variable cams
05-10-2002, 06:06 AM
#6
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05-10-2002, 06:24 AM
#7
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Yes, VTEC and variable cam timing (CVTC is Nissan's) are completely different systems. VTEC uses two or more cam lobes on the same camshaft. At a certain rpm, a mechanism switches the valve lifters to follow the more aggressive cam profile. CVTC simply uses a variable camshaft sproket to rotate the sprocket in relation to the cam, the result being advancing or delaying valve timing events. CVTC is less effective than VTEC, but offers smoother operation with no sudden jumps. It can create a very smooth torque curve. VTEC ultimately offers more power potential because it offers increased valve lift and optimizes valve timing (rather than just advancing or retarding valve timing), but offers a less-smooth torque curve due to the two or three discrete cam profiles.
Originally posted by Anachronism
I have seen VTEC described as changing cam profiles at a certain RPM and opening the second intake/exhaust valves at a certain RPM. Are their two different systems or is sombody describing it wrong?
I have seen VTEC described as changing cam profiles at a certain RPM and opening the second intake/exhaust valves at a certain RPM. Are their two different systems or is sombody describing it wrong?
05-10-2002, 07:00 AM
#8
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Posts: 1,362
Originally posted by Keven97SE
Yes, VTEC and variable cam timing (CVTC is Nissan's) are completely different systems. VTEC uses two or more cam lobes on the same camshaft. At a certain rpm, a mechanism switches the valve lifters to follow the more aggressive cam profile. CVTC simply uses a variable camshaft sproket to rotate the sprocket in relation to the cam, the result being advancing or delaying valve timing events. CVTC is less effective than VTEC, but offers smoother operation with no sudden jumps. It can create a very smooth torque curve. VTEC ultimately offers more power potential because it offers increased valve lift and optimizes valve timing (rather than just advancing or retarding valve timing), but offers a less-smooth torque curve due to the two or three discrete cam profiles.
Yes, VTEC and variable cam timing (CVTC is Nissan's) are completely different systems. VTEC uses two or more cam lobes on the same camshaft. At a certain rpm, a mechanism switches the valve lifters to follow the more aggressive cam profile. CVTC simply uses a variable camshaft sproket to rotate the sprocket in relation to the cam, the result being advancing or delaying valve timing events. CVTC is less effective than VTEC, but offers smoother operation with no sudden jumps. It can create a very smooth torque curve. VTEC ultimately offers more power potential because it offers increased valve lift and optimizes valve timing (rather than just advancing or retarding valve timing), but offers a less-smooth torque curve due to the two or three discrete cam profiles.
My current issue of Motercyclist magizine (may 2002) reviews the VTEC equiped Honda VFR and describes the system as only using one intake/exhaust valve at low RPMs and two intake/exhast valve after the switchover. I have also seen it described as you say, with a different cam profile after switchover.
05-10-2002, 07:11 AM
#9
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VTEC comes in a lot of different flavors...only intake cam timing changes, both intake and exhaust, 3 different cam profiles, one vs two valves opening, etc. Look, VTEC just means "switchable cam profiles". There are multiple things you can do with that technology, all of which you're referring. CVTC just means "phaseable cam timing", ie variable cam sprockets. That's it.
Originally posted by Anachronism
I am only talking about Hondas VTEC, I have seen it described as working in two different ways and wondered if there are two different VTEC systems or if sombody is wrong.
My current issue of Motercyclist magizine (may 2002) reviews the VTEC equiped Honda VFR and describes the system as only using one intake/exhaust valve at low RPMs and two intake/exhast valve after the switchover. I have also seen it described as you say, with a different cam profile after switchover.
I am only talking about Hondas VTEC, I have seen it described as working in two different ways and wondered if there are two different VTEC systems or if sombody is wrong.
My current issue of Motercyclist magizine (may 2002) reviews the VTEC equiped Honda VFR and describes the system as only using one intake/exhaust valve at low RPMs and two intake/exhast valve after the switchover. I have also seen it described as you say, with a different cam profile after switchover.
05-10-2002, 08:07 AM
#10
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Join Date: Jan 2001
Posts: 1,816
Originally posted by Keven97SE
VTEC comes in a lot of different flavors...only intake cam timing changes, both intake and exhaust, 3 different cam profiles, one vs two valves opening, etc. Look, VTEC just means "switchable cam profiles". There are multiple things you can do with that technology, all of which you're referring. CVTC just means "phaseable cam timing", ie variable cam sprockets. That's it.
