Need a Road Race cam
09-06-2018, 10:51 AM
#21
That is slightly "bigger" than the GM ASA cam that I use. Makes excellent power in a stock LS6, with very smooth power delivery, and a fairly flat torque curve. The lower lift should help the springs last a lot longer. I keep red line at 6,400. Which is probably lower than it needs to be.
09-07-2018, 01:33 AM
#22
1) Intake duration, exhaust duration, lobe separation angle, advance. This is unfortunately the standard way that cams are marketed to consumers.
2) The crankshaft angles at which the intake and exhaust valves open and close - usually referred to as the "valve events." With trivial math you can get the overlap from the exhaust valve close angle and intake valve open angle.
They are two different ways to measure the same thing. And they're both somewhat inadequate - but they're all we have, and we have to make decisions based on the facts that we have.
Given either set of numbers, you can use math to calculate the other set, preferably with Excel or with a utility like Cam Motion's "Cam Timer" for Windows.
#1 is the most common approach, but it sucks for consumers. Looking at camshaft properties from that perspective makes a lot of sense if you are configuring a machine to grind the cam, but it's a crappy way to describe a cam if you want to know how your engine will perform with that cam. With enough experience and mental arithmetic, people can get an intuitive understanding of how a cam will perform.... but with a moderate amount of experience and little or no arithmetic, most people just end up with an intuitive misunderstanding of how a cam will perform. There are a couple of threads stickied to the top of the Gen III Internals subforum that go into more detail about why this approach to cam description sucks. One of them is called "LSA doesn't matter" or something like that (I would have called it "why LSA is misleading" but the provocative title gets more people to read it, and that's a win, so I salute the author).
#2 is less common. But when you measure the cam that way, you have numbers that are much more useful for predicting how your engine will behave. Of these numbers, the intake valve closing angle and overlap are the most interesting. The others matter too - don't get me wrong - but those two give you the context to avoid getting misled by the "duration/duration LSA" numbers.
The durations and events are given at some amount of lift (usually 0.006 or 0.050, sometimes 0.200) or better yet at multiple lifts. If you know the durations at multiple lifts, you can guesstimate how aggressive the lobes are. They don't give you the whole story, as WS6Store said. But, like I said, we can only make our decisions based on what that we have.
Now, with all of that said...
Truck cams tend to have intake valve closing events (@ 0.050) in the 30s, for torque at low RPM. Aftermarket enthusiast tend to be in the mid-40s, maybe 50 or so, and race cams go higher for more power at high RPM. 45ish is pretty typical.
More overlap = lumpier idle, more surging at low RPM, more power at high RPM (assuming naturally aspirated engine). The only way I know of to estimate how a cam with a given amount of overlap will drive in your car is to find messages from people with that amount of overlap, in an engine with the same displacement, and see what they have to say about how their cars drive. But if you know the overlaps for two cams, you can get a pretty good idea which one is going to have the lumpier idle, and which will be easiest to drive around at low RPM.
09-07-2018, 03:22 AM
#23
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Let's back up a little bit... There are two common ways to describe a cam:
1) Intake duration, exhaust duration, lobe separation angle, advance. This is unfortunately the standard way that cams are marketed to consumers.
2) The crankshaft angles at which the intake and exhaust valves open and close - usually referred to as the "valve events." With trivial math you can get the overlap from the exhaust valve close angle and intake valve open angle.
They are two different ways to measure the same thing. And they're both somewhat inadequate - but they're all we have, and we have to make decisions based on the facts that we have.
Given either set of numbers, you can use math to calculate the other set, preferably with Excel or with a utility like Cam Motion's "Cam Timer" for Windows.
#1 is the most common approach, but it sucks for consumers. Looking at camshaft properties from that perspective makes a lot of sense if you are configuring a machine to grind the cam, but it's a crappy way to describe a cam if you want to know how your engine will perform with that cam. With enough experience and mental arithmetic, people can get an intuitive understanding of how a cam will perform.... but with a moderate amount of experience and little or no arithmetic, most people just end up with an intuitive misunderstanding of how a cam will perform. There are a couple of threads stickied to the top of the Gen III Internals subforum that go into more detail about why this approach to cam description sucks. One of them is called "LSA doesn't matter" or something like that (I would have called it "why LSA is misleading" but the provocative title gets more people to read it, and that's a win, so I salute the author).
#2 is less common. But when you measure the cam that way, you have numbers that are much more useful for predicting how your engine will behave. Of these numbers, the intake valve closing angle and overlap are the most interesting. The others matter too - don't get me wrong - but those two give you the context to avoid getting misled by the "duration/duration LSA" numbers.
