Big valves or small valves

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Jseng wrote " worntorn - a 1007cc Norton should give you what you want. All it takes is $"

Too much $!

I've been building a lightweight 920 for the job.
The RGM 920 kit was about $300. Add in some work and you get a displacement increase of 11%.
The 1007 will set you back another 25- $30,000 just for motor and required TTI trans. It will only add another 9% of engine displacement over the 920. That is expensive displacement!
Going with the 920 and removing 30% of the motorcycle weight seemed a better option.

Roadster/Interstate/Thruxton R tank (2020)

The latest task is an alloy fuel tank for the lightweight 920 Commando project. I purchased a Thruxton R fairing for the project as they are such a beautifully shaped item. The problem with that is they are not at all universal. Most fairings just kind of terminate mid space but the Thruxton...
www.accessnorton.com www.accessnorton.com
 
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Porting for performance is about achieving the best balance between velocity and CFM.

Depending on the desired use, that balance may skew one way or the other. The FA ports were designed by JC for ’streetable’ performance, hence they give such good velocity numbers, and velocity gives ‘below the curve’ performance as JC puts it. Whereas a Maney stage 3 is more skewed towards max flow for higher rpm power, for example.

In his head flow testing thread JC highlighted how the RH10 with his mild, but well thought out porting, and mild valve size increase, yielded big gains in velocity and gains in flow which would translate into increased mid and top end power. Fitting this to the bike and testing it on the dyno absolutely confirmed this with a lot more power available from 3,000 upwards.

I discussed head choices extensively with JC at the time (top marks for patience Jim) and the summary was that a FA head gives increased performance, a ported RH10 with a milder big valve job gives more, and a ported big valve FA would give more still.

The before and after flow and velocity graphs for my RH10 are on p28 of the head flow test thread here:

Head flow testing.

The RH7 head starts with the same casting as the standard 850, but has the intake guide at a steeper angle (26.5 instead of 28 degrees off vertical) and has a fully sphered combustion chamber with no squish band. ... Ken The fully sphered RH7 combustion chamber could use fully domed piston...
www.accessnorton.com www.accessnorton.com

“Big valve” does not have to mean sticking randomly chosen dinner plate Gold Star valves in there. As I said before, I prefer the term “correct valves”. In my opinion, if Doug Hele was starting with a blank sheet of paper designing a 920 Norton based twin, he would design ports and valves for it that would be different to what he did for the 750.
 
@worntorn

In easy short words:
Use the cam with the highest possible lift and reasonably low overlap and reasonably short duration with let's say MX or Enduro characteristics.

Have a defined venturi/throttle area shortly before the valve guide.

In case shape the SSR to look like a D laying flat to lower gas velocity on the SSR and lower tendency of turbulences, which throttle the flow as well as lower the coeff/disch.
And having corresponding dynamic compr..ratio as well also helps a lot to compensate for lost static compression caused by later intake closing.

Kind regards

Christian

@Fast Eddie

Sorry just read your comment now.
Perfect just about how I as well see things.
 
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@worntorn

Hey just came to my mind right now (i have somewhat delayed circuits up there haha),
how about contacting the guy (forgot unfortunately his name) that competes in LSR from Vancouver?
I mean triumph or Norton, but the underlying physical principles are the same, and to compete "successfully" one has to comprehend all of it.

Kind regards
Christian

Ps: in case needed i could try to organize his email address or phone number through colleagues of work.
 
If it's Tom Mellor, I see him now and then. His expertise is at getting very high speed from highly modified Triumph triples.

I'm going to start with the stock RH10 on the 920.
I suspect it will work well up to an rpm where the valves and ports will start to be a limitation. That might be around 5500 rpm.
The stock cam makes max torque at 5000rpm, max bhp at 5800.

If you are doing a conventional hop up with big cam then the max torque rpm moves up the scale quite a bit.
At that point, with a 920, the stock valves would really hinder things.
For a lower rpm setup with the stock cam, the stock valves should not hinder output. That's the info I've been given and it seems to jive with the online valve size calculators.
One of the calculators showed that the stock valves are correct for a 5500 rpm 920, the other came out at 5700.
Too be efficient above those rpms, larger intake valves are needed.
The stock cam is made to work at or below those rpms +-

Glen
 
Fuel injection BMW R1250GS

Not too many motorcycles will pull hard in top gear from 4000 RPM climbing at a 10K altitude unless geared so they didn't go over 60 mph at 8K RPM in top gear.

