What I've Learned in My Search for a Torque Cam for my LS3
12-12-2011, 12:24 AM
#1
Instructor
Thread Starter
What I've Learned in My Search for a Torque Cam for my LS3
It seems I’m not the only one looking for more LOW end out of an LS3 motor, so I thought I’d share some of what I learned in my search for a cam that would add torque, but not necessarily horsepower.
My goals were to add boost between 2500-4500 rpm, that range that we spend the most time in when we’re passing a car or jetting under a yellow on the street. I don’t race my car, and I commonly have a passenger, so here was the cam criteria:
1. Add 20 – 30 ft/lbs above a stock torque curve between 2500 – 4500 rpm.
2. Keep the car as “driveable” as the stock car; and that means easy starting, smooth part throttle operation, absolutely no surging at part throttle or lower rpm.
3. Keep the noise level down as close to stock as possible.
4. No loping.
5. Keep lifts moderate to minimize valve train wear.
6. Adding more peak horsepower was fine, but just a bonus, not the goal.
So the standard formula for this is described as “high lift, low duration”. Seems simple enough. What I learned, though, is that high lift and low duration only create the potential for a low end cam – how you position the lobes and why you put them there is what this post is all about.
Two of the main contributors to low end torque are Cold Cranking Pressure (sometimes called “Dynamic Compression”), and how long we can apply the pressure to the piston.
CCP is not compression ratio – it is the actual combustion chamber pressure at TDC in Pounds per Square Inch, or PSI. This is determined, in a large way, by the point at which the upcoming piston actually starts to compress the incoming fresh fuel/air mix, which is determined by the point at which the intake valve closes. I can have a motor that is set up with 11:1 compression creating 185 psi CCP, and/or a motor with a 10:1 compression ratio generating 195 psi CCP – and it all depends on the cam. So before you go decking your heads, find out where the intake valve is going to close with your new cam, and add that into the equation.
Rule number 1: A cam with an early intake closing will increase low end torque.
Seems pretty easy. But in the world of cams, as you will see, everything is a trade off. The more I increase CCP, the more I increase the chances of detonation. To prevent detonation, I roll back the timing, which rolls back the power. It’s a balancing act. Where you end up is up to you.
Okay, so now that I’ve compressed the fuel/air mix as far as I dare, the ignition ignites it, and the piston heads down on the power stroke. The second way to increase low end torque is to keep all that pressure applied to the piston as long as possible; and what relieves the pressure is the opening of the exhaust valve, which occurs long before Bottom Dead Center. So we want that exhaust valve to open as late as possible. I can certainly design a cam with a very late exhaust opening, so that one should be easy. Or is it?
Rule number 2: A cam with a late exhaust opening will increase low end torque.
With the exhaust valve open, the piston “turns the corner” at BDC and rushes to the top of the cylinder, pushing out the burned fuel/air mix. But we also know that that fuel/air exiting the exhaust port has momentum, and that momentum will create a suction as the piston stops pushing up. And by keeping the exhaust valve open past Top Dead Center, that suction will help to pull the new fuel/air mix past the intake valve, which opened before TDC. To a point. Knowing this, engineers design cams with “overlap” – which is the number of degrees during which the intake valve has opened, but the exhaust valve has not yet closed. This overlap creates one of the greatest design compromises, and has one of the largest effects on how a cam will cause your motor to behave. Here’s why:
In the overall 720 degrees of a 4-stroke cycle, this overlap occurs for a relatively short period of time – some 20 to sixty degrees of crankshaft revolution (from seat to seat). It’s brief. And as the motor revs up, the period of actual time that the two valves are open and affecting each other shortens, until the exhaust is having minimal effect on the intake charge. But wait… can’t I control that…? If I close the exhaust valve later, the exhaust charge will affect the intake for a longer period of time, right?
Right. Unfortunately, that same overlap will be there when the motor is at a lower rpm – and instead of just creating a suction that will assist the incoming fuel charge, as the piston rounds the corner at a slower speed, not only will the suction stop, but the receding piston will start to draw the exiting exhaust back into the incoming fuel/air mix through the not-yet-closed exhaust valve. Gaaaa! So which way do I go?
