Cam suggestions for 455 with ported L92s
12-26-2007, 07:48 AM
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Cam suggestions for 455 with ported L92s I have a 408 now with 10.7:1 compression and am running a 236/238 with .595/.598 lift on 114 LSA. Car idles and drives just right but I think I could run more on a 455 with 11.2:1
I'm thinking I should run more lift because the L92s flow so well between .600 and .700 lift. Also it seems like I need a bigger split... But should I still consider more intake duration?
I'm thinking I should run more lift because the L92s flow so well between .600 and .700 lift. Also it seems like I need a bigger split... But should I still consider more intake duration?
12-26-2007, 12:57 PM
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Well, I like the way you think.... but I have to drive this thing about 500 miles a week for work. It's been getting around 26 mpg. with the 408 and the current cam, I'd like to keep it around there and a surge free cruise at 1800 rpm.
Doesn't shortening the intake duration a little improve torque production down low? I was thinking something like the Katech torquer except a little more intake duration, something like 228/248 .640/.640 on 114 lsa with 1.7 L92 rocker. They say you don't need as much intake duration with these heads and I want horsepower and torque output to be very similar, like 580rwhp/580rwtq
Anyone want to chime in?
Doesn't shortening the intake duration a little improve torque production down low? I was thinking something like the Katech torquer except a little more intake duration, something like 228/248 .640/.640 on 114 lsa with 1.7 L92 rocker. They say you don't need as much intake duration with these heads and I want horsepower and torque output to be very similar, like 580rwhp/580rwtq
Anyone want to chime in?
12-26-2007, 01:50 PM
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Well, I like the way you think.... but I have to drive this thing about 500 miles a week for work. It's been getting around 26 mpg. with the 408 and the current cam, I'd like to keep it around there and a surge free cruise at 1800 rpm.
Doesn't shortening the intake duration a little improve torque production down low? I was thinking something like the Katech torquer except a little more intake duration, something like 228/248 .640/.640 on 114 lsa with 1.7 L92 rocker. They say you don't need as much intake duration with these heads and I want horsepower and torque output to be very similar, like 580rwhp/580rwtq
Anyone want to chime in?
Doesn't shortening the intake duration a little improve torque production down low? I was thinking something like the Katech torquer except a little more intake duration, something like 228/248 .640/.640 on 114 lsa with 1.7 L92 rocker. They say you don't need as much intake duration with these heads and I want horsepower and torque output to be very similar, like 580rwhp/580rwtq
Anyone want to chime in?
Why not go with something in the 232/248 range.... keep in mind that those are fake numbers and seat timing needs to be looked at. The 230's duration on the intake in a cubed motor will act like a 220's! My 244 seems to drive and sound like a small 230 cam. i also wouldnt do that lift. Based on my flow numbers for my ported L92's, I didnt pick up much after .620 lift.... .why give the springs extra bind and wear? Last but not least... the 114 LSA will be good on MPG and idle smoother than a 111 or 112.
your seat timing events on that 232/248 number are:
5 intake open
47 intake close
61 exhaust open
7 exhaust close
12 degrees of overlap and 3 degrees advance if the ICL is 111
These seat timing numbers is what you need to look at..... duration and split are not what makes cams perform well. Ask someone who understands seat timing and you will get a cam that not only idles well... but also performs.
12-26-2007, 01:54 PM
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btw... a 238/248 actually looks nice.
8 intake open
50 intake close (something Patrick G said would work nice on an L92 iirc by keeping the DCR up)
61 exhaust open
7 exhaust close
15 degrees of overlap (should keep the idle nice and easy
with a ICL of 111 you will have 3 degrees of advance.
8 intake open
50 intake close (something Patrick G said would work nice on an L92 iirc by keeping the DCR up)
61 exhaust open
7 exhaust close
15 degrees of overlap (should keep the idle nice and easy
with a ICL of 111 you will have 3 degrees of advance.
Ok, now this is my understanding of things. There are four timing parameters that define how your engine will operate. These are intake valve opening (IVO), intake valve closing (IVC), exhaust valve opening (EVO) and exhaust valve closing (EVC). It is relatively easy to derive these parameters from the specs supplied by camshaft vendors (lobe center angle (LCA), intake centerline (IC), intake duration (ID), and exhaust duration (ED)) assuming all these parameters are specified.
IVO = ID/2 – IC
IVC = ID – IVO – 180
EVO = ED – EVC – 180
EVC = ED/2 – 2*LCA – IC
To really appreciate how an engine works, and how to get the most performance, we must talk about wave dynamics. But I should warn you that even this discussion is a simplified view of engine operation. As gases move in and out of an engine, they are constantly compressed and expanded, heated and cooled, with laminar and turbulent flow. Each valve edge, bend in a pipe, gasket, fitting, thermal change, etc. has an affect on how these gases flow and will affect the behavior of the engine. Even complex computer simulations cannot fully predict engine behavior, but they can come pretty close. When valves open in an internal combustion engine, gases don’t just flow smoothly into or out of the cylinder. There is usually a significant pressure differential between the two sides of the valve when it opens. This causes a sudden acceleration of gas molecules that form a pressure wave. This is similar to an acoustic wave caused by clapping your hands, but the pressure waves have thousands of times higher pressure differentials.
