VVT effect on DCR. (question)
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From: Elswhere
VVT effect on DCR. (question) I've recently been studying the way VVT effects dynamic compression, and have a basic question; can you design a cam that can cover a wide range dynamic compressions? Also, what is the change in compression on a stock l92/99 from full advance to full retard? Maybe not the most accurate point of comparison, taking into account the economy based tune, but I still think the information could be useful. I'm mainly thinking about how VVT could help forced induction, considering that it lacks compression out of boost.
Last edited by Mr. Sir; Feb 7, 2012 at 06:45 AM.
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From: PA/MD
I have no clue, but I'm in for answers
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I would like to see what using the technology for vvt economy could do if used for increasing power output. Or even better, how about somehow using oil pressure through a switch, or magnetic variable/ adjustable rocker ratio?
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I would like to see what using the technology for vvt economy could do if used for increasing power output. Or even better, how about somehow using oil pressure through a switch, or magnetic variable/ adjustable rocker ratio?
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it changes the centerline by advancing or retarding the camshaft in thus changin valve events advancing the camshaft will yield a higher cylinder pressure and retarding will bleed pressure off as the piston travles on the compression stroke as of the intake valve will partially still be open
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From: Elswhere
Broader power band. Something I could use the generate good top end power, while supporting an idea like this on the low end (another thread of mine):
https://ls1tech.com/forums/automatic...ble-stall.html
And the oil activated/magnetic variable ratio rockers... look at VANOS (BMW). I personally think vtek is less accident prone, and catastrophic failure is pretty unlikely, as opposed to VANOS. Implementing either into an ohv application would be quite a hurdle. And retrofitting it to older ohv motors... fjdfdshugkj.
I understand that much. What I really want to know is to what degree you can effect the dcr with proper valve events, and if those valve events, while generating a wide range of dcr's, have been compromised to the point that your net power doesn't increase over a more conventional set of valve events not aimed at significantly changing the DCR.
So I want to know if two cams can generate similar theoretical flow numbers, and if the one capable of higher DCR will generate more low end, but at full retard have a low enough dcr to run significant boost. (wide range of dcr's)
https://ls1tech.com/forums/automatic...ble-stall.html
And the oil activated/magnetic variable ratio rockers... look at VANOS (BMW). I personally think vtek is less accident prone, and catastrophic failure is pretty unlikely, as opposed to VANOS. Implementing either into an ohv application would be quite a hurdle. And retrofitting it to older ohv motors... fjdfdshugkj.
I understand that much. What I really want to know is to what degree you can effect the dcr with proper valve events, and if those valve events, while generating a wide range of dcr's, have been compromised to the point that your net power doesn't increase over a more conventional set of valve events not aimed at significantly changing the DCR.
So I want to know if two cams can generate similar theoretical flow numbers, and if the one capable of higher DCR will generate more low end, but at full retard have a low enough dcr to run significant boost. (wide range of dcr's)
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From: Elswhere
So... you think I'm a ricer? I didn't know Honda made Camaro's.
I've studied all types of engines AND their technologies. If I didn't, I'd come on here with questions and get told to use the search button (which is horribly broken by the way).
I've studied all types of engines AND their technologies. If I didn't, I'd come on here with questions and get told to use the search button (which is horribly broken by the way).
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You do really need how to use the search button in here to find what your looking for...can use it and still look all day and not find what your looking for if you don't put in the right word or phrase.
Anyway, back on topic. 1st off who cares it he is s Honda guy or a hardcore Ford or Chevy guy? The question is still a very good one.
Kind of along the same line, how about dual overhead cam engines (like Honda)....what if you could have two sets of tensioners that could be moved together (1 between the cams, 1 before or after the cams) to change the lobe separation through the rpm and throttle range to always have optimum cam operation along with Vtec, vvt or whatever each company calls there setup.
I know Vtec is good for around a whooping peak 5-10 HP, but if you could always have the optimum lsa you might be able to get that extra 5-10 across the whole rpm range...maybe even more, plus better fuel mileage...which gets us back to the original question, any time you change the intake valve timing you will change dynamic compression...the later the valve closes the lower the dynamic compression,the earlier it closes the higher your dynamic compression.
Anyway, back on topic. 1st off who cares it he is s Honda guy or a hardcore Ford or Chevy guy? The question is still a very good one.
Kind of along the same line, how about dual overhead cam engines (like Honda)....what if you could have two sets of tensioners that could be moved together (1 between the cams, 1 before or after the cams) to change the lobe separation through the rpm and throttle range to always have optimum cam operation along with Vtec, vvt or whatever each company calls there setup.
I know Vtec is good for around a whooping peak 5-10 HP, but if you could always have the optimum lsa you might be able to get that extra 5-10 across the whole rpm range...maybe even more, plus better fuel mileage...which gets us back to the original question, any time you change the intake valve timing you will change dynamic compression...the later the valve closes the lower the dynamic compression,the earlier it closes the higher your dynamic compression.
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From: PA/MD
But even the I-Vtec uses fixed lobes and fixed cam positions, just locks and unlocks the rockets on the 3rd lobe....I'm talking about actually changing the cam positions relative to each other on a variable basis, not just like an on/off switch like the hondas do
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From: Elswhere
From Wikipedia: "The performance i-VTEC system is basically the same as the DOHC VTEC system of the B16A's; both intake and exhaust have 3 cam lobes per cylinder. However the valve train has the added benefit of roller rockers and continuously variable intake cam timing".
So I guess I misread, the VVT is only for the intake cam. However, The system is still more versatile, because it can adjust timing and LSA (as opposed to timing only), plus it has 3 lobes. Still not sure how much it can change DCR though. Anybody have thoughts on that part? ANYONE?
So I guess I misread, the VVT is only for the intake cam. However, The system is still more versatile, because it can adjust timing and LSA (as opposed to timing only), plus it has 3 lobes. Still not sure how much it can change DCR though. Anybody have thoughts on that part? ANYONE?
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From: PA/MD
the longer duration intake lobe closes later, so your dynamic compression would slightly drop, but by having both intake and exhaust valves cracked open at the same time (overlap) the escaping spent exhaust gases leaving the cylinder create a super low pressure which pulls more intake charge in giving a more complete cylinder fill...so in theory with the right valve timing even though your dynamic compression drops you can have well over a 100% VE.
but I'm sure on stock applications we are talking VERY small changes.
but I'm sure on stock applications we are talking VERY small changes.
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From: Elswhere
... Well, this isn't going anywhere. Pat G, if you see this thread, could you grace it with your presence? If you do I'll go into all the "cam recommendations" threads and put in your contact info. If they ask for more recommendations, I'll do it again.