Rule number 3: Shorter overlaps will be likely to contribute more to low end torque. Longer overlaps will be likely to contribute more to top end horsepower.
Okay, so now it’s starting to fall into place. If I want a low end cam, I want the exhaust valve to open as late as possible, but the more I turn that lobe to “later”, the later the exhaust valve is going to close as well, increasing overlap! The solution: SHORTEN THE DURATION. See? Everything you do in cam design affects something else, and it’s all a compromise. Let’s take a look at the intake. I know that I want the intake to close as early as possible to increase CCP, but the more I turn the intake toward “early”, the earlier it opens as well, and guess what? Increases overlap. The solution? SHORTEN THE DURATION. Using a shorter duration decreases overlap, and overlap decreases effective combustion at lower rpm.
Unfortunately, short duration also limits the amount of fuel and air I can move through the motor, so that’s not very helpful. What good is adding 20 ft/lbs at 3,000 rpm if I lose 50 at the top? The only way to get more air into the cylinder in a shorter period of time is to make the hole bigger – which means more lift. (Or add manifold pressure with a supercharger, but that’s another story.) How much lift you add depends on how much wear and tear you’re willing to accept on your valve train, and how little piston-to-valve clearance you’re willing to risk – one more reason to consider earlier IVC instead of head decking, and yup, another compromise.
So now we see that its not short duration that necessarily makes more low end torque, short duration just allows me to set timing points that are likely to make low end torque. And although high lift will almost certainly allow more fuel and air into the engine, in our case, it is a necessity brought on by the compromise of the shorter duration.
Okay, back to overlap. There’s a lot of talk about “LSA” (Lobe Separation Angle) when we’re deciding on a cam, and a general feeling that lower LSA creates loping. Well, it might… and it might not. What actually causes loping is low vacuum in the MAP sensor, at the intake. And what causes low vacuum at the intake…? Our old friend Overlap. We know that the exhaust charge helps to suck in the fresh intake charge, but as the overlap now increases due to early intake opening (read: longer duration intake lobes or an attempt to get an earlier IVC) there is not enough exhaust velocity yet at low rpm to create an effective vacuum, and, in fact, the exhaust actually starts getting pushed out the intake tract, cancelling the momentum of the incoming charge and turning the intake column into a series of choppy waves instead of a smooth flow of air through the MAP sensor. Some high end cams won’t even idle at normal rpm, and have to be turned up just to run. In less severe cases, the motor “lopes” due to the choppy character of the intake charge, which kind of “bunches” the incoming charge together in blobs and creates misfires until the rpm comes up and that long overlap becomes very effective at sucking in the intake charge, effectively enhancing atmospheric pressure like a supercharger. So what does this have to do with LSA?
A smaller LSA closes the intake valve sooner, (good!) opens the exhaust valve later (good!) aaaaaaaand….. increases overlap. Darn. There had to be a compromise there somewhere. But it’s okay for us low end guys, because in general (this is just a rule of thumb) a motor will start loping not a specific LSA, but at a specific overlap (low vacuum, remember?) and that point is right around zero degrees with valve lift measured at .050. Once again, our short duration cam lobes save us – a 218/222 cam with a LSA of 114 and an Intake Centerline of 109 gives us an IVC of 38 degrees ABDC (pretty early); an EVO of 50 degrees BBDC (pretty late); and an overlap of negative 8 (well below zero), so we should be well within our goal of a smooth idle and good low rpm cruising while maximizing our two primary torque criteria, higher CCP and longer pressure application. Not a bad compromise… this was the cam that I designed for my LS3, and I can only hope (being untested) that I haven’t designed in any reversion waves that will create sags in the torque curve. We’ll find out when I get it installed!
Our last goal was noise… or lack thereof. The good news is that our late exhaust opening is a lot more likely to attenuate the sound wave generated by combustion; but in the example I listed above, we are still opening 12 degrees earlier than the stock LS3 cam. GM would love to design a cam for maximum performance everywhere, but they are handicapped by the EPA and other government agencies that limit noise and emissions. So it looks like my cam design will be a little louder than stock – and the NPP flaps are gonna be closed at low rpm again.