VTEC comes in a lot of different flavors...only intake cam timing changes, both intake and exhaust, 3 different cam profiles, one vs two valves opening, etc. Look, VTEC just means "switchable cam profiles". There are multiple things you can do with that technology, all of which you're referring. CVTC just means "phaseable cam timing", ie variable cam sprockets. That's it.
05-10-2002, 11:23 AM
#12
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CVTC stands for continuously variable timing control. This is used on the VQ35DE motors. The VE30DE motors used VTC, or variable timing control. As is inferred, VTC is not continuously adjustable. The camshafts are either advanced fully or not at all. CVTC incrementally adjusts cam timing.
CVTC is better. Supposedly more robust as well. VTC was a neat system, especially being 10 years ago, but reliability was not-so-good.
CVTC is better. Supposedly more robust as well. VTC was a neat system, especially being 10 years ago, but reliability was not-so-good.
Originally posted by Chinkzilla
Would the CVTC you described be the mechanism from the 3rd gen VE's or the 2002 VQ35? Or have these two engines been confirmed to have the same type of variable valve timing?
Would the CVTC you described be the mechanism from the 3rd gen VE's or the 2002 VQ35? Or have these two engines been confirmed to have the same type of variable valve timing?
05-10-2002, 11:47 AM
#13
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Join Date: Oct 2000
Posts: 1,677
Does anyone remember a thread started by someome who worked for a automotive company that was working on making a VTEC-equivalent system for engines that did not come with it. He posted a website with info and proof that it worked on a DSM?
He said his company might look into doing that for VQs.
The knowledgeable members of our board made that thread informative and interesting.
Anyone have any follow up on that?
He said his company might look into doing that for VQs.
The knowledgeable members of our board made that thread informative and interesting.
Anyone have any follow up on that?
05-10-2002, 12:02 PM
#14
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FYI it was a totally different method of adjusting valve timing than VTEC or VTC. It used very light sleeves that slipped over the seating portion of the intake valves. When the intake valve opens, any backflow of air out of the cylinder (which would otherwise happen with an aggressive intake cam) would cause the small sleeve to dislodge from the intake valve seat surface and move up, blocking backflow of air back into the intake ports.
Neat concept, but they are totally, way out there in terms of availability for mass marketing. Don't hold your breathe. It'll be years before those are even available, if ever. Last time I looked there had been no updates at all.
Neat concept, but they are totally, way out there in terms of availability for mass marketing. Don't hold your breathe. It'll be years before those are even available, if ever. Last time I looked there had been no updates at all.
Originally posted by mAdD MAX
Does anyone remember a thread started by someome who worked for a automotive company that was working on making a VTEC-equivalent system for engines that did not come with it. He posted a website with info and proof that it worked on a DSM?
He said his company might look into doing that for VQs.
The knowledgeable members of our board made that thread informative and interesting.
Anyone have any follow up on that?
Does anyone remember a thread started by someome who worked for a automotive company that was working on making a VTEC-equivalent system for engines that did not come with it. He posted a website with info and proof that it worked on a DSM?
He said his company might look into doing that for VQs.
The knowledgeable members of our board made that thread informative and interesting.
Anyone have any follow up on that?
05-11-2002, 07:39 AM
#15
Senior Member
Join Date: Jan 2001
Posts: 1,816
Originally posted by Keven97SE
CVTC stands for continuously variable timing control. This is used on the VQ35DE motors. The VE30DE motors used VTC, or variable timing control. As is inferred, VTC is not continuously adjustable. The camshafts are either advanced fully or not at all. CVTC incrementally adjusts cam timing.
CVTC is better. Supposedly more robust as well. VTC was a neat system, especially being 10 years ago, but reliability was not-so-good.
CVTC stands for continuously variable timing control. This is used on the VQ35DE motors. The VE30DE motors used VTC, or variable timing control. As is inferred, VTC is not continuously adjustable. The camshafts are either advanced fully or not at all. CVTC incrementally adjusts cam timing.
CVTC is better. Supposedly more robust as well. VTC was a neat system, especially being 10 years ago, but reliability was not-so-good.
unfortunately, this just makes it all the harder to camwork on my car.. grrr...
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