LIFT AND DURATION
#1
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LIFT AND DURATION
Can someone explain to me the effect of changing cams on a turbo engine that:
a. have more lift
b. have more duration
I would like to understand the independent effect of changing the lift or duration.
Many thanks
a. have more lift
b. have more duration
I would like to understand the independent effect of changing the lift or duration.
Many thanks
#2
Well in theory both will give you more power at the top end at the expense of the bottom end.
BUT there are a lot of key things to consider, such as the ramp times and lift on overlap etc, turbo motors dont like to see both valves open at the same time the way that N/A motors do
BUT there are a lot of key things to consider, such as the ramp times and lift on overlap etc, turbo motors dont like to see both valves open at the same time the way that N/A motors do
#5
I cant find anything, only thing i could see is:
Which doesnt actually tell you ANYTHING about engines or how it effects the power, purely how to measure the cams themsleves.
and it certaily doesnt mention anything about turbo motors or things like the way they differ in cam requirements from N/A motors.
Is there another page which does have that info, or were you just mistaken?
Lift: This can be cam lift or valve lift. The latter being the cam lift multiplied by the rocker ratio. All lift figures in this catalogue refer to valve lift.
Duration: This is the length of time, measured in crankshaft degrees that the valve is off its seat. In the catalogue pages, Piper give you this figure as well as the timing figures. To calculate the duration, add the timing numbers together and add 180. EXAMPLE: a cam with timing figures of 23/67 added, totals 90, plus 180, gives 270 deg duration.
Overlap: The number of crankshaft degrees were both the inlet and exhaust valve are open at the same time. To calculate overlap: Add the opening number of the inlet cam to the closing number of the exhaust cam, ie the first and last numbers of the cam timing. Using our same example of the 23/67 inlet and 67/23 exhaust (usually referred to as 23/67 - 67/23), add together the first and last numbers (23 and 23) and the total (46) is the overlap. In general terms the larger this number or the greater the overlap, the hotter the cam.
Cam Timing: The position of the camshaft relative to the crankshaft. This is expressed as the number of degrees that full lift occurs after top dead centre (tdc) in the case of the inlet, and before tdc for the exhaust. This figure is included in the catalogue pages, but to calculate this, take the duration figure and divide by 2. EXAMPLE: With an inlet cam of 23/76, the duration is the addition of these two numbers, plus 180, equals 270. Then divide by 2 resulting in 135. Deduct the number of degrees before tdc that the valve started to open, ie 23 degrees - the result 112. The valve is correctly timed with full lift 112 degrees after tdc.
Valve Timing: The opening and closing position of inlet and exhaust valves relative to the crankshaft as figures before and after TDC and BDC
Lobe Angle: The angle between the inlet and exhaust lobe, measure in degrees.
Ramp: The ramp is the part of the profile that takes up the valve clearance and slack in the valve train gradually, before the valve is actually lifted from the seat. It also rests the valve gently back to the seat after the closing flank. Mechanical profiles use a much larger ramp than hydraulic ones, as the hydraulic cam follower should be in contact with the lobe at all times. The height of the ramp dictates what measurement the valve clearances should be set to.
Flank: This is the part of the profile between the ramp and nose. It is the most important part of the whole design. The flank controls the velocity and acceleration of the valve train. The acceleration / deceleration rate must be within the working limits of the valve spring, too much and valve float with occur. Generally high acceleration & velocity figures are beneficial to engine performance.
Nose radius: The larger the nose radius the better. Our profiles are designed to utilise the biggest nose radius possible to keep the stresses to a minimum.
Dwell: As the valve reaches full lift it will stop moving for a few degrees before starting to drop back towards the seat, this period is known as the dwell. When checking the cam timing using the full lift figure method the mid-point of the dwell should be taken as exact full lift.
Rocker Ratio: The ratio between valve motion vs cam follower motion. Push rod engines typically use a ratio of between 1.1:1 & 2.0:1. Over head cam, direct operating engines obviously have no rocker ratio as the cam follower motion is exactly the same as the valve motion.
Overall height: The measurement from the nose of the lobe to the bottom of the base circle, in a straight line through the centre of the lobe.
Base circle diameter: The measurement across the lobe, calculated by measuring the overall height and subtracting the cam lift.
Duration: This is the length of time, measured in crankshaft degrees that the valve is off its seat. In the catalogue pages, Piper give you this figure as well as the timing figures. To calculate the duration, add the timing numbers together and add 180. EXAMPLE: a cam with timing figures of 23/67 added, totals 90, plus 180, gives 270 deg duration.
Overlap: The number of crankshaft degrees were both the inlet and exhaust valve are open at the same time. To calculate overlap: Add the opening number of the inlet cam to the closing number of the exhaust cam, ie the first and last numbers of the cam timing. Using our same example of the 23/67 inlet and 67/23 exhaust (usually referred to as 23/67 - 67/23), add together the first and last numbers (23 and 23) and the total (46) is the overlap. In general terms the larger this number or the greater the overlap, the hotter the cam.