So there you have it. I hope that’s helpful to some of you starting to negotiate the complex world of cams. I am not a cam designer, nor an engine builder with years of experience – just a guy who spent a lot of time trying to get to the bottom of WHY cams do what they do, and I thought I would pass on my research (for what it’s worth) to the rest of you. Cam experts, PLEASE feel free to chime in if you feel any of this is just outright wrong – the idea is to inform, not mislead. Thanks! Jon
My goals were to add boost between 2500-4500 rpm, that range that we spend the most time in when we’re passing a car or jetting under a yellow on the street. I don’t race my car, and I commonly have a passenger, so here was the cam criteria:
1. Add 20 – 30 ft/lbs above a stock torque curve between 2500 – 4500 rpm.
2. Keep the car as “driveable” as the stock car; and that means easy starting, smooth part throttle operation, absolutely no surging at part throttle or lower rpm.
3. Keep the noise level down as close to stock as possible.
4. No loping.
5. Keep lifts moderate to minimize valve train wear.
6. Adding more peak horsepower was fine, but just a bonus, not the goal.
So the standard formula for this is described as “high lift, low duration”. Seems simple enough. What I learned, though, is that high lift and low duration only create the potential for a low end cam – how you position the lobes and why you put them there is what this post is all about.
Two of the main contributors to low end torque are Cold Cranking Pressure (sometimes called “Dynamic Compression”), and how long we can apply the pressure to the piston.
CCP is not compression ratio – it is the actual combustion chamber pressure at TDC in Pounds per Square Inch, or PSI. This is determined, in a large way, by the point at which the upcoming piston actually starts to compress the incoming fresh fuel/air mix, which is determined by the point at which the intake valve closes. I can have a motor that is set up with 11:1 compression creating 185 psi CCP, and/or a motor with a 10:1 compression ratio generating 195 psi CCP – and it all depends on the cam. So before you go decking your heads, find out where the intake valve is going to close with your new cam, and add that into the equation.
Rule number 1: A cam with an early intake closing will increase low end torque.
Seems pretty easy. But in the world of cams, as you will see, everything is a trade off. The more I increase CCP, the more I increase the chances of detonation. To prevent detonation, I roll back the timing, which rolls back the power. It’s a balancing act. Where you end up is up to you.
Okay, so now that I’ve compressed the fuel/air mix as far as I dare, the ignition ignites it, and the piston heads down on the power stroke. The second way to increase low end torque is to keep all that pressure applied to the piston as long as possible; and what relieves the pressure is the opening of the exhaust valve, which occurs long before Bottom Dead Center. So we want that exhaust valve to open as late as possible. I can certainly design a cam with a very late exhaust opening, so that one should be easy. Or is it?
Rule number 2: A cam with a late exhaust opening will increase low end torque.
With the exhaust valve open, the piston “turns the corner” at BDC and rushes to the top of the cylinder, pushing out the burned fuel/air mix. But we also know that that fuel/air exiting the exhaust port has momentum, and that momentum will create a suction as the piston stops pushing up. And by keeping the exhaust valve open past Top Dead Center, that suction will help to pull the new fuel/air mix past the intake valve, which opened before TDC. To a point. Knowing this, engineers design cams with “overlap” – which is the number of degrees during which the intake valve has opened, but the exhaust valve has not yet closed. This overlap creates one of the greatest design compromises, and has one of the largest effects on how a cam will cause your motor to behave. Here’s why:
In the overall 720 degrees of a 4-stroke cycle, this overlap occurs for a relatively short period of time – some 20 to sixty degrees of crankshaft revolution (from seat to seat). It’s brief. And as the motor revs up, the period of actual time that the two valves are open and affecting each other shortens, until the exhaust is having minimal effect on the intake charge. But wait… can’t I control that…? If I close the exhaust valve later, the exhaust charge will affect the intake for a longer period of time, right?
Right. Unfortunately, that same overlap will be there when the motor is at a lower rpm – and instead of just creating a suction that will assist the incoming fuel charge, as the piston rounds the corner at a slower speed, not only will the suction stop, but the receding piston will start to draw the exiting exhaust back into the incoming fuel/air mix through the not-yet-closed exhaust valve. Gaaaa! So which way do I go?
