Pazon Sure Fire
- Thread starter Howard
- Start date
That suggests that they work. My doubts are less over twin plugs per se, as twin plugs on Vincents. My original Manx Norton head (replaced by a Summerfield "bathtub / Ilmor" replica) had been converted to twin plugs, then converted back again to single plugs. I assumed there turned out to be no advantage. Nor can I think of any modern engine fitted with twin plugs as original equipment. I'm open to correction.
I dont know if you would call it modern, but the 650 honda deauville came as standard with two plug heads.
stumpy.
stumpy.
Don't know about in the bike world, but the Alpha Romeo "twin spark" cars have them as do some Mercedes Benz models, but in the main you are correct. With modern electronics it is simple to build in a "kick up" at the top end of the advance curve without affecting settings elsewhere in the rev range. This makes twin plugs unnecessary, certainly on road bikes and, I suspect, many race machines. John.
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It is not just the number of spark plugs which is important but also their position. Vincent and original Manx Norton heads with high compression pistons have a fairly awful shape. If the plug is off to one side then the flame front has to travel a long way and over the bump in the middle (the piston crown). Tom, like me, is old enough to remember all the experiments in the fifties by the best tuners at the time into swirl and squish. Several years ago I happened to see the cylinder head of some bog standard small Japanese car (I think that it was a small Nissan) and was surprised to see just how much swirl and what huge squish bands were built into this non sporty engine. The difference which can be made by incorporating such items into a Vincent engine is remarkable. Several years ago I was helping Roy Robertson at Brands Hatch and was going to move his bike to a different part of the paddock. I made a total prat of myself be stalling the engine three times while trying to gently let the clutch out at 2,000 rpm. The bike would produce about 100 h.p. flat out and yet at 2,000 rpm there was only about enough power to keep the engine ticking over. Later Roy fitted Terry Prince cylinder heads which have serious squish bands. Top end power is about the same but at the bottom end the bike is like a traction engine. The turbulence in the combustion chamber, created by the squish bands, also ensures that for road use a compression ratio of about 10:1 can be used without the unpleasant side effects that would generally occur with the original combustion chamber shape. Perhaps I should say that I have no financial connection with Terry Prince but did provide him with the copy of the ‘George Brown’ fairing which he uses to such good effect on his outfit.
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Hi Time Traveller,
Is there any chance of getting hold of a drawing of what shape the vincent combustion chamber should have to achieve the results described for Roy Robertsons bike?
Obviously i´m not looking for 100+ bhp (i´d be happy with the described 55
I´ve been following various discussions on squish heads, and am finding it more and more difficult to discard the fact that they´ve been using this technology since the late sixtys + the fact that fuel + ignition settings are becoming more difficult (fuel dependant), i feel that a lot could be gained for road use through modding the existing combustion chambers.
Is there any chance of getting hold of a drawing of what shape the vincent combustion chamber should have to achieve the results described for Roy Robertsons bike?
Obviously i´m not looking for 100+ bhp (i´d be happy with the described 55
I´ve been following various discussions on squish heads, and am finding it more and more difficult to discard the fact that they´ve been using this technology since the late sixtys + the fact that fuel + ignition settings are becoming more difficult (fuel dependant), i feel that a lot could be gained for road use through modding the existing combustion chambers.
Dear Vince,
If you are searching for 55 hp you may be better off starting on a dyno. Careful preparation and tuning should get you there. If you fall short, I would not find the combustion chamber of a stock head to be the likely target. I suspect that Roy may have milled the "bathtub" out of the TP heads as that shape did not produce any top end, but only low down torque. I do not want to put words in Roy's mouth, but Carleton Palmer had his TP head flowed and the bathtub was removed and the "D" shaped exhuast port was removed. After the mods were done the HP was up by 5. Terry and I have spoken about modifying new heads, but they are designed for the street which is where the customers are and the process of modifying new production heads is quite expensive. Terry's heads are essetially big port heads, so there is plenty there to modify.
My general comment would be that the exhaust port is the culprit followed by the exhaust system. Because it is easier to alter the pipes, that is where I would start.
David
If you are searching for 55 hp you may be better off starting on a dyno. Careful preparation and tuning should get you there. If you fall short, I would not find the combustion chamber of a stock head to be the likely target. I suspect that Roy may have milled the "bathtub" out of the TP heads as that shape did not produce any top end, but only low down torque. I do not want to put words in Roy's mouth, but Carleton Palmer had his TP head flowed and the bathtub was removed and the "D" shaped exhuast port was removed. After the mods were done the HP was up by 5. Terry and I have spoken about modifying new heads, but they are designed for the street which is where the customers are and the process of modifying new production heads is quite expensive. Terry's heads are essetially big port heads, so there is plenty there to modify.
My general comment would be that the exhaust port is the culprit followed by the exhaust system. Because it is easier to alter the pipes, that is where I would start.
David
My general comment would be that the exhaust port is the culprit followed by the exhaust system. Because it is easier to alter the pipes, that is where I would start.
David[/QUOTE]
David's comment is easy to prove, if you doubt it. Just take off the silencer and replace with a length of exhaust that reaches the rear wheel spindle - that's tuned for about 4000 rpm. The problem for road users is the trade off between power and noise.
H
David[/QUOTE]
David's comment is easy to prove, if you doubt it. Just take off the silencer and replace with a length of exhaust that reaches the rear wheel spindle - that's tuned for about 4000 rpm. The problem for road users is the trade off between power and noise.
H
Hi Vince998, Roy does not use this Forum but I hope to see him tonight. If I do then I will check with him what he had to do. We do have another member, John Emmanuel, who totally independent of Terry Prince started from scratch with a modern gas flow rig and with access to a rolling road. He and a pal of his who tunes modern bikes played around with plasticine on a standard head and the gas flow rig and ended up with a very similar shape to Terry's earlier heads. I have not seen the latest heads. John also found that tick over and low end torque were much improved. More later.