H.P mods ?

You need to upgrade that oil pump asap

worntorn said:

You need to upgrade that oil pump asap

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Oh I dunno. Seems to flow really well. Especially when parked up for a few weeks...

Fast Eddie said:

There are many paths to enlightenment...

The stock cam is a good path... I gotta step in here before this generates into an ‘all performance cams are crap’ thread and defend the fact that there are other paths...

If someone were to stick a race cam into an engine (any engine) and do nothing else, the results will range from disappointing to dire. No arguments there !

But, JC also said in another thread, dynoing each individual change is a waste of time because tuning is about ‘the package’.

I‘ve ridden stock 850 Commandos, they’re bloody great, and more than enough for most owners requirements most of the time. But, my tuned 850 had more bottom end, more mid range roll on, and (way) more high rpm power than my mates low miles 850 that was stock apart from EI and peashooters. Mine just left his for dead in every scenario we tried. And it continued to do so when we swapped bikes. It produced peak power at less than 6500rpm and I seldom went ov

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Fast Eddie said:

There are many paths to enlightenment...

The stock cam is a good path... I gotta step in here before this generates into an ‘all performance cams are crap’ thread and defend the fact that there are other paths...

If someone were to stick a race cam into an engine (any engine) and do nothing else, the results will range from disappointing to dire. No arguments there !

But, JC also said in another thread, dynoing each individual change is a waste of time because tuning is about ‘the package’.

I‘ve ridden stock 850 Commandos, they’re bloody great, and more than enough for most owners requirements most of the time. But, my tuned 850 had more bottom end, more mid range roll on, and (way) more high rpm power than my mates low miles 850 that was stock apart from EI and peashooters. Mine just left his for dead in every scenario we tried. And it continued to do so when we swapped bikes. It produced peak power at less than 6500rpm and I seldom went over 6000rpm as the torque / power spread just didn’t warrant it

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One other thought here- your bike has been lightened quite a lot. In the weight thread a couple of years back you mention that it weighed 387 wet at that time but further weight reductions were coming.
I weighed my MK3 wet and it is 215 kgs, 481 lbs.
So your bike is roughly 100 pounds lighter than your friend's MK3
We are told that , for acceleration, 6 lbs = 1 HP.
So your bike would need to produce 16 HP less than your friend's bike for the bike's to perform equally. If your bike produced the same HP as his, yours would rocket away.
The extra HP of your engine would only add to that. So perhaps a chunk of the performance difference you saw was in the power to weight advantage due to weight reduction.


I put this to my test with the 348lb Egli. For the first year I ran it with the standard engine from my Rapide. I did get to test it on the highway against the ultimate hotrod Black Shadow- the bike that won the " Fastest Roadgoing Vincent " trophy at the Sulby Sprint in 99 against scores of others. It runs 11 to 1 pistons, big flat slide carbs, hot cam and modified ports to name some of the hot-rodding. It is lightened a bit but probably is still about +100 lbs vs my Egli.
The stock 47Rapide engine in the lightweight rolling chassis left the hotrod Shadow behind rather convincingly.

Less HP but way less weight more than made up for it.


Glen

Yeah, that’s a fair point Glen.

I did save more weight off the bike. Coincidentally / disappointingly the electric start I fitted at the same time brought it back to almost exactly the same!

So it‘s now a 390lbs electric start Commando, that’s with all oil and an almost full roadster tank.

I do sometimes contemplate removing the e start and enjoying the lightness, but it’s so difficult to kick over, and so easy to press that little red button...

One day I hope to persuade my mate to put his stocker on the dyno.

I think people might be surprised how low the figures would be in real life (I recall dynodave posting something about this when they held a club dyno day).

Stock 850s are realistically around the low 40s rwhp figure (stick a single carb on it and you’re into the high 30s).

My first iteration was 56rwhp. The second iteration with JC head job was 65. Haven’t been able to do the 920 yet (covid etc).

To be honest, it’s possible the standard engine is as good, perhaps even better, below 2,500 rpm, but that is of no interest to me or my riding style.

Agreed, with the Commando, 2-3000 rpm is just a vibe zone to get thru quickly and not revisit until forced to by traffic.

Fast Eddie said:

One day I hope to persuade my mate to put his stocker on the dyno.

I think people might be surprised how low the figures would be in real life (I recall dynodave posting something about this when they held a club dyno day).

Stock 850s are realistically around the low 40s rwhp figure (stick a single carb on it and you’re into the high 30s).

My first iteration was 56rwhp. The second iteration with JC head job was 65. Haven’t been able to do the 920 yet (covid etc).

To be honest, it’s possible the standard engine is as good, perhaps even better, below 2,500 rpm, but that is of no interest to me or my riding style.

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'Classic Bike' magazine put two readers bikes on the dyno in their October 2009 issue, both allegedly: 'Stock' bikes, though their Mk3 had no balance pipe and peashooters.....
850 showed: 39.7 bhp @ 5700rpm.. 41.5lb/ft torque @ 4450rpm
750 showed: 47.5 bhp @ 6175rpm.. 43.6lb/ft torque @ 5300rpm

Both bikes reached 110mph top speed, though the 750 got there a good deal sooner than the 850...

That’s not too surprising. Although I’m surprised the difference between them is quite so much. Can you recall which 750 it was, stock or Combat?

The 750 must have had lower gearing because with 20% more power, it should have a higher top speed (not that that actually matters of course).

Fast Eddie said:

That’s not too surprising. Although I’m surprised the difference between them is quite so much. Can you recall which 750 it was, stock or Combat?

The 750 must have had lower gearing because with 20% more power, it should have a higher top speed (not that that actually matters of course).