Rule number 3: Shorter overlaps will be likely to contribute more to low end torque. Longer overlaps will be likely to contribute more to top end horsepower.
Okay, so now it’s starting to fall into place. If I want a low end cam, I want the exhaust valve to open as late as possible, but the more I turn that lobe to “later”, the later the exhaust valve is going to close as well, increasing overlap! The solution: SHORTEN THE DURATION. See? Everything you do in cam design affects something else, and it’s all a compromise. Let’s take a look at the intake. I know that I want the intake to close as early as possible to increase CCP, but the more I turn the intake toward “early”, the earlier it opens as well, and guess what? Increases overlap. The solution? SHORTEN THE DURATION. Using a shorter duration decreases overlap, and overlap decreases effective combustion at lower rpm.
Unfortunately, short duration also limits the amount of fuel and air I can move through the motor, so that’s not very helpful. What good is adding 20 ft/lbs at 3,000 rpm if I lose 50 at the top? The only way to get more air into the cylinder in a shorter period of time is to make the hole bigger – which means more lift. (Or add manifold pressure with a supercharger, but that’s another story.) How much lift you add depends on how much wear and tear you’re willing to accept on your valve train, and how little piston-to-valve clearance you’re willing to risk – one more reason to consider earlier IVC instead of head decking, and yup, another compromise.
So now we see that its not short duration that necessarily makes more low end torque, short duration just allows me to set timing points that are likely to make low end torque. And although high lift will almost certainly allow more fuel and air into the engine, in our case, it is a necessity brought on by the compromise of the shorter duration.
Okay, back to overlap. There’s a lot of talk about “LSA” (Lobe Separation Angle) when we’re deciding on a cam, and a general feeling that lower LSA creates loping. Well, it might… and it might not. What actually causes loping is low vacuum in the MAP sensor, at the intake. And what causes low vacuum at the intake…? Our old friend Overlap. We know that the exhaust charge helps to suck in the fresh intake charge, but as the overlap now increases due to early intake opening (read: longer duration intake lobes or an attempt to get an earlier IVC) there is not enough exhaust velocity yet at low rpm to create an effective vacuum, and, in fact, the exhaust actually starts getting pushed out the intake tract, cancelling the momentum of the incoming charge and turning the intake column into a series of choppy waves instead of a smooth flow of air through the MAP sensor. Some high end cams won’t even idle at normal rpm, and have to be turned up just to run. In less severe cases, the motor “lopes” due to the choppy character of the intake charge, which kind of “bunches” the incoming charge together in blobs and creates misfires until the rpm comes up and that long overlap becomes very effective at sucking in the intake charge, effectively enhancing atmospheric pressure like a supercharger. So what does this have to do with LSA?
A smaller LSA closes the intake valve sooner, (good!) opens the exhaust valve later (good!) aaaaaaaand….. increases overlap. Darn. There had to be a compromise there somewhere. But it’s okay for us low end guys, because in general (this is just a rule of thumb) a motor will start loping not a specific LSA, but at a specific overlap (low vacuum, remember?) and that point is right around zero degrees with valve lift measured at .050. Once again, our short duration cam lobes save us – a 218/222 cam with a LSA of 114 and an Intake Centerline of 109 gives us an IVC of 38 degrees ABDC (pretty early); an EVO of 50 degrees BBDC (pretty late); and an overlap of negative 8 (well below zero), so we should be well within our goal of a smooth idle and good low rpm cruising while maximizing our two primary torque criteria, higher CCP and longer pressure application. Not a bad compromise… this was the cam that I designed for my LS3, and I can only hope (being untested) that I haven’t designed in any reversion waves that will create sags in the torque curve. We’ll find out when I get it installed!
Our last goal was noise… or lack thereof. The good news is that our late exhaust opening is a lot more likely to attenuate the sound wave generated by combustion; but in the example I listed above, we are still opening 12 degrees earlier than the stock LS3 cam. GM would love to design a cam for maximum performance everywhere, but they are handicapped by the EPA and other government agencies that limit noise and emissions. So it looks like my cam design will be a little louder than stock – and the NPP flaps are gonna be closed at low rpm again.