The durations and events are given at some amount of lift (usually 0.006 or 0.050, sometimes 0.200) or better yet at multiple lifts. If you know the durations at multiple lifts, you can guesstimate how aggressive the lobes are. They don't give you the whole story, as WS6Store said. But, like I said, we can only make our decisions based on what that we have.
Now, with all of that said...
Truck cams tend to have intake valve closing events (@ 0.050) in the 30s, for torque at low RPM. Aftermarket enthusiast tend to be in the mid-40s, maybe 50 or so, and race cams go higher for more power at high RPM. 45ish is pretty typical.
More overlap = lumpier idle, more surging at low RPM, more power at high RPM (assuming naturally aspirated engine). The only way I know of to estimate how a cam with a given amount of overlap will drive in your car is to find messages from people with that amount of overlap, in an engine with the same displacement, and see what they have to say about how their cars drive. But if you know the overlaps for two cams, you can get a pretty good idea which one is going to have the lumpier idle, and which will be easiest to drive around at low RPM.
1) Intake duration, exhaust duration, lobe separation angle, advance. This is unfortunately the standard way that cams are marketed to consumers.
2) The crankshaft angles at which the intake and exhaust valves open and close - usually referred to as the "valve events." With trivial math you can get the overlap from the exhaust valve close angle and intake valve open angle.
They are two different ways to measure the same thing. And they're both somewhat inadequate - but they're all we have, and we have to make decisions based on the facts that we have.
Given either set of numbers, you can use math to calculate the other set, preferably with Excel or with a utility like Cam Motion's "Cam Timer" for Windows.
#1 is the most common approach, but it sucks for consumers. Looking at camshaft properties from that perspective makes a lot of sense if you are configuring a machine to grind the cam, but it's a crappy way to describe a cam if you want to know how your engine will perform with that cam. With enough experience and mental arithmetic, people can get an intuitive understanding of how a cam will perform.... but with a moderate amount of experience and little or no arithmetic, most people just end up with an intuitive misunderstanding of how a cam will perform. There are a couple of threads stickied to the top of the Gen III Internals subforum that go into more detail about why this approach to cam description sucks. One of them is called "LSA doesn't matter" or something like that (I would have called it "why LSA is misleading" but the provocative title gets more people to read it, and that's a win, so I salute the author).
#2 is less common. But when you measure the cam that way, you have numbers that are much more useful for predicting how your engine will behave. Of these numbers, the intake valve closing angle and overlap are the most interesting. The others matter too - don't get me wrong - but those two give you the context to avoid getting misled by the "duration/duration LSA" numbers.
The durations and events are given at some amount of lift (usually 0.006 or 0.050, sometimes 0.200) or better yet at multiple lifts. If you know the durations at multiple lifts, you can guesstimate how aggressive the lobes are. They don't give you the whole story, as WS6Store said. But, like I said, we can only make our decisions based on what that we have.
Now, with all of that said...
Truck cams tend to have intake valve closing events (@ 0.050) in the 30s, for torque at low RPM. Aftermarket enthusiast tend to be in the mid-40s, maybe 50 or so, and race cams go higher for more power at high RPM. 45ish is pretty typical.
More overlap = lumpier idle, more surging at low RPM, more power at high RPM (assuming naturally aspirated engine). The only way I know of to estimate how a cam with a given amount of overlap will drive in your car is to find messages from people with that amount of overlap, in an engine with the same displacement, and see what they have to say about how their cars drive. But if you know the overlaps for two cams, you can get a pretty good idea which one is going to have the lumpier idle, and which will be easiest to drive around at low RPM.
09-10-2018, 05:22 AM
#25
Crane 2019381 cam in my circuit car's crate LS3, engine dyno tested to give 520 hp @ 6400, 492 ft/lb @ 4800. Specs are dur 220/236, lift 0.590"/0.624", LSA 113. If relevant it idles fine @ 1000 rpm.
09-10-2018, 10:26 PM
#26
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11-09-2018, 10:21 AM
#29
Using a endurance style cam with beehive springs will yield a nice torque curve without the need to spin the motor above 6800 rpm's. My stock LS1 motor made 505 hp / 465 lbs ft on the engine dyno with a 231/237 598/610 114+4 CAM, only other changes were springs, a Dailey Dry Sump System and Holley EFI. Plot should be attached , I questioned the engine shop owner about the lift of this cam as being too aggressive. I was thinking something more in the .575 range. But he assured me that it's the ramp angles that stress the valve train and with an endurance CAM profile the valves are opening and closing more gradually and this prevents the valves from slamming shut and bouncing at higher RPM's. He also explained that the lift puts the valves when open where the heads flow the most so it makes good power. And with a dedicated track car he advised that if I put fresh valve springs in ever few seasons the reliability would be fine.
