pistons - the shape of things to come

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acotrel said:
I think that at 7000 RPM in a normal Commando engine, the piston speed is high enough to get ring flutter. But if you go short stroke, the bike might be more difficult to ride well. What I have noticed with my bike, is it is much easier to ride fast than anything else I have ever been on. - More horsepower is good, but with a race bike it is the whole package which counts. What amazes me is that PW beat the two-strokes with a Commando - the difference in horsepower is enormous. You are talking about 80 BHP max. for the Commando and over 100 BHP for the two-strokes. The rider does not do much other than turn the handle.
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So do tell me where did PW beat the two strokes in the 1970s this is news to me!!!
 
Chris,
I've got that whole package concept in my noggin already, and couldn't agree more. Plus 1 on advice as well. I generally don't take advice from the internet on any subject. Experts made daily.

I don't really know what technique Barlow actually used on the head I have. All the receipt says is remodel head. He did poke a 1/16th inch hole through the side of the left intake port about an inch into the port while opening up the entrance. I had to epoxy fill it. I cleaned up the exhaust side myself. Motor works great, but the cam isn't real big, so probably doesn't mean a lot. It suits the 2S cam, whatever percentage the crank was balanced to (not OEM balance), my home made intake lengths, the Mikuni carburetors, and my 2 into 1 exhaust configuration.

I think I'll add a balance tube to the intake manifolds today, and see what kind of trouble I can get into. I haven't had a balance tube on the ole road motor since taking the Amal carburetors off in '93.
 
The hole in the intake that Fred Barlow created while porting my head is about 2 inches in and on the right side of the left hand intake port. It's a little below the roof line. He definitely went up as much as he could with the roof and when working around in the valve guide area. I was going to take a pic while I had the intake manifolds off, but it just looks like a black booger in there.

The balance tube between the Mikuni carburetors worked great on my little putt putt. Didn't have to do a thing with the tune. Should have done it a long time ago.

Back on OP subject. Yeah those fantasy pistons look interesting.
 
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Bernhard said:
So do tell me where did PW beat the two strokes in the 1970s this is news to me!!!
Click to expand...
I think it was in an F750 race at Silverstone. Which to my mind is a power circuit. I don't keep records of this stuff, I only know what I have read in magazines. I remember being a bit amazed at the time when I read it. It is something I would not forget. I would have thought a 750 two-stroke would beat a 750 Commando on every circuit.
 
jseng1 said:
Auto desk image of weight efficient piston. Note the internal skirt struts. I'm not promoting this as a potential Norton piston option - just showing where things may be headed (never mind the missing oil ring).
pistons - the shape of things to come
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Look at these 3D printed porche pistons
autos.yahoo.com

Porsche's 3D Printed Pistons Could Add 30 HP to the 911 GT2 RS

The advantage to this new method is that the resulting pistons are lighter and have an integrated cooling system.
autos.yahoo.com autos.yahoo.com
 
Chris said:
Hi Schwany
Fred had a very good reputation as do most of the classic tuners. I know of nobody who hogs out the intakes or exhausts. However progress & development means new ideas come along. The most important thing with all tuning is that it's a package. Porting without a cam will make a difference with a good cam a difference, but all together! porting cam , carbs, exhaust shape & size. Then you find out how important crank balance is. I have 2 of Steve Maneys heads also a Mez head & a head from an ex Thruxton race shop racer/ engineer. Who raced production. He cleaned the ports up & sunk the inlet valves into the head because he believed the valve masked the flow. Kens Fullato head with Comnoz porting has more downdraft with extra material in the port. I think this is a big plus. All of them are beautifully done! On a road bike match what you do & buy for your engine, to how you want your bike to perform. Don't take advice from someone who runs on methanol.
Click to expand...

Schwany said:
Not being a wise guy, just asking. Have you ever ridden a Fred Barlow Spares (FBS) ported Norton with stock valve sizes and a race cam in it? Fred Barlow was pretty good at porting on the inlet side. I don't have what would be considered a race cam. I do have an FBS ported head and a 2S cam in a little 750, and it does not lack anywhere in the power band. I have no idea how that would translate to a 4S or larger cam and really tall gears. My gearing is higher than what my little bike came with, but not that high. I don't use Amal carburetion and use a lot of home garage shade tree engineered parts. My Norton is not what I would consider a fast bike by any stretch of the delusional imagination, and I'm pretty darn delusional. I think my Delta Box FZR 400 was quicker.

Anyhow, a member here named Chris has a Norton prepped for racing with a Fred Barlow ported head, a 4S cam in it, and a bunch of other nice parts. He would know more than I ever will about whether or not a FBS ported Norton head was a mistake on a race bike.
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This is very interesting to me. I bought a FBS ported head off an Irish roadracer I met at Spa several years ago. He had it lying under his bench for many years, and could not tell me anything about it (he's a Honda man actually!). I had Steve Maney convert it for use on my 850. Steve commented that the porting looked good to him. My impression is that it works very well with a 10.5:1 CR and a PW3 cam.
 
acotrel said:
I think it was in an F750 race at Silverstone. Which to my mind is a power circuit. I don't keep records of this stuff, I only know what I have read in magazines. I remember being a bit amazed at the time when I read it. It is something I would not forget. I would have thought a 750 two-stroke would beat a 750 Commando on every circuit.
Click to expand...

Would it have been the race he led until he ran out of fuel? he did say it was one of his best moments.
 
oldbeezer said:
Look at these 3D printed porche pistons
Click to expand...