So there you have it. I hope that’s helpful to some of you starting to negotiate the complex world of cams. I am not a cam designer, nor an engine builder with years of experience – just a guy who spent a lot of time trying to get to the bottom of WHY cams do what they do, and I thought I would pass on my research (for what it’s worth) to the rest of you. Cam experts, PLEASE feel free to chime in if you feel any of this is just outright wrong – the idea is to inform, not mislead. Thanks! Jon
Last edited by Nexus9; 04-12-2013 at 12:16 PM.
12-12-2011, 10:50 AM
#2
Instructor
Thread Starter
Resources
If any of this has inspired you to do a little of your own cam design, you may find these sites helpful:
http://www.wallaceracing.com/Calculators.htm
http://www.bigboyzheadporting.com/calculators.htm
Both sites contain a series of calculators that will show the results and affects of resizing or repositioning cam lobes. By inputting the data you have, or using the data you get from the calculators, you can figure out IVC, EVO, overlap, dynamic compression ratio (CCP) and so on, to give you an idea of what your cam may be like. You can also clearly see how moving one point affects another, so you're making the best compromise. The Big Boyz site is motorcycle oriented, but allows you to override the constant values to any that you choose. What's nice about it is that your constants stay in place every time you calculate, whereas with the Wallace site, all fields go blank after every calculation, and you have to enter constant data in every field every time, even though it hasn't changed. (grrrrrrr......)
Useful data in making calculations for an LS3 motor:
Bore: 103.25 mm or 4.065 inches
Stroke: 92 mm or 3.62 inches
Connecting rod length: 154.89 mm or 6.098 inches
Combustion chamber volume: I've seen 70cc and 72cc - and of course, the only way to know for sure is to measure, as even from the factory it can vary. I believe it is 70cc by itself, 72cc with a head gasket. Anybody know for sure?
Stock compression ratio: 10.7:1
If you're feeling confident about your new design and want to turn it into reality, here's one place you can do that:
http://www.texas-speed.com/p-161-com...-camshaft.aspx
Enjoy!
http://www.wallaceracing.com/Calculators.htm
http://www.bigboyzheadporting.com/calculators.htm
Both sites contain a series of calculators that will show the results and affects of resizing or repositioning cam lobes. By inputting the data you have, or using the data you get from the calculators, you can figure out IVC, EVO, overlap, dynamic compression ratio (CCP) and so on, to give you an idea of what your cam may be like. You can also clearly see how moving one point affects another, so you're making the best compromise. The Big Boyz site is motorcycle oriented, but allows you to override the constant values to any that you choose. What's nice about it is that your constants stay in place every time you calculate, whereas with the Wallace site, all fields go blank after every calculation, and you have to enter constant data in every field every time, even though it hasn't changed. (grrrrrrr......)
Useful data in making calculations for an LS3 motor:
Bore: 103.25 mm or 4.065 inches
Stroke: 92 mm or 3.62 inches
Connecting rod length: 154.89 mm or 6.098 inches
Combustion chamber volume: I've seen 70cc and 72cc - and of course, the only way to know for sure is to measure, as even from the factory it can vary. I believe it is 70cc by itself, 72cc with a head gasket. Anybody know for sure?
Stock compression ratio: 10.7:1
If you're feeling confident about your new design and want to turn it into reality, here's one place you can do that:
http://www.texas-speed.com/p-161-com...-camshaft.aspx
Enjoy!
12-12-2011, 11:50 AM
#4
_Sloth Whisperer_
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Accuracy notwithstanding (not saying it isn't, because it all sounds right, but like you said it's one man's findings so far), this is still a really well written manifest. Thanks a ton for posting it, and the contexts and perspectives are all easy to follow and understand.
Lets see what the cam experts have if any different or in clarification.
Lets see what the cam experts have if any different or in clarification.
12-12-2011, 12:08 PM
#5
Safety Car
Part of what you are looking for is throttle response, I'm assuming. How often are you WOT at 2500 and get out of it at 4500? At WOT, a bigger cam is going to make more torque, especially in the 3500 - 4500 range.