11-10-2018, 02:15 PM
#31
^ Not specifically, my previous engine was pretty stout for a NA six and may 310 lbs ft starting at around 4500rpm on the engine dyno with a 5 speed and 3:73 gears, it had plenty of torque to pull my 2600lb car out of the corners. It dropped off pretty sharply below 4500. With a bump of ~ 150 lbs ft with this LS1 it's going to be difficult to modulate the throttle to prevent the rear end from kicking loose. It's still making north of 400 lbs ft from 3000 rpm up. I really wouldn't want much more as it would overwhelm the chassis and make the car a real handful to drive
11-12-2018, 07:32 AM
#32
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That works out to an 12.5 degrees of overlap, and an intake valve closing of 44.5 degrees.
That works out to 11 degrees of overlap and an IVC of 43.
Not so different in overlap or IVC, but more duration with the Cam Motion cam, and more lift with the high-lift ASA.
I really wonder how they would differ on the track.
That works out to 11 degrees of overlap and an IVC of 43.
Not so different in overlap or IVC, but more duration with the Cam Motion cam, and more lift with the high-lift ASA.
I really wonder how they would differ on the track.
You can use it for a comparison as long as you're measuring all cams that way, but it shouldn't be used to calculate dynamic compression.
11-13-2018, 01:04 AM
#33
Calculating IVC from .050" lift is a bit of a misdirection, since you're not actually determining the closing of the intake valve, but the cam degree where the intake valve is at .050" lift while closing. Its not technically closed.
You can use it for a comparison as long as you're measuring all cams that way, but it shouldn't be used to calculate dynamic compression.
You can use it for a comparison as long as you're measuring all cams that way, but it shouldn't be used to calculate dynamic compression.
Why .050? Beats me. But it's the convention. So be it.
0.006 is the convention for dynamic compression math, but that's a different conversation.
11-19-2018, 11:48 AM
#34
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IVC @ .050 is a convention that you'll find in a whole bunch of valve-event discussion threads here on this forum. See the "Valve Events" sticky at the top of this subforum, for example.
Why .050? Beats me. But it's the convention. So be it.
0.006 is the convention for dynamic compression math, but that's a different conversation.
Why .050? Beats me. But it's the convention. So be it.
0.006 is the convention for dynamic compression math, but that's a different conversation.
.050" is used because .006" valve events aren't always known/advertised, so its the only way to get a level playing field.
Its also inaccurate. The valve is still flowing enough at .050" with enough room left on the lobe for a wide range of ramp angles that dynamic compression can't be accurately calculated, so a ballpark torque estimate (in a pretty damn big ballpark) is loose at best.
11-19-2018, 01:16 PM
#35
So then how would you go about making a decision based on the available data?
11-19-2018, 06:01 PM
#36
There is so much more to a camshaft as this thread shows. The idea of comparing @.050 os relatively more "new" than comparing lift. You can ALWAYS tell some guy is either stuck in the 80s and heard on his DRAG TIMES VHS tape that lift means everything. They will quote lift and nothing else and expect you to guess how it runs or what it does or acts. That may have been true when there were only 5 or 10 cams out there and half were by isky and the rest by crane and duntov.
You can tell who tries to carry over gen0 SBC ideas to the LS crowd. I deal with 5 to 10 a day and can spot them nearly immediately. Or if they are shooting for 8.5:1 for a 600hp turbo build.
Its not accurate at all today with asymmetric lobes and different profiles that ramp up lobe area. The jargon and old school guys just havent caught up yet.
Still the rule of thumb carries somewhat true comparing @.050 for the most part, but if every cam were the same above and below that then there wouldnt be many cams to choose from and they would all run the same.
11-19-2018, 10:38 PM
#37
Sure there are lots of variables in cam design. But we gotta make the best decisions we can based on the information we have. At least, that's how I like to approach things... 
Half the reason I posted the numbers above was to help the OP make a better decision, and half the reason was just to move the discussion forward in hopes of learning more myself.
You see pretty interested in dynamic compression. Why? (Honest question!) You say it matters a lot for torque - does it tell you more about how much torque to expect, or what RPM range to expect torque to be strong, or...?