Cam Timing: The position of the camshaft relative to the crankshaft. This is expressed as the number of degrees that full lift occurs after top dead centre (tdc) in the case of the inlet, and before tdc for the exhaust. This figure is included in the catalogue pages, but to calculate this, take the duration figure and divide by 2. EXAMPLE: With an inlet cam of 23/76, the duration is the addition of these two numbers, plus 180, equals 270. Then divide by 2 resulting in 135. Deduct the number of degrees before tdc that the valve started to open, ie 23 degrees - the result 112. The valve is correctly timed with full lift 112 degrees after tdc.
Valve Timing: The opening and closing position of inlet and exhaust valves relative to the crankshaft as figures before and after TDC and BDC
Lobe Angle: The angle between the inlet and exhaust lobe, measure in degrees.
Ramp: The ramp is the part of the profile that takes up the valve clearance and slack in the valve train gradually, before the valve is actually lifted from the seat. It also rests the valve gently back to the seat after the closing flank. Mechanical profiles use a much larger ramp than hydraulic ones, as the hydraulic cam follower should be in contact with the lobe at all times. The height of the ramp dictates what measurement the valve clearances should be set to.
Flank: This is the part of the profile between the ramp and nose. It is the most important part of the whole design. The flank controls the velocity and acceleration of the valve train. The acceleration / deceleration rate must be within the working limits of the valve spring, too much and valve float with occur. Generally high acceleration & velocity figures are beneficial to engine performance.
Nose radius: The larger the nose radius the better. Our profiles are designed to utilise the biggest nose radius possible to keep the stresses to a minimum.
Dwell: As the valve reaches full lift it will stop moving for a few degrees before starting to drop back towards the seat, this period is known as the dwell. When checking the cam timing using the full lift figure method the mid-point of the dwell should be taken as exact full lift.
Rocker Ratio: The ratio between valve motion vs cam follower motion. Push rod engines typically use a ratio of between 1.1:1 & 2.0:1. Over head cam, direct operating engines obviously have no rocker ratio as the cam follower motion is exactly the same as the valve motion.
Overall height: The measurement from the nose of the lobe to the bottom of the base circle, in a straight line through the centre of the lobe.
Base circle diameter: The measurement across the lobe, calculated by measuring the overall height and subtracting the cam lift.
Which doesnt actually tell you ANYTHING about engines or how it effects the power, purely how to measure the cams themsleves.
and it certaily doesnt mention anything about turbo motors or things like the way they differ in cam requirements from N/A motors.
Is there another page which does have that info, or were you just mistaken?
#6
10K+ Poster!!
Lift is how far the valve comes off the seat... all turbo engines love lift.... the problem with incresing lift is that you physically need to open the vlave faster if you want it to move furthur in the same amount of time - great but puts strain on the valve train and cam lobes.
Duration is how long the valve is left open for... this increases somthing call over lap - where the inlet and exhaust valves are open at the same time. This is not a huge problem on NA cars but once you add a turbo its not really a great help blowing boost down the exhaust.
Alex
Duration is how long the valve is left open for... this increases somthing call over lap - where the inlet and exhaust valves are open at the same time. This is not a huge problem on NA cars but once you add a turbo its not really a great help blowing boost down the exhaust.
Alex
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#8
doug, thats cause we dont have "all the gear and no idea" like on the MLR
you must fit in really well over there
did you get my text about the ring?
fancy coming along?
im sure lots of people can give you a passenger ride if you (understandabley) dont want to take your just built car over.
you must fit in really well over there
did you get my text about the ring?
fancy coming along?
im sure lots of people can give you a passenger ride if you (understandabley) dont want to take your just built car over.
#9
DEYTUKURJERBS
LOL@Chip, sounds like the GTR board too
They all go for 270-280deg cams then wonder why their cars have wank powerbands I had a massive argument with them on a thread years ago about this, i get a sneaky feeling I got thru in the end.
Thing is there, most people are too spineless so I had tons of people PMing me saying i was right and they all wankers, but nobody dared to post
Turbo and n/a cam tuning is VERY different, madness tuning a turbo car like a n/a, you arnt making the most the advantages you have.
What J871yhk/Alex said is spot on- Lift is nice and will have little if any downsides, duration can give you more power, but can totally fuck powerband iof done wrong.
They all go for 270-280deg cams then wonder why their cars have wank powerbands I had a massive argument with them on a thread years ago about this, i get a sneaky feeling I got thru in the end.
Thing is there, most people are too spineless so I had tons of people PMing me saying i was right and they all wankers, but nobody dared to post
Turbo and n/a cam tuning is VERY different, madness tuning a turbo car like a n/a, you arnt making the most the advantages you have.
What J871yhk/Alex said is spot on- Lift is nice and will have little if any downsides, duration can give you more power, but can totally fuck powerband iof done wrong.
#11
Originally Posted by Itsmeagain
Turbo and n/a cam tuning is VERY different, madness tuning a turbo car like a n/a, you arnt making the most the advantages you have.
People would do well to look towards N/A tuning techniques (like headwork) earlier on with tuning turbos rather than just grabbing for the bleed valve or whatever.
#15
DEYTUKURJERBS
oh yea, shape etc is cool, i was almost thinking you talking the traditional GTR route of humungous ports and 280deg 11mm lift cams on relativley mild power engines
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