I'll be interested to see if it runs out of breath at 6000 rpm or before. You didn't specify the lobes, but if you are using a faster ramp than stock, then you will be closing the intake valve a lot sooner than stock. IMO, you could dial the advance back a couple degrees and preserve some more top end. I think you could do something like a 222/226 115 +4 and have a better overall curve and enjoy excellent throttle response at 2500. If you are self tuning and a novice, I see the point of being at -8 overlap, but with a little tuning skill you could go between -4 and 0 overlap and achieve your goals.
Not sure if you have headers, but they add a lot of torque in the range you are looking at. Also, if you're an M6, 4.10s may be the best thing for your driving goals. They feel great and make the car seem much more responsive at 2500 rpm.
I'll be interested to see if it runs out of breath at 6000 rpm or before. You didn't specify the lobes, but if you are using a faster ramp than stock, then you will be closing the intake valve a lot sooner than stock. IMO, you could dial the advance back a couple degrees and preserve some more top end. I think you could do something like a 222/226 115 +4 and have a better overall curve and enjoy excellent throttle response at 2500. If you are self tuning and a novice, I see the point of being at -8 overlap, but with a little tuning skill you could go between -4 and 0 overlap and achieve your goals.
Not sure if you have headers, but they add a lot of torque in the range you are looking at. Also, if you're an M6, 4.10s may be the best thing for your driving goals. They feel great and make the car seem much more responsive at 2500 rpm.
12-12-2011, 12:15 PM
#6
_Sloth Whisperer_
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More good points^. In regards to headers, it's worth mentioning that 1 3/4" primaries are basically a necessity to stay with the mid-curve torque theme, as 1 7/8" versions will put a pothole in the middle of the dyno curve he's after.
12-12-2011, 01:23 PM
#7
Instructor
Thread Starter
Yah, good points. I'm leaning on this motor from a few angles, and have purchased an LG Motorsports 1-3/4 long tube Super Pro exhaust, which I intend to use with my stock NPP mufflers; and a K&N FIPK. I'm hoping that a good tuner will get the most out of this combination, and the design goal is to get a total of 50 ft/lbs at 3,000 rpm (WOT), without the sags, or "potholes" in the torque curve anywhere along the way. Ambitious, I know.
A big part of the experience for me is how the car feels at part throttle in normal day to day driving - which is harder to quantify, because we don't have a dyno chart for it. I followed this same philosophy in building a 103 inch Harley Ultra motor, and the results were great - it seems the more I practice, the luckier I get.
Although those numbers look small compared to what we're used to seeing, most guys seem to think they want horsepower, so we're used to seeing some pretty big numbers. The intake duration is actually 14* longer than stock in this design, the exhaust is 11* longer than stock, the overlap is TWENTY degrees longer than stock (overlap also affects emissions, so GM is pretty tight with it), and the lift is .047 (.598)and .080 (.602) higher than stock respectively. I used the Comp Cams LXL lobe design, which is a little less steep, and a little gentler on the valve train than the popular XFI lobe (see design criteria #5). I'm not too concerned about actually losing torque on top, but I am concerned about having designed reversion waves into the airflow, since I just used math, not cam design software. And that's a pretty big job to re-do if I got it wrong! I'll let you know how it feels when I get it all done.
A big part of the experience for me is how the car feels at part throttle in normal day to day driving - which is harder to quantify, because we don't have a dyno chart for it. I followed this same philosophy in building a 103 inch Harley Ultra motor, and the results were great - it seems the more I practice, the luckier I get.
Although those numbers look small compared to what we're used to seeing, most guys seem to think they want horsepower, so we're used to seeing some pretty big numbers. The intake duration is actually 14* longer than stock in this design, the exhaust is 11* longer than stock, the overlap is TWENTY degrees longer than stock (overlap also affects emissions, so GM is pretty tight with it), and the lift is .047 (.598)and .080 (.602) higher than stock respectively. I used the Comp Cams LXL lobe design, which is a little less steep, and a little gentler on the valve train than the popular XFI lobe (see design criteria #5). I'm not too concerned about actually losing torque on top, but I am concerned about having designed reversion waves into the airflow, since I just used math, not cam design software. And that's a pretty big job to re-do if I got it wrong! I'll let you know how it feels when I get it all done.
