1 3/4" Vs 1 7/8" Header Swap Results.
01-28-2009, 10:17 PM
#1
Le Mans Master
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Location: Greater Detroit Metro MI, when I'm not travelling.
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1 3/4" Vs 1 7/8" Header Swap Results.
The purpose of this test was to find out how much, if any, power stands to be gained by increasing the header primary size from 1 3/4" to 1 7/8" in a supercharged car. The general consensus on the forum has been that the larger diameter primaries will produce more top end, at the cost of some low end torque gains.
What really interested me were some claims that very large amounts of power was being held back by the 1 3/4" headers, because their primaries were "restrictive". I decided to investigate:
So here it is: we baselined my car, a 2006 Corvette C6 Z-51 with a ported TB and Intake manifold, an A&A V2 Si-Trim Vortech Supercharger running a 3.8" Pulley, and Kooks 1 3/4" Headers with a 3" catted X-pipe and Z06 Exhausts.
Then we swapped the headers for 1 7/8" American Racing headers with a 3" catted X- pipe keeping the same Z06 Exhaust.
Same Car
Same Fuel
Same Dyno
Same Correction Factors
Same Smoothing
Same Atmospheric Conditions
Same temperatures
Same day
4 hours apart.
The results, before re-tuning for the headers, are as close to a real back to back comparison as you can get. There was:
No change in the boost level whatsoever,
A leaning in the Air/Fuel Ratio of about 0.1points.
Julio then attempted to add timing, as per my request, in an attempt to make more power from the 1 7/8" headers. Adding time anywhere caused the ECU to pull it back out: this is really as much power as the car can make.
The car was tuned before hand to make as much power as we could safely get from the setup with the 1 3/4" headers. It is now tuned the same way for the 1 7/8" headers.
The before and after dyno charts are posted below.
My thoughts:
1- The boost does not change *AT ALL*. It looks like a solid line but in fact it consists of two lines perfectly over each other. This means that swapping the headers did not reduce exhaust backpressure in any way shape or form. That is why little power was gained.
2- I expected a loss of low end torque from the swap, but I was wrong: the 1 7/8" headers gave up nothing over the 1 3/4" ones. This is very nice
Here are all the relevant dynos. 001 through 005 were for injector resizing. 006 is the best tune with 1 3/4" headers. 07 is the 1 7/8" header dyno and 08 is the 1 7/8" dyno with a tune. Boost and AFR below.
Conclusion: The 1 7/8" headers gave up *nothing* in the low end, in fact gaining a small amount of torque, while maing slightly more power. If you aready have 1 3/4" headers, and are making similar numbers, spending the money to "upgrade" to 1 7/8" is not a good investment given the minimal gains
If you have a F/I car, or are thinking of going to F/I, there is no reason not to get 1 7/8" headers, given the extra power with no trade-offs
If you have a F/I car making a LOT more power than me, you stand to gain a LOT more from the header swap, since smaller primaries will always "max out" sooner. That said, 600WHP does not appear to be the point where they max out.
Finally, it is now clear to me that the headers are NOT a restriction to how much power a basic supercharged car makes. The 10PSI boost is a considerable number given the power made; a MUCH better place to remove airflow restriction and lower that number while making more power would be the camshaft; I believe a good cam could make 50HP or more at 2PSI or less boost. Perhaps this can be my next mod?
And last but not least... Guys, it cost me over $2000 to do this back to back comparison just for the sake of knowledge. Please be nice and don't get my tread locked?
Thank you!
What really interested me were some claims that very large amounts of power was being held back by the 1 3/4" headers, because their primaries were "restrictive". I decided to investigate:
So here it is: we baselined my car, a 2006 Corvette C6 Z-51 with a ported TB and Intake manifold, an A&A V2 Si-Trim Vortech Supercharger running a 3.8" Pulley, and Kooks 1 3/4" Headers with a 3" catted X-pipe and Z06 Exhausts.
Then we swapped the headers for 1 7/8" American Racing headers with a 3" catted X- pipe keeping the same Z06 Exhaust.
Same Car
Same Fuel
Same Dyno
Same Correction Factors
Same Smoothing
Same Atmospheric Conditions
Same temperatures
Same day
4 hours apart.
The results, before re-tuning for the headers, are as close to a real back to back comparison as you can get. There was:
No change in the boost level whatsoever,
A leaning in the Air/Fuel Ratio of about 0.1points.
Julio then attempted to add timing, as per my request, in an attempt to make more power from the 1 7/8" headers. Adding time anywhere caused the ECU to pull it back out: this is really as much power as the car can make.
