Vtec
Thread Starter
TECH Apprentice
Joined: Oct 2004
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Vtec We all have heard about VTEC, knocked VTEC, etc, etc.
I finally saw an illustration of the main components of VTEC, and actually the design looks like a good idea. You don't need 4 valves for a VTEC either.
The VTEC design showed a cam with two intake lobes and two exhaust lobes for a given bank of valves.
It allows you to have two cam profiles in the same engine, with one kicking in at higher RPM.
The premise is it allows you to have all the high rpm or a serious amount of high rpm power, with a moderate cam design for lower engine speeds. Imagine if you may an engine that can have a 218@.05" with hi TQ lift lobe and a 245@.05" hi lift high rpm lobe in the engine at the same time.
Your on the 218@.05" lobe under idle-3000 RPM, but with the pedal at greater than 70% and above 3000RPM a mechanical actuator will have you on the 245@.05" lobe.
Means you can pass emissions, have strong lowerspeed TQ while having the high rpm power in the same engine.
I'm sure fullest implementation of vtec is the dual cam profiles, and some varying timing on the valve sprokets to allow change in LSA, ICL, etc dynamically.
Sounds good to me!
I finally saw an illustration of the main components of VTEC, and actually the design looks like a good idea. You don't need 4 valves for a VTEC either.
The VTEC design showed a cam with two intake lobes and two exhaust lobes for a given bank of valves.
It allows you to have two cam profiles in the same engine, with one kicking in at higher RPM.
The premise is it allows you to have all the high rpm or a serious amount of high rpm power, with a moderate cam design for lower engine speeds. Imagine if you may an engine that can have a 218@.05" with hi TQ lift lobe and a 245@.05" hi lift high rpm lobe in the engine at the same time.
Your on the 218@.05" lobe under idle-3000 RPM, but with the pedal at greater than 70% and above 3000RPM a mechanical actuator will have you on the 245@.05" lobe.
Means you can pass emissions, have strong lowerspeed TQ while having the high rpm power in the same engine.
I'm sure fullest implementation of vtec is the dual cam profiles, and some varying timing on the valve sprokets to allow change in LSA, ICL, etc dynamically.
Sounds good to me!
Thread Starter
TECH Apprentice
Joined: Oct 2004
Posts: 329
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Whistler,
Thanks. I was saying I knew what it was without seeing how it works. I didnt realize how much it brought to the table or how simple the design was. Some of us "old school" will say - well theres more things to break!
Thanks. I was saying I knew what it was without seeing how it works. I didnt realize how much it brought to the table or how simple the design was. Some of us "old school" will say - well theres more things to break!
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Teching In
Joined: Mar 2006
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i doubt it could be done to a pushrod engine because of the different lifter design and the cam lobes are already pretty close together. on a vtech, u got 2 sets of rockers contacting the lobes. that means that ull have 2 different lifters fdor each intake and/or exhaust valve? no room for that.
what would be possible is changing the rocker ratio somehow to allow more or less lift according to rpm. it would actually not be that hard and im surprised the manufacturers havent thought of it yet. just make it so the pivot point can shift into different positions
what would be possible is changing the rocker ratio somehow to allow more or less lift according to rpm. it would actually not be that hard and im surprised the manufacturers havent thought of it yet. just make it so the pivot point can shift into different positions
I think one of the reason that GM didn't intergrate a similar technology is because of how bad it would mess up everything if they had to compensate for a longer motor in everyone of their platforms. Too expensive but an awesome idea.
Having a physical camshaft is a big limitation.
The end all be all in my opinion is camless valve managments, valves are operated by electromagnets/pnuematics and a computer this means you have an unlimited number of "lobe profiles-duration" etc.... think about an engine that adapts completely to your driving habits and the more aggressive you are with the pedal the more lobe you get, add a CVT and it would feel like its pulling smoothly forever.
The day will come when all you do is tune the PCM to change valve events.
BMW currently has a camless motor in production
The end all be all in my opinion is camless valve managments, valves are operated by electromagnets/pnuematics and a computer this means you have an unlimited number of "lobe profiles-duration" etc.... think about an engine that adapts completely to your driving habits and the more aggressive you are with the pedal the more lobe you get, add a CVT and it would feel like its pulling smoothly forever.
The day will come when all you do is tune the PCM to change valve events.
BMW currently has a camless motor in production
The I6 Traiblazers feature variable valve timing which is different from Vtec but in the same spirit.
Without going into too many details...
I spent probally 25 dyno runs on my stock trailblazer remapping my camshaft timing profile vs. RPM. The result? in most areas I picked up 25+ rwhp with 40 rwhp in some other areas. The results where really counter intiutive to what I expected and in hindsight the dyno time was very much worth it because the engine really liked pretty much somthing completely different per 500rpm or so.
Without going into too many details...
I spent probally 25 dyno runs on my stock trailblazer remapping my camshaft timing profile vs. RPM. The result? in most areas I picked up 25+ rwhp with 40 rwhp in some other areas. The results where really counter intiutive to what I expected and in hindsight the dyno time was very much worth it because the engine really liked pretty much somthing completely different per 500rpm or so.
Thread Starter
TECH Apprentice
Joined: Oct 2004
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Quesiton is. On a good induction system.
Say one that can do 500rwhp with a stock block 346. And 430rwtq, the 500rwhp made by 6500 and the 430rwtq is 5400 rpm.
IF you could do a vtec in there, and swap out whatever cam pulls you to this mark for a near stock cam for idle to 3000 rpm.
Would fuel mileage change much? We know from going to a 235@05" cam to a 210@.05" cam, idle vacuum is going to go up 4-6". Your going to be able to have a 600 or 700 rpm stable idle, but is the gain that much for cruising range?
Say one that can do 500rwhp with a stock block 346. And 430rwtq, the 500rwhp made by 6500 and the 430rwtq is 5400 rpm.
IF you could do a vtec in there, and swap out whatever cam pulls you to this mark for a near stock cam for idle to 3000 rpm.
Would fuel mileage change much? We know from going to a 235@05" cam to a 210@.05" cam, idle vacuum is going to go up 4-6". Your going to be able to have a 600 or 700 rpm stable idle, but is the gain that much for cruising range?
VTEC actually uses a different lobe on the cam when activated. Variable valve timing just does what the name implies.
Both can very much help... Variable intake geometry and exhaust runner length can also help.. now, does the gains offset the cost... ???
Both can very much help... Variable intake geometry and exhaust runner length can also help.. now, does the gains offset the cost... ???
Originally Posted by RussStang
What engine is this? It isn't their I6, V8, V10, or V12. Not any diesels I am aware of either.