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Re: Flowed a ported 440-1 with different backcuts..results
[Re: ChevyTS]
#1938410
10/25/15 05:58 PM
10/25/15 05:58 PM
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Joined: Sep 2014
Posts: 4,457
Washington
madscientist
master
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master
Joined: Sep 2014
Posts: 4,457
Washington
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I should have added that the flow chart posted with no backcut was something done a week prior before his 4.50" Chrysler bore plate arrived. I just wanted a quick test to see if they were worth a crap and as advertised all around since I got them thru an Ebay auction. They were tested on a 4.35" Chevy bore plate and possibly centered over the cylinder too much so perhaps that inflated the #'s? That was my initial thought, but we also tested the 30° backcut that day on the same plate and the #'s then were very similar to the ones posted here from the Chrysler plate. Just a few cfm higher in the low and mid-lift #'s on the Chrysler plate with nearly identical #' from .500 on. I'm sure the 10cfm given up on the peak lift #'s is worth less power than all the low and mid lift flow gained with a backcut. Some of this isn't quite so. I always look for ways to kill low lift (low lift being relative here, as low lift for a .600 lift cam is not the same as low lift for a 1.000 lift cam) in most everything I do. As for the mids,...if I'm testing and the low lift goes away and takes a bit of the mid with it, as long as I gain some back at MAX lift for the cam you are using I ignore it. The confusion come in with what is low lift, what is mid lift etc. Anything under .600 is a street cam so low lift would be .100-.250 or so. If you were using an .800 lift cam I would spend time at .100-.300 trying to lose some flow to gain it elsewhere. All that said, when talking back cuts, usually I give the number of degrees less than the seat angle as the back cut angle. Since air doesn't bend more than 7-8 degrees, that is about all the back cut they will take. For example, if you are using a 45* seat, a 7 degree back cut would equal a 38* degree cut (45-38). You actually used a 10 and 15 degree back cut. I can tell you I actually quit using back cuts a while ago. I have learned the hard way that even if a back cut increases flow anywhere in the curve, you can (and probably will) lose horsepower. I have done many heads that had a flow LOSS that picked up HP, for many reasons. Most of the time is was not back cutting the valves. An increase in airflow won't always mean an increase in HP. I would love to see what information brought you to these conclusions. What is it you are asking to see, flow bench data? Dyno sheets? Time slips? I can tell you it's almost across the board as brand irrelevant. I stumbled onto this by mistakenly testing some SB chevy heads. I can tell you that the more serious the head is to begin with, the less it wants back cuts. As I said, I have actually done heads that flowed LESS when I was done with them, and they were faster.
Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
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Re: Flowed a ported 440-1 with different backcuts..results
[Re: madscientist]
#1938744
10/26/15 02:13 AM
10/26/15 02:13 AM
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Joined: Jul 2004
Posts: 19,318
State of confusion
Thumperdart
I Live Here
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I Live Here
Joined: Jul 2004
Posts: 19,318
State of confusion
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This is why I don`t put much emphasis on dyno numbers, flow sheets or crazy math formulas to determine what size carb I need. When I was done installing 2.19 in. valves and fully porting my rpm`s, I asked Pettis if they could flow em and they couldn`t for a few days so being impatient as I am I put em on and ran faster than ever first pass off the trailer. Even if he flowed em and they didn`t post the "numbers" I`d like or had "issues", I`d still run em cos I had a couple of people who know there stuff look at em and that`s good enuff 4 me.......
72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB Dominic Thumper for videos and lots of carb pics......760-900-3895.....
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Re: Flowed a ported 440-1 with different backcuts..results
[Re: Charger453]
#1939008
10/26/15 04:36 PM
10/26/15 04:36 PM
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Joined: Mar 2005
Posts: 576
Texas
ChevyTS
mopar
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mopar
Joined: Mar 2005
Posts: 576
Texas
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See may not have been the best word for me to use. I would like to hear more about the testing that convinced you that diminishing low lift CFM in favor of high lift CFM increased HP. And your theory on why that was. I'm not being ugly. I am open minded and truly interested.
