Evolved Member
As noted above, what I was pointing out was that the pressure at which the flows were measured was higher than commonly used, which is less useful in comparisons to real world use, even when recognizing that static flow testing is not directly comparable to what happens when the head is part of a functioning motor.
Valve shrouding is a more important concern with oversize valves, which move the flow closer to the sides of the combustion chamber. It would not account for the decrease in stock head measured flow at .350+ unless it were even more exaggerated with the Cosworth's 1mm larger valves. It simply is a factor in determining whether larger valves have any performance benefit, considering the entire configuration of the combustion chamber and bore. That is why overbored engines sometimes show flow improvements, because the overbore operates to partially unshroud the valve.
High static flow does not necessarily translate into higher real world horsepower. Flow velocity at all areas under the curve that are part of the powerband being targeted is also critical. It's well known that too much porting in the wrong places can actually reduce the power a head can make.
Valve shrouding is a more important concern with oversize valves, which move the flow closer to the sides of the combustion chamber. It would not account for the decrease in stock head measured flow at .350+ unless it were even more exaggerated with the Cosworth's 1mm larger valves. It simply is a factor in determining whether larger valves have any performance benefit, considering the entire configuration of the combustion chamber and bore. That is why overbored engines sometimes show flow improvements, because the overbore operates to partially unshroud the valve.
High static flow does not necessarily translate into higher real world horsepower. Flow velocity at all areas under the curve that are part of the powerband being targeted is also critical. It's well known that too much porting in the wrong places can actually reduce the power a head can make.
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BTW, I am just kidding with you, but my point is clear.
this is what I understand: All of the data in the comparison table is measured at 28" H2O so it is apples to apples. Originally Posted by 240Z TwinTurbo
I am not very good at math, but let me take a stab at responding. If you take the square root of your question and divide it by the IQ of a gerble, you will see that 335cfm was not achieved using the industry standard 28.0". You may not be able to verify this as I am using a special decoder ring from a cracker jack box. BTW, I am just kidding with you, but my point is clear.
The 41.5" data at "peak lift" (.500") was listed for some reason- maybe to be impressive- but it's not relevant because it can be derived mathematically from the 28" data as I showed. So, the 41.5" figure should just be ignored because posting it with 28 " data is like saying "I can drive faster in 2nd gear than 1st at the same engine RPM".
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I must play nice Originally Posted by Steve_P
The 41.5" data at "peak lift" (.500") was listed for some reason- maybe to be impressive- but it's not relevant because it can be derived mathematically from the 28" data as I showed.
I obviously lack the ability to be serious about your response so can someone please tell SteveP why the 41" was posted.
Evolved Member
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Intake flow at 28.0"
Lift_________Stock________Cosworth
.500________226.5________277.6
Then, "at peak lift the bench was cranked up to achieve 335cfm (Cosworth's number) and the test pressure (to achieve that flow figure) was 41.5" H20.
I'll take a straight faced stab at it. Originally Posted by 240Z TwinTurbo
This post is only indended to provide independent evaluation of the stock EVO VIII head vs. the head available from Cosworth. Both heads were flowed on the same bench.Intake flow at 28.0"
Lift_________Stock________Cosworth
.500________226.5________277.6
Then, "at peak lift the bench was cranked up to achieve 335cfm (Cosworth's number) and the test pressure (to achieve that flow figure) was 41.5" H20.
Since in order to achieve Cosworth's reported flow figures, the flow bench had to be cranked from 28 inches (a pressure number) to 41 inches of pressure, one might question that the Cosworth flow number was inflated compared to the usual US testing procedures...
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You did, but Steve P wouldn't listen Originally Posted by TEC
Hmmm, I thought that is what I said back in post #14.
Evolved Member
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Since in order to achieve Cosworth's reported flow figures, the flow bench had to be cranked from 28 inches (a pressure number) to 41 inches of pressure, one might question that the Cosworth flow number was inflated compared to the usual US testing procedures...
Originally Posted by CO_VR4
I'll take a straight faced stab at it. Since in order to achieve Cosworth's reported flow figures, the flow bench had to be cranked from 28 inches (a pressure number) to 41 inches of pressure, one might question that the Cosworth flow number was inflated compared to the usual US testing procedures...
