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Alright, after 6 months or so of off and on work I finally finished the research project today. The link to the site is posted below, if you cant click on it then just copy and paste it into your web browser and then click download (You will need microsoft Excel to run the file and no, I PROMISE there are no viruses in the file). I will now write an analysis of all the numbers, figures and theory you will see in the file. Some of you will probably be familiar with the tests I ran and some of the beginners will not but it is all pretty easy to follow if you just read it. Before you read, I would like to make it clear that all my research is based on facts so dont get pissed off if you dont like somethin. Also, I am not biased in any way towards one vendor or another, I had my own heads ported from a local shop. I was not able to research zzperformance on actual facts but I will analyze them to the best of my knowledge. The reason why they do not post their flow numbers are as follows in the email they sent me below:
" I'm sorry, we don't list published flow numbers because too many of our competitors lie. Our customers compare flow numbers when shopping heads and this puts us in a position where we have to lie to compete. We refuse to do this and therefore prove our products with dyno numbers, 1/4 miles times and a repuations for heads that don't have valve guide failures."
Also, when reading keep in mind that there are dozens of complimentary upgrades to a set of heads, and a certain head design may not be best for you as it was for someone else due to the cam selection, fuel and so forth. Finally, do not rely just on what you read. Go research all this yourself so you can compare everything and see what works best for you.
Link:
cylinder_head_research.xls
If that link doesnt work then try this one:
http://storeandserve.com/download/12...earch.xls.html
Analysis:
I started out by comparing just bare flow numbers, both exhaust and intake based on pertentages. You can see all the calculations I did, sorry these may be a little confusing. In regards to peak flow numbers you can see in the graphs starting out with the intake that Intense has the highest peak numbers, followed by Abbott and then SSM. In regards to exhaust, Intense has the highest peak numbers followed by SSM and then Abbott.
However, when dealing with flow numbers you CANNOT just look at the peak flow numbers for oftentimes the heads with the highest flow numbers are the heads that produce significantly less power. When looking at the flow numbers most people will say look at the mid-lift numbers because that is where the lift spends the majority of its time, which is true but it is more or less a rule of thumb. I believe a more accurate approach is to integrate the area under the entire curve and whichever flow has the largest area is the one that flows the best. This approach takes into account not only midlift but also low lift and high lift which are essential for torque and peak horsepower. When integrating all the areas it turns out that with respect to intake, Abbott flows the best followed by Intense then SSM. With respect to the exhaust it turns out that Intense flows the best followed by SSM and then Abbott. When making conclusions about which is best overall, you have to keep in mind that exhaust is most effective from low to mid-lift whereas intake is most effective from mid to high-lift. My conclusion when viewing just bare flow numbers is that Abbott flows the best overall. Their Intake area/numbers really outdo both SSM and Intense. On the exhaust side, remembering that low to mid-lift is the most important, yes Intense does flow better but NOT by much. All three are very close and can be logically assumed that all three will perform almost equally on the exhaust port from low to mid-lift. I will further analyze high exhaust numbers in the section below.
Flow numbers however are FAR from what makes a good head port job. You also have to take in effect velocity, the path taken through the port, valve size and volumetric efficiency. These are not all the variables but some of the important ones when designing a good head.
Next, I am going to discuss a theory called the Exhaust-to-intake ratio. Many of you probably know what this is but for those of you who dont, it is important that you consider this. This is essentially a pertentage where you take the exhaust flow and divide it by the intake flow at the same lift. A good representative lift to use is known as the optimum lift (lift at which the valve flows most, while spending the most time from 0.00 lift to max lift). Normally this optimum lift is between .300 and .400. For our purposes I just used .300 lift. When these two figures are divided a good number/percentage to come out with is between 70-80%. A head is considered a good flowing head if it reaches this level. A head with a ratio of 85% is even better but anything over that should be considered suspicious. This is due to the fact that after a pertentage of 85% the cylinder begins to overscavenge itself creating a very inefficient flow especially if its for a street application; if its for a drag application, a higher percentage is not as harmful. As you can see in my calculations, Stock actually has the best Ratio at 84%!! But since we are focusing on aftermarket port jobs then you can see that Abbott has the next best ratio followed by SSM then Intense @ 98%!! For intense, This means the exhaust is almost more than the intake flow! The only perk I can see to a head like Intense having high flow numbers and a very high E-I ratio is in a drag application as mentioned before. When the motor is constantly running on high rpms then a large E-I ratio is more desirable. You would also need a larger cam for this application as well to allow for the powerband to be shifted to where the flow numbers are greatest.