Anywho, downshifting would be cheaper. ;)
 
You would be surprised.
A standard Vincent 1000 works quite well for this even 2 up. It doesn't use 4000 rpm either, more like 3200 in top at 70 mph.
The 850 Commando with 20 tooth has good power on those climbs too. I would always like more, of course!
There is a big difference between the 850 and 750 for this usage. It doesn't show up when hooliganing around on the flatland. The 750 is probably more fun there.



Downshifting works great for the small hills you find in the UK and many other places.
The BC Salmo Creston climb is 30 miles long and steep. There are several climb/descents within it so strong non-fading brakes are needed too.
Those with any degree of mechanical sympathy will not enjoy perpetually requiring 3rd gear on those long climbs.

Glen
 
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Glen,
I am surprised. I didn't know a Vincent had that much grunt at 10K feet. I would think a flat land tune would go to hell at that altitude. Maybe I just don't know how to tune. That would not surprise me much.

I'm down to nothing in the garage but the 750 Norton. I know it won't do what you are talking about. I think it needs to be wound up a lot tighter and the turn radiuses ahead bigger to stay in 4th. My motor is good for 80 in 3rd, but it sounds like an F1 car (no tach), and I don't know how long I could ride it like that before some of that mechanical sympathy kicked in.

I've gone over a few passes on motorcycles built in the 1990's. Unfortunately, I don't think I paid that much attention to the tach, and I probably wasn't in top gear unless most of the turns ahead were sweepers.

Sort of on topic, but more of a personal problem. Modifying the head for big valves on a street bike seems like throwing money away. Even if I were 40 years old again, I don't think I'd do it. Everything else Jim does BSA followers, KW BD valves, improved springs, different cam profiles and so on with the valve train makes sense to me. I'm not sure about the valve train geometry being ideal the way Norton did it, but the stock size valves seem to work alright on the street. Racing is a whole nether kettle of fish. There big valves make some sense. Do I sound like captain obvious? Probably so.
 
Is there room for bigger valves in the Norton head? Yes there is. There is room on the 750 because they offset the combustion chamber compared to the 650. There is even more room on the 850 on up. You can increase the valve size until you get cylinder wall shrouding.

Regarding ports - my 750 has slightly raised Axtell style ports as laid out in the race manual. Even with a stock cam there is a significant performance improvement. Its still has a good usable power band for the street - you can putt around at lower RPM but when you want to rock it comes on hard at 4000 RPM.
 
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jseng1 said:
Is there room for bigger valves in the Norton head? Yes there is. There is room on the 750 because they offset the combustion chamber compared to the 650. There is even more room on the 850 on up. You can increase the valve size until you get cylinder wall shrouding.

Regarding ports - my 750 has slightly raised Axtell style ports as laid out in the race manual. Even with a stock cam there is a significant performance improvement. Its still has a good usable power band for the street - you can putt around at lower RPM but when you want to rock it comes on hard at 4000 RPM.
Click to expand...
Man I have misunderstood this entire discussion. I thought the head had to be reworked (valve guide angle, seats and so on) to get bigger valves in it. All that welding talk through me for a loop. ;)
 
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What I meant is that there is more room in the combustion chamber and bore size for larger valves. Yes it does need reangled guides and larger seats for bigger intake valves. Without re-angling the valves can clash - especially with hotter cams.
 
@worntorn
I'm just going through my notes from work back then, i remember he worked at the port of Vancouver and was in a team with his bro' and sine other dude.
Worked all day long today on my, brrrr (attention i say Jehova) XS650/880 so im kinda worn, but will try to get back to your question regarding cams within the next 2-3days, ok?

@Schwany
If one takes care to not change kinematics (angularity etc) it's no issue to change valve angle by 1-2degrees.
It's a lot heftier to put in a high lift short duration cam, but oh well, as we say in Austria, some way if death one has to day eventually.