The car was tuned before hand to make as much power as we could safely get from the setup with the 1 3/4" headers. It is now tuned the same way for the 1 7/8" headers.
The before and after dyno charts are posted below.
My thoughts:
1- The boost does not change *AT ALL*. It looks like a solid line but in fact it consists of two lines perfectly over each other. This means that swapping the headers did not reduce exhaust backpressure in any way shape or form. That is why little power was gained.
2- I expected a loss of low end torque from the swap, but I was wrong: the 1 7/8" headers gave up nothing over the 1 3/4" ones. This is very nice
Here are all the relevant dynos. 001 through 005 were for injector resizing. 006 is the best tune with 1 3/4" headers. 07 is the 1 7/8" header dyno and 08 is the 1 7/8" dyno with a tune. Boost and AFR below.
Conclusion: The 1 7/8" headers gave up *nothing* in the low end, in fact gaining a small amount of torque, while maing slightly more power. If you aready have 1 3/4" headers, and are making similar numbers, spending the money to "upgrade" to 1 7/8" is not a good investment given the minimal gains
If you have a F/I car, or are thinking of going to F/I, there is no reason not to get 1 7/8" headers, given the extra power with no trade-offs
If you have a F/I car making a LOT more power than me, you stand to gain a LOT more from the header swap, since smaller primaries will always "max out" sooner. That said, 600WHP does not appear to be the point where they max out.
Finally, it is now clear to me that the headers are NOT a restriction to how much power a basic supercharged car makes. The 10PSI boost is a considerable number given the power made; a MUCH better place to remove airflow restriction and lower that number while making more power would be the camshaft; I believe a good cam could make 50HP or more at 2PSI or less boost. Perhaps this can be my next mod?
And last but not least... Guys, it cost me over $2000 to do this back to back comparison just for the sake of knowledge. Please be nice and don't get my tread locked?
Thank you!
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Elijah71 (01-01-2021)
01-28-2009, 10:22 PM
#3
Tech Contributor
With no agenda or allegiance to a brand, spending 1700+ bucks plus dyno time for 5hp shows me its for real. I can see wanting an investment to pay off but when it doesnt, it shows at least honesty.
I'm surprised the tuner didnt want to 'donate' some dyno time to contribute but....
Thanks for the honest assesment. I think others with different results (gaining more) had too many variables such as x-pipe diameter and tuning issues.
I'll stay with the LG's.
I'm surprised the tuner didnt want to 'donate' some dyno time to contribute but....
Thanks for the honest assesment. I think others with different results (gaining more) had too many variables such as x-pipe diameter and tuning issues.
I'll stay with the LG's.
01-28-2009, 10:32 PM
#4
Le Mans Master
The purpose of this test was to find out how much, if any, power stands to be gained by increasing the header primary size from 1 3/4" to 1 7/8" in a supercharged car. The general consensus on the forum has been that the larger diameter primaries will produce more top end, at the cost of some low end torque gains.
What really interested me were some claims that very large amounts of power was being held back by the 1 3/4" headers, because their primaries were "restrictive". I decided to investigate:
So here it is: we baselined my car, a 2006 Corvette C6 Z-51 with a ported TB and Intake manifold, an A&A V2 Si-Trim Vortech Supercharger running a 3.8" Pulley, and Kooks 1 3/4" Headers with a 3" catted X-pipe and Z06 Exhausts.
Then we swapped the headers for 1 7/8" American Racing headers with a 3" catted X- pipe keeping the same Z06 Exhaust.
Same Car
Same Fuel
Same Dyno
Same Correction Factors
Same Smoothing
Same Atmospheric Conditions
Same temperatures
Same day
4 hours apart.
The results, before re-tuning for the headers, are as close to a real back to back comparison as you can get. There was:
No change in the boost level whatsoever,
A leaning in the Air/Fuel Ratio of about 0.1points.
Julio then attempted to add timing, as per my request, in an attempt to make more power from the 1 7/8" headers. Adding time anywhere caused the ECU to pull it back out: this is really as much power as the car can make.
The car was tuned before hand to make as much power as we could safely get from the setup with the 1 3/4" headers. It is now tuned the same way for the 1 7/8" headers.
The before and after dyno charts are posted below.
My thoughts:
1- The boost does not change *AT ALL*. It looks like a solid line but in fact it consists of two lines perfectly over each other. This means that swapping the headers did not reduce exhaust backpressure in any way shape or form. That is why little power was gained.
