Why LSA doesn't matter
12-10-2014, 12:04 PM
#101
My question is this: what determines when the intake/exhaust valve opens on a motor?
IE: on the LS1 motor, at what degree do you want the valves to open? What determines this? I talked with roger vinci some years ago about this but memory fades me.
I know there's a too early and late degree range.
IE: on the LS1 motor, at what degree do you want the valves to open? What determines this? I talked with roger vinci some years ago about this but memory fades me.
I know there's a too early and late degree range.
The exhaust valve opening event determines when blow down begins.
Both are important, but it's hard to generically state when they should be timed to open.
If you could give me a combination to use as an example, I could give you a much better explanation for why the IVO event and EVO event should occur at a certain piston position.
12-11-2014, 07:12 AM
#102
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The intake valve opening event determines when valve overlap begins.
The exhaust valve opening event determines when blow down begins.
Both are important, but it's hard to generically state when they should be timed to open.
If you could give me a combination to use as an example, I could give you a much better explanation for why the IVO event and EVO event should occur at a certain piston position.
The exhaust valve opening event determines when blow down begins.
Both are important, but it's hard to generically state when they should be timed to open.
If you could give me a combination to use as an example, I could give you a much better explanation for why the IVO event and EVO event should occur at a certain piston position.
There's a point where it's just ineffective to open on intake. And there's a "given range" where to open the valve. What is that range. Is it say 0-12* atdc is where it's best to start opening?
Same with exhaust stroke. Say 0-12* abdc?
12-11-2014, 11:12 AM
#103
Let me try a different explanation. We know tdc is 0* and bdc is 180*. so halfway up on exhaust is 90* btdc and half way down on intake is 90* atdc.
There's a point where it's just ineffective to open on intake. And there's a "given range" where to open the valve. What is that range. Is it say 0-12* atdc is where it's best to start opening?
Same with exhaust stroke. Say 0-12* abdc?
There's a point where it's just ineffective to open on intake. And there's a "given range" where to open the valve. What is that range. Is it say 0-12* atdc is where it's best to start opening?
Same with exhaust stroke. Say 0-12* abdc?
Every combination will be different.
A 9,000RPM 440" motor with a 4.0" stroke is going to have a different intake opening and exhaust opening requirement than a 3.622" stroke engine turning 7000rpm.
Other variables such as header primary diameter, length, I/E%, intake runner length, intake runner cross section, EFI or Carb, intake valve size, intake port cross section, and on and on and on.
All of those variables will change where the IVO and EVO events need to occur.
That is why I asked if you could give me an application to use for an example. If you give me a specific combination I can tell you my opinion on where I feel the IVO and EVO events need to occur.
Otherwise just giving generalities on cam timing is just going to get you confused and lead you to believe that all engines or all combinations need a certain set of IVO and EVO events.
If there is one thing I've learned about cam timing it is that there is NO generality that can be made regarding what is best for all engines. Each engine will always want something different than the next.
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12-21-2014, 07:27 PM
#107
If you give me a specific combination I can tell you my opinion on where I feel the IVO and EVO events need to occur.
If there is one thing I've learned about cam timing it is that there is NO generality that can be made regarding what is best for all engines. Each engine will always want something different than the next.
If there is one thing I've learned about cam timing it is that there is NO generality that can be made regarding what is best for all engines. Each engine will always want something different than the next.
Current cam 247/265 113+4.....I have my thoughts, but what say you?
12-22-2014, 02:43 PM
#108
Okay then...specific combo...416 ci 4.07x4.0, LS3 heads, 13.6CR, Mast single plane, 1.875 headers(although I think they are too small), 2500lb. car, 4600 2 step, 7000rpm shift, falls back to 6000, 7500rpm stripe.
Current cam 247/265 113+4.....I have my thoughts, but what say you?
Current cam 247/265 113+4.....I have my thoughts, but what say you?
12-22-2014, 03:40 PM
#109
Martin, more of what you think is wrong with the events. Some say there is more than one way to skin a cat. Consensus is that 30 degrees isn't enough overlap and power is being lost out the exhaust. I had an older racer tell me once the cam timing is like skeet shooting. The faster the target flies, the more you have to lead it to hit the target.
