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Disclaimer:
This thread is for informational purposes only. There have been many questions about "How much power are headers worth on our cars?" and as it so happened, I was in a position to try to find out. This thread will NOT guarantee you XX gains, nor will it differentiate between brands of headers. Many cars are fast, and there are many ways to be fast - this thread is NOT about being fast: Simply put, this thread is about comparing headers to the popular factory exhaust (with cat-delete). I will be stating all dyno pulls in "RWHP / RWTQ" format.
Background:
I own a 2013 Manual CTSV Wagon. It started with a Mamofied throttle body and an Airaid CAI. I had a cam and pulley "Stage 1.5" completed on February 20th @ Cincy Speed for my Stage 1.5. The cam is a mild version of LT1z' popular Stage 2. We made several baseline runs and dyno'd again after the 10.5" lower, LT1z cam, BTR springs and Trunion upgrade were completed. The primary catalytic converters were removed and straight-pipe was welded in, however no other exhaust modifications were performed (we left in the Secondary Cats). Those runs will be listed below:
02/20/15 baseline (with Airaid, Mamofied factory Throttle Body): 495/460
02/20/15 final numbers after cam, pulley and cat-delete: 610 / 581*
* Boost was just under 15psi, as expected.
Although I had planned to keep the factory exhaust, the SOUND of the primary cat-delete was horrible, so within days I had placed an order with American Racing Headers for 1 7/8th primaries, X-pipe and mid-pipes into factory mufflers; and I had them drop-shipped to Calico Coatings for their standard black "ceramic" thermal coating. ARH stated that they had updated their hi-flow converters in 2013 after having issues, with the new variants being rated for 2400* EGT, or roughly up to 20psi boost. I also ordered 2.5" Magnaflow resonators (turned out to be a mistake) to help quiet the car while keeping factory mufflers.
One month later, the coated headers arrived literally on the day of the install. Cincy Speed went to some length to humor my needs here, and we were able to "baseline" the car again a few times as I wanted to account for warm weather changes. We did notice belt slip with the factory upper pulley whenever the belt was "cold." so many of the dyno charts will reflect this. However, the first runs were often the best due to colder IAT2. Per my build thread, I expected to gain around 25 RWHP and lose a pound of boost - there is quite a bit of discussion on the what-if's in that thread that I will link below that are good to ponder.
03/19/15 "Baseline" to account for weather: : 610 / 565 (same RWHP, but ~15 less RWTQ as previous best)
03/19/15 Final numbers after ARH 1 7/8" coated headers with cats and dual 2.5" resonators into factory mufflers: 653 / 634*
* Boost was just under 14psi, as expected (around 13.8psi).
* Total Gain: no less than +40 RWHP, +50 RWTQ,using "best" runs from each session.
Dyno Graph:
Note how the powerband is actually more broad than baseline - if the peak numbers shifted higher, it's only by a few hundred RPM?
![]()
Key: Run 08 was the 2nd baseline run (the only without belt slip). Run 11 was our best and final run of the day.
Notes:
Dyno tricks, tunes, and AFR:
* The Calibrator stated only one-half degree of timing was actually added, and only above 5K RPM on the retune.
* AFR was highly consistent, and ranged from 11.2 - 11.5 on all runs (tailpipe). Best power was around 11.2 AFR.
* When comparing baselines and mods, all numbers were SAE correction on the same dyno, with the same tuner.
* The correction factor was almost identical for all runs: surprising shop conditions were highly similar from February (Correction factor 0.99) to yesterday's March runs (Correction factor 1.00). This explains why peak RWHP was essentially identical one month to the next.
* The tuner was not aware of any "wager" or purpose to the test, other than to see what headers would bring to my Daily Driver.
My Choices for Exhaust:
* The factory exhaust is cast iron, and approximately 1 3/4" primary diameter. The OEM converters are 600 cell.
* The ARH hi-flow converters were changed in 2013, are 200 cell and rated for 2400 degrees. ARH estimates no more than 5RWHP parasitic loss, probably closer to 2-3 HP at my levels.