2- I expected a loss of low end torque from the swap, but I was wrong: the 1 7/8" headers gave up nothing over the 1 3/4" ones. This is very nice
Here are all the relevant dynos. 001 through 005 were for injector resizing. 006 is the best tune with 1 3/4" headers. 07 is the 1 7/8" header dyno and 08 is the 1 7/8" dyno with a tune. Boost and AFR below.
Conclusion: The 1 7/8" headers gave up *nothing* in the low end, in fact gaining a small amount of torque, while maing slightly more power. If you aready have 1 3/4" headers, and are making similar numbers, spending the money to "upgrade" to 1 7/8" is not a good investment given the minimal gains
If you have a F/I car, or are thinking of going to F/I, there is no reason not to get 1 7/8" headers, given the extra power with no trade-offs
If you have a F/I car making a LOT more power than me, you stand to gain a LOT more from the header swap, since smaller primaries will always "max out" sooner. That said, 600WHP does not appear to be the point where they max out.
Finally, it is now clear to me that the headers are NOT a restriction to how much power a basic supercharged car makes. The 10PSI boost is a considerable number given the power made; a MUCH better place to remove airflow restriction and lower that number while making more power would be the camshaft; I believe a good cam could make 50HP or more at 2PSI or less boost. Perhaps this can be my next mod?
And last but not least... Guys, it cost me over $2000 to do this back to back comparison just for the sake of knowledge. Please be nice and don't get my tread locked?
Thank you!
What really interested me were some claims that very large amounts of power was being held back by the 1 3/4" headers, because their primaries were "restrictive". I decided to investigate:
So here it is: we baselined my car, a 2006 Corvette C6 Z-51 with a ported TB and Intake manifold, an A&A V2 Si-Trim Vortech Supercharger running a 3.8" Pulley, and Kooks 1 3/4" Headers with a 3" catted X-pipe and Z06 Exhausts.
Then we swapped the headers for 1 7/8" American Racing headers with a 3" catted X- pipe keeping the same Z06 Exhaust.
Same Car
Same Fuel
Same Dyno
Same Correction Factors
Same Smoothing
Same Atmospheric Conditions
Same temperatures
Same day
4 hours apart.
The results, before re-tuning for the headers, are as close to a real back to back comparison as you can get. There was:
No change in the boost level whatsoever,
A leaning in the Air/Fuel Ratio of about 0.1points.
Julio then attempted to add timing, as per my request, in an attempt to make more power from the 1 7/8" headers. Adding time anywhere caused the ECU to pull it back out: this is really as much power as the car can make.
The car was tuned before hand to make as much power as we could safely get from the setup with the 1 3/4" headers. It is now tuned the same way for the 1 7/8" headers.
The before and after dyno charts are posted below.
My thoughts:
1- The boost does not change *AT ALL*. It looks like a solid line but in fact it consists of two lines perfectly over each other. This means that swapping the headers did not reduce exhaust backpressure in any way shape or form. That is why little power was gained.
2- I expected a loss of low end torque from the swap, but I was wrong: the 1 7/8" headers gave up nothing over the 1 3/4" ones. This is very nice
Here are all the relevant dynos. 001 through 005 were for injector resizing. 006 is the best tune with 1 3/4" headers. 07 is the 1 7/8" header dyno and 08 is the 1 7/8" dyno with a tune. Boost and AFR below.
Conclusion: The 1 7/8" headers gave up *nothing* in the low end, in fact gaining a small amount of torque, while maing slightly more power. If you aready have 1 3/4" headers, and are making similar numbers, spending the money to "upgrade" to 1 7/8" is not a good investment given the minimal gains
If you have a F/I car, or are thinking of going to F/I, there is no reason not to get 1 7/8" headers, given the extra power with no trade-offs
If you have a F/I car making a LOT more power than me, you stand to gain a LOT more from the header swap, since smaller primaries will always "max out" sooner. That said, 600WHP does not appear to be the point where they max out.
Finally, it is now clear to me that the headers are NOT a restriction to how much power a basic supercharged car makes. The 10PSI boost is a considerable number given the power made; a MUCH better place to remove airflow restriction and lower that number while making more power would be the camshaft; I believe a good cam could make 50HP or more at 2PSI or less boost. Perhaps this can be my next mod?
And last but not least... Guys, it cost me over $2000 to do this back to back comparison just for the sake of knowledge. Please be nice and don't get my tread locked?
Thank you!
In addition I would conclude that when chosing headers for the first time 1 7/8 isn't the wrong choice.
I also want to add that for drag strip guys the gain may be more. The dyno and the track are 2 different things. I've seen .1-.2 gain with a simple header swap in the right direction on a s/c car.