Another important conclusion that I have made when considering flow numbers and the exhaust to intake ratio is velocity. Ask yourself the question.....what good is a head which has huge flow numbers but takes twice as long to fill the cylinder? The object is to fill the cylinder with as much air as possible in the shortest amount of time. Unfortunately, I dont have the port depth and length figures to precisely determine velocity but I can logically assume that Abbott has the fastest velocity (not by much) due to the valve efficiency. Valve efficiency can be derived by taking the flow at the optimum lift and dividing it by the product of the valve size, pi and optimum lift. (Eg: 156/(1.8" x pi x .300)). The answer to this equation is an acceleration (CFM/in^2). Abbott flows 107 cfm per inch squared of the valve; SSM goes 98 and intense right behind at 97. Here, you can clearly see the difference Abbott has over the rest showing how it has a faster velocity over the others. In respect to cam selection, since the heads of Abbott have a relatively high velocity, they dont need a large cam. Only enough duration, LSA and overlap to fill the cylinder to the highest pressure.
With respect to ZZP, although we can not make a concrete comparison, we can use the table I compiled at the bottom of the spreadsheet. What is it is the volume of one cylinder at the top, for us we will just use 40 since the actual is 3.8. Since ZZP reccommends raising the redline to 6500 and over for their cams in conjunction with their heads we can use the table and see that at a little over 6500rpms the head will flow 235 CFM which is comparable to both Abbott and Intense. In terms of velocity since we have the valve sizes, which are between Abbott and Intense, I would say the velocity is a little under Abbott's, maybe flowing 102 CFM/in^2. I believe that these heads perform very well and would consider them closely with Abbott.
You can take this information anyway you like, but like I said before, everything except the analysis on ZZP is based on facts. Also, I disclose that these are not the only sources for a good port job. My local porter was great and I know of a couple others that have awesome timeslips from even porting them themselves. If you have any questions please ask.
- Neal
" I'm sorry, we don't list published flow numbers because too many of our competitors lie. Our customers compare flow numbers when shopping heads and this puts us in a position where we have to lie to compete. We refuse to do this and therefore prove our products with dyno numbers, 1/4 miles times and a repuations for heads that don't have valve guide failures."
Also, when reading keep in mind that there are dozens of complimentary upgrades to a set of heads, and a certain head design may not be best for you as it was for someone else due to the cam selection, fuel and so forth. Finally, do not rely just on what you read. Go research all this yourself so you can compare everything and see what works best for you.
Link:
cylinder_head_research.xls
If that link doesnt work then try this one:
http://storeandserve.com/download/12...earch.xls.html
Analysis:
I started out by comparing just bare flow numbers, both exhaust and intake based on pertentages. You can see all the calculations I did, sorry these may be a little confusing. In regards to peak flow numbers you can see in the graphs starting out with the intake that Intense has the highest peak numbers, followed by Abbott and then SSM. In regards to exhaust, Intense has the highest peak numbers followed by SSM and then Abbott.
