Bigger Valves for the RH 10 Head?

@Dan1950 : Remind me again what ignition system you are running?

And do you have a specific performance target in mind?

I run into this at work all the time - customers are always asking for more power, which I can deliver, but they won't necessarily tell you exactly what kind of power they need. We have started using drive-cycle simulation to benchmark performance gains. High end for this kind of stuff, but similar to Glen's Dyno Hill experiments, only done virtually. Far more informative than peak power and torque numbers, and takes into consideration driveline gearing as well as parasitic loads.

Which brings up another point - you may want to consider dropping a tooth on the transmission sprocket (21 to a 20) - bike will still be capable of over 100 mph... just a thought. Performance gains without breaking the bank...

FWIW
 
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Since this is the second post in which you've mentioned needing more power from 6000RPM up, I think you might be expecting too much from an old Norton in stock trim. Either that or your cam is a little flat, or your carburetor tune or timing may not optimal WOT.

Speaking of cams, Andover sent out an email recently with a few of their NV cam choices in it. You probably got it if you have purchased parts from them. Unfortunately, they have nothing in the way of descriptions of the parts they sell. James Comstock likes and sells Webcam. Jim Schmidt sells his soft ramp cams. Schmidt does provide descriptions of what he is trying to accomplish with the cams he sells. I've never done business with James Comstock other than a couple of PMs here. I've done business with Jim Schmidt. I'm not recommending anything, but I know what works well in my street 750.

My head is ported, but it was done in Europe before Mr. Comstock had much of a reputation with Norton heads. I'm not sure he was doing it at the time, or Phil Radford would have mentioned him. Well, unless they did not get along. The port work did make a difference with stock valve sizes, but I also installed a 2S cam when it was done. I liked that cam. What I have now is a soft ramp PW3 (JS2SS). I'm still using the stock valve sizes. The JS2SS is a better all around cam. Motor is awake from idle to WOT and produces plenty of usable street torque. I don't care enough about my "package" (yes, I said that) to get a dyno read out, but my little 750 runs well enough to make me smile. The same package in an 850 Norton would make most motorcyclists smile. I could list the parts, but the list is similar to what FF did in his 850, but my cam is bigger and the lifters are BSA.

I think doing the head work is nice, but it would be nicer if you get a hotter cam to go with it if looking for the elusive pull of a freight train. Some tuning may or may not be required to get you where you want to be.
 
Schwany said:
Since this is the second post in which you've mentioned needing more power from 6000RPM up, I think you might be expecting too much from an old Norton in stock trim. Either that or your cam is a little flat, or your carburetor tune or timing may not optimal WOT.

Speaking of cams, Andover sent out an email recently with a few of their NV cam choices in it. You probably got it if you have purchased parts from them. Unfortunately, they have nothing in the way of descriptions of the parts they sell. James Comstock likes and sells Webcam. Jim Schmidt sells his soft ramp cams. Schmidt does provide descriptions of what he is trying to accomplish with the cams he sells. I've never done business with James Comstock other than a couple of PMs here. I've done business with Jim Schmidt. I'm not recommending anything, but I know what works well in my street 750.

My head is ported, but it was done in Europe before Mr. Comstock had much of a reputation with Norton heads. I'm not sure he was doing it at the time, or Phil Radford would have mentioned him. Well, unless they did not get along. The port work did make a difference with stock valve sizes, but I also installed a 2S cam when it was done. I liked that cam. What I have now is a soft ramp PW3 (JS2SS). I'm still using the stock valve sizes. The JS2SS is a better all around cam. Motor is awake from idle to WOT and produces plenty of usable street torque. I don't care enough about my "package" (yes, I said that) to get a dyno read out, but my little 750 runs well enough to make me smile. The same package in an 850 Norton would make most motorcyclists smile. I could list the parts, but the list is similar to what FF did in his 850, but my cam is bigger and the lifters are BSA.

