How many HP on my MK3

Actually from a technical perspective I find it rather interesting
lazyeye6 said:
What is the point of calculating potential HP? Bragging rights? If the point is to enhance performance for racing purposes, I get it.
But otherwise it seems an academic excercise in arm wrestling. Sorry if I have offended performance purists out there. Will crawl
back under my rock.
Click to expand...
,
 
SteveBorland said:
It actually gives a very realistic and relevant answer to that question. Its probably more realistic and honest than most humans :cool:
Click to expand...
For my bike, "Based on a modern Dynojet chassis dyno, this specific engine combination is projected to deliver 62 to 66 horsepower at the rear wheel. The peak output is driven by the synergy between Jim Comstock’s high-velocity head work, 9.5:1 compression, a Webcam 312a, and the scavenging effects of the Brooking850-Maney 2-into-1 exhaust. Reliable delivery of this power is secured by the stable fueling of the large-jetted Amal Premiers and the precise timing of the Tri-Spark ignition."
 
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Back when I was getting work done on my race Hayabusa engines I had to keep to the same dyno each time, as that was the only way to prove if something had worked or made it worse. Different days and different air temps could also make the numbers inconclusive. To say engine A made more or less power than engine B when they were both tested on a different make of dyno at different altitudes was ridiculous.
 
This is half the reason I never dyno'd my motor.

The other half is i never intended to race it, so i think I have gotten 95% out of it with generous use of fresh plugs/chopping at the outset and that's good enough for me to tootle around the countryside.
 
A riding mate has said he can't stick with my single carb, fat arse, mk3 850, when on his modern Royal Enfield 650 twin Interceptor. That has a claimed 47 BHP. So, maybe 40BHP on the road. So, mid to upper 40s for mine would be my guess. It feels quicker than my 4cyl CB750K6, which was 60BHP claimed, 50 years and 45,000 miles ago. 🙂
 
My very stock mk3 49hp at the rear wheel on Brett Roberts dyno in Paeroa NZ.
He’d said he’d done a 750 Laverda sf2 at 50 the prior day
 
I think 50 RWHP give or take a few HP is a reasonable estimate for a stock 850.

Norton 850 dyno.jpg
 
A word about "arse dynos"; in an earlier life I taught a course that included a story about listening to the customers. Years ago Ford pickup trucks were thought to accelerate more slowly than GM or Dodge/RAM. Researchers determined that by making the seats 'looser' or softer customers then felt that the Fords were significantly faster than the competition......
 
Back in the 60/70s 60HP was pretty good at the time, now we have sport bikes that come stock at 250+ HP on the roads and even building our old Norton's for performance the HP figures won't be much higher as revving them past 7500 RPMs you be pushing close to bottom end failure, with a big bang, but building a fast Norton there is more to it than just HP, making the bike lighter, better handling, rider skill etc all play a part for a faster Norton and rider skill is the best way to make any bike quicker, single cam, pushrods slows things down compared to over head muti cams.
You can throw a lot of money into our road going Norton's to perform better but the HP figures won't go up by much, well maybe a little, but for a old design 50+ year motors, its more about the torque of a well set up push rod twin and what I have done with my 850 when I built it back in the early 80s, I no need to know how much HP it produces, I built it for my likes and I don't need to prove anything and its build for my riding style and for the tight twisties up in the ranges, it shows up a lot of modern faster more HP bikes where I ride my Norton hard, but these modern times the fun police has taken a lot of fun from us, hidden speed cameras, cops hiding behind trees, cop cars and bikes with radar on them, lower speed limits in our favorite places, I miss the old days when we got away with the things we did on our old bikes.
If your bike is set up right, running great, tuned good who really care how much HP it produces, just enjoy it, I need to get back on my old Norton, but I have to prove to others that I can still ride with a peg leg, the B S I have to go through to get back on me bike.

Ashley
 
An old 750 Norton can be built to rev beyond 7500 RPM and not snap the bottom end. The same is true for an 850. Only thing building such an engine proves is the guy doing the build knows what he is doing and likes doing it.

Vidar, I like your build list. A higher lift cam and a stronger lighter aftermarket crank would help to make a fractional HP difference you could feel without a dyno, but might not be as user friendly on the street as your engine. Nortons are kind of limp on HP, but they are still head turners and fun to ride. Your engine is probably making somewhere in the high 50's low 60's HP wise at the rear wheel. Not sure it's worth finding out though. They do get thrashed on a dyno run based on what I have seen. I've thought about doing it, but I've never done it, cuz I don't trust the modern bike tuners that have dynos anywhere near me.

Good luck and I hope what you find out makes you happy if you do follow through.
 
A bog standard MK3 850 I suspect would be pushing its luck around mid 40's - there was a well known tuner in the UK who suggested a MK3 in standard trim would at best hit 40. I run a similar set up to the OP and mine pushes out 50, I also know another owner in the UK who tested his well built and expensively modified 850 engine with all the nice tuning parts and large valves etc and that was hitting 58 and that was on the same dyno with same settings. Realistically the 850 will benefit massively from larger valves and the other parts to accommodate them. The 850 capacity versus the valve size is at the very limit for the standard valves. What the OP has noticed is that the torque curve is most probably raising quicker at lower revs and remaining pretty flat through the rev range which makes for a comfortable and easy riding bike. Having max HP but only using it less than 5% of ride or not at all on public highway is pretty pointless, try and get the power and the torque to where you are going to use it, and if I had the one answer that suits all for road and race bikes I would be selling it. A dyno run is well worth it, you can see the curves and monitor the fuelling mixture and carburettor response when changing gear, if you are scared of wrecking it the tester will not thrash the balls off it.
 
Schwany

Yes, I am very satisfied with how the engine performs. How flexible and smooth it is. I’ve been thinking about the crankshaft — it’s a shame I didn’t replace it when I had the engine apart, so everything inside would have been new. But now it’s there, and it’s doing an excellent job.”
Vidar
 
I second what Ashley says about the numbers.

And also about the valve sizes. Some will recall that when I first ‘hot rodded’ my 850 with cam and carbs and high CR etc I left the head stock. In my second iteration I got Comnoz to port the RH10 head. At the time he was doing a LOT of head flow bench testing and had got it down to a fine art on Commando heads (there’s a LONG thread about it). He left the ports at 30mm but did a lot of detail work in and around the valve throat and fitted larger valves. With no other changes, and on the same dyno, this head work gave my motor an extra 9rwhp !!

THATS when a Dyno pays dividends, when you can confirm the results of work done.

@vidar hjelm johansen unless you dyno’d the bike before this work was done, or you intend to do future work, getting some dyno numbers won’t help you at all. However, if you want to ensure carbs and ign are optimally dialled in, it could be very worthwhile.
 

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