Kenny Dreer 880 pistons

I just got this photo of some Kenny Dreer 880 pistons. You can see the extra metal added to improve the air turbulance by redesigning and tighening up the squish band. Unfortunately this added weight to the pistons and increased vibration stress at high RPM. The pistons are 79mm which is about as big as you can go with stock cylinders. Years ago Kenny D contacted me about lighter pistons, but it was too late by then and he was moving on to the completely redesigned 961.

I'd be interested to see the combustion chamber in the head, with that kind of deck height on the piston. Sinking valves so they didn't clash and all that I imagine!

Interesting design!

Reduced shank studs too.

I have a set of these Dreer 79mm pistons under an RH10 head which was built by the same guy that Dreer used (Baisley Performance). The bike has Keihin FCR's and a Keith Johnson J360 cam. It all seems works together fine.

Gerald Jensen said:

I have a set of these Dreer 79mm pistons under an RH10 head which was built by the same guy that Dreer used (Baisley Performance). The bike has Keihin FCR's and a Keith Johnson J360 cam. It all seems works together fine.

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Nice, you running a lightened crank, stock or??

Very interesting dish in a dome moon crater design. Valves have got to be right at the minimum clearance everywhere because the reliefs don't look that deep in the pic. Of course, the head was probably unique as well, but I know absolutely nothing about the 880.

Those look like cNw 5/16" reduced shank studs up front.

I have sometimes wondered about raising comp. ratio to get more power. Comp ratio, ignition advance, fuel octane rating, and jetting all affect coombustion conditions. When the motor is running, those foyr factors are in balance. If you increase the ignition advance, it usually produces the same effect as leaning-off the jetting or raising the comp. ratio. I have noticed that when using methanol fuel, the jeting at 12 to 1 comp. ratio is substantially larger then when 10 to 1 comp. is used. If the extra fuel is all efficiently burned, then there should be more power developed. But that does not always seem to be the case. In the old days, when we went racing, we fitted high comp. pistons and used methanol. I do not think many racers ever tried using methanol at low compression.
One of Phil Irving's statements was 'if you run methanol rich, you still get good power'. That is true, but I have found - if you run methanol jetted correctly at low comp., you get results which are just as good, as running it rich at high comp.
Petrol as a fuel, behaves similarly to methanol. But because methanol jets are much bigger than petrol jets, the relative jetting errors are smaller. Methanol has 0.8 times the calorific value of petrol, but at 12 to 1 comp. , you use twice as much. So theorectically you should get more power. But what is a 'quench effect' ?

Schwany said:

Very interesting dish in a dome moon crater design. Valves have got to be right at the minimum clearance everywhere because the reliefs don't look that deep in the pic. Of course, the head was probably unique as well, but I know absolutely nothing about the 880.

Those look like cNw 5/16" reduced shank studs up front.

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When racing Triumphb 650s, we always used 12 to 1 Hepolite pistons with methanol. In one petrol motor, Iused two standard compression BSA Gold STar pistons, and machined the adges of rge crown to fit closely into the Trumph head - effectively making a squish band similar to the one in a Jawa Speedway motor. The pistons were lighter, and there was less obstruction to gas flow actross the crown of the piston, when both valves are open at TDC. Even with four stroke engines, there are Kadency Effects.
Kadency Effects are not only about scavenging. In my 850 motor, there are no steps in the exhaust ports or where the pipes fit, and I use skinny pipes, not fat ones.
At TDC, exhaust gas travels in two directions, some contains fuel mixture. The exhaust system resonates.

Schwany said:

Very interesting dish in a dome moon crater design. Valves have got to be right at the minimum clearance everywhere because the reliefs don't look that deep in the pic. Of course, the head was probably unique as well, but I know absolutely nothing about the 880.

Those look like cNw 5/16" reduced shank studs up front.

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Those pistons look as though their design was based on speculation rather than experience. Kenny Dreer probably never played wiith two-strokes.

Gerald Jensen said:

I have a set of these Dreer 79mm pistons under an RH10 head which was built by the same guy that Dreer used (Baisley Performance). The bike has Keihin FCR's and a Keith Johnson J360 cam. It all seems works together fine.

Click to expand...

I would imagine they do, it looks like a great design to me, they run a very functional squish / quench area and create some useful swirl etc.