* I went with ARH 1 7/8" primaries as conventional wisdom suggests a 2" primary may be "too big" - I suspect 2" headers may be even better, or at least pose no significant loss in my situation.
* The 2.5" Magnaflow resonators are actually a bottle-neck! We placed them right after the ARH X-pipe, and had to weld 3" pipe OVER the 2.5" ends to mate things up. So the ARH 3" X-pipe is going right into a 2.5" lip (the resonators), then back to 3" pipes into 2.5" mufflers! This was an oversight on my part, but we had to make it work due to time constraints.
Final Thoughts:
* Clearly, the factory exhaust was a significant restriction at 600 RWHP.
* I made +40 / +50 with one pound LESS boost: "More power, Less Boost, Less Heat." The final numbers are irrelevant, the DELTA is what counts!
* My cam likely contributed to these huge gains; however +30 / +20 was seen on a pullied, factory cam V (HauvaSteve).
* I would never want to attempt this install in a driveway, on jack stands!
* Anyone who wants to run resonators: ARH is 3" diameter all the way back! 2.5" resonators do NOT fit (even though we welded mine in).
* Your mileage may vary! Brand/design of pipes, primary diameter, converter brands, tune and conditions all may affect your results!
Links:
My Build Thread: Stage 1.75 Header Comparison Blowout!
How Much Power Can Stock Exhaust Handle?
HauvaSteve's Kooks Headers HiFlow Cats Install Project thread
Thanks!
![]()
Run 000: That morning's second baseline; First run was higher (610 / 565) but doesn't look pretty due to significant belt slip.
Run 010, 011: Final two runs after exhaust buttoned up.
Update 02/20/2017: The x pipe (with cats) failed on me yesterday, and Mike @ ARH says the warranty died as soon as I had them ceramic coated. I've been happy with the subsequent two years of performance from these headers, but based on the succinct lack of customer service I can't say I'm really pleased with ARH going forward. I would have expected better service from the rip-off resellers on ebay (ie at the least a replacement part at-cost, or something).
This thread is for informational purposes only. There have been many questions about "How much power are headers worth on our cars?" and as it so happened, I was in a position to try to find out. This thread will NOT guarantee you XX gains, nor will it differentiate between brands of headers. Many cars are fast, and there are many ways to be fast - this thread is NOT about being fast: Simply put, this thread is about comparing headers to the popular factory exhaust (with cat-delete). I will be stating all dyno pulls in "RWHP / RWTQ" format.
Background:
I own a 2013 Manual CTSV Wagon. It started with a Mamofied throttle body and an Airaid CAI. I had a cam and pulley "Stage 1.5" completed on February 20th @ Cincy Speed for my Stage 1.5. The cam is a mild version of LT1z' popular Stage 2. We made several baseline runs and dyno'd again after the 10.5" lower, LT1z cam, BTR springs and Trunion upgrade were completed. The primary catalytic converters were removed and straight-pipe was welded in, however no other exhaust modifications were performed (we left in the Secondary Cats). Those runs will be listed below:
02/20/15 baseline (with Airaid, Mamofied factory Throttle Body): 495/460
02/20/15 final numbers after cam, pulley and cat-delete: 610 / 581*
* Boost was just under 15psi, as expected.
Although I had planned to keep the factory exhaust, the SOUND of the primary cat-delete was horrible, so within days I had placed an order with American Racing Headers for 1 7/8th primaries, X-pipe and mid-pipes into factory mufflers; and I had them drop-shipped to Calico Coatings for their standard black "ceramic" thermal coating. ARH stated that they had updated their hi-flow converters in 2013 after having issues, with the new variants being rated for 2400* EGT, or roughly up to 20psi boost. I also ordered 2.5" Magnaflow resonators (turned out to be a mistake) to help quiet the car while keeping factory mufflers.