Last edited by Nexus9; 12-12-2011 at 01:34 PM.
12-12-2011, 02:00 PM
#8
Safety Car
Headers and a tune could get you 30 ft-lbs at 3k by themselves. I went with the LG Pros for the midrange gain too. 
Keep in mind, when you talk about "The intake duration is actually 14* longer than stock in this design, the exhaust is 11* longer than stock," that is at .05. I always look at .006 or .004 duration when evaluating low speed drivability. This gives the true timing of the actual intake close, an issue for very low rpm torque (e.g. idle and off-idle rpms in parking lot maneuvers) and when exhaust valve starts to come off the seat. The stock lobes take more than 60* to go from .05 down to .004, whereas the fast aftermarket lobes are around 52* to go from .05 to .006.
Keep in mind, when you talk about "The intake duration is actually 14* longer than stock in this design, the exhaust is 11* longer than stock," that is at .05. I always look at .006 or .004 duration when evaluating low speed drivability. This gives the true timing of the actual intake close, an issue for very low rpm torque (e.g. idle and off-idle rpms in parking lot maneuvers) and when exhaust valve starts to come off the seat. The stock lobes take more than 60* to go from .05 down to .004, whereas the fast aftermarket lobes are around 52* to go from .05 to .006.
12-12-2011, 02:55 PM
#9
Instructor
Thread Starter
Keep in mind, when you talk about "The intake duration is actually 14* longer than stock in this design, the exhaust is 11* longer than stock," that is at .05. I always look at .006 or .004 duration when evaluating low speed drivability. This gives the true timing of the actual intake close, an issue for very low rpm torque (e.g. idle and off-idle rpms in parking lot maneuvers) and when exhaust valve starts to come off the seat. The stock lobes take more than 60* to go from .05 down to .004, whereas the fast aftermarket lobes are around 52* to go from .05 to .006.
12-12-2011, 04:37 PM
#10
Race Director
Excellent write up although in the opening sentence I was thinking a gear change.I run the 4:10's and love them for the vary reason you desire. Why go to all the work of opening up the motor and what goes with it.
12-12-2011, 06:34 PM
#11
Instructor
Thread Starter
Hey Boomer,
You know, I get that a lot. And technically, you're correct - changing the gearing will increase torque. But I've always felt that it's just a band aid solution, I would think that driving a six speed with 4.10s would require a lot more shifting, no?
I think I'd rather actually build the thrust into the motor and pull a longer gear, even though it's probably a lot more work to install it. But thanks for contributing, it's a sound idea.
You know, I get that a lot. And technically, you're correct - changing the gearing will increase torque. But I've always felt that it's just a band aid solution, I would think that driving a six speed with 4.10s would require a lot more shifting, no?
I think I'd rather actually build the thrust into the motor and pull a longer gear, even though it's probably a lot more work to install it. But thanks for contributing, it's a sound idea.
12-12-2011, 06:57 PM
#12
Team Owner
I don't see a problem that a E-Force won't cure. Loads of low end torque, without all that fuss about designing a "perfect" cam.
12-12-2011, 08:40 PM
#14
Safety Car
Before you spend $400 on a cam, you could get one of the cheaper programs like Desktop Dyno and run your numbers through it. It also has an Iterator to help select cam timing, you can save them and it has other tools you may find helpful.
Or you could step up to one of the programs from Performance Trends
Or you could step up to one of the programs from Performance Trends
12-12-2011, 08:44 PM
#15
Instructor
Thread Starter
12-12-2011, 08:46 PM
#16
Instructor
Thread Starter
Before you spend $400 on a cam, you could get one of the cheaper programs like Desktop Dyno and run your numbers through it. It also has an Iterator to help select cam timing, you can save them and it has other tools you may find helpful.
Or you could step up to one of the programs from Performance Trends
Or you could step up to one of the programs from Performance Trends
That's a great contribution, I didn't even know about that!