But the pressure waves still behave in much the same way as acoustic waves. Pressure waves can be positive compression waves, or negative expansion waves (sometimes called rarefaction waves). The behavior of these pressure waves in a pipe is very important to understanding engine performance.
When a pressure wave traveling down a pipe encounters a closed end (such as a closed valve), it will be reflected back in its original form (i.e., a compression wave is reflected back as a compression wave). But when a pressure wave encounters an open end (such as open headers), it is reflected back “out of phase”, so the reflected compression wave becomes an expansion wave. These reflected waves can be used to great value in optimizing engine performance.
Valve timing events are referenced to TDC (top dead center – the piston is at the top of its travel) and BDC (bottom dead center – piston at the bottom). If a valve event is specified as 20 degrees ATDC, this means that it occurs when the crankshaft has rotated 20 degrees past (after) when the piston was at TDC. Likewise BBDC means crankshaft degrees before bottom dead center.
In a simple engine model, we’d expect the exhaust valve to open at the end of the POWER stroke when the crank was at BDC. The piston would then force the exhaust our of the cylinder during the EXHAUST stroke. It turns out that this valve timing is very inefficient. By the time the crank has reached 25 to 30 degrees past TDC during the POWER stroke, almost all the power has been transferred to the crank. By opening the exhaust valve (EVO) during the middle of the POWER stroke, we can take advantage of the residual pressure in the cylinder to start to blow the exhaust our instead of forcing the piston to pump the exhaust out. Of course, there’s a delicate balance between the power wasted by opening the valve too early and the power wasted by forcing the engine to pump out the exhaust.
But there’s an added benefit of early EVO. The high pressure in the cylinder when the valve opens will cause a strong compression wave to be generated out the exhaust port. This compression wave will reach the end of the headers and reflect back as an expansion wave. If this expansion wave reaches the cylinder before the exhaust valve closes, and can further assist in removing the last remnants of exhaust from the cylinder and even assist in starting with the intake of fresh fuel/air mixture as we’ll discuss below.
A mild street cam generally sets EVO at 65 to 66 degrees BBDC, while an aggressive racing cam might set EVO as much as 85 degrees BBDC (although keep in mind that this is when the valve just starts to open, not when significant flow can occur).
The next valve timing event to occur is the intake valve opening (IVO). Note that this occurs before the exhaust valve is closed. IVO is the least sensitive of the valve timing events, but an earlier valve opening can benefit from a broad expansion wave from the exhaust system to help accelerate the air/fuel mixture. If an expansion wave is not present, early IVO timing will allow exhaust gases to flow into the induction system since the cylinder pressure will almost certainly be higher than the intake pressure. This is called reversion and will have a damaging effect on performance by contaminating the fresh fuel/air mixture and heating it up (making it less dense).
A typical mild street cam will open the intake valve around 10-12 degrees BTDC. The IVO for an aggressive race cam will be as early as 50 degrees BTDC. For a high performance street engine, the benefits of going beyond 20-25 degrees BTDC do not seem to outweigh the risks of reversion at lower RPM.
The next valve timing event is EVC, exhaust valve closing. This determines the end of the overlap period (when both valves are open) and, of course, the end of the exhaust cycle. If a strong scavenging wave from the exhaust system is present, a later EVC can provide significant help in drawing in the gasses from the intake. With properly tuned headers, the scavenging expansion wave will be at its peak at the RPM that delivers maximum power, further increasing power. But at lower RPMs, this expansion wave will arrive early and will be followed by a positive compression wave. If this compression wave arrives before EVC, reversion will result, significantly affecting performance. This is why “hot” cams that are designed to maximize high RPM horsepower have such poor idle characteristics.
Exhaust valve closing typically occurs around 10 degrees ATDC with a mild street cam and can occur as late as 50 degrees ATDC on a hot race cam. Typical high performance street engines will have EVC at around 30 degrees ATDC.
The final valve timing event is the intake valve closing. This is probably the most important valve event and the most sensitive to the induction system used on the engine. The more fuel/air mixture that can be forced into the cylinder, the higher the performance will be. So IVC is normally delayed until well into the COMPRESSION stroke. But if IVC is delayed too far, the building pressure in the cylinder due to the piston upswing will exceed the induction systems ability (through pressure waves and gas molecule momentum) to hold back the pressure and fuel/air will flow back out of the cylinder.