The idea that compression doesn't start until the valve closes sort of implies that the piston is pushing air backward through the intake tract from BDC to IVC - which might be true at idle, but surely isn't the case at high RPM. So I've never been clear on what to make of DCR numbers.
Half the reason I posted the numbers above was to help the OP make a better decision, and half the reason was just to move the discussion forward in hopes of learning more myself.
You see pretty interested in dynamic compression. Why? (Honest question!) You say it matters a lot for torque - does it tell you more about how much torque to expect, or what RPM range to expect torque to be strong, or...?
The idea that compression doesn't start until the valve closes sort of implies that the piston is pushing air backward through the intake tract from BDC to IVC - which might be true at idle, but surely isn't the case at high RPM. So I've never been clear on what to make of DCR numbers.
11-21-2018, 07:32 AM
#38
Restricted User
The SLIGHT compression that happens as the piston is coming up and air is still moving into the cylinder with the valve open isn't relevant to dynamic compression.
That has more to do with volumetric efficiency and the benefits of top-end oriented camshaft. Two different things.
Static compression is the ratio of volume uncompressed vs compressed. Dynamic compression is the ratio of volume uncompressed at the time the intake valve closes to the compressed volume.
If you've ever had an assumption that static compression ratio had an effect on torque, it should be very clear why dynamic compression ratio should have even more of an effect on it.
Throwing in volumetric efficiency vs dynamic compression can be though as similar to the relationship between torque and power.
One is a constant. An instanteous measurement that shows how well the given air mass/mixture can be used. The other is the same thing, but with a function of RPM.
That has more to do with volumetric efficiency and the benefits of top-end oriented camshaft. Two different things.
Static compression is the ratio of volume uncompressed vs compressed. Dynamic compression is the ratio of volume uncompressed at the time the intake valve closes to the compressed volume.
If you've ever had an assumption that static compression ratio had an effect on torque, it should be very clear why dynamic compression ratio should have even more of an effect on it.
Throwing in volumetric efficiency vs dynamic compression can be though as similar to the relationship between torque and power.
One is a constant. An instanteous measurement that shows how well the given air mass/mixture can be used. The other is the same thing, but with a function of RPM.
11-21-2018, 08:39 PM
#39
I'm trying to figure out two thigns.. First, why you think its misleading to look at IVC @ 050 when comparing cams. Second, why you think DCR is important.
For IVC @ 050, trucks are in the low 30s, Stock LS6 in the high 30s (37? 39?), cams aimed at top end go mid-40s or higher... Seems like there's a pretty clear correlation there, with IVC indicating where the powerband is going to be (earlier = stronger down low, later = stronger up high).
For DCR, again, does that tell you something about the peak torque number, or the shape of the curve, or torque at some rev range, or what? I mean, when you say "torque" do you mean the peak torque number, or the RPM of peak torque, or... People use and abuse that word a lot, so I'm trying to figure out where you're coming from.
An early IVC goes hand-in-hand with a higher DCR, so more torque at low RPM... But an earlier IVC / higher DCR also means less torque at the top of the RPM range, therefore lower peak power, doesn't it?
For IVC @ 050, trucks are in the low 30s, Stock LS6 in the high 30s (37? 39?), cams aimed at top end go mid-40s or higher... Seems like there's a pretty clear correlation there, with IVC indicating where the powerband is going to be (earlier = stronger down low, later = stronger up high).
For DCR, again, does that tell you something about the peak torque number, or the shape of the curve, or torque at some rev range, or what? I mean, when you say "torque" do you mean the peak torque number, or the RPM of peak torque, or... People use and abuse that word a lot, so I'm trying to figure out where you're coming from.
An early IVC goes hand-in-hand with a higher DCR, so more torque at low RPM... But an earlier IVC / higher DCR also means less torque at the top of the RPM range, therefore lower peak power, doesn't it?
Last edited by NSFW; 11-21-2018 at 10:24 PM.
12-10-2018, 02:35 PM
#40
to OP:
Been there, done that. i highly suggest you read this/my entire thread
https://ls1tech.com/forums/generatio...-race-cam.html
even got most of the biggest names in the custom cam world involved.
in the end i wasnt happy. cam ran out too early. you could feel it flat line up top, not continue to build power.
was if faster? too many other variables to ever know that.
Been there, done that. i highly suggest you read this/my entire thread
https://ls1tech.com/forums/generatio...-race-cam.html
even got most of the biggest names in the custom cam world involved.
in the end i wasnt happy. cam ran out too early. you could feel it flat line up top, not continue to build power.
was if faster? too many other variables to ever know that.