We all know how easy it is to manipulate cfm thru a head
Evolved Member
Digging up an old thread.
I've seen some pretty reputable head porters from the domestic world say the 28" standard is a bunch of crap, since the engine operates at MUCH higher pressures. Basically, they will crank up the flow bench as high as they possibly can to get port velocity up as high as possible. The higher port velocity means you have to be more careful with port shape due to the higher airflow inertia and higher Reynolds Number.
Basically, testing the head at higher pressures is more relevant to the actual performance of the head then testing at the "standard" 28" H20. Cosworth has the stock head flow numbers with the numbers from their head on the same sheet on their web page. It should be pretty obvious that the numbers need to be adjusted to compare to others. But I doubt they are doing it to show over inflated numbers and they are testing the head at higher pressures simply because it is more relevant to the performance of the head.
I've seen some pretty reputable head porters from the domestic world say the 28" standard is a bunch of crap, since the engine operates at MUCH higher pressures. Basically, they will crank up the flow bench as high as they possibly can to get port velocity up as high as possible. The higher port velocity means you have to be more careful with port shape due to the higher airflow inertia and higher Reynolds Number.
Basically, testing the head at higher pressures is more relevant to the actual performance of the head then testing at the "standard" 28" H20. Cosworth has the stock head flow numbers with the numbers from their head on the same sheet on their web page. It should be pretty obvious that the numbers need to be adjusted to compare to others. But I doubt they are doing it to show over inflated numbers and they are testing the head at higher pressures simply because it is more relevant to the performance of the head.
Evolving Member
28" shows alot, but not everything. That doesn't make it crap though. Live engine average is closer to 60", with peaks far exceeding 100". Actual port development in both production and racing is done in the 28-60" range, and still most of it it to the lower end of that range. Within that range there is usually very little to no difference that shows up, especially on typical 4V heads. Typical 2V shows up more difference because the port has to make a significant turn towards cylinder axis.
In some racing development like F1 and IRL, they may pull over 100" but that is mainly for checking and not development. With ports that have such a straight shot with such even velocity distribution vs domestic 2V head, you'll never go turbulent in the body of the port as long as the basics are adhered to. What they use it for is checking for turbulence from valve and seat angles , bowl-seat-chamber transitions, and less so divider position/style and downstream effects.
The smaller a port is and the less it flows, the easier it is to test at higher depressions. The domestic guys have a difficult time trying to pull 100" on a 500-600 CFM @ 28" head. It is alot easier when your head flows only 200-300 CFM.
Cosworth should publish some industry standard numbers just for reference sake. Relevance to live engine should be separate issue because even at over 100" it isn't even close to live. It is closer, but still far from. For one with a turbocharged engine, you have to simulate pushing the air, as well as pulling it. Plain pulling is for NAs. So you have to push at all the right pressures and temperatures, and then how much of the intake tract are you doing to put upstream of the port? How far do you want to take it? And then pulse simulation and pulse interaction between cylinders.. it goes on forever....
In some racing development like F1 and IRL, they may pull over 100" but that is mainly for checking and not development. With ports that have such a straight shot with such even velocity distribution vs domestic 2V head, you'll never go turbulent in the body of the port as long as the basics are adhered to. What they use it for is checking for turbulence from valve and seat angles , bowl-seat-chamber transitions, and less so divider position/style and downstream effects.
The smaller a port is and the less it flows, the easier it is to test at higher depressions. The domestic guys have a difficult time trying to pull 100" on a 500-600 CFM @ 28" head. It is alot easier when your head flows only 200-300 CFM.
Cosworth should publish some industry standard numbers just for reference sake. Relevance to live engine should be separate issue because even at over 100" it isn't even close to live. It is closer, but still far from. For one with a turbocharged engine, you have to simulate pushing the air, as well as pulling it. Plain pulling is for NAs. So you have to push at all the right pressures and temperatures, and then how much of the intake tract are you doing to put upstream of the port? How far do you want to take it? And then pulse simulation and pulse interaction between cylinders.. it goes on forever....
Evolved Member
I thought Cosworth made it clear that their advertised numbers were flowed at 50"?
When I am doing my own flow testing I flow at 50, but when I am finished I always flow at 28 just to see where I stand compared to the industry standard advertised numbers. Whether it makes sense or not, 28" is where 90% of the industry advertises their numbers.