As with the exhaust, a pressure wave will be generated in the intake as well. In this case, an expansion wave is generated although will less amplitude than the exhaust pressure wave. The strength of this wave will be determined by the amount of suction that can be created in the cylinder resulting from the piston downswing and the exhaust scavenging wave.
When the expansion wave reaches the end of the intake runners (or the top of the air horns in they EFI system we’re using), it is reflected back as a compression wave. By the time this wave reaches the cylinder, the intake valve is closed and the wave bounces back out. This wave continues to oscillate in the intake system until the next time the intake valve opens. Since the length of the intake runners are typically significantly shorter than the exhaust headers, the frequency of the pressure wave is considerably higher – usually two to three times higher – so by the time IVO occurs, the wave has bounced back and forth several times.
As with headers, the intake system must be tuned for a particular RPM to deliver the most benefit from this pressure wave oscillation. The air horns on some induction systems (Webers, TWM, Kinsler) are designed to spread the reflection wave so that it will provide benefit over a broader RPM range.
Intake Valve Closing is typically set at around 60 degrees after BDC on a mild street came, and as much as 85 degrees ABDC (almost to TDC) on a very hot race cam. An engine with this kind of hot cam will have a very narrow power peak and be designed to run at very high RPMs. For a high performance street engine with a well tuned induction system, IVC should be 65 to 70 degrees ABDC.
IVO = ID/2 – IC
IVC = ID – IVO – 180
EVO = ED – EVC – 180
EVC = ED/2 – 2*LCA – IC
To really appreciate how an engine works, and how to get the most performance, we must talk about wave dynamics. But I should warn you that even this discussion is a simplified view of engine operation. As gases move in and out of an engine, they are constantly compressed and expanded, heated and cooled, with laminar and turbulent flow. Each valve edge, bend in a pipe, gasket, fitting, thermal change, etc. has an affect on how these gases flow and will affect the behavior of the engine. Even complex computer simulations cannot fully predict engine behavior, but they can come pretty close. When valves open in an internal combustion engine, gases don’t just flow smoothly into or out of the cylinder. There is usually a significant pressure differential between the two sides of the valve when it opens. This causes a sudden acceleration of gas molecules that form a pressure wave. This is similar to an acoustic wave caused by clapping your hands, but the pressure waves have thousands of times higher pressure differentials.
But the pressure waves still behave in much the same way as acoustic waves. Pressure waves can be positive compression waves, or negative expansion waves (sometimes called rarefaction waves). The behavior of these pressure waves in a pipe is very important to understanding engine performance.
When a pressure wave traveling down a pipe encounters a closed end (such as a closed valve), it will be reflected back in its original form (i.e., a compression wave is reflected back as a compression wave). But when a pressure wave encounters an open end (such as open headers), it is reflected back “out of phase”, so the reflected compression wave becomes an expansion wave. These reflected waves can be used to great value in optimizing engine performance.
Valve timing events are referenced to TDC (top dead center – the piston is at the top of its travel) and BDC (bottom dead center – piston at the bottom). If a valve event is specified as 20 degrees ATDC, this means that it occurs when the crankshaft has rotated 20 degrees past (after) when the piston was at TDC. Likewise BBDC means crankshaft degrees before bottom dead center.
In a simple engine model, we’d expect the exhaust valve to open at the end of the POWER stroke when the crank was at BDC. The piston would then force the exhaust our of the cylinder during the EXHAUST stroke. It turns out that this valve timing is very inefficient. By the time the crank has reached 25 to 30 degrees past TDC during the POWER stroke, almost all the power has been transferred to the crank. By opening the exhaust valve (EVO) during the middle of the POWER stroke, we can take advantage of the residual pressure in the cylinder to start to blow the exhaust our instead of forcing the piston to pump the exhaust out. Of course, there’s a delicate balance between the power wasted by opening the valve too early and the power wasted by forcing the engine to pump out the exhaust.
But there’s an added benefit of early EVO. The high pressure in the cylinder when the valve opens will cause a strong compression wave to be generated out the exhaust port. This compression wave will reach the end of the headers and reflect back as an expansion wave. If this expansion wave reaches the cylinder before the exhaust valve closes, and can further assist in removing the last remnants of exhaust from the cylinder and even assist in starting with the intake of fresh fuel/air mixture as we’ll discuss below.
A mild street cam generally sets EVO at 65 to 66 degrees BBDC, while an aggressive racing cam might set EVO as much as 85 degrees BBDC (although keep in mind that this is when the valve just starts to open, not when significant flow can occur).
The next valve timing event to occur is the intake valve opening (IVO). Note that this occurs before the exhaust valve is closed. IVO is the least sensitive of the valve timing events, but an earlier valve opening can benefit from a broad expansion wave from the exhaust system to help accelerate the air/fuel mixture. If an expansion wave is not present, early IVO timing will allow exhaust gases to flow into the induction system since the cylinder pressure will almost certainly be higher than the intake pressure. This is called reversion and will have a damaging effect on performance by contaminating the fresh fuel/air mixture and heating it up (making it less dense).
