variocam or varioram -whats the difference?
Discussion
my 968 has variocam, the concept of which I think I understand, vaguely. later 993s had varioram. paying little attention to spelling, I thought this was the same principle applied to the 993 engine as had been applied to the 944S2 whaen they changed it to the 968. But I think I'm wring, arent I? so what is varioram? what does it do, and does it bear any relationship to variocam?
From 911&PW:
"Varioram is a Porsche-patented design that was first seen on the 1992 964-model 911 Carrera RS. Operated (in very simple terms) by the vacuum generated by the engine breathing in, the system alters the length of the inlet ducting depending upon engine speed and load. This (in equally simple terms) optimises the volumetric efficiency at different engine speeds.
Up to 5000rpm the inlet tracts are almost twice the length of those in the earlier 993s (ie those built for the 1994 and 1995 model years). Above 5000rpm the tract length reduces in two stages, and above 5800rpm the two banks of inlet ducts are joined to improve volumetric efficiency still further."
Dan
can be seen here.softinthehead said:
my 968 has variocam, the concept of which I think I understand, vaguely. later 993s had varioram. paying little attention to spelling, I thought this was the same principle applied to the 993 engine as had been applied to the 944S2 whaen they changed it to the 968. But I think I'm wring, arent I? so what is varioram? what does it do, and does it bear any relationship to variocam?
I have also wondered if the 2 things (Variocam and Varioram) are one and the same.
Doesn't anyone know?
They aren't the same thing, but they are similar in what they are trying to achieve.
In both cases they aim to improve the performance of an engine by dynamically controlling aspects of an engine which have traditionally been static.
Quite often with engines, ancilliary components (to the combustion chamber), are designed to be optimal for a particular engine speed. With any cyclic system there is the critical issue of how fast gasses flow, and materials move. These sorts of things are fixed by the natural world, there is nothing we can do about them directly.
At a given engine speed, there is a requirement for a short movement of air and fuel into the combustion chamber. Critically it is not a continuous flow. Within the cycle the air has to start moving, move, and stop moving. The rate at which air moves is fixed, but as the engine speed changes, the rate that you require the air to move changes.
By changing the effective volume (capacity) of the induction system you change it's resonant frequency. A bit like blowing across the top of a milk bottle, as you put more water in the squeak changes pitch. The same is true with the varioram induction system. Rather than trying to make the air do something it doesn't want to, the resonance of the intake system is changed to allow efficient intake. When the actual combustion chamber is is breathing air is supplied from the system. When it is not, movement in the induction system continues, because there is space for it to do so, but the air is compressed. When the combustion chamber is ready to breathe again the air is already compressed and waiting to enter.
Variocam is similar in the sense that a particular valve event duration and size is naturally appropriate for a particular engine speed and loading condition. Rather than use a single cam to control valve events, multiple cams are used. A special cam follower combines the inputs from each of the cams to control valve timing and lift. The combination is variable, one cam being optimised for low speed running and one for high speed. As the engine speed (and possibly load?) change the proportions of input from the respective cams change.
IMO, the idea is similar, but the implementation is quite different. Variocam is about camshafts, Varioram is about ram pipes.
>> Edited by dilbert on Friday 25th February 12:07
In both cases they aim to improve the performance of an engine by dynamically controlling aspects of an engine which have traditionally been static.
Quite often with engines, ancilliary components (to the combustion chamber), are designed to be optimal for a particular engine speed. With any cyclic system there is the critical issue of how fast gasses flow, and materials move. These sorts of things are fixed by the natural world, there is nothing we can do about them directly.
At a given engine speed, there is a requirement for a short movement of air and fuel into the combustion chamber. Critically it is not a continuous flow. Within the cycle the air has to start moving, move, and stop moving. The rate at which air moves is fixed, but as the engine speed changes, the rate that you require the air to move changes.
By changing the effective volume (capacity) of the induction system you change it's resonant frequency. A bit like blowing across the top of a milk bottle, as you put more water in the squeak changes pitch. The same is true with the varioram induction system. Rather than trying to make the air do something it doesn't want to, the resonance of the intake system is changed to allow efficient intake. When the actual combustion chamber is is breathing air is supplied from the system. When it is not, movement in the induction system continues, because there is space for it to do so, but the air is compressed. When the combustion chamber is ready to breathe again the air is already compressed and waiting to enter.
Variocam is similar in the sense that a particular valve event duration and size is naturally appropriate for a particular engine speed and loading condition. Rather than use a single cam to control valve events, multiple cams are used. A special cam follower combines the inputs from each of the cams to control valve timing and lift. The combination is variable, one cam being optimised for low speed running and one for high speed. As the engine speed (and possibly load?) change the proportions of input from the respective cams change.
IMO, the idea is similar, but the implementation is quite different. Variocam is about camshafts, Varioram is about ram pipes.
>> Edited by dilbert on Friday 25th February 12:07
clubsport said:
Varioram on the 964 RS sounds like tosh to me.
Perfectly willing to believe it, that was a straight copy & paste from the 911&PW article, link here:
www.chpltd.com/911_porsche_world/distance.html
For the avoidance of doubt I know eff all about it ...
gr4 said:
Might it be the '92 Cup car or something similarly exotic that debuted Varioram ?
