Variable length intakes
Discussion
Are these systems as good as I think they are? Sort of like a VTEC system only at much lower revs?
I recently was lucky enough to drive a late Porsche 993 which had a huge kick that came in at 3000 rpm, and it felt very brawny. The way the kick came in was quite sudden (enough to cause clutch slip on this car which had a worn clutch) and it was very noticeable, and very pleasant
. I'm guessing was due to a variable intake device - Varioram in Porsche's case?
The effect was much more effective than any variable valve timing system I know, as it gave you a kick at such low RPM. Which came first and which is better? Is it to do with long intake being good for torque, short intake being good for power ?
What other cars have this and is it as good? I heard the Ford Probe V6 (mazda engine) has it? I have also seen an aftermarket one on a VW VR6 (dyno chart vs standard VR6 dyno chart)- I wish I could get one for my Mercedes cosworth 2.5 - it is not what you'd call brawny, with its 177 lb ft at 5000 rpm. Supposedly they were fitted with a long intake to limit power and it does feel like it dies off over 6000 rpm, but it's not very torquey in the mid range either??
I recently was lucky enough to drive a late Porsche 993 which had a huge kick that came in at 3000 rpm, and it felt very brawny. The way the kick came in was quite sudden (enough to cause clutch slip on this car which had a worn clutch) and it was very noticeable, and very pleasant
. I'm guessing was due to a variable intake device - Varioram in Porsche's case? The effect was much more effective than any variable valve timing system I know, as it gave you a kick at such low RPM. Which came first and which is better? Is it to do with long intake being good for torque, short intake being good for power ?
What other cars have this and is it as good? I heard the Ford Probe V6 (mazda engine) has it? I have also seen an aftermarket one on a VW VR6 (dyno chart vs standard VR6 dyno chart)- I wish I could get one for my Mercedes cosworth 2.5 - it is not what you'd call brawny, with its 177 lb ft at 5000 rpm. Supposedly they were fitted with a long intake to limit power and it does feel like it dies off over 6000 rpm, but it's not very torquey in the mid range either??
I would have thought a turbo/supercharger was cheaper to rig. Variable timing yes, variable intake lengths, perhaps. Only a bit though, how would it wear, how quick would it be to respond. What you are looking at is a ram charger. Perhaps it gives a fraction better %V.E but not that much. I suppose it depends on the port/valve/cam/etc and would be more handy on a full race engine. Even the lowest pressure (4psi or so) turbo would give a lot more power and be a lot more simple to rig/fuel.
Be interesting to know how it fitted in with the engine management system
Be interesting to know how it fitted in with the engine management system
Well my cars got variable inlet tube length, the simplest systems work with a flap that opens to let a second resonance chamber open at a certain rev range.
Probably not that hard to rig up, however a the end of the day your car won't ever have the mid range punch a 911 does, due amongst other factors to the engine size (I'm not pulling your car down I love merc cossies and considerd getting one a year or so ago).
I would have thought you would maybe see a much greater improvement going for throttle bodies on that engine, or bike carbs, but throttle bodies especially if the fuel injection is direct in to the chamber, combined with a nice programmable ecu should see a big hike in HP and torque.
Probably not that hard to rig up, however a the end of the day your car won't ever have the mid range punch a 911 does, due amongst other factors to the engine size (I'm not pulling your car down I love merc cossies and considerd getting one a year or so ago).
I would have thought you would maybe see a much greater improvement going for throttle bodies on that engine, or bike carbs, but throttle bodies especially if the fuel injection is direct in to the chamber, combined with a nice programmable ecu should see a big hike in HP and torque.
Dont get variable intake confused with variable cam/valve timing (VTEC), completely different and are often used together.
The intake length adjusts at different RPM, at each different rpm the ideal intake length varies and the idea is that with the variable length tracts the intake is optimized throughout a vast majority of the rpm range.