A typical mild street cam will open the intake valve around 10-12 degrees BTDC. The IVO for an aggressive race cam will be as early as 50 degrees BTDC. For a high performance street engine, the benefits of going beyond 20-25 degrees BTDC do not seem to outweigh the risks of reversion at lower RPM.
The next valve timing event is EVC, exhaust valve closing. This determines the end of the overlap period (when both valves are open) and, of course, the end of the exhaust cycle. If a strong scavenging wave from the exhaust system is present, a later EVC can provide significant help in drawing in the gasses from the intake. With properly tuned headers, the scavenging expansion wave will be at its peak at the RPM that delivers maximum power, further increasing power. But at lower RPMs, this expansion wave will arrive early and will be followed by a positive compression wave. If this compression wave arrives before EVC, reversion will result, significantly affecting performance. This is why “hot” cams that are designed to maximize high RPM horsepower have such poor idle characteristics.
Exhaust valve closing typically occurs around 10 degrees ATDC with a mild street cam and can occur as late as 50 degrees ATDC on a hot race cam. Typical high performance street engines will have EVC at around 30 degrees ATDC.
The final valve timing event is the intake valve closing. This is probably the most important valve event and the most sensitive to the induction system used on the engine. The more fuel/air mixture that can be forced into the cylinder, the higher the performance will be. So IVC is normally delayed until well into the COMPRESSION stroke. But if IVC is delayed too far, the building pressure in the cylinder due to the piston upswing will exceed the induction systems ability (through pressure waves and gas molecule momentum) to hold back the pressure and fuel/air will flow back out of the cylinder.
As with the exhaust, a pressure wave will be generated in the intake as well. In this case, an expansion wave is generated although will less amplitude than the exhaust pressure wave. The strength of this wave will be determined by the amount of suction that can be created in the cylinder resulting from the piston downswing and the exhaust scavenging wave.
When the expansion wave reaches the end of the intake runners (or the top of the air horns in they EFI system we’re using), it is reflected back as a compression wave. By the time this wave reaches the cylinder, the intake valve is closed and the wave bounces back out. This wave continues to oscillate in the intake system until the next time the intake valve opens. Since the length of the intake runners are typically significantly shorter than the exhaust headers, the frequency of the pressure wave is considerably higher – usually two to three times higher – so by the time IVO occurs, the wave has bounced back and forth several times.
As with headers, the intake system must be tuned for a particular RPM to deliver the most benefit from this pressure wave oscillation. The air horns on some induction systems (Webers, TWM, Kinsler) are designed to spread the reflection wave so that it will provide benefit over a broader RPM range.
Intake Valve Closing is typically set at around 60 degrees after BDC on a mild street came, and as much as 85 degrees ABDC (almost to TDC) on a very hot race cam. An engine with this kind of hot cam will have a very narrow power peak and be designed to run at very high RPMs. For a high performance street engine with a well tuned induction system, IVC should be 65 to 70 degrees ABDC.
Last edited by WizeAss; 12-26-2007 at 02:01 PM.
12-28-2007, 04:00 PM
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Wow... in order to get close to the numbers this guy recommends for a "mild street cam) I had to plug in 252/262 duration on a 114 LSA with no adv./ret. (basically 114 IC).
Is anyone running a cam that hot in a 427 or 454? How does it idle, cruise, etc. and what does the torque band look like?
Is anyone running a cam that hot in a 427 or 454? How does it idle, cruise, etc. and what does the torque band look like?
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12-29-2007, 11:53 AM
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240/252 .650/.661 here, it chops, bucks once in a while (cruises like stock in 6th gear), but its **** and very tolerale, tune has a lot to do with driveability and how the car behaves
12-29-2007, 12:13 PM
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46 intake close
60 exhaust open
12 exhaust close
26 degrees of overlap and 4 degrees advance with the following Lobe Separation: 110 +4 LSA......
what was yours ground on?
vs:
18 intake open
50 intake close
67 exhaust open
19 exhaust close
37 degrees overlap and 4 degrees advance.
vs
TREX??
242/248 110+0
11 intake open
51 intake close
54 exhaust open
14 exhaust close
25 degrees of overlap
HMMMM.... interesting information nonetheless.
Last edited by WizeAss; 12-29-2007 at 12:19 PM.
12-29-2007, 01:10 PM
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9 intake open
51 intake close
63 exhaust open
9 exhaust close
18 degrees of overlap and 3 degrees advance ground in.
LSK.... damn... wonder what the .006 numbers look like!
With the 18.... overlap.... no wonder it is fairly quiet.