There isn’t that much extra material on the crown (esp compared to the old / original 10.25:1 Omega’s etc) so provided the rest of the piston has been well designed (with weight in mind) they should be great.

acotrel said:

When racing Triumphb 650s, we always used 12 to 1 Hepolite pistons with methanol. In one petrol motor, Iused two standard compression BSA Gold STar pistons, and machined the adges of rge crown to fit closely into the Trumph head - effectively making a squish band similar to the one in a Jawa Speedway motor. The pistons were lighter, and there was less obstruction to gas flow actross the crown of the piston, when both valves are open at TDC. Even with four stroke engines, there are Kadency Effects.
Kadency Effects are not only about scavenging. In my 850 motor, there are no steps in the exhaust ports or where the pipes fit, and I use skinny pipes, not fat ones.
At TDC, exhaust gas travels in two directions, some contains fuel mixture. The exhaust system resonates.

Kadenacy effects?

It would be very easy to turn straight away to the practical workshop aspects of improving the performance of two stroke engines. Eventually, of course, we mus

bsabantamracing.editboard.com

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Sounds like fun doing the work on your Triumph 650.

The Kadency discussion and 2 stroke references got me nowhere. It left me unsure of what was being proven exactly. Does gas return to the combustion chamber or not in a 4 stroke. What happens with a 2 stroke seems a bit off topic. I did some fun things with single cylinder 2 strokes though. Fairly easy to improve on cast port work found in bikes right off the showroom floor.

I foolishly port matched my exhaust ports to my 1.5" exhaust headers on my 750. So if gas can return to the combustion chamber, it is returning with a vengeance, and would explain some things I won't talk about. Could just be user errors on my part.

On the subject of being off the topic: I had a little Triumph Tiger with 11:1 pistons in it. That bike was fun to ride. I screwed it up by putting lower compression pistons in it. It never ran as strong after I did that, and being young and impatient never could figure out how to stop the push rod tubes from leaking. Probably sold it for $450 or less in the 70's. That I can put on my regrets list.

Schwany said:

Sounds like fun doing the work on your Triumph 650.

The Kadency discussion and 2 stroke references got me nowhere. It left me unsure of what was being proven exactly. Does gas return to the combustion chamber or not in a 4 stroke. What happens with a 2 stroke seems a bit off topic. I did some fun things with single cylinder 2 strokes though. Fairly easy to improve on cast port work found in bikes right off the showroom floor.

I foolishly port matched my exhaust ports to my 1.5" exhaust headers on my 750. So if gas can return to the combustion chamber, it is returning with a vengeance, and would explain some things I won't talk about. Could just be user errors on my part.

On the subject of being off the topic: I had a little Triumph Tiger with 11:1 pistons in it. That bike was fun to ride. I screwed it up by putting lower compression pistons in it. It never ran as strong after I did that, and being young and impatient never could figure out how to stop the push rod tubes from leaking. Probably sold it for $450 or less in the 70's. That I can put on my regrets list.

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If you lower the compresiion ratio, you need to either lean-off the jetting or increase the ignition advance to get the same level of power you had prevuipusly. If you change the exhaust system, you need to tune the cam timing and jetting to suit it. More advance on a Commando cam gives better valve opening points, but the noise increases. The cam in my 850 is almost standard - it is advanced 12 degrees. But I use methanol fuel, so heat is not such a problem.

With expansion chambers on a two stroke. With the TR250 Suzuki chambers, there is a parallel part in the crentre, if it it 5mm fatter, you get more torque. Also for sidecar work, larger diameter stingers are better. The exhaust system resonates much more strongly than one on a four stroke. But an expansion chamber would also work on a four stroke. One of the reasons a Norton engine is better than a Triumph engine, is the high compression ratio without the high crown on the pistons. I once ran a Triumph 650 on methanol with 7 to 1 flat top pistons. It was fast enough to race, If you look at Triumph 12 to 1 comp pistons, after thery have been raced for a while, there is always coke on the sides of the crowns which are away from the spark plugs. Some guys have fitted 10mm spark plugs to fire in that area. But it becomes complicated. There is no way with a Commando engine, thet the extra plugs could be fitted and there would probably be no advantage anyway. The head and port design is superior. In a Triumph head, the inlet posts have less down angle. And the ones in a Bonneville head are not pointed towards the exhaust ports so for flow across the crown the gas has to turn. You might get better swirl that way, but if there is a Kadency effect, it woin't be as good.

Schwany said:

Sounds like fun doing the work on your Triumph 650.