Kind regards and happy Sunday folks

Christian
 
Schwany said:
Glen,
I am surprised. I didn't know a Vincent had that much grunt at 10K feet. I would think a flat land tune would go to hell at that altitude. Maybe I just don't know how to tune. That would not surprise me much.

I'm down to nothing in the garage but the 750 Norton. I know it won't do what you are talking about. I think it needs to be wound up a lot tighter and the turn radiuses ahead bigger to stay in 4th. My motor is good for 80 in 3rd, but it sounds like an F1 car (no tach), and I don't know how long I could ride it like that before some of that mechanical sympathy kicked in.

I've gone over a few passes on motorcycles built in the 1990's. Unfortunately, I don't think I paid that much attention to the tach, and I probably wasn't in top gear unless most of the turns ahead were sweepers.

Sort of on topic, but more of a personal problem. Modifying the head for big valves on a street bike seems like throwing money away. Even if I were 40 years old again, I don't think I'd do it. Everything else Jim does BSA followers, KW BD valves, improved springs, different cam profiles and so on with the valve train makes sense to me. I'm not sure about the valve train geometry being ideal the way Norton did it, but the stock size valves seem to work alright on the street. Racing is a whole nether kettle of fish. There big valves make some sense. Do I sound like captain obvious? Probably so.
Click to expand...
Agreed, the big valve makes sense on a racing motor that already has the other Norton twin limitations removed.
Some of those are-
Crankshaft strength and rpm limit
Conrod strength
Crankcase strength and rpm limit
Gearbox strength

To prepare the Commando for racing, locate the Engine and gearbox.
Remove those and store them for safekeeping.

Find suitable aftermarket high strength $custom engine parts and construct engine. Do use larger valves!

Glen
 
When I buy my FA head, I am definitely going to fit bigger valves. If the cause does not give the desired effect I am going to complain. In your posts, you guys use the word 'would' a lot of times. My 850 is fast enough, it just has to be used a bit differently from other bikes. Methanol fuel just helps me get the jetting right. Motorcycle road racing is an exercise in pattern recognition. You need to be able to rationalise the variables.
If you want a faster motor, move the power band up the rev range, then adjust the rest of the bike to suit it. A lighter crank might give better throttle response, but while you are at it, why not add a couple more cylinders with four-valve heads ?
What is 'the law of diminishing returns' ? - Of course 'every little bit counts', so learn to ride faster. I avoid racing on big race circuits, because they are usually 'power circuits'.
 
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Schwany said:
Man I have misunderstood this entire discussion. I thought the head had to be reworked (valve guide angle, seats and so on) to get bigger valves in it. All that welding talk through me for a loop. ;)
Click to expand...

The more extreme mods do require re-angling, welding, machining, etc. But the Commando head will accept up to .060" larger intakes without any mods to the head except cutting or grinding the valve seats to suit, typically a three angle cut and some hand blending. You do have to be careful about valve-to-valve clearance to avoid contact. Depending on cam used you might have to sink the valve seats a little deeper to avoid valve clash. That issue has been pretty well documented here by Jim Schmidt:

Setting up valve clash clearance with race cams and big valves

I’ve been going through a lot of cams lately and came up with some notes for helping engine builders set up their valve arrangements per cam lift/duration. Most stock heads have about .185" between the valves when they are on the seats. Race cams have more lift and so the valves come into...
www.accessnorton.com www.accessnorton.com

I ran a couple of 750 race heads that were fitted with .042" larger intake valves and .018" larger exhausts, and one with .060" larger intakes and stock exhausts, and had no valve interference problems. The race cams I was using did have less overlap than most of the other Norton race cams at that time.

Ken
 
jseng1 said:
Time Warp - the FA head may match at the manifolds (for marketability) but it narrows top to bottom to about 25mm height deeper in the intake port. Unfortunately the FA port floor level doesn't match the manifold floor level - its way off. Compare floor of stock port floor (green line) to angle of FA floor. See image.
Click to expand...

Thanks for the reply and port comparison overlays which I was not aware of at purchase.
 