T & K Performance
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Re: Flowed a ported 440-1 with different backcuts..results
[Re: ChevyTS]
#1939022
10/26/15 04:53 PM
10/26/15 04:53 PM
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Joined: Sep 2014
Posts: 4,457
Washington
madscientist
master
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master
Joined: Sep 2014
Posts: 4,457
Washington
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See may not have been the best word for me to use. I would like to hear more about the testing that convinced you that diminishing low lift CFM in favor of high lift CFM increased HP. And your theory on why that was. I'm not being ugly. I am open minded and truly interested. Let me think about it. I'm not always big on posting info that cost me and/or my customers huge amounts of time to figure out. On the other hand, I want this hobby/sport to grow, and there are way too many old wives tales still floating around. I used to used some fairly hard "rules of thumb" like 52-54% of bore size for intake valve diameter, but strokers have screwed that up because they screw up the bore to stroke rule of thumb. Guy are typically using way bigger throats with 45* seats than I ever have and that may contribute to some of what I have learned. Let me think on it for a bit. And always remember what low lift really is. It is relevant only to what ever cam you are talking about at that moment. If you are running 1.0xx lift, anything under about .450 I would not really care about. If you are running .600 lift, then low lift is another set of numbers altogether. As a last thought for now...I think I always [censored] to the cam guys about LSA more than they like. I think in most applications, guys are using wider LSA's (again, relatively speaking because displacment, rod lenth or more correctly rod/stroke ratio, intake/exhaust flow ratio and transmission choice among other things figure in here) than they need, because they are overlooking overlap and what effect it has on port flow. So to make it easier, they use a wider LSA rather than fixing overlap issues somewhere else.
Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
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Re: Flowed a ported 440-1 with different backcuts..results
[Re: Thumperdart]
#1939381
10/27/15 12:29 AM
10/27/15 12:29 AM
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Joined: Jan 2003
Posts: 5,486
SoCal
Brian Hafliger
master
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master
Joined: Jan 2003
Posts: 5,486
SoCal
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This is why I don`t put much emphasis on dyno numbers, flow sheets or crazy math formulas to determine what size carb I need. When I was done installing 2.19 in. valves and fully porting my rpm`s, I asked Pettis if they could flow em and they couldn`t for a few days so being impatient as I am I put em on and ran faster than ever first pass off the trailer. Even if he flowed em and they didn`t post the "numbers" I`d like or had "issues", I`d still run em cos I had a couple of people who know there stuff look at em and that`s good enuff 4 me....... The thing is, if you HAD flowed them, and compared velocity readings, then you would have DATA from before and after... Something to think about.....
Brian Hafliger
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Re: Flowed a ported 440-1 with different backcuts..results
[Re: madscientist]
#1939388
10/27/15 12:36 AM
10/27/15 12:36 AM
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Joined: Jan 2003
Posts: 5,486
SoCal
Brian Hafliger
master
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master
Joined: Jan 2003
Posts: 5,486
SoCal
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See may not have been the best word for me to use. I would like to hear more about the testing that convinced you that diminishing low lift CFM in favor of high lift CFM increased HP. And your theory on why that was. I'm not being ugly. I am open minded and truly interested. Let me think about it. I'm not always big on posting info that cost me and/or my customers huge amounts of time to figure out. On the other hand, I want this hobby/sport to grow, and there are way too many old wives tales still floating around. I used to used some fairly hard "rules of thumb" like 52-54% of bore size for intake valve diameter, but strokers have screwed that up because they screw up the bore to stroke rule of thumb. Guy are typically using way bigger throats with 45* seats than I ever have and that may contribute to some of what I have learned. Let me think on it for a bit. And always remember what low lift really is. It is relevant only to what ever cam you are talking about at that moment. If you are running 1.0xx lift, anything under about .450 I would not really care about. If you are running .600 lift, then low lift is another set of numbers altogether. As a last thought for now...I think I always [censored] to the cam guys about LSA more than they like. I think in most applications, guys are using wider LSA's (again, relatively speaking because displacment, rod lenth or more correctly rod/stroke ratio, intake/exhaust flow ratio and transmission choice among other things figure in here) than they need, because they are overlooking overlap and what effect it has on port flow. So to make it easier, they use a wider LSA rather than fixing overlap issues somewhere else. Even at 1.00+ lift .450 lift is very relevant....CONTROL...controlling air speed, controlling reverse flow, controlling the airs exit speed into the cylinder...these things are KEY to making power! A wider LCA can mean a very strong flowing port doesn't get wasted out the exhaust! If we really want to know something for sure, I have to break down and test it accurately...no other way. Typically the poorer the port is the tighter the LCA will get....from my experience. Brian
