gains from stroking
11-12-2010, 07:28 PM
#41
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The laws of physics don't change in an engine just because there is an AFR logo on the side of the heads. Tony is good with cylinder heads, but I wouldn't give him THAT much credit, lol.
That IS the test though. To see what happens when displacement increases, and everything else, to include the induction package, stays the same.
You're right, but you're looking at it the wrong way. An increase in TQ will always equate to an increase in HP, but only at that same RPM. More displacement will create more overall TQ, but since the larger displacement demands more air at any given RPM, the entire TQ curve shifts left to a lower RPM because the engine is now "more restricted". This mathematically explains why the peak HP stays the same: the increase in TQ is offset by the lower RPM in which it occurs.
To take advantage of the larger displacement, you must increase the airflow capabilities of the induction package to shift the TQ curve back to the right. Without doing that, you still make more overall power and torque, but the peak power stays almost exactly the same.
That IS the test though. To see what happens when displacement increases, and everything else, to include the induction package, stays the same.
You're right, but you're looking at it the wrong way. An increase in TQ will always equate to an increase in HP, but only at that same RPM. More displacement will create more overall TQ, but since the larger displacement demands more air at any given RPM, the entire TQ curve shifts left to a lower RPM because the engine is now "more restricted". This mathematically explains why the peak HP stays the same: the increase in TQ is offset by the lower RPM in which it occurs.
To take advantage of the larger displacement, you must increase the airflow capabilities of the induction package to shift the TQ curve back to the right. Without doing that, you still make more overall power and torque, but the peak power stays almost exactly the same.
Why are we dancing around the obvious and something I noted a long time ago?
11-12-2010, 08:12 PM
#42
You took an engine that was already limited by airflow. The heads were at their max. A stock LSx is not at it's peak or limited by airlfow. When it's not limited, the bigger displacement can make more power.
Why are we dancing around the obvious and something I noted a long time ago?
Why are we dancing around the obvious and something I noted a long time ago?
How can you say that a 346ci LSx with stock heads is not limited by airflow, but a 347ci LSx with AFR heads is limited by airflow?
11-12-2010, 09:27 PM
#43
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They're both limited by airflow, that's why there is a peak torque value. If the engine wasn't limited by airflow, it would just climb in power forever.
How can you say that a 346ci LSx with stock heads is not limited by airflow, but a 347ci LSx with AFR heads is limited by airflow?
How can you say that a 346ci LSx with stock heads is not limited by airflow, but a 347ci LSx with AFR heads is limited by airflow?
Because the one with AFR heads has a **** ton of other mods like a cam to take advantage of more heads.
Airflow isn't binary It's not just "restricted" or "not restricted."
I hate to be the one to break this to you, but there are times when a greater pressure differential (in this case, more vacuum) will draw more air.
"A little bit of knowledge can be very dangerous."
11-13-2010, 10:14 AM
#44
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Just wonderring. Those tests were done over 5 yrs ago. Has anything changed parts wise or setup wise that would make the 383 make more power with the same setup as 346?
I could not see the graphs but you picked up 40 ftlbs of tq over the 346. Was tq picked up throughout the power band?
I could not see the graphs but you picked up 40 ftlbs of tq over the 346. Was tq picked up throughout the power band?
11-13-2010, 01:28 PM
#45
Because the one with AFR heads has a **** ton of other mods like a cam to take advantage of more heads.
Airflow isn't binary It's not just "restricted" or "not restricted."
I hate to be the one to break this to you, but there are times when a greater pressure differential (in this case, more vacuum) will draw more air.
"A little bit of knowledge can be very dangerous."
Airflow isn't binary It's not just "restricted" or "not restricted."
I hate to be the one to break this to you, but there are times when a greater pressure differential (in this case, more vacuum) will draw more air.
"A little bit of knowledge can be very dangerous."
You're the one that was talking about restriction with your '86 TBI example. Just as there are instances when greater pressure delta increases the airflow rate, there are instances when a greater pressure delta doesn't increase airflow. What is it that you think happens when the TQ peaks and then falls off?
You still have yet to come up with any evidence at all to support your claim. Maybe you should dig up a real world example first before trying to aimlessly argue the validity of Tony Mamo's test that I used, or make any more smartass quotes about knowledge.