I would doubt whether you would find a large performance increase by fitting one, espeicially for the effort required to get it working properly. You'd be far better off sticking some throttle bodies on as then you have no inlet restriction to worry about.
Variable valve timing is more of an emissions thing, it gives very low emissions at low rpm but good power at high rpm. For any real tuning you would throw away the VVT and replace them with solid cams.
The intake length adjusts at different RPM, at each different rpm the ideal intake length varies and the idea is that with the variable length tracts the intake is optimized throughout a vast majority of the rpm range.
I would doubt whether you would find a large performance increase by fitting one, espeicially for the effort required to get it working properly. You'd be far better off sticking some throttle bodies on as then you have no inlet restriction to worry about.
Variable valve timing is more of an emissions thing, it gives very low emissions at low rpm but good power at high rpm. For any real tuning you would throw away the VVT and replace them with solid cams.
The Corrado VR6 was meant to be manufactured with a variable-length inlet manifold but it was deleted by the beancounters before launch. 
It's still available as an aftermarket fit and does give a really good slug of low-down torque without losing anything at the top end (in fact there is a modest improvement of around 10bhp on the top end as well).
Haven't got one myself as they're around £1,700 + VAT, but I have been out on a Corrado that has one and it was very noticeable.
Edit: I wouldn't even think of designing one yourself though - tuning the inlet manifolds is an exact science (or a black art, depending on how you look at it) and would require 100's of hours of work to get right, I would imagine.
It's still available as an aftermarket fit and does give a really good slug of low-down torque without losing anything at the top end (in fact there is a modest improvement of around 10bhp on the top end as well).
Haven't got one myself as they're around £1,700 + VAT, but I have been out on a Corrado that has one and it was very noticeable.
Edit: I wouldn't even think of designing one yourself though - tuning the inlet manifolds is an exact science (or a black art, depending on how you look at it) and would require 100's of hours of work to get right, I would imagine.
Edited by JonRB on Friday 5th January 13:34
nightdriver said:
Dont get variable intake confused with variable cam/valve timing (VTEC), completely different and are often used together.
The intake length adjusts at different RPM, at each different rpm the ideal intake length varies and the idea is that with the variable length tracts the intake is optimized throughout a vast majority of the rpm range.
I would doubt whether you would find a large performance increase by fitting one, espeicially for the effort required to get it working properly. You'd be far better off sticking some throttle bodies on as then you have no inlet restriction to worry about.
Variable valve timing is more of an emissions thing, it gives very low emissions at low rpm but good power at high rpm. For any real tuning you would throw away the VVT and replace them with solid cams.
The intake length adjusts at different RPM, at each different rpm the ideal intake length varies and the idea is that with the variable length tracts the intake is optimized throughout a vast majority of the rpm range.
I would doubt whether you would find a large performance increase by fitting one, espeicially for the effort required to get it working properly. You'd be far better off sticking some throttle bodies on as then you have no inlet restriction to worry about.
Variable valve timing is more of an emissions thing, it gives very low emissions at low rpm but good power at high rpm. For any real tuning you would throw away the VVT and replace them with solid cams.
If you are talking race cams then yes, perhaps.
The VVT combines the opening time of the valve with the optimum ram charging of that length tube. This is also true for the zorst (but for shockwaves instead). I would say that a race cam and VVT would be of benefit. So, why don't people use it? Perhaps the cams are too complex to machine and a regrind gives silly ramp rates and huge loads. Having a think about it, it's not much of a significant effect. You can bet your bottom dollar that if it was, Harry Weslake would have thought about it and used it lots
Having said, he may have done
love machine said:
nightdriver said:
Dont get variable intake confused with variable cam/valve timing (VTEC), completely different and are often used together.
The intake length adjusts at different RPM, at each different rpm the ideal intake length varies and the idea is that with the variable length tracts the intake is optimized throughout a vast majority of the rpm range.