However, when dealing with flow numbers you CANNOT just look at the peak flow numbers for oftentimes the heads with the highest flow numbers are the heads that produce significantly less power. When looking at the flow numbers most people will say look at the mid-lift numbers because that is where the lift spends the majority of its time, which is true but it is more or less a rule of thumb. I believe a more accurate approach is to integrate the area under the entire curve and whichever flow has the largest area is the one that flows the best. This approach takes into account not only midlift but also low lift and high lift which are essential for torque and peak horsepower. When integrating all the areas it turns out that with respect to intake, Abbott flows the best followed by Intense then SSM. With respect to the exhaust it turns out that Intense flows the best followed by SSM and then Abbott. When making conclusions about which is best overall, you have to keep in mind that exhaust is most effective from low to mid-lift whereas intake is most effective from mid to high-lift. My conclusion when viewing just bare flow numbers is that Abbott flows the best overall. Their Intake area/numbers really outdo both SSM and Intense. On the exhaust side, remembering that low to mid-lift is the most important, yes Intense does flow better but NOT by much. All three are very close and can be logically assumed that all three will perform almost equally on the exhaust port from low to mid-lift. I will further analyze high exhaust numbers in the section below.
Flow numbers however are FAR from what makes a good head port job. You also have to take in effect velocity, the path taken through the port, valve size and volumetric efficiency. These are not all the variables but some of the important ones when designing a good head.
Next, I am going to discuss a theory called the Exhaust-to-intake ratio. Many of you probably know what this is but for those of you who dont, it is important that you consider this. This is essentially a pertentage where you take the exhaust flow and divide it by the intake flow at the same lift. A good representative lift to use is known as the optimum lift (lift at which the valve flows most, while spending the most time from 0.00 lift to max lift). Normally this optimum lift is between .300 and .400. For our purposes I just used .300 lift. When these two figures are divided a good number/percentage to come out with is between 70-80%. A head is considered a good flowing head if it reaches this level. A head with a ratio of 85% is even better but anything over that should be considered suspicious. This is due to the fact that after a pertentage of 85% the cylinder begins to overscavenge itself creating a very inefficient flow especially if its for a street application; if its for a drag application, a higher percentage is not as harmful. As you can see in my calculations, Stock actually has the best Ratio at 84%!! But since we are focusing on aftermarket port jobs then you can see that Abbott has the next best ratio followed by SSM then Intense @ 98%!! For intense, This means the exhaust is almost more than the intake flow! The only perk I can see to a head like Intense having high flow numbers and a very high E-I ratio is in a drag application as mentioned before. When the motor is constantly running on high rpms then a large E-I ratio is more desirable. You would also need a larger cam for this application as well to allow for the powerband to be shifted to where the flow numbers are greatest.
Another important conclusion that I have made when considering flow numbers and the exhaust to intake ratio is velocity. Ask yourself the question.....what good is a head which has huge flow numbers but takes twice as long to fill the cylinder? The object is to fill the cylinder with as much air as possible in the shortest amount of time. Unfortunately, I dont have the port depth and length figures to precisely determine velocity but I can logically assume that Abbott has the fastest velocity (not by much) due to the valve efficiency. Valve efficiency can be derived by taking the flow at the optimum lift and dividing it by the product of the valve size, pi and optimum lift. (Eg: 156/(1.8" x pi x .300)). The answer to this equation is an acceleration (CFM/in^2). Abbott flows 107 cfm per inch squared of the valve; SSM goes 98 and intense right behind at 97. Here, you can clearly see the difference Abbott has over the rest showing how it has a faster velocity over the others. In respect to cam selection, since the heads of Abbott have a relatively high velocity, they dont need a large cam. Only enough duration, LSA and overlap to fill the cylinder to the highest pressure.
With respect to ZZP, although we can not make a concrete comparison, we can use the table I compiled at the bottom of the spreadsheet. What is it is the volume of one cylinder at the top, for us we will just use 40 since the actual is 3.8. Since ZZP reccommends raising the redline to 6500 and over for their cams in conjunction with their heads we can use the table and see that at a little over 6500rpms the head will flow 235 CFM which is comparable to both Abbott and Intense. In terms of velocity since we have the valve sizes, which are between Abbott and Intense, I would say the velocity is a little under Abbott's, maybe flowing 102 CFM/in^2. I believe that these heads perform very well and would consider them closely with Abbott.
You can take this information anyway you like, but like I said before, everything except the analysis on ZZP is based on facts. Also, I disclose that these are not the only sources for a good port job. My local porter was great and I know of a couple others that have awesome timeslips from even porting them themselves. If you have any questions please ask.
- Neal
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