11-13-2010, 04:56 PM
#46
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The cam doesn't matter in this case. The peak numbers would still stay the same had the engine started with a stock cam or a 224/228 cam. It could have had stock heads instead of AFR heads. These variables you're trying to say matter actually don't. If you add displacement and keep the induction package the same (all stock or all aftermarket), the peak HP number will be the same.
You're the one that was talking about restriction with your '86 TBI example. Just as there are instances when greater pressure delta increases the airflow rate, there are instances when a greater pressure delta doesn't increase airflow. What is it that you think happens when the TQ peaks and then falls off?
You still have yet to come up with any evidence at all to support your claim. Maybe you should dig up a real world example first before trying to aimlessly argue the validity of Tony Mamo's test that I used, or make any more smartass quotes about knowledge.
You're the one that was talking about restriction with your '86 TBI example. Just as there are instances when greater pressure delta increases the airflow rate, there are instances when a greater pressure delta doesn't increase airflow. What is it that you think happens when the TQ peaks and then falls off?
You still have yet to come up with any evidence at all to support your claim. Maybe you should dig up a real world example first before trying to aimlessly argue the validity of Tony Mamo's test that I used, or make any more smartass quotes about knowledge.
Torque is basically volumetric efficiency at a given RPM, less friction.
When the restriction is very high, a greater pressure differential isn't going to do much. If you're already pumping a **** ton of air through a pinhole, doubling the pressure differential won't do much. If you have a moderate flow of air through a hole and double the pressure differential, the airflow will increase significantly.
11-13-2010, 06:21 PM
#47
You know that's pretty much physically impossible, right? Flowrate is governed by pressure differential (assuming cross section is constant).
Torque is basically volumetric efficiency at a given RPM, less friction.
When the restriction is very high, a greater pressure differential isn't going to do much. If you're already pumping a **** ton of air through a pinhole, doubling the pressure differential won't do much. If you have a moderate flow of air through a hole and double the pressure differential, the airflow will increase significantly.
Torque is basically volumetric efficiency at a given RPM, less friction.
When the restriction is very high, a greater pressure differential isn't going to do much. If you're already pumping a **** ton of air through a pinhole, doubling the pressure differential won't do much. If you have a moderate flow of air through a hole and double the pressure differential, the airflow will increase significantly.
"CHOKED FLOW is a fluid dynamic condition associated with the Venturi effect which occurs when the mass flow rate will not increase with a further decrease in the downstream pressure environment while upstream pressure is fixed."
Click and learn
11-13-2010, 06:40 PM
#48
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Are you sure about that?
"CHOKED FLOW is a fluid dynamic condition associated with the Venturi effect which occurs when the mass flow rate will not increase with a further decrease in the downstream pressure environment while upstream pressure is fixed."
Click and learn
"CHOKED FLOW is a fluid dynamic condition associated with the Venturi effect which occurs when the mass flow rate will not increase with a further decrease in the downstream pressure environment while upstream pressure is fixed."
Click and learn
Air velocity can't increase anymore because (in short) it is at its max speed without a divergent nozzle.
I spent about 1/3 of my fluid dynamics class studying compressible flow and about a year at Pratt & Whitney developing convergent and divergent nozzles for military aircraft.
Nevertheless, you're agreeing with me and disagreeing with yourself.
Read what you posted:
"CHOKED FLOW is a fluid dynamic condition associated with the Venturi effect which occurs when the mass flow rate will not increase with a further decrease in the downstream pressure "
"If you're already pumping a **** ton of air through a pinhole, doubling the pressure differential won't do much."
Fluid dynamics isn't a topic that is generally intuitive, but this isn't that hard to picture. Think about it from a common sense point of view. You have a 6 hole you're sucking fluid though. Apply a little vacuum and little fluid goes through. Apply moderate amount of vacuum and even more fluid goes through. Apply a huge amount of vacuum and even more air goes through. Double that huge vacuum and maybe a bit more fluid goes through. Double that again and you get virtually no gain.
But I'll tell you what- when you figure out a way to increase flow by decreasing the pressure drop (by decreasing the pressure at one end without changing the restriction/cross section), you give me a call. I'll help you patent it.