I would doubt whether you would find a large performance increase by fitting one, espeicially for the effort required to get it working properly. You'd be far better off sticking some throttle bodies on as then you have no inlet restriction to worry about.
Variable valve timing is more of an emissions thing, it gives very low emissions at low rpm but good power at high rpm. For any real tuning you would throw away the VVT and replace them with solid cams.
The intake length adjusts at different RPM, at each different rpm the ideal intake length varies and the idea is that with the variable length tracts the intake is optimized throughout a vast majority of the rpm range.
I would doubt whether you would find a large performance increase by fitting one, espeicially for the effort required to get it working properly. You'd be far better off sticking some throttle bodies on as then you have no inlet restriction to worry about.
Variable valve timing is more of an emissions thing, it gives very low emissions at low rpm but good power at high rpm. For any real tuning you would throw away the VVT and replace them with solid cams.
If you are talking race cams then yes, perhaps.
The VVT combines the opening time of the valve with the optimum ram charging of that length tube. This is also true for the zorst (but for shockwaves instead). I would say that a race cam and VVT would be of benefit. So, why don't people use it? Perhaps the cams are too complex to machine and a regrind gives silly ramp rates and huge loads. Having a think about it, it's not much of a significant effect. You can bet your bottom dollar that if it was, Harry Weslake would have thought about it and used it lots
Having said, he may have done
What do you mean by ram charging?
From my experience all engines which are sold in production cars with VVT, VTEC etc have them removed for race usage. Main reason seems to be keeping the friction to a minimum but also when running throttle bodies there is no pulse tuning to be done and emissions/low engine speeds are of little concern so the VVT has no use, its just an added complication that can fail at high speeds.
Doubt they would have had the correct methods of controlling such systems in the days of Weslake!
Well I wouldn't expect the pull of a 911, but if the engine had the same broad spread of torque, as opposed to being rather linear but with most of its go at the top end, it would be pretty awesome. However since the cossie engine came out in 1984 that's probably asking a lot.
I thought throttle bodies weren't so good for mid range or low down torque?
Aftermarket engine management would be nice but requires a conversion of the mechanical injection, which involves fabricating a fuel rail, finding injectors and so on..
JonRB - I linked to dyno charts from a Golf VR6 with that aftermarket variable inlet thing, plus it had cams, maybe other stuff (I think owner is on vr6oc.co.uk)
I thought throttle bodies weren't so good for mid range or low down torque?
Aftermarket engine management would be nice but requires a conversion of the mechanical injection, which involves fabricating a fuel rail, finding injectors and so on..
JonRB - I linked to dyno charts from a Golf VR6 with that aftermarket variable inlet thing, plus it had cams, maybe other stuff (I think owner is on vr6oc.co.uk)
Jaguar S type has a variable resonance inlet manifold I was involved in the design of.
It's a painstaking process, you're not going to be able to rig one up yourself.
You'll have to calculate and fabricate the correctly sized plenums and inlet runners.
Also- sealing is critical in any variable intake system and this won't be easy to do.
It's possible- but you have to have the correct software and test facilities at your disposal
It's a painstaking process, you're not going to be able to rig one up yourself.
You'll have to calculate and fabricate the correctly sized plenums and inlet runners.
Also- sealing is critical in any variable intake system and this won't be easy to do.
It's possible- but you have to have the correct software and test facilities at your disposal
I thought most new high-spec German engines had two sets of different length intakes these days. The costs are a lot lower than running a full variable system with simple butterfly valves the give three inlet lengths to approximatly map to the resonance levels for three sections of the rev range?
They work by minimising the effort needed to suck air into the engine by mapping (I guess matching?) the intake resonance frequency with the engine revs (per cylinder, all cylinder? I have no idea).
I always wondered why these aren't on exhausts more. I know they'd cost more due to dealing with the engergy levels involved, but just purely dealing with the much higher energy levels would result in higher gains. Who else other than Ferrari use them??
