Available engine performance

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Hi all,

I read the posts like the recent one on major head modification with great interest, including the photos and flow chart graphs.
Unfortunately as an owner without the benefit of a machine shop or the time and skill to perform major modifications, it is hard to appreciate what performance gains are being achieved and how useable the extra power obtained is In normal use.
So I guess the question is, what mods provide the best ‘bang for bucks’ in normal fast road riding? City riding doesn’t exist for me.
At around 198 cm (6’6’’) with a girth to match, the old 850 is probably pulling as much weight around solo as it would have with a couple of young kids on it, back in the seventies when it was new.
I guess if asked I would like sparkling performance with buckets of low and mid-range power but probably never really want to rev it above 6000 rpm. Terminal velocity is rather irrelevant but reliable long distance riding approaching 80 mph (125 km/hr) with plenty of overtaking power available is the goal.
To reduce this question to rather basic terms, how much power is easily and reliably available from an 850 Commando? What is the path to this improved performance.
For example, in comparison to it’s contemporaries, can a Commando match a Kawasaki Z900 performance wise. With a suitably small rider on it, can it get it’s quarter mile times down to the low 12s or beyond?
Please don’t get the wrong idea, obviously we are dealing with a very old design that was technically ‘past it’s prime’ when new so I’m not looking for miracles. As is the Norton certainly puts a smile on my face but it doesn’t have the ‘arm stretching’ acceleration that is referred to in other posts.
I haven’t counted the sprocket teeth but it seemes rather highly geared, perhaps approaching 18 mph per 1000 rpm in fourth gear.
Regards
Al
 
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grandpaul

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"Easily" and "Cheaply" are relative terms.

I'd say a Megacycle 560-00 cam with radiused followers (Megacycle can do the radius job), then modestly high compression pistons at nominal oversize, a very tight valve job, new Burlen Amal Premier carbs, and larger diameter headers with straight through glass-pack peashooters should be more than enough for the engine.

ASSUMING THE BOTTOM END IS IN GOOD SHAPE, OF COURSE.

The possibilities are endless, but if your bike is "fine" otherwise, I wouldn't need to go much further than that to coax a noticeable increase in power out of it. In fact, if your carbs and pipes are in great shape, you just saved a short stack of money

My 880 with Megacycle cam was the first Commando I ever wheelied with throttle alone.
 
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ashman

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You can open a can of worms for performance upgrades, when I converted my 850 to the Featherbed back in the 80s I did a few good upgrades to my motor that made it better all round, crank balanced stock cam built up to a 2S cam profile head shaved and ported but still run the original valves, carbies re jetted, upgrade ignition and open mufflers, it was a cheap upgrade way back in the 80s and I am still running the same set up today, bike is very reliable, still good to ride around town and cruises lovely on the highway and still running the gearing it came out of the factory, its my hotrod street bike even after 46 years of ownership.
But of course you can spend a lot of money these days in what's around but my pockets aren't that deep and everyone has different opinions in what is needed, but getting the bike to breath also plays a big part.

Ashley
 

concours

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The 1973 Cycle magazine road test of at least 6 750's and a Sportster, it was faster than everything EXCEPT the Kwacker triple, which edged it out by .4 second in the 1/4 mile.

I run a 22t sprocket, 80-85 cruising is very comfortable. All stock, except for a .023" head gasket. 240lb rider
 

Time Warp

.......back to the 70's.
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Just keep adding aftermarket engine bits until it becomes a new Triumph and anything Commando is just a memory.

You might be able to get 58/60 RWHP, then you add decent wheels, brakes, suspension.
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Derek Wilson

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As 50 year old motorcycles go, a good working, relatively stock Commando goes down the road pretty good. I ride mine with both the vintage crowd and my sport bike friends. I think my sport bike friends just tolerate me - LOL - but unless they are doing stupid fast straight line stuff, I can keep up okay in the twisty stuff.

Like you said, making power and putting that power to the ground is two different things. I run an upgraded upgraded Combat motor, and it does pretty well. 850's can get a bit asthmatic at high revs, but they more than make up for it on the bottom end. Maybe a cam (only if I had the motor apart already) and a bit of carb/timing work is all I would do.

Your height is going to be the biggest challenge. I have a friend your size, and he actually put on a set of custom lowered rearsets, much higher bars and converted to an interstate set up. His clutch takes a beating, but I am not sure if that is his size or just his riding style.

The place to spend your money is suspension and handling. Good tires, good isolastics, a good headsteady, good brakes - all part of building a Commando that is enjoyable to ride.