I think doing the head work is nice, but it would be nicer if you get a hotter cam to go with it if looking for the elusive pull of a freight train. Some tuning may or may not be required to get you where you want to be.
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Yes, your cam is hotter than mine. The package of work you have done should indeed make for a great hot rod motor!
I ‘only’ have the JS#1. Like you, I also have the JS rods and pistons, mine is 10.5:1. And the Comnoz head work plus FCRs. The 850 motor in this spec is SO good, torquey, revvy, smooth and super responsive.
In fact I currently have it disassembled on the bench and am considering re fitting it… got another idea for the 920 motor.
 
lcrken said:
Well, it would be hard to argue with Steve A's post. But, getting back to the original question, you can normally fit larger intake valves, out to the limit of the seat insert, without any guide mods, but you do have to check for valve-to-valve interference for anything other than the stock cam. The valve can go at least .060" larger on the stock seat, and maybe slightly more. My memory says I used 1/16" larger intakes back in the day. That's what Axtell used on his 750 race ported heads back in the '70s and '80s. Worked ok with his cams, but might have valve-to-valve interference with some of the high lift, wide overlap cams. Kibblewhite sells a .060" oversize Commando valve that I've used to convert heads a couple of times with no problems. But if you want the full benefit of the larger valve, you need some port work to blend the new seat into the port and combustion chamber. That used to take a lot of hand work with a porting tool. It's a little better now with contoured carbide cutters and such, but it still takes some hand work to finish. Still, you'd probably pick up some performance improvement from just the larger valves and a decent multi-angle valve job.

Ken
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Jim Comstock suggesting that with 0.060" or 1.5mm oversize inlet, and a high lift cam, without re angling the valves you should expect clash, but you can avoid it if you fit an undersized exhaust valve.

Way back in the day, John Hudson, Mr Norton, felt that rather than fit oversized valves it was best to maximize the flow around them!

FE's comment about the valve sizes really being too small for an 850 is born out by evidence, on race bikes at the top end.

I am also inclined to agree that 6000 up isn't what you should be looking for on a Commando road bike!!

My standard Fullauto head is on a full race 750 Short Stroke motor that has revved between 7500 and 8000, I really cannot imagine using over 6500 through the box in any road situation!

(mind you I live in the country where most roads I use have bends)

I would be looking to improve what it does between 4000 and 6000, and I don't think upping valve sizes and wild cams will do what is needed. More cubes might.

But as noted elsewhere, I am feeling my age at the moment!
 
According to Comnoz, bigger valves will increase power and torque throughout the rev range, with no down side.

A bigger cam however generally gives more high rpm power at the expense of some low end power.

But… it’s ALL relative. It’s quite probable that a well packaged motor, even with a (mildly) higher lift cam that produces less low end torque ‘alone’, will produce more power everywhere compared to a 50 year old factory production engine.

And as others have said, the stock motor doesn’t produce ANY extra power over 6 and a bit thousand. My 850 with all the work done to it still produces peak power at 6,300 (and stayed almost flat through to 7,000).
Not everyone wants their Norton to ride like a Harley though! There’s a definite fun to be had keeping a nice sporty engine ‘on the cam’. And that engine will still run perfectly well at low speeds when wanted. That why I like my motor so much.

Then again, some peoples idea of fun is riding around at 50mph and wanting max pull in top gear.

So, before any tuning work is done, the desired outcome needs to be clarified, and the whole suite of engine work seen as a ‘package’.

As a well rounded motor designed to suit the 95 percentile without exploding every weekend, I’d say Norton nailed it. So there’s no point in doing anything different to that unless you want something different to that.

IMHO at least.
 