I'll have a quick dig for links.
They work by minimising the effort needed to suck air into the engine by mapping (I guess matching?) the intake resonance frequency with the engine revs (per cylinder, all cylinder? I have no idea).
I always wondered why these aren't on exhausts more. I know they'd cost more due to dealing with the engergy levels involved, but just purely dealing with the much higher energy levels would result in higher gains. Who else other than Ferrari use them??
I'll have a quick dig for links.
Toyota used two systems -
TVIS - late 80's/early 90's - 8 inlet ports (for 8 inlet valves), 4 covered by butterflies at low engine speed (<4000 ish)
Later they moved towards ACIS - 4 inlet ports (for 8 inlet valves), an extra chamber allmost like a second plenum half way allong the runners, opened at high engine speed (>5000 ish). I think later on still they used 3-stage ACIS.
I did have a PDF once of a lengthy testing report about all kinds of different schemes they tried, different connections, crossovers, switches etc etc. If I can dig it out I'l post it!
TVIS - late 80's/early 90's - 8 inlet ports (for 8 inlet valves), 4 covered by butterflies at low engine speed (<4000 ish)
Later they moved towards ACIS - 4 inlet ports (for 8 inlet valves), an extra chamber allmost like a second plenum half way allong the runners, opened at high engine speed (>5000 ish). I think later on still they used 3-stage ACIS.
I did have a PDF once of a lengthy testing report about all kinds of different schemes they tried, different connections, crossovers, switches etc etc. If I can dig it out I'l post it!
Quick links...
http://en.wikipedia.org/wiki/Variable
and
http://auto.howstuffworks.com/questio
for the (very) basic theory.
http://en.wikipedia.org/wiki/Variable
and
http://auto.howstuffworks.com/questio
for the (very) basic theory.
MTv Dave said:
Quick links...
http://en.wikipedia.org/wiki/Variable
and
http://auto.howstuffworks.com/questio
for the (very) basic theory.
http://en.wikipedia.org/wiki/Variable
and
http://auto.howstuffworks.com/questio
for the (very) basic theory.
Good stuff, thanks
MTv Dave said:
I thought most new high-spec German engines had two sets of different length intakes these days. The costs are a lot lower than running a full variable system with simple butterfly valves the give three inlet lengths to approximatly map to the resonance levels for three sections of the rev range?
They work by minimising the effort needed to suck air into the engine by mapping (I guess matching?) the intake resonance frequency with the engine revs (per cylinder, all cylinder? I have no idea).
I always wondered why these aren't on exhausts more. I know they'd cost more due to dealing with the engergy levels involved, but just purely dealing with the much higher energy levels would result in higher gains. Who else other than Ferrari use them??
I'll have a quick dig for links.
They work by minimising the effort needed to suck air into the engine by mapping (I guess matching?) the intake resonance frequency with the engine revs (per cylinder, all cylinder? I have no idea).
I always wondered why these aren't on exhausts more. I know they'd cost more due to dealing with the engergy levels involved, but just purely dealing with the much higher energy levels would result in higher gains. Who else other than Ferrari use them??
I'll have a quick dig for links.
Audi 4.2 V8 in the A8/S8 of old had tripple intake tracts, when most others notable at the time only had two.
Seems like alot of effort. IF torque spread is that important, and the added complexity and weight are considered allowable in that application then I'd just say (esp with todays tech) that a nice small low pressure turbo would be much more effective!
Dave
HarryW said:
How do you calculate optimum intake length for a given rpm, seems to recall something like 80000 being in the equation 
Following on from this rather than start a new thread I found this link www.bgsoflex.com/intakeln.html for a calculator for runner length. Any one know what the runner length is of the AJP8 in 4.2 and 4.5 guise as standard
Don't know if this is in the current range of cars but it seems BMW have a variable intake runner see here http://67.153.245.114/speawards/2003A
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