Here's the 3d printed porche piston compared with the piston that started this thread. There are similarities.

pistons - the shape of things to come


pistons - the shape of things to come


The question now is can either design save weight compared to the simple design below.

pistons - the shape of things to come
 
SteveBorland said:
This is very interesting to me. I bought a FBS ported head off an Irish roadracer I met at Spa several years ago. He had it lying under his bench for many years, and could not tell me anything about it (he's a Honda man actually!). I had Steve Maney convert it for use on my 850. Steve commented that the porting looked good to him. My impression is that it works very well with a 10.5:1 CR and a PW3 cam.
Click to expand...

The FBS ported Atlas head on my little 750 works fine and is a big improvement over a stock later model Commando head when measured on fast rural winding roads with a butt dyno. The stock Commando head on the same motor was very pedestrian IMO. Doesn't mean a lot. One bike isn't much of a sampling, and butt dynos are notoriously inaccurate. That said, the FBS ported head is on my motor, and the Commando head is in a box on the shelf. It could also be that a later 750 Commando head doesn't work that well on a Atlas oriented engine. The intake ports in the stock Commando head are not shaped anything like the FBS ported Atlas head. The roof is much higher and wider on the FBS ported head. I have no idea what current wisdom is with regard to Norton port shaping, but my sample says Fred Barlow knew what he was doing.

I know how people like to correct anything they feel is inaccurate, misleading, or might change the course of human history forever via a forum message box. You can't put Commando rocker side oiler heads on an Atlas set of cylinders without changing the threads for larger diameter bolts near the spark plugs. That was done. Also had to open up the holes on the Atlas head near the plugs to put it back on the cylinders after changing the cylinders for the Commando head. If I'm wrong about that, I'm sure somebody will point it out.

Far enough off topic?

OK I'll STFU.
 
This is the way forward...a piston you can store very easily in your tool box :p


Or this one if your handy with a chisel, or like to whittle with your Swiss Army knife
 
storm42 said:
Would it have been the race he led until he ran out of fuel? he did say it was one of his best moments.
Click to expand...
It really says something to me. I would note even race my Seeley 850 on a big power circuit. It is all probably relative, but I firmly believe you cannot win a drag race with a Commando. The speeds PW would have been doing in the corners must have been horrendous.
 
Schwany said:
The FBS ported Atlas head on my little 750 works fine and is a big improvement over a stock later model Commando head when measured on fast rural winding roads with a butt dyno. The stock Commando head on the same motor was very pedestrian IMO. Doesn't mean a lot. One bike isn't much of a sampling, and butt dynos are notoriously inaccurate. That said, the FBS ported head is on my motor, and the Commando head is in a box on the shelf. It could also be that a later 750 Commando head doesn't work that well on a Atlas oriented engine. The intake ports in the stock Commando head are not shaped anything like the FBS ported Atlas head. The roof is much higher and wider on the FBS ported head. I have no idea what current wisdom is with regard to Norton port shaping, but my sample says Fred Barlow knew what he was doing.

I know how people like to correct anything they feel is inaccurate, misleading, or might change the course of human history forever via a forum message box. You can't put Commando rocker side oiler heads on an Atlas set of cylinders without changing the threads for larger diameter bolts near the spark plugs. That was done. Also had to open up the holes on the Atlas head near the plugs to put it back on the cylinders after changing the cylinders for the Commando head. If I'm wrong about that, I'm sure somebody will point it out.

Far enough off topic?

OK I'll STFU.
Click to expand...

It probably does not matter much what shape the ports are in a long stroke Commando engine, as long as they are not too big. Commando engines are usually about torque and smaller ports are better for that.
 
acotrel said:
I think it was in an F750 race at Silverstone. Which to my mind is a power circuit. I don't keep records of this stuff, I only know what I have read in magazines. I remember being a bit amazed at the time when I read it. It is something I would not forget. I would have thought a 750 two-stroke would beat a 750 Commando on every circuit.
Click to expand...
I think you are referring to the F750 race at the 1973 TT were Norton won for the first time in 12 years. He beat Jack Findlay on a Suzuki.
PW was also leading the production race on a Commando by 8 seconds until the last lap when he broke down.
 
TomU said:
I'm no piston engineer, but that looks pretty extreme. I'd think you'd need a certain minimum skirt length as a proportion to the piston diameter, to offset a propensity of the piston wanting to rotate along the wrist pin
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It's conservative re the skirt length actually, at least for competition.
We are running 2 ring pistons successfully to 15000+ rpm with skirts no lower than the center of the pin.
 
jseng1 said:
Ken
Another rod you can add to your list is the Ultralight JS rod with only 95 grams on the small end. Its stronger than a stock Norton rod and is rated for 75 hp by Carrillo with their safety margin for endurance racing type applications. Recommended for solid frame 750s etc.

If you could have a stock Norton alum rod that was longer you would have a good rod with a light small end.
Another way is to eliminate the small end bronze bush and use a DLC coated pin with a steel rod to lose weight without losing strength.
Click to expand...
No need for a bush or DLC. Far higher performance bike engines than Nortons run steel on steel.
I've never seen a bushed or DLC Honda rod.
DLC/bushes perhaps yes in very high vacuum car stuff.
 
I went to bushless rods because that's what the Nascar people were doing - they had to because their bronze bushes were deforming at 9000 RPM.
 
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