X-pipe with cats vs Headers with X pipe and cats - Dyno results

In the past there have been many heated discussions here and on other Mustang forums on if long tube headers on a 3V S197 actually give any significant gains over a good X pipe and better flowing cats while keeping the stock manifolds in a NA car. Some have said that the exhaust side of the head doesn't flow well enough to justify headers on a NA car compared to high flow cats and an X pipe.

The 2005 Mustang GT I bought came with a Bassani X pipe and aftermarket cats. I was interested in getting baseline numbers before I started modifying the car. I took the car to a Performance Specialties, Inc. in Pottstown, PA and dynoed the car. It produced 329 HP and 312 ft-lbs of torque. Power modifications on the car are:

C&L racer intake
Bassani X-pipe
SLP Loudmouth axle back
CMCV delete plates
Comp Cams NSR cams
Steeda underdrive pullies
SCT Xcal3 tuner with a Bama 93 octane tune

About a week and a half ago, I installed the Kooks headers with cats and X pipe. Then I took the car back to the same shop to have it dynoed again. The results were 347 HP and 320 ft-lbs of torque. Weather conditions for both days were similar. It was 80 degrees with 46% humidity when I got the baseline numbers and 83 degrees with 46% humidity when I dynoed the car with the headers on. No other changes were made to the car. Both dynos were done on a tank full of 10% ethanol 93 octane gasoline from the same Hess station. Ethanol free gasoline isn't available from any stations near where I live.



The results show an 18 HP gain peak and power gains everywhere with the headers over the X pipe with cats. Even the uncorrected result show a 17 HP gain peak and power gains everywhere. After these results, I really can't see why people believe that using an X pipe while keeping the stock manifolds gives the same power gains as headers on NA 3V S197's.

The only thing I'm curious about at this point is if there is mroe power to be had if the car is tuned for the cams.

Tuning for the cams would definitely result in more power. Even just going with a mild cam can see better gains after tuning.

I know there's been a lot of debate about the new 2011+ 5.0L Mustangs when it comes to the value of putting on LTH's if you already have a good O/R X-Pipe. I'm in the camp that says unless you're going F/I, the better dollar to performance mod would be just the X-Pipe since we see some huge gains by getting rid of the cats on these cars. But I had no idea there was that much drama over the cars with the 4.6L.

VTXFrank said:

Tuning for the cams would definitely result in more power. Even just going with a mild cam can see better gains after tuning.

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Yea, that's what I thought, but I wasn't sure since they are sold as, "No tuning required."

VTXFrank said:

But I had no idea there was that much drama over the cars with the 4.6L.

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Funny how all the people who disagreed with me so much about if headers add more power than an X pipe and high flow cats haven't replied yet.

Who said this? Of course longtubes with an xpipe are going to show more gains than stock manifolds with an xpipe. Whats the a/f look like?

Very nice...definitely interested in A/F...

Lightblade said:

Who said this? Of course longtubes with an xpipe are going to show more gains than stock manifolds with an xpipe.

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This.

Lightblade said:

Who said this? Of course longtubes with an xpipe are going to show more gains than stock manifolds with an xpipe. Whats the a/f look like?

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TrickyP said:

Very nice...definitely interested in A/F...

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I didn't check the air/fuel ratio this time. On my red '08 GT when I put in the kooks headers and catted H pipe, the air/fuel didn't really change before and after, so I didn't check it this time. It was between 12.5:1 and 13.0:1 between 2500 RPM and 6500 RPM both before and after the headers on the other GT I had with similar mods.

I'll have a wideband O2 sensor and gauge hooked up soon so I'll have results on this car.

With aftermarket cams the addition of long tubes would yield greater gains than with stock cams.

Lightblade said:

Who said this? Of course longtubes with an xpipe are going to show more gains than stock manifolds with an xpipe. Whats the a/f look like?

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TrickyP said:

Very nice...definitely interested in A/F...

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For an answer to the A/F question, I installed my AEM UEGO A/F ratio gauge on Friday. At full throttle the A/F ratio stays between 12.5 and 13.0. It runs a little closer to 12.5 below 4000 RPM and is in the range of 12.7-12.9 above 4000 RPM.

Vapour Trails said:

With aftermarket cams the addition of long tubes would yield greater gains than with stock cams.

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I agree with that. With stock cams the horsepower gains from the headers would have been a little less. However it does prove my point that the people who said an aftermarket X pipe and high flow cats is just as good as long tubes for power gains were wrong. The horsepower gains I had from installing the headers were pretty significant. All the other variables were kept as close to the same as possible. Same dyno, same person strapping the car down in the same method, same wheels tires, same air pressure, similar air temperature, similar humidity, same gas station for the fuel and same octane fuel with the same percentage of ethanol.

There were people in other posts about long tubes claiming that you'll lose low end torque with them and you won't gain power over stock manifolds and an X pipe. No one has bothered to test an aftermarket X pipe vs. headers on the same car and same dyno before. If anyone has any results that contradict this, I'd like to see them. If not, we can stop beating a dead horse now in the headers vs aftermarket X pipe discussions about power gains.

That looks really good! As for the cam tuning, we're maxed out at what we can do with the VCT table, so you should be getting the FULL affect. Looks good, and it sounds like air/fuel ratio is good as well.

The Longtube Header tuning, for the person that asked above, is simply to make sure that the PCM receives the most accurate feedback possible from the upstream (front) o2 sensors, since they've been moved further downstream. That's all...

I'm happy with the results with just the old BAMA 93 race tune that was on the car. However I'm sure a tune for the cams will improve it a bit and maybe add some midrange power.