And then get out and ride it. You won't truly know what you like and what your bike might need until you do. I have spent the last 20 years off and on tweeking mine. That is part of the enjoyment for me.

FWIW
 
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H
Just keep adding aftermarket engine bits until it becomes a new Triumph and anything Commando is just a memory.

You might be able to get 58/60 RWHP, then you add decent wheels, brakes, suspension. View attachment 80325
Hi,
What is the generally accepted conversion from crank horsepower as advertised by manufacturers and genuine rear wheel horsepower? I believe all manufacturers used ‘a Parker pen’ (cheated somewhat) when providing figures. Were they all as bad as each other or did different manufacturers use different levels of fiction in their figures?
I only mentioned the Kawasaki Z900 in my post as it was a common very high performance bike in it’s day that most older riders have probably ridden. In my youth I was always trying to match my mates Z1000 on my T160. Never got him in a straight line though point to point it was a different matter
What sprockets give what road speeds per 1000 rpm
with thanks
Al
 
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Damn! Here I am still enjoying what mine does as it came. Acceleration is good(plenty quick), cruise 80mph without complaint, smooth, reliable, etc. Oh, it stops pretty good also. As I view things squeezing more power out of 50 yr. old high mileage parts/motors is risky at best. If I need the high performance I'd preserve my 850 and just purchase something which delivers such........ My 850 never stood a chance against the only kawa 900 I ever got it on with 40+ years ago on a straight road. 850 hit 4th and 900 began to pull away very quickly. Just not a good match IMO. Twisty road may have improved things but none were available.
 
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Mart UK

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H

What sprockets give what road speeds per 1000 rpm
with thanks
Al
23T = 20mph per 1,000rpm, give or take, about 3500rpm at 70mph. My 850 has a single mk2 Amal 34. It pulls really well from 2500rpm. I expect I lose a fair amount of point and squirt type acceleration with this set up, but I love the character it brings to the ride. It's certainly fast enough to ride in groups with modern bikes and relaxed enough for ride all day comfort. I truly love this bike!
 
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23T = 20mph per 1,000rpm, give or take, about 3500rpm at 70mph. My 850 has a single mk2 Amal 34. It pulls really well from 2500rpm. I expect I lose a fair amount of point and squirt type acceleration with this set up, but I love the character it brings to the ride. It's certainly fast enough to ride in groups with modern bikes and relaxed enough for ride all day comfort. I truly love this bike!
if you go to https://www.gearingcommander.com/ , there is a setup for the 750 commando. Just change the gearbox sprocket to what you haver and it will give you a heap of info.
 
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Losing weight off yourself or the bike is the cheapest way to improve performance ;) . The Commando is a really light bike to start with when compared to say the Trident or the Z900 or the day, a 100lbs at least lighter. Adding performance with wild cams will get you more top end but you will lose in the mid range, its the mid range which is the best thing about the Commando which is where it got its good 1/4 mile figures from linked to the lower weight.
 

Fast Eddie

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Many, many different ways of skinning a cat. Many, many different ways of interpreting’best bang for the buck’ too!

In general, ‘best bang for the buck’ is probably Nitros oxide injection… but I’m guessing that’s not where you wanna go?

Many favour the stock cam, siting it was actually quite a performance based grind for the day. And delivers good all round performance.

Many say stock CR is best and raising it yields little. Ditto carbs, valves, etc.

So it’s kinda easy to end up saying stock is best. And stock is indeed a well proven package, lots of grunt, and reliable.

But when I first hot rodded my 850 with a JS#1 cam, 10.5:1 CR, and FCR 35mm carbs the difference in the before and after was staggering. The difference side-by-side with my mates near stock mk111 was equally staggering. There was just no comparison, at any revs, irrespective of who was riding each bike.

I should add that the JS#1 isn’t a lot higher light than the stock cam to be honest. You can see the lift curves here: https://jsmotorsport.com/js-motorsport-technical-camshafts/

Then when I had the head ported and bigger valves fitted, another 9rwhp was released !

In this guise there was more torque and power everywhere above 3k. So it’s not necessarily the automatic case that performance tuning equals more top and and less mid range (unless you go radical).

Even without the head work (which an expensive and time consuming project by itself) the improvements were dramatic and I’d definitely describe it as ‘arm stretching’ as you put it.

Power and torque was very flat up to a peak of just over 6k so I virtually never went above that, even on track days.

Not saying this is the only way, or the way you should go, just sharing the experience.