12-22-2014, 04:04 PM
#110
Martin, more of what you think is wrong with the events. Some say there is more than one way to skin a cat. Consensus is that 30 degrees isn't enough overlap and power is being lost out the exhaust. I had an older racer tell me once the cam timing is like skeet shooting. The faster the target flies, the more you have to lead it to hit the target.
Personally I think your IO event is much too late for such a short runner intake that is turning 7500rpm. I also think there is a ton more potential with more RPM as long as the valve train stays stable.
I have 4-5 guys right now turning over 7500rpm with hydraulic roller combinations. I have several lobe combinations that work exceptionally well at these RPM's that I have a lot of confidence in even with big stainless valves.
I think your EO event personally is too early. I remember we talked about new headers for your car a while back and doing a double or even a triple step and changing the length as well and/or collector design.
I also think your IC event is too early as well and that the engine is being forced to pump against pressure for too long on the compression stroke. I think there is more TQ and HP to be made in your operating range with a later IC event.
The EC is also too early IMO and isn't taking enough advantage of resonance available at higher RPM from 5000-6500rpm.
Here is what I would do personally:
255/267 .653/.632 112+2
Last edited by Sales@Tick; 12-22-2014 at 04:28 PM.
12-29-2014, 08:13 PM
#111
So glad to see you lay all this out Martin. I was literally writing all the same stuff up for a sticky for the carb section and if you will allow me to quote this, you will save me a bunch of work.
I think explaining this in such a way that your average racer/rodder can visualize it is the hardest part. I am most glad that you talked about mass. That is the part that I think makes the visualization all come together. Understanding that the mass of air and fuel rushing in to filling the cylinder is like compressing a spring. We want to close the intake valve at close to the exact moment the spring is most compressed (most air and fuel in the cylinder) before it springs back and pushes the air and fuel back out of the cylinder. I think that visualization really works.
In a previous conversation with Martin, I had taken a similar position. My argument was that it is just different ways to express the exact same thing. And, that you could get to the same place regardless of the method that you used to express it.
I have since came to see it the way Martin does. The reason is, when I really started comparing successful combos using the exact valve events, I saw correlations in valve events that I would not have realized using duration/LSA/advance definitions. Having IVO IVC EVO EVC is just so much easier to visualize what you are actually doing compared to duration/LSA/advance.
I think explaining this in such a way that your average racer/rodder can visualize it is the hardest part. I am most glad that you talked about mass. That is the part that I think makes the visualization all come together. Understanding that the mass of air and fuel rushing in to filling the cylinder is like compressing a spring. We want to close the intake valve at close to the exact moment the spring is most compressed (most air and fuel in the cylinder) before it springs back and pushes the air and fuel back out of the cylinder. I think that visualization really works.
In a previous conversation with Martin, I had taken a similar position. My argument was that it is just different ways to express the exact same thing. And, that you could get to the same place regardless of the method that you used to express it.
I have since came to see it the way Martin does. The reason is, when I really started comparing successful combos using the exact valve events, I saw correlations in valve events that I would not have realized using duration/LSA/advance definitions. Having IVO IVC EVO EVC is just so much easier to visualize what you are actually doing compared to duration/LSA/advance.
Both your post and Martins, are excellent and the reason why I have just asked Martin to design and supply a camshaft etc for my road racing application we we need to turn 8,000 plus all day long.
Cheer's,
Mark.
12-30-2014, 06:54 AM
#112
High RPM N/A and nitrous are totally separate worlds from boost and you really have to cross your T's and dot your I's to make power. There are a lot of physics that have to all come together at the perfect moment to make it all work. I like to think I've helped spell out some of what it does take here in this thread.
Thanks for the compliments.