Er, no.......but 964's do have a valve somewhere to combine the inlet tracts/crossover over a certain revs. Geoff Everett explained it to me once....but long forgotten...where's Belton when you need him!!
AFAIK, VarioRAM applies to 993 only.....but then, what do I know...
And to think I came on here for relaxation having just had to work out square metreages for re-flooring and replastering a circular oast house!!!
Rgds
Mel
danww said:
Varioram on the 964 RS sounds like tosh to me.
Perfectly willing to believe it, that was a straight copy & paste from the 911&PW article, link here:
www.chpltd.com/911_porsche_world/distance.html
For the avoidance of doubt I know eff all about it ...
Hopefully Domster will be along to sort out this 964RS conundrum, after many years of driving the Baron on road and track and ensuing engine rebuilds, if anyone can clear this up I am sure it is he!
johnny senna said:
IMO, the idea is similar, but the implementation is quite different. Variocam is about camshafts, Varioram is about ram pipes.
That is very useful. Thanks.
If i'm not mistaken, Porsche actually developed both systems. VarioRAM for the 993's (and prior). VarioCAM for the 996's (future). The Ram' system is about volumetric air intake. The Cam' system is all about Variable valve timing, and yes it has different sized cams and all that...
dilbert said:
Variocam is similar in the sense that a particular valve event duration and size is naturally appropriate for a particular engine speed and loading condition. Rather than use a single cam to control valve events, multiple cams are used. A special cam follower combines the inputs from each of the cams to control valve timing and lift. The combination is variable, one cam being optimised for low speed running and one for high speed. As the engine speed (and possibly load?) change the proportions of input from the respective cams change.
As I understand it, Variocam is not about low speed and high speed cams, but a simple way to overlap the timing of the inlet and exhaust cams. This has the effect of giving more torque in the lower areas of the rev range. There's an explanation here:
www.porsche968uk.co.uk/porsche-variocam.htm
Paul
vario ram was only fitted to the 993,never 964 by the factory for production. Peter Morgan often gets things wrong, As clubsport said Tosh!
I am not sure the total explanation of the vario ram is strictly correct either. I think basically the shorter the inlet tract is for tourque at lower rpm and longer in higher rpm for good tourque.The vario ram does not ram anything, but purely changes the length of the inlet tract i think! Its been along time for me, since studying vario ram,as i threw it away for throttle bodies in the end. It produced a good job of spreading the torque out nicely for a production car though.
But not as good as a 964rs/cup/993 cup inlet system on motec or a properly mapped ecu.
The 964 & 993 cup have the extra resonance flap that opens around the 6000rpm ish ,via a vacuum/electric valve.The yellow car that clubsport has for sale would prove this,its the fastest 964 3.6 normaly aspirated car around.Pretty shore it has 340bhp and 410nm of tourque,its bloody fast!
Alot of racers cable tie these flaps open, but we found we were losing about 25bhp on the top end with the valve open all the time on the rolling road.
Don’t know to much about vario cam, its for those water cooled things isnt it.
I am sure Colin will correct any thing i have said here, with out giving away any of his secrets!!
I am not sure the total explanation of the vario ram is strictly correct either. I think basically the shorter the inlet tract is for tourque at lower rpm and longer in higher rpm for good tourque.The vario ram does not ram anything, but purely changes the length of the inlet tract i think! Its been along time for me, since studying vario ram,as i threw it away for throttle bodies in the end. It produced a good job of spreading the torque out nicely for a production car though.
But not as good as a 964rs/cup/993 cup inlet system on motec or a properly mapped ecu.
The 964 & 993 cup have the extra resonance flap that opens around the 6000rpm ish ,via a vacuum/electric valve.The yellow car that clubsport has for sale would prove this,its the fastest 964 3.6 normaly aspirated car around.Pretty shore it has 340bhp and 410nm of tourque,its bloody fast!
Alot of racers cable tie these flaps open, but we found we were losing about 25bhp on the top end with the valve open all the time on the rolling road.
Don’t know to much about vario cam, its for those water cooled things isnt it.
I am sure Colin will correct any thing i have said here, with out giving away any of his secrets!!
Well I'm prepared to give that the explanation for variocam is a bit off. Not owning an appropriately appended engine, I'd always assumed that vario cam was the same basic idea as the Honda VVT system.
I suppose I had assumed this because the Honda system, that I described, is superior. It is now clear, however, that Porsche do not use the superior system.
As for the varioram system, well, I'm not clear why I'm wrong about that. My description might be a bit "iffy", and I can accept that. On the other hand the chap that was "having a go" on this front suggested that it is all about resonance, which I am in full agreement with.
If you wish to try and explain it better than I can, there is nothing stopping you.
I suppose I had assumed this because the Honda system, that I described, is superior. It is now clear, however, that Porsche do not use the superior system.
As for the varioram system, well, I'm not clear why I'm wrong about that. My description might be a bit "iffy", and I can accept that. On the other hand the chap that was "having a go" on this front suggested that it is all about resonance, which I am in full agreement with.
If you wish to try and explain it better than I can, there is nothing stopping you.
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