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Fast Eddie said:
Yes, your cam is hotter than mine. The package of work you have done should indeed make for a great hot rod motor!
I ‘only’ have the JS#1. Like you, I also have the JS rods and pistons, mine is 10.5:1. And the Comnoz head work plus FCRs. The 850 motor in this spec is SO good, torquey, revvy, smooth and super responsive.
In fact I currently have it disassembled on the bench and am considering re fitting it… got another idea for the 920 motor.
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I can only imagine what tricks you have in store. :cool:

Only meant the cam was not the same. Not measuring swords. he he

Power delivery is surprisingly linear, and not all up top. The Commando stage 2 (JS2SS is what is stamped on the cam) PW3 profile feels like it makes more usable mid-range and a touch more top end HP than the 2S did. Small numbers with a Norton, but more is always more fun even on the street when you want to pass somebody. It may work that way in my motor, because the port work is mild, it has the stock valves, and the inlet ports are only 31mm. In addition, I did lower the compression with a thicker .025 copper base gasket and a .040 copper head gasket. I believe it would have a different power delivery with your higher compression and Comstock head. Might be more of a hot rod. Obviously, I'm just babbling and guessing how it would work on your 850.
 
SteveA said:
Jim Comstock suggesting that with 0.060" or 1.5mm oversize inlet, and a high lift cam, without re angling the valves you should expect clash, but you can avoid it if you fit an undersized exhaust valve.

Way back in the day, John Hudson, Mr Norton, felt that rather than fit oversized valves it was best to maximize the flow around them!

FE's comment about the valve sizes really being too small for an 850 is born out by evidence, on race bikes at the top end.

I am also inclined to agree that 6000 up isn't what you should be looking for on a Commando road bike!!

My standard Fullauto head is on a full race 750 Short Stroke motor that has revved between 7500 and 8000, I really cannot imagine using over 6500 through the box in any road situation!

(mind you I live in the country where most roads I use have bends)

I would be looking to improve what it does between 4000 and 6000, and I don't think upping valve sizes and wild cams will do what is needed. More cubes might.

But as noted elsewhere, I am feeling my age at the moment!
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I've got this 920 with stock cam and 10 to 1cr, much weight removed from the bike. It outdoes my 161bhp Sportbike for top gear roll on.

One day I might sneak slightly larger intake valves in. That should give a bit stronger top without hurting the mid.
Definitely not needed though.
According to Jim's dyno, of all the various cam profiles for the Norton twin, the stock cam gives the greatest power in the 4 to 5k range, even with fancy headwork and big valves.

Glen

The 650 valves are 1.41. 750 and 850 1.5. The 850 valves should be about 1.6" to be on par with the 750.
 
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colin davie said:
Fast Eddie said:
As I understand it, that’s coz the valves (unchanged from the 650 I believe) aren’t really big enough in an 850 to allow it to properly benefit from other flow work.
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mind you as he said the 750 reacts better to tuning than a 850, It did take me almost 20 months of persuasion to have him take it on though but its great .
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That is exactly why I want to increase the intake valve diameter.
 
Derek Wilson said:
@Dan1950 : Remind me again what ignition system you are running?

And do you have a specific performance target in mind?

I run into this at work all the time - customers are always asking for more power, which I can deliver, but they won't necessarily tell you exactly what kind of power they need. We have started using drive-cycle simulation to benchmark performance gains. High end for this kind of stuff, but similar to Glen's Dyno Hill experiments, only done virtually. Far more informative than peak power and torque numbers, and takes into consideration driveline gearing as well as parasitic loads.

Which brings up another point - you may want to consider dropping a tooth on the transmission sprocket (21 to a 20) - bike will still be capable of over 100 mph... just a thought. Performance gains without breaking the bank...

FWIW
Click to expand...
I'm running Tri Spark ignition.

I want to increase midrange torque and raise the power curve from 3000-7000 RPM.

A mild static CR boost and appropriate cam grind will also be employed.
 
