EVOM?
Billy Boat?
Agency Power?
Fab Speed?
X51 headers?

I find NO evidence that headers by themselves add any HP!!

If you guys have some independent DYNO tests that would be helpful.

Test
- Stock exhaust - ____ HP
- Stock exhaust with aftermarket headers. -_____ HP

 

I was told by GMG that they don't add much hp, but they do help the turbos spool a little faster........

Chris

 

Hp gains with a set of headers are neglegable at best, maybe a few in the mid range. A header is all about torque. There are lots of factors which determine a headers efficency as well as in what RPM range this torque is most effective. Things such as primary tube length as well as collector design influence this most dramatically. Shorter length primary header tubes apply torque above the peak rpm point and reduce it below it, while longer primary tube lengths do the opposite above and below. Pipe diameter is also a factor, bigger isnt always better (as your neighbors son with the 1994 civic with the cannon exhaust would like to think) as a smaller diam produce better flow velocity= better cyl scavenging (removal of spent exhaust gases from the combustion chamber) Exhaust gas scavenging is a direct result of back pressure as well. While turbo vechicles dont like back pressure (as that reduces turbine speed), NA cars such as yours require a little bit in order to facilitate this exhasut gas scavenging. Since the motor is a big air pump, how efficently you can get in all in and out is what makes power. For your 996 c4s I would be looking for a header with equal length tubing. In addition a collector is also important as collector length, diameter and quality affects scavenging on all cyls (primary tube length affects it only on that one particular cyl), A merge style collector is even better as it keeps exhaust gas velocity up (really important on turbos). Lastly (but definately not least), material quality- look for something made from high quality stainless (t-316 or v4a). bottom line, do the headers if you can afford to and keep in mind a lot goes into a set of headers and they can get pricey, but even though there is not much to gain on the ponies, you'll get what you pay for!

 

............+1

You can feel a difference.....But its very small.

 

very minimal difference.

 

unless you are driving above stock rpms and above torque bands at lengthy intervals (such as the tracks or racing). the lose of torque down low isn't worth it. esp on the street. more noise less power out the hole.

 

More noise

 

I can't speak for turbos, but my NA car picked up quite a bit of HP to the wheels. Around 20 plus midrange and 10 on top. I have the dyno sheets posted on here somewhere (look for Suncoast Header Review or something like that). I did before and after dyno runs on the same day. So I guess the results depend on the header and the car they're being installed on.

 

AWE found that there were no hp gains with the stock vgt turbos. They only saw a difference on the dyno after replacing the factory vgt's with bigger ones.

 

some have actually lost power.

 

Agree.

One the 996TT we tried 3 different header configurations and not one of them made any improvement. They either did nothing or we went backwards. Please note that we never did development past the K24's, so I can't comment on gains or loses above 600hp.

On our new 997TT, headers did nothing until the larger turbos were added. We tested them at stock and chipped power levels first. No gain.

 

Although everything you guys are saying is probably true, the fact of the matter remains that the OP has a NA car and not a turbo.

 

then it would be even more noticeable. esp low end torque.

 

Well, speaking from personal experience, it's not that noticeable. Maybe it's more of an issue with you turbo guys.

Although, I did lose some bottom end, it wasn't horrible and was well worth the gains from the midrange up.

I don't know about you, but I personally don't hot rod around at 2K rpms so the low end torque loss is a mute point for me

 

it's not soo much at low rpm's but at low end torque. you can be cruising at 3-3.5k and from a dig you will notice the drop in torque. once the back pressure has released and the engine is up in the higher rpm range is where you might notice some slight gain. unless you are driving your engine at near redline on the street, it isn't worth the loss in torque. imho.