The Kadency discussion and 2 stroke references got me nowhere. It left me unsure of what was being proven exactly. Does gas return to the combustion chamber or not in a 4 stroke. What happens with a 2 stroke seems a bit off topic. I did some fun things with single cylinder 2 strokes though. Fairly easy to improve on cast port work found in bikes right off the showroom floor.

I foolishly port matched my exhaust ports to my 1.5" exhaust headers on my 750. So if gas can return to the combustion chamber, it is returning with a vengeance, and would explain some things I won't talk about. Could just be user errors on my part.

On the subject of being off the topic: I had a little Triumph Tiger with 11:1 pistons in it. That bike was fun to ride. I screwed it up by putting lower compression pistons in it. It never ran as strong after I did that, and being young and impatient never could figure out how to stop the push rod tubes from leaking. Probably sold it for $450 or less in the 70's. That I can put on my regrets list.

Click to expand...

If you lower the compresiion ratio, you need to either lean-off the jetting or increase the ignition advance to get the same level of power you had prevuipusly. If you change the exhaust system, you need top tune the cam timing and jetting to suit it. More advance on a Commando cam gives better valve opening points, but the noise increases. The cam in my 850 is almost standard - it is advanced 12 degrees. But I use methano fuel, so heat is not such a problem.

Exhaust systems are not only just about extracting gas They resonate and the effect of the punses can add, or they can neutralise each other if the lengths are wrong. I did not calculate the lengths of the header pipes on the 2 into 1 on my Seeley. Those pipes are simply the ones which are use to make the 4 into 1 race pipes for the Z900 Kawsaki. The revs are similar. If there is one standing wave in a header pipe, my tail pipe is the same length but must resonate at twice the frequency. You can calculare the optimum length for one rev level, by dividing the speed of sound by the frequency. I did not bother to do that, because I knew what works. The most imortant thing is the diameter of the tail pipe. It has to be big enough to offer no restriction.
My 850 motor surprises me. It is extremely good for such an idiot thing. I know I think differently to many other people. I have to live with that.
I don't think I am a better rider than many others,, but my Seeley 850 helps me to be faster. The other thing is these days most racing is historic - the other guys might have become slower. The faster guys in Period 4 historic ride Rex Wolfenden's 1100cc CB750 Hondas which do not handle. In corners they form a procession out on the ripple strip. On a right hander, the right side of the track is always open. Same on the left. There is always room to pass them. In the old days, they used to be everywhere in corners. I was always afraid I might hit one. I was always faster in corners.
A Commando engine will never be fast enough to be quicker down the straights. But it is much better in corners. I do not ride on power circuits.

MichaelB said:

Nice, you running a lightened crank, stock or??

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Stock bottom end.

Fast Eddie said:

I would imagine they do, it looks like a great design to me, they run a very functional squish / quench area and create some useful swirl etc.

There isn’t that much extra material on the crown (esp compared to the old / original 10.25:1 Omega’s etc) so provided the rest of the piston has been well designed (with weight in mind) they should be great.

Click to expand...

The Dreer pistons were made by JE. I'm guessing that if you have the money, JE would make more in any bore size that you like.

Gerald Jensen said:

The Dreer pistons were made by JE. I'm guessing that if you have the money, JE would make more in any bore size that you like.

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Probably not, unless you get Kenny to give permission. Those are his proprietary designs, not a JE stock item. On the other hand, Kenny would probably do so. He's not selling them any more, and he's a good guy.

Ken

lcrken said:

Probably not, unless you get Kenny to give permission. Those are his proprietary designs, not a JE stock item. On the other hand, Kenny would probably do so. He's not selling them any more, and he's a good guy.

Ken

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You're probably right.

jseng1 said:

I just got this photo of some Kenny Dreer 880 pistons. You can see the extra metal added to improve the air turbulance by redesigning and tighening up the squish band. Unfortunately this added weight to the pistons and increased vibration stress at high RPM. The pistons are 79mm which is about as big as you can go with stock cylinders. Years ago Kenny D contacted me about lighter pistons, but it was too late by then and he was moving on to the completely redesigned 961.

Click to expand...

Would anyone be interested in purchasing a cylinder and set of these pistons. I have such a set up, serial marked #506

I tend to think about two-strokes and four-strokes in pretty much the same way. To get a two -stroke going fast, jetting, ignition advance and resonance are critical aspects. Why would it be different with a four-stroke ? The relationship between port timings in a two-stroke engine, is similar to the relationship in a four-stroke engine, but the strengths of the resonance pulses are greater.