One month later, the coated headers arrived literally on the day of the install. Cincy Speed went to some length to humor my needs here, and we were able to "baseline" the car again a few times as I wanted to account for warm weather changes. We did notice belt slip with the factory upper pulley whenever the belt was "cold." so many of the dyno charts will reflect this. However, the first runs were often the best due to colder IAT2. Per my build thread, I expected to gain around 25 RWHP and lose a pound of boost - there is quite a bit of discussion on the what-if's in that thread that I will link below that are good to ponder.
03/19/15 "Baseline" to account for weather: : 610 / 565 (same RWHP, but ~15 less RWTQ as previous best)
03/19/15 Final numbers after ARH 1 7/8" coated headers with cats and dual 2.5" resonators into factory mufflers: 653 / 634*
* Boost was just under 14psi, as expected (around 13.8psi).
* Total Gain: no less than +40 RWHP, +50 RWTQ,using "best" runs from each session.
Dyno Graph:
Note how the powerband is actually more broad than baseline - if the peak numbers shifted higher, it's only by a few hundred RPM?
Key: Run 08 was the 2nd baseline run (the only without belt slip). Run 11 was our best and final run of the day.
Notes:
Dyno tricks, tunes, and AFR:
* The Calibrator stated only one-half degree of timing was actually added, and only above 5K RPM on the retune.
* AFR was highly consistent, and ranged from 11.2 - 11.5 on all runs (tailpipe). Best power was around 11.2 AFR.
* When comparing baselines and mods, all numbers were SAE correction on the same dyno, with the same tuner.
* The correction factor was almost identical for all runs: surprising shop conditions were highly similar from February (Correction factor 0.99) to yesterday's March runs (Correction factor 1.00). This explains why peak RWHP was essentially identical one month to the next.
* The tuner was not aware of any "wager" or purpose to the test, other than to see what headers would bring to my Daily Driver.
My Choices for Exhaust:
* The factory exhaust is cast iron, and approximately 1 3/4" primary diameter. The OEM converters are 600 cell.
* The ARH hi-flow converters were changed in 2013, are 200 cell and rated for 2400 degrees. ARH estimates no more than 5RWHP parasitic loss, probably closer to 2-3 HP at my levels.
* I went with ARH 1 7/8" primaries as conventional wisdom suggests a 2" primary may be "too big" - I suspect 2" headers may be even better, or at least pose no significant loss in my situation.
* The 2.5" Magnaflow resonators are actually a bottle-neck! We placed them right after the ARH X-pipe, and had to weld 3" pipe OVER the 2.5" ends to mate things up. So the ARH 3" X-pipe is going right into a 2.5" lip (the resonators), then back to 3" pipes into 2.5" mufflers! This was an oversight on my part, but we had to make it work due to time constraints.
Final Thoughts:
* Clearly, the factory exhaust was a significant restriction at 600 RWHP.
* I made +40 / +50 with one pound LESS boost: "More power, Less Boost, Less Heat." The final numbers are irrelevant, the DELTA is what counts!
* My cam likely contributed to these huge gains; however +30 / +20 was seen on a pullied, factory cam V (HauvaSteve).
* I would never want to attempt this install in a driveway, on jack stands!
* Anyone who wants to run resonators: ARH is 3" diameter all the way back! 2.5" resonators do NOT fit (even though we welded mine in).
* Your mileage may vary! Brand/design of pipes, primary diameter, converter brands, tune and conditions all may affect your results!
Links:
My Build Thread: Stage 1.75 Header Comparison Blowout!
How Much Power Can Stock Exhaust Handle?
HauvaSteve's Kooks Headers HiFlow Cats Install Project thread
Thanks!
Run 000: That morning's second baseline; First run was higher (610 / 565) but doesn't look pretty due to significant belt slip.
Run 010, 011: Final two runs after exhaust buttoned up.
Update 02/20/2017: The x pipe (with cats) failed on me yesterday, and Mike @ ARH says the warranty died as soon as I had them ceramic coated. I've been happy with the subsequent two years of performance from these headers, but based on the succinct lack of customer service I can't say I'm really pleased with ARH going forward. I would have expected better service from the rip-off resellers on ebay (ie at the least a replacement part at-cost, or something).