Schwany said:
I can only imagine what tricks you have in store. :cool:

Only meant the cam was not the same. Not measuring swords. he he

Power delivery is surprisingly linear, and not all up top. The Commando stage 2 (JS2SS is what is stamped on the cam) PW3 profile feels like it makes more usable mid-range and a touch more top end HP than the 2S did. Small numbers with a Norton, but more is always more fun even on the street when you want to pass somebody. It may work that way in my motor, because the port work is mild, it has the stock valves, and the inlet ports are only 31mm. In addition, I did lower the compression with a thicker .025 copper base gasket and a .040 copper head gasket. I believe it would have a different power delivery with your higher compression and Comstock head. Might be more of a hot rod. Obviously, I'm just babbling and guessing how it would work on your 850.
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If you had a 5 speed gearbox with a low first gear and the other 4 gears close and high, you might pass other people much faster. A well tuned unmodified 850 motor is probably fast enough for most people. But with a 4 speed wide ratio gearbox, you cannot do much with it. If you fit a hotter cam, you can end up with a surge of power at the revs where the cam starts to work. It might help you leap into the back of a car.

With my motor, I believe Norton knew what they were doing with ports and valves, all I have done is fit bigger carbs and blended in the first part of the ports. My cam is modified, but i have no idea what it is. One day I might clock it. When I had it ground, the guy who did it worked for Eddie Thomas' Speed Shop and had ground bike cams for decades. I just asked him for his best Norton grind - it is almost nothing. I knew whatever it was, I could get it to work. The main thing with any cam is it must not be a valve dropper. The closing rate of the cam is important - too quick is bad. Every cam is different and where you position it, is important - depends on the exhaust system, I like bikes which do not have a big bump in their power delivery.
 
Dan1950 said:
I'm running Tri Spark ignition.

I want to increase midrange torque and raise the power curve from 3000-7000 RPM.

A mild static CR boost and appropriate cam grind will also be employed.
Click to expand...
That’s a typo right?

You meant 3,000-6,000 right?
 
Fast Eddie said:
That’s a typo right?

You meant 3,000-6,000 right?
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Nope. If I could ring out 5,500 RPM on a 4.520 inch stroke, in a Panhead hog, I see no reason why I can't get 7000 out of a 3.5 inch stroke.

That is if I can get the top end to breathe. The Panhead had oversized intake valves and Port work behind a 1 7/8" manifold.
 
Fast Eddie said:
According to Comnoz, bigger valves will increase power and torque throughout the rev range, with no down side.

A bigger cam however generally gives more high rpm power at the expense of some low end power.

IMHO at least.
Click to expand...
The same can be said for higher compression. Power across the whole RPM range as long as detonation doesn't become an issue. The right cam grind can reduce cylinder pressure at lower RPMs to alleviate detonation. The higher static compression ratio coupled with larger valves will help broaden the usable power band with the higher revving cam.
 
Dan1950 said:
Nope. If I could ring out 5,500 RPM on a 4.520 inch stroke, in a Panhead hog, I see no reason why I can't get 7000 out of a 3.5 inch stroke.

That is if I can get the top end to breathe. The Panhead had oversized intake valves and Port work behind a 1 7/8" manifold.
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You will get 7000 rpm
But you'll be lucky to find more power there
 
Dan1950 said:
Trixie needs to be woken up, nothing drastic, just a combination that will give me more midrange and top end power. An 850 Combat so to speak.

10:1 static CR with a cam grind that will yield a dynamic CR similar to the stock 850 Commando.

Static Vs Dynamic Compression Ratio | Piston Ratio

Static vs Dynamic compression ratio and how Camshaft duration and lift effects overall engine motor compression in the combustion cycle and tuning
www.enginebasics.com

Slightly larger intake valves with some bowl and seat work.

I just want to wake it up in the 6000-7000 RPM range while still having a user friendly motorcycle.

What sort of pitfalls as far as IN/EX valve head interference do I need to watch for with various cam grinds.

I do not want to alter the valve guide angle in the head so please refrain from going down that route.