Feel free to read through this meandering waffle as far as your interest and patience will allow:

 
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One word,... "Hayabusa".
It fits your stature , and the performance is incredible! A fair condition used Busa properly serviced ( tires, brakes, etc ) will be cheaper than trying to modify your Norton,
and be reliable. Plus, you won't bodge up an otherwise nice bike & destroy its value at the same time.
Use your Commando as is and enjoy its personality.
Cheers
 
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Haha, I couldn’t agree more. I was going to suggest it but thought I’d better keep quiet. As a serial Busa owner of 22 years during which I’ve had 5, ranging from 1300, with nitrous. 1400, and nitrous, 1340, and 1340 with stage 2 turbo, I can tell you there’s really nothing to match a sorted one. But if you want to stay stock (it gets expensive real fast wanting to go faster) then go for a ZZR1400 (ZX14 in US speak) which is still ‘the daddy’ , oh, I’ve had 3 of those as well. Still got a ‘99 Busa and a ‘15 ZZR. Best of both worlds alongside the 5 times winner of the Bike of the Year Commando.
 
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As mentioned, the best performance modification for a Norton is weight reduction.
I've nearly finished a lightened Commando and it is 120 lbs lighter than a regular Commando or 150 lbs lighter than a MK3 or early standard bike with estart added.
With 6 lbs equating to 1 bhp that should equal a bhp gainvs standard of 20 or 25 bhp, depending on which type of standard Commando is used for comparison.
The engine is bored to 81mm to give 920cc which, in theory at least, should give and additional 10bhp +- at 9.5 to 1 Cr.
It's only done a few miles so I cannot say if the 920 mod is viable. The 81 mm bore size has not worked well for some other owners. Several bikes have been put back to stock 828 after trying the 920 size.
As far as cams go, about a year ago I was surprised to see that Jim Comstock has gone back to the stock profile with his much modified test bike.
If I remember correctly, that bike in its current form is 924ccs .The 924 cc was acheived by boring and stroking to avoid the usual 920 problems. It has raised compression, a much modified head ( he did the head mods on Fast Eddie's bike) fuel injection and a whole host of other performance and durability mods.
He found that the stock cam profile gave the greatest midrange urge. I take that as proven as he uses his own dyno to check these things.
That nice to know because the stock cam is also easy on the valve train as compared to bigger cams.

Glen
 

SteveA

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Oh Dear! This question has been asked before, it seems to me several times. Do try a search of the site.

Just blueprint your engine. Give it a good overhaul, maybe use the stage 1 notes published by Norton in the '70s, but only take the compression up just a touch with a clear idea of fuel needs over 9:1 and avoid any temptation to use a 'hot cam' and fancy valve gear.

Spend some time correctly setting up timing and carburation.

More than gaining performance, you will probably reduce vibration and get smoother running, and you will feel good about your bike! Stick to your 6000rpm and everything will be fine even with standard pistons and rods.

A well-built 'standard' engine will actually fit what you are asking for much closer than you probably imagine.
 
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You're from Down Under... ever seen Stone? :cool:
Yes, I certainly have.
When it came out I was too young to get in and see it as it was R rated. Eventually I was able to sneak in to a theatre, I just loved it. It was an anthem to us. As a Northern Suburb Sydney boy I could recognise all the locations and when I somehow managed to buy a Yamaha TX 500 at 16 and 9 months (L Plate age), complete with custom paint and bikini fairing I was right there in my mind, through the bends of River Rd where many scenes were filmed.
Many rears later, perhaps the early 2000s, the producer of Stone visited our town (Bombala) to give a talk about the making of the movie and a special showing on the antique carbon arc projector equipmen. The story of how it was made, the cat and mouse battle with the police who were trying to prevent the street scenes wer unbelievable. The riders (A graders from Willoughby Motor Cycle Club had large 16mm movie cameras strapped to their helmet. The first time this had ever been attempted.
Also amazing was Kawasaki Australia’s unbelievable generosity and faith in the production in giving them unlimited access to brand new Kawasaki Z900 motorcycles. And they wrecked a few! It absolutely put that fine bike on the map in Australia
Of course the big road race between the policeman (Stone) on his Commando and the aboriginal bikie on a 900 was the highlight of the movie for me (barracking for the Norton of course) . At the last minute the Norton crashes and the Kwacker wins.
At the special showing the producer mentioned the possibility of a sequel (it never occurred) and tongue in cheek I asked him if he would get the riding scenes correct in the next movie. He asked what I meant and I quipped that the Norton should have won, with a wink.
A great movie!
al
 
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