On my SF1020 I see 208 cfm @ 28" out of an EVO head. I have tested many of your favorite vendor's heads, and they are less than impressive. They all show about half the gains they claim. I have yet to flow a Cosworth head, but I did take a good look at one out of the case at SEMA and it looks pretty nice. I can see it being 50cfm better than stock and worth every penny they are asking. I am getting over 270 on my bench without getting too crazy and my exhaust is even more impressive, but I have not tested it on a big turbo car yet. On my stock turbo car with a big lift cam it is a blast. I am going to try and move the port around a bit and see what I can come up with. There is easily more flow...but most people wouldn't pay for something like that.
When I am doing my own flow testing I flow at 50, but when I am finished I always flow at 28 just to see where I stand compared to the industry standard advertised numbers. Whether it makes sense or not, 28" is where 90% of the industry advertises their numbers.
On my SF1020 I see 208 cfm @ 28" out of an EVO head. I have tested many of your favorite vendor's heads, and they are less than impressive. They all show about half the gains they claim. I have yet to flow a Cosworth head, but I did take a good look at one out of the case at SEMA and it looks pretty nice. I can see it being 50cfm better than stock and worth every penny they are asking. I am getting over 270 on my bench without getting too crazy and my exhaust is even more impressive, but I have not tested it on a big turbo car yet. On my stock turbo car with a big lift cam it is a blast. I am going to try and move the port around a bit and see what I can come up with. There is easily more flow...but most people wouldn't pay for something like that.
Evolving Member
At some point you guys are going to have to start talking valve sizes, and port minimum and average cross sectional areas to get comparable coefficients. Also comparison of entire lift range and beyond is preferable vs just max flow.
Evolved Member
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The 1m os valve only makes up for ~10 of the cfm gain...and a majority of the guys getting this serious with a head are going to be using the big valve. The lower lift areas are picked up by the valve job. With a good port that flows really well at .500 who gives a **** if it causes you lose 5 cfm at .200? I guess the guys who would care are the majority here because they are sticking these silly little shelf cams in their "race" ported heads...then on the other hand you have guys sticking the Revolver and Piper in a stock head that is done at .350 Originally Posted by ShaunSG
At some point you guys are going to have to start talking valve sizes, and port minimum and average cross sectional areas to get comparable coefficients. Also comparison of entire lift range and beyond is preferable vs just max flow.
Evolved Member
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When I am doing my own flow testing I flow at 50, but when I am finished I always flow at 28 just to see where I stand compared to the industry standard advertised numbers. Whether it makes sense or not, 28" is where 90% of the industry advertises their numbers.
On my SF1020 I see 208 cfm @ 28" out of an EVO head. I have tested many of your favorite vendor's heads, and they are less than impressive. They all show about half the gains they claim. I have yet to flow a Cosworth head, but I did take a good look at one out of the case at SEMA and it looks pretty nice. I can see it being 50cfm better than stock and worth every penny they are asking. I am getting over 270 on my bench without getting too crazy and my exhaust is even more impressive, but I have not tested it on a big turbo car yet. On my stock turbo car with a big lift cam it is a blast. I am going to try and move the port around a bit and see what I can come up with. There is easily more flow...but most people wouldn't pay for something like that.
where do you live? i have a cosworth head that you could flow?Originally Posted by DRAG
I thought Cosworth made it clear that their advertised numbers were flowed at 50"?When I am doing my own flow testing I flow at 50, but when I am finished I always flow at 28 just to see where I stand compared to the industry standard advertised numbers. Whether it makes sense or not, 28" is where 90% of the industry advertises their numbers.
On my SF1020 I see 208 cfm @ 28" out of an EVO head. I have tested many of your favorite vendor's heads, and they are less than impressive. They all show about half the gains they claim. I have yet to flow a Cosworth head, but I did take a good look at one out of the case at SEMA and it looks pretty nice. I can see it being 50cfm better than stock and worth every penny they are asking. I am getting over 270 on my bench without getting too crazy and my exhaust is even more impressive, but I have not tested it on a big turbo car yet. On my stock turbo car with a big lift cam it is a blast. I am going to try and move the port around a bit and see what I can come up with. There is easily more flow...but most people wouldn't pay for something like that.