01-01-2015, 06:48 PM
#113
I posted this in a post of mine but here goes again. Can a 4.185 x3.62(398) ls3 motor be cammed properly for the street and what would recc? I heard how I should just stroke it instead but I am curious to seehow with would perform as a street motor with a 150 shot. My daily driver is a bmw 740i with 4.4l v8. The motor is over square. This thing kicks *** and is quite good on fuel if u keep your foot out of it.rated at 282hp this thing is putting out 270 at the wheels.I know that is a dohc motor but a ls3 has good heads also. My 4.4 has a 10.0 compression also. I fig that the combo mentioned would have a great flat curve and make excellent power to boot with the huge bore.help please martin lol. Just want an answer that I can understand instead of just y a 4" crank is better
01-02-2015, 05:35 PM
#114
I posted this in a post of mine but here goes again. Can a 4.185 x3.62(398) ls3 motor be cammed properly for the street and what would recc? I heard how I should just stroke it instead but I am curious to seehow with would perform as a street motor with a 150 shot. My daily driver is a bmw 740i with 4.4l v8. The motor is over square. This thing kicks *** and is quite good on fuel if u keep your foot out of it.rated at 282hp this thing is putting out 270 at the wheels.I know that is a dohc motor but a ls3 has good heads also. My 4.4 has a 10.0 compression also. I fig that the combo mentioned would have a great flat curve and make excellent power to boot with the huge bore.help please martin lol. Just want an answer that I can understand instead of just y a 4" crank is better
All of this comes into play when building the best engine for an application.
01-02-2015, 07:20 PM
#115
Here's me on the 108LSA cam.
Blows the tires loose from a roll like it was its job
(and before people tell me to fix the idle on startup, im working on it)
Also Martin did you happen to know UDHarold at all? Cam designer that changed many things in the industry passed away recently. I feel like it's up to guys like you to continue pushing the REAL science behind cam design theory, and not what you can pull off a shelf. There is ALOT of good info in here that more people need to read.
01-02-2015, 07:22 PM
#116
87 Buick regal 4l60e 3.23 rear, 26.1tire 2800 stall currently a/c street strip more street. will use a ported l92 intake and throttle body. 1 7/8 in long tubes into x-piped 3" exhaust.going for 11.5 comp.the ls3hewds will have ported exhaust ports.
01-05-2015, 09:54 AM
#117
108LSA LS1 Camshaft - YouTube
Here's me on the 108LSA cam.
Blows the tires loose from a roll like it was its job
(and before people tell me to fix the idle on startup, im working on it)
Also Martin did you happen to know UDHarold at all? Cam designer that changed many things in the industry passed away recently. I feel like it's up to guys like you to continue pushing the REAL science behind cam design theory, and not what you can pull off a shelf. There is ALOT of good info in here that more people need to read.
Here's me on the 108LSA cam.
Blows the tires loose from a roll like it was its job
(and before people tell me to fix the idle on startup, im working on it)
Also Martin did you happen to know UDHarold at all? Cam designer that changed many things in the industry passed away recently. I feel like it's up to guys like you to continue pushing the REAL science behind cam design theory, and not what you can pull off a shelf. There is ALOT of good info in here that more people need to read.
That is not to say that a shorter stroke big bore application cannot make torque, the physics behind a long arm just make more sense in regards to low speed torque production when it comes to a street application with 3.23 gears and a 2800 stall.
01-05-2015, 02:29 PM
#119
Something I've never understood is the difference between generic overlap, positive overlap, and negative overlap. What's the calculation to determine whether overlap is positive or negative? Under which conditions would you prefer positive vs negative overlap?
01-05-2015, 09:22 PM
#120
With that put aside, how much overlap and the function of overlap is one of the main things this thread is all about. There is a ton of information out there about the function overlap going way back to when Ed "The Godfather" Iskenderian introduced his "5 cycle" cam marketing campaign.
There is an intricate relationship between the exhaust system, header design, valve layout, intake configuration and camshaft valve event overlap. In short, the scenario is that the exhaust rushing out past the exhaust valve will leave a vacuum in its wake which will pull on the intake tract during the time when both valves are open at TDC (overlap).
The benefit is that it can increase cylinder filling and volumetric efficiency in the midrange and upper RPM. The detriment is that it reduces engine idle vacuum while diminishing low speed response and efficiency.
What is ideal for any given engine application depends on that intricate relationship between the exhaust system, header design, valve layout, intake configuration and camshaft valve event overlap. It also should including the desired engine characteristics of the end user.