Klaus Monning said:
Hello All.
Here is what I found with converting Norton cylinder heads:
750- heads with 1/2" outer guide diameter:
For re- angling you have to bore the guide bore with the new angle which opens the bore to about 14,5 or 15mm. I always use standard 850 bronce guides and turn them down (between centres) to the suitable diameter. So you never are in need of special guides, you can always use 850guides and turn them down. The bigger intake valve would be 41mm. The exhaust is left with 33mm, because you simply don't get bigger valves into the bore.
750- heads converted for use in 850 (or bigger) engines:
Both valves have to be re- angled depending on size with different angles. This is also quite an easy job. Additionally you have to re- position the outer 4 bolt bores to suit the 850 hole pattern. This is what Steve Maney did .
850- heads converted to for bigger valves.
This is a very complex job. I cut a thread (M16x1, M17x1 or M18x1) and turn suitable flanged bushes with a suitable outer thread with a 8mm Bore. This hole is used for matching the valve shaft with the adjustment screws. The plug is inserted into the threaded guide- bore and locked with a high temperature valve locker (similar to loctite, but it withstands temperatures up to 1100°C. It's some American stuff.
It's very easy to do a big valve conversion for standard sized 750 valve guides. I have done quite a few big valve conversions now. Here is one I did for Yves van Heers from Belgium.

Big valves conversion made in Germany

Hi there, Here be the big valves conversion made by Klaus Moning from Germany, Klaus is specialised in conversion from british cylinder heads, He changes my Fullauto head to plus 3mm valves on inlet and exhaust, I am very happy with is work. If you wish to contact him, feel free to PM me Yves...
www.accessnorton.com www.accessnorton.com
It was a Fullauto- head, which had the big advantage to have 1/2" guides as standard. I thinks Yves turned out to be 15mm outer diameter.
Certainly it would be a big advantage to have floor- raised intake- ports. In this case you certainly also have to raise the roof of tha port. But this makes things difficult, you have to weld. There is a guy near me who does laser- welding. But I guess, it will be rather expensive.
Best Regards
Klaus
Click to expand...
Please show photos of the threaded valve guide collars etc. And what is the name of the " high temperature valve locker (similar to loctite, but it withstands temperatures up to 1100°C."
 
Fast Eddie said:
Porting for performance is about achieving the best balance between velocity and CFM.

Depending on the desired use, that balance may skew one way or the other. The FA ports were designed by JC for ’streetable’ performance, hence they give such good velocity numbers, and velocity gives ‘below the curve’ performance as JC puts it. Whereas a Maney stage 3 is more skewed towards max flow for higher rpm power, for example.

In his head flow testing thread JC highlighted how the RH10 with his mild, but well thought out porting, and mild valve size increase, yielded big gains in velocity and gains in flow which would translate into increased mid and top end power. Fitting this to the bike and testing it on the dyno absolutely confirmed this with a lot more power available from 3,000 upwards.

I discussed head choices extensively with JC at the time (top marks for patience Jim) and the summary was that a FA head gives increased performance, a ported RH10 with a milder big valve job gives more, and a ported big valve FA would give more still.

The before and after flow and velocity graphs for my RH10 are on p28 of the head flow test thread here:

Head flow testing.

The RH7 head starts with the same casting as the standard 850, but has the intake guide at a steeper angle (26.5 instead of 28 degrees off vertical) and has a fully sphered combustion chamber with no squish band. ... Ken The fully sphered RH7 combustion chamber could use fully domed piston...
www.accessnorton.com www.accessnorton.com

“Big valve” does not have to mean sticking randomly chosen dinner plate Gold Star valves in there. As I said before, I prefer the term “correct valves”. In my opinion, if Doug Hele was starting with a blank sheet of paper designing a 920 Norton based twin, he would design ports and valves for it that would be different to what he did for the 750.
Click to expand...
'I discussed head choices extensively with JC at the time (top marks for patience Jim) and the summary was that a FA head gives increased performance, a ported RH10 with a milder big valve job gives more, and a ported big valve FA would give more still.'
- You used the word 'would', perhaps you meant to say 'might' ? - You do not know what you are going to get until you have done the deed. If you are wrong, you have probably stuffed the cylinder head.
 
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