Brian Hafliger
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Re: Flowed a ported 440-1 with different backcuts..results
[Re: Brian Hafliger]
#1939456
10/27/15 03:28 AM
10/27/15 03:28 AM
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Joined: Jul 2004
Posts: 19,318
State of confusion
Thumperdart
I Live Here
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I Live Here
Joined: Jul 2004
Posts: 19,318
State of confusion
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This is why I don`t put much emphasis on dyno numbers, flow sheets or crazy math formulas to determine what size carb I need. When I was done installing 2.19 in. valves and fully porting my rpm`s, I asked Pettis if they could flow em and they couldn`t for a few days so being impatient as I am I put em on and ran faster than ever first pass off the trailer. Even if he flowed em and they didn`t post the "numbers" I`d like or had "issues", I`d still run em cos I had a couple of people who know there stuff look at em and that`s good enuff 4 me....... The thing is, if you HAD flowed them, and compared velocity readings, then you would have DATA from before and after... Something to think about..... Never flowed em after the first port job so really have no data but kinda wish I did just didn`t want to wait. I`ll have Pettis flow em before I sell em and go Max wedge.......
72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB Dominic Thumper for videos and lots of carb pics......760-900-3895.....
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Re: Flowed a ported 440-1 with different backcuts..results
[Re: Brian Hafliger]
#1939792
10/27/15 06:20 PM
10/27/15 06:20 PM
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Joined: Sep 2014
Posts: 4,457
Washington
madscientist
master
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master
Joined: Sep 2014
Posts: 4,457
Washington
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See may not have been the best word for me to use. I would like to hear more about the testing that convinced you that diminishing low lift CFM in favor of high lift CFM increased HP. And your theory on why that was. I'm not being ugly. I am open minded and truly interested. Let me think about it. I'm not always big on posting info that cost me and/or my customers huge amounts of time to figure out. On the other hand, I want this hobby/sport to grow, and there are way too many old wives tales still floating around. I used to used some fairly hard "rules of thumb" like 52-54% of bore size for intake valve diameter, but strokers have screwed that up because they screw up the bore to stroke rule of thumb. Guy are typically using way bigger throats with 45* seats than I ever have and that may contribute to some of what I have learned. Let me think on it for a bit. And always remember what low lift really is. It is relevant only to what ever cam you are talking about at that moment. If you are running 1.0xx lift, anything under about .450 I would not really care about. If you are running .600 lift, then low lift is another set of numbers altogether. As a last thought for now...I think I always [censored] to the cam guys about LSA more than they like. I think in most applications, guys are using wider LSA's (again, relatively speaking because displacment, rod lenth or more correctly rod/stroke ratio, intake/exhaust flow ratio and transmission choice among other things figure in here) than they need, because they are overlooking overlap and what effect it has on port flow. So to make it easier, they use a wider LSA rather than fixing overlap issues somewhere else. Even at 1.00+ lift .450 lift is very relevant....CONTROL...controlling air speed, controlling reverse flow, controlling the airs exit speed into the cylinder...these things are KEY to making power! A wider LCA can mean a very strong flowing port doesn't get wasted out the exhaust! If we really want to know something for sure, I have to break down and test it accurately...no other way. Typically the poorer the port is the tighter the LCA will get....from my experience. Brian Well here you go. Brian has said what I was trying to say with way fewer words. The answer is CONTROL. Gases (air/fuel) will take the path of least resistance, regardless if that path is what we want or not. So you have to find out how to CONTROL airspeed, direction and all that crap. That is why I was talking about top cuts (on the combustion chamber, not on the valve...ever), because you may lose some flow at a given point in the curve, but you may gain something somewhere else (think directional here). In the 1.00 lift example and talking about .450 lift, when you plot things out, in reality with today's lobes the valve spends relatively little time there, either opening or closing, but, depending on the lobe and which side of the lobe we are looking at, (opening side here) the valve is begining to slow down to get over the nose. On the other side of the lobe, the valve is probably right in the middle of it's maximum closing velocity. All things you have to think about. And then try to control. Brians answer is still better than mine.
Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
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