I was watching a replay of the Spanish round of World Superbikes and was impressed by the winning Aprilia. I dug a little on the web to learn more about the bike and discovered that it has both 4 valves and 2 plugs per pot (it's a 1000cc V twin). The bore size is huge (97mm), very similar to what you'd find in an F1 engine, although the stroke is much longer (67.5mm). Given the nature of the combustion chamber in an F1 engine, it seems reasonable to expect there might be some benefit to this arrangement there as well. My question is can anyone explain how the plugs/valves are arranged in the Aprilia? 4 valve heads don't seem suited to a twin-plug arrangement.[p][Edited by desmo on 06-27-2000]
Aprilia - 4 Valves, 2 Sparkplugs per cylinder
Started by
desmo
, Jun 27 2000 07:11
4 replies to this topic
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#2
EddieJF1
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Posted 27 June 2000 - 15:37
Maybe they are angled in at the top of the chamber, kind of like a 5 port design? Not a lot of metal there for strength, though. A diagram or pic would be nice if someone digs one up.
#3
davo
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Posted 28 June 2000 - 03:07
Desmo,
I have seen SOME twin plug heads used on road and road modified race engines. One plug being conventional in that it is centrally located - between the valves (two or four as per the design). The additional plug has been located adjacent to the exhaust valve(s) on the perimeter of the bore but still in the head (sorry for the cumbersome description).
The explanation which I took away from this was that the second plug suppressed knock. The plugs were fired together and the flame front grew away from the hotest part of the head. When the secondary plug was turned off there was knock.
The theory being that this area of the chamber is the hottest and with the plug turned off needs to wait for the flame front to spread to burn the air/fuel in that area. If the engine is already on the verge of knock the temp and pressure rise can lead to knock in this area.
A four valve head would have the 2nd plug between the Ex valves on the perimeter. Current F1 engines would be able to hide this 2nd plug within the cam box if they wanted to.
I would be guessing Aprilla are not keen to show us their head design but an external close up would still be a give away on a bike engine.
I have seen SOME twin plug heads used on road and road modified race engines. One plug being conventional in that it is centrally located - between the valves (two or four as per the design). The additional plug has been located adjacent to the exhaust valve(s) on the perimeter of the bore but still in the head (sorry for the cumbersome description).
The explanation which I took away from this was that the second plug suppressed knock. The plugs were fired together and the flame front grew away from the hotest part of the head. When the secondary plug was turned off there was knock.
The theory being that this area of the chamber is the hottest and with the plug turned off needs to wait for the flame front to spread to burn the air/fuel in that area. If the engine is already on the verge of knock the temp and pressure rise can lead to knock in this area.
A four valve head would have the 2nd plug between the Ex valves on the perimeter. Current F1 engines would be able to hide this 2nd plug within the cam box if they wanted to.
I would be guessing Aprilla are not keen to show us their head design but an external close up would still be a give away on a bike engine.
#4
Ray Bell
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Posted 28 June 2000 - 04:27
Logic says they might be each side, ie. angling in between the exhaust and inlets opposite each other.
#5
desmo
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Posted 28 June 2000 - 17:10
davo,
It's a feature of the production RSV Mille as well, so it isn't any sort of secret. I even found a cross-section of the engine that incredibly didn't show the sparkplug arrangement.
Ray,
That arrangement seems likely, but given the architecture of a four-valve combustion chamber it would surprise me if they didn't utilise the central location in the chamber. It's just too inviting to put it there. It looks like the only location that doesn't comprimise valve diameter and circumference.
It's a feature of the production RSV Mille as well, so it isn't any sort of secret. I even found a cross-section of the engine that incredibly didn't show the sparkplug arrangement.
Ray,
That arrangement seems likely, but given the architecture of a four-valve combustion chamber it would surprise me if they didn't utilise the central location in the chamber. It's just too inviting to put it there. It looks like the only location that doesn't comprimise valve diameter and circumference.