Last edited by treyZ28; 11-13-2010 at 06:50 PM.
11-13-2010, 07:05 PM
#49
I'm already aware of that. Are you aware that you're agreeing with me and disagreeing with yourself? Also, are you aware that choked flow generally only at issue when we're talking about super-sonic/near super sonic air? Just wondering. It's when you have a convergent-divergent nozzle to accelerate air to the throat, make it go supersonic, then accelerate it after the throat. I spent about 1/3 of my fluid dynamics class studying the principals around this and about a year at Pratt & Whitney developing convergent and divergent nozzles for military aircraft.
Nevertheless, you're agreeing with me and disagreeing with yourself.
Read what you posted:
"CHOKED FLOW is a fluid dynamic condition associated with the Venturi effect which occurs when the mass flow rate will not increase with a further decrease in the downstream pressure "
"If you're already pumping a **** ton of air through a pinhole, doubling the pressure differential won't do much."
Nevertheless, you're agreeing with me and disagreeing with yourself.
Read what you posted:
"CHOKED FLOW is a fluid dynamic condition associated with the Venturi effect which occurs when the mass flow rate will not increase with a further decrease in the downstream pressure "
"If you're already pumping a **** ton of air through a pinhole, doubling the pressure differential won't do much."
You know that's pretty much physically impossible, right? Flowrate is governed by pressure differential (assuming cross section is constant).
BTW, still waiting on you to provide evidence regarding the original topic...
11-13-2010, 07:07 PM
#50
Fluid dynamics isn't a topic that is generally intuitive, but this isn't that hard to picture. Think about it from a common sense point of view. You have a 6 hole you're sucking fluid though. Apply a little vacuum and little fluid goes through. Apply moderate amount of vacuum and even more fluid goes through. Apply a huge amount of vacuum and even more air goes through. Double that huge vacuum and maybe a bit more fluid goes through. Double that again and you get virtually no gain.
11-14-2010, 01:20 AM
#51
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Unless you develop a system which will literally do the impossible- run PERFECTLY at the limit of compressible flow, there will some marginal increase in airflow with an increase in negative pressure (relative). For what it's worth, that's impossible. There will always be a very very very marginal increase. There is no sense in arguing with you. If I'm technically correct, you say I'm not correct in practicality. If I'm right in practicality, your cite supersonic compressible flow.
Like I said, a little bit of knowledge can be a very dangerous thing. In this case, you have a little bit of knowledge. If you'd like to discuss this in advanced tech, I'd be happy to do so. Please PM me if you decide to take it there. I'm not really interested in debating this with you any further over here.
Like I said, a little bit of knowledge can be a very dangerous thing. In this case, you have a little bit of knowledge. If you'd like to discuss this in advanced tech, I'd be happy to do so. Please PM me if you decide to take it there. I'm not really interested in debating this with you any further over here.
11-14-2010, 11:30 AM
#52
Unless you develop a system which will literally do the impossible- run PERFECTLY at the limit of compressible flow, there will some marginal increase in airflow with an increase in negative pressure (relative). For what it's worth, that's impossible. There will always be a very very very marginal increase. There is no sense in arguing with you. If I'm technically correct, you say I'm not correct in practicality. If I'm right in practicality, your cite supersonic compressible flow.
Like I said, a little bit of knowledge can be a very dangerous thing. In this case, you have a little bit of knowledge. If you'd like to discuss this in advanced tech, I'd be happy to do so. Please PM me if you decide to take it there. I'm not really interested in debating this with you any further over here.
Like I said, a little bit of knowledge can be a very dangerous thing. In this case, you have a little bit of knowledge. If you'd like to discuss this in advanced tech, I'd be happy to do so. Please PM me if you decide to take it there. I'm not really interested in debating this with you any further over here.
Last edited by KCS; 11-14-2010 at 12:03 PM.
11-14-2010, 11:39 AM
#53
little chevy, i have a very similar setup as you but i used the eagle rotating assembly with the prc 5.3 stage 2 heads, ms4, fast 92 and 1 3/4 headers. i made 460/430 to the wheels through a 6 speed and the clutch was slipping. also ran 125mph in the 1/4. i might be selling the heads/cam if your interesed
