocating parts and
2.) less rotational mass due to the lower bob weight requirements and
3.) less translational mass to move down the track.

It has nothing to do with the term "breathing" as commonly used in reference to engines.

I thought Dave Watson did more to his engine than lighter pistons and rods.
Inquisitive minds want to know.