I've been down this road before with Panhead Hogs and SB Chevy V-8s. Both were running 10.5:1 static CR but utilized cam grinds to reduce low RPM cylinder pressure with great results. Both engines ran well on unleaded 91 octane fuel and were well mannered for daily use. Docile under 3000 RPM but came on like a freight train above that.
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This is a good read with A/B graphs comparing many cams.

Cams (2012)

Here is some of the more popular cam graphs I have compiled. First is the PW3 vs Js2 , they are nearly the same. The pw3 has a little more lift and the js2 has a little more overlap. I would expect similar performance. Next is the Norris D+ vs the Megacycle 560N480 Here is the Megacycle...
www.accessnorton.com www.accessnorton.com

I mated the 312a with 9.5:1 pistons, radiused lifters and the head work I linked earlier.


comnoz said:
I like to use the 312a with a radius ground stock follower for the street. That moves the turnover point down to about 4000 and is easy on the valvetrain. [it's what is in my bike]

Like any cam change, the power gain is going to depend on how well matched the exhaust, compression and porting is to the cam.

And like any other performance cam change -if it's just dropped into a stock engine, your going to loose a couple horses down low and gain a couple up higher.
Click to expand...

The 312a is a fairly hot grind for the street when used with flat lifters. It's turnover point [where it starts making more power than stock] is about 4500 rpm.
 
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You would probably get more acceleration from a Commando by changing nothing other than the taper on the carb needles. When you go to pass another vehicle, you wind the throttle on. That raises the needles - a quick taper delivers more fuel to compensate for the loss of vacuum which is caused by the inertia of the heavy crank. But even a slightly rich mixture will make the motor sluggish. If the taper on the needles is slower, you need to wind the throttle on slower, but the bike will accelerate faster. If you are ham-fisted, you might get a gasp and the bike will slow.
The needles in a Commando carbs were probably selected to suit inexperienced riders
The Japanese know about this stuff. In the 1970s, every one of their new models had different tapered needles.
A Commando with fuel injection would be much faster - but what would it be ?
 
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acotrel said:
You would probably get more acceleration from a Commando by changing nothing other than the taper on the carb needles. When you go to pass another vehicle, you wind the throttle on. That raises the needles - a quick taper delivers more fuel to compensate for the loss of vacuum which is caused by the inertia of the heavy crank. But even a slightly rich mixture will make the motor sluggish. If the taper on the needles is slower, you need to wind the throttle on slower, but the bike will accelerate faster. If you are ham-fisted, you might get a gasp and the bike will slow.
The needles in a Commando carbs were probably selected to suit inexperienced riders
The Japanese know about this stuff. In the 1970s, every one of their new models had different tapered needles/
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My bike does great when I roll the throttle on to pass a car. Problem is it runs out of steam as
baz said:
You will get 7000 rpm
But you'll be lucky to find more power there
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Well if I do get 7,000 RPM it will be more power because right now I can't get anywhere near it in 3rd or 4th gear.

Granted I know it's running rich but since I need to pull the head and most likely the cylinders anyway I'm not going to go halfway on this thing.

I've always been able to extract extraordinary power without sacrificing reliability or driveability. I have a knack for putting a package together.

Here is my 4300# 2006 Dodge Charger running 12 flat on the motor.



It got 26 MPG, 2 MPG better than stock and put 426 HP to the rear wheels.
 
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I love the heavy crank in the Commando. Once it is spinning high, nothing stops it. Race-changing up through a close ratio box with that crank is really great. You can play it like a piano.
 
acotrel said:
I love the heavy crank in the Commando. Once it is spinning high, nothing stops it. Race-changing up through a close ratio box with that crank is really great. You can play it like a piano.
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I loved the modified Flathead 80 flywheels I had in my Panhead.

Everyone told me I was building it wrong, that I needed light flywheels so I could get my revs up.

My reply was that I only had to get them up once.

I had a 2.60 Andrews low gear that would wind out to about 55 mph. When I shifted the second it would jump to 70 mph and then it was time to shift to the close ratio third. I could hit 4th in the 8th mile.
 
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