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They just quote: 1971 Roadster. It was drum braked, though, but still stopped quicker than the porky 850 which was in interstate trim...
But, re: Top speed, they put the disclaimer that the 750: '..might have gone faster but we experienced an alarming wobble which we later found out was due to engine bolts vibrating loose'..

A ‘71 with drum brake isn’t a Combat.
Loose engine bolts?
Cradle must have been powder coated !!

Here are the Dynodave numbers Nigel mentioned-
"A half a day at the 1992 INOA rally dyno session gave some results.
Typical was 750-38-43 RWHP, 850-39-45 RWHP, My combat 47RWHP(best stock bike)- Pete Kogut real 750 Yellow Peril(track race bike) 55RWHP( he was extremely disappointed) ......- Might have been IIRC, Pete Breidermier-sp-closer to 60 RWHP. Best NHT show of the day...920??unknown"

So that's quite a different result, with multiple runs on the same dyno, same day, the 850s made a bit more than the 750s, other than Dave's Combat which made 47?
These are peak numbers at peak or near peak rpm which tell us nothing about the area under the curve.
I ride at peak rpm even less than at 2500 rpm.
And if you ran that Combat at peak rpm for any length of time ...we know the result.
Doesn't seem worth it for a couple of hp.
Norton didn't think so, that's why they strengthened, detuned and bored to 850, saying it gave similar performance to a Combat without being highly stressed.
Similar performance, probably not the same.
Maybe a little slower in the ever important 1/4 mile and a lot stronger dragging up some mountain pass laden with gear.

It would mean more to see the actual comparative charts rather than just a peak number. But peak numbers are usually what is quoted.

Glen

All graphs are in the magazine quoted, but I can't reproduce them nor would I try given copyright issues etc..

EstuaryBoy said:

All graphs are in the magazine quoted, but I can't reproduce them nor would I try given copyright issues etc..

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Does Classic Bike offer an electronic [PDF] subscription? If so, does that subscription allow you to access the "old issue library? I ask, as I subscribe to several other [non motorcycle related] magazines which do.

Here's the only comparative chart I've found. This is from Mick Duckworth's book.
Aside from writing books about motorcycles, Mick Duckworth is the man who repaired Mick Hemmings stripped Commando exhaust port threads before Mick Hemmings learned how to do this. Those threads have been a problem for a very long time!
He also helped Mick Hemmings get started in business.

Note the relative peak power amounts are same as dynodaves 1992 report, just moved up a bit. Could be that the Duckworth figures are corrected to SAE or just a difference in dynos.
We know that is normal and unavoidable.

The blue line at 4000 rpm is me climbing White Bird pass in Southern Idaho.
The green line is my friends 750 that I passed as soon as we hit the climb.
We didn't have an original Combat along, but if one was there it would be a bit slower than the regular 750 on that grind.

Glen

chaztuna said:

Does Classic Bike offer an electronic [PDF] subscription? If so, does that subscription allow you to access the "old issue library? I ask, as I subscribe to several other [non motorcycle related] magazines which do.

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TBH I haven't a clue. I possess that article and many others because 10 years ago when I was looking to buy a Commando I scooped up every bit of literature both new and second hand for: 'Research purposes'
By coincidence, I was given a current issue a month or so back, but I wouldn't buy it off the shelf....
Last related literature I subscribed to was OBM, but that was back in my: 'Spend, spend, spend' days, now long gone...
Did find one on ebay:

If all the dynos were calibrated in the same way, horsepower comparisons might mean something. There is a difference between accuracy and precision. Joe Craig claimed 50 BHP for his 500cc Manc Nortons. That is probably a reliable figure. In the old days, they used to do things right. His dyno would have been calibrated against national standards.. In those days we had real engineers - who were not guys just making a quick buck. - People such as Joe Craig and Phil Irving were university qualified and experienced. They also received shit wages.

Quite a few years ago on the way back from Wyoming, I was riding two up with luggage over the Chief Joseph pass. The bike was a pretty stock 850 MK II with a single 38mm carb. The altitude was around 10,000 feet and we were passing Harleys 12 at a time! I think the standard 850 engine is pretty good as it is, and the 750 engine is similar. Just make sure it isn't to corked up with some restrictive mufflers.

Knucles said:

what can be done to increase h.p. In the 750 cc engines ?
what is the most h.p. You can get to with street fuel ?
i just have an interest in what can be done .
not that I want to do it on mine . I want to stay with reliability .
I can remember about 40 years ago a friend had a bunch of work done on his . He seemed to have a lot of problems and the bike was being fixed very often .
I don’t remember what he had done .
what mods can be done on a street bike and what hp increases do they give ?

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MexicoMike said:

As pointed out, mods must be sorted to work together with the stock parts or other mods. Just changing to a "high performance" item and expecting it to increase power is expecting too much. I have seen "high performance" camshafts, exhausts and an almost endless number of "bigger carburetors" reduce performance over stock.

Ironically, in almost every case, the owner (who was often the installer) "could feel the added power." But 1/4 mile and/or dyno tests proved the opposite.

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EstuaryBoy said:

'Classic Bike' magazine put two readers bikes on the dyno in their October 2009 issue, both allegedly: 'Stock' bikes, though their Mk3 had no balance pipe and peashooters.....
850 showed: 39.7 bhp @ 5700rpm.. 41.5lb/ft torque @ 4450rpm
750 showed: 47.5 bhp @ 6175rpm.. 43.6lb/ft torque @ 5300rpm

Both bikes reached 110mph top speed, though the 750 got there a good deal sooner than the 850...

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So an 850 Commando has as much power as a very good 350cc BSA Gold Star DBD32 or a 7R AJS ? ?
I often wondered why 500 cc Manx Nortons were so quick with only 50 BHP.. In Australia in the 1950s, the only bike which could beat them was a 100 BHP Norvin on a big circuit.