01-28-2009, 10:32 PM
#5
Tech Contributor
I believe a good cam could make 50HP or more at 2PSI or less boost. Perhaps this can be my next mod?
And last but not least... Guys, it cost me over $2000 to do this back to back comparison just for the sake of knowledge. Please be nice and don't get my tread locked?
Thank you!
And last but not least... Guys, it cost me over $2000 to do this back to back comparison just for the sake of knowledge. Please be nice and don't get my tread locked?
Thank you!
01-28-2009, 10:34 PM
#6
Le Mans Master
Thread Starter
Member Since: Oct 2007
Location: Greater Detroit Metro MI, when I'm not travelling.
Posts: 6,149
Likes: 0
Received 10 Likes
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10 Posts
Thanks for the writeup.
In addition I would conclude that when chosing headers for the first time 1 7/8 isn't the wrong choice.
I also want to add that for drag strip guys the gain may be more. The dyno and the track are 2 different things. I've seen .1-.2 gain with a simple header swap in the right direction on a s/c car.
In addition I would conclude that when chosing headers for the first time 1 7/8 isn't the wrong choice.
I also want to add that for drag strip guys the gain may be more. The dyno and the track are 2 different things. I've seen .1-.2 gain with a simple header swap in the right direction on a s/c car.
01-28-2009, 10:37 PM
#8
Tech Contributor
Thanks for the writeup.
In addition I would conclude that when chosing headers for the first time 1 7/8 isn't the wrong choice.
I also want to add that for drag strip guys the gain may be more. The dyno and the track are 2 different things. I've seen .1-.2 gain with a simple header swap in the right direction on a s/c car.
In addition I would conclude that when chosing headers for the first time 1 7/8 isn't the wrong choice.
I also want to add that for drag strip guys the gain may be more. The dyno and the track are 2 different things. I've seen .1-.2 gain with a simple header swap in the right direction on a s/c car.
Dave Busch formerly at Cartek said that the 1 3/4 results at the track were better for their cars and didnt recomend the 1 7/8 for this reason.
01-28-2009, 10:53 PM
#11
Team Owner
The big gains I showed are looking like the difference is in the x-pipe as I changed from 2 1/2 to 3 inch along with the primary change. Timing and tune were close I am running only 1-2 degrees more timing, 12 before to 13-14 after. While your swap was primary size only, I was hopeing along with you. For a bigger gain. Since you spent so much testing, I was able to get 1100.00 on the sale forum for my old Kook's taking the sting out of it!**But a least there is some gain everywhere in curve. Even down low!
How does it feel driving wise?
01-28-2009, 10:55 PM
#12
Team Owner
I wasnt going to swap out my LG 1 3/4 for 1 7/8 on my Vortech equipped car anyway but its intresting to see results that are pretty darn close. Thanks for your research results.
01-28-2009, 10:57 PM
#13
Le Mans Master
Thread Starter
Member Since: Oct 2007
Location: Greater Detroit Metro MI, when I'm not travelling.
Posts: 6,149
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Very nice. The big gains I showed are looking like the difference is in the x-pipe as I changed from 2 1/2 to 3 inch along with the primary change. Timing and tune were close I am running only 1-2 degrees more timing, 12 before to 13-14 after. While your swap was primary size only, I was hopeing along with you. For a bigger gain. Since you spent so much testing, I was able to get 1100.00 on the sale forum for my old Kook's taking the sting out of it!**
But a least there is some gain everywhere in curve. Even down low!
How does it feel driving wise?
The big gains I showed are looking like the difference is in the x-pipe as I changed from 2 1/2 to 3 inch along with the primary change. Timing and tune were close I am running only 1-2 degrees more timing, 12 before to 13-14 after. While your swap was primary size only, I was hopeing along with you. For a bigger gain. Since you spent so much testing, I was able to get 1100.00 on the sale forum for my old Kook's taking the sting out of it!**But a least there is some gain everywhere in curve. Even down low!
How does it feel driving wise?
The only thing I can confirm is that it sounds different, and I really like the way it sounds. I'm also happy it gained everywhere but was certainly hoping for more! I am chalking up your gains to the X-Pipe too, or clogged cats, or a tune... That's why it is good when we compare each other's work
Definitely selling my old headers...
Last edited by PowerLabs; 01-28-2009 at 11:03 PM.
01-29-2009, 12:18 AM
#17
Team Owner
Excellent info, thanks for doing the research. 
I was actually on my way to the shop at around 5pm but I got a little sidetracked, I almost got to see most of this happen firsthand.
I was actually on my way to the shop at around 5pm but I got a little sidetracked, I almost got to see most of this happen firsthand.
