why x51 is header better or worse than aftermarket
 

hi all, i have been looking at the pictures of the x51 header for the 997.it looks like 3 chambers go into the main chamber seprately.while all other after market header companys say the reason there headers are better is because ,they have the merge collector..if the merge collector is better.why does porsche not do this with there x51 headers ...thanks for any help i am really confused about this one.:confused:

p.s. attached picture of x51 and and aftermarket header.x51 is the 1st one.

I believe the reverse is true!
Look at pictures of standard vs X51 Headers for the Carrera S!

The X-51 Headers are much improved over stock mainly due to the increase in diameter and better flow design,..
http://i12.tinypic.com/2wqd1qo.jpg

After Market headers use the merge design which makes the flow a little better then the x-51 headers, that design makes for less restriction. Aftermarket headers also have an increased diameter over the X-51 headers.
The fabspeed headers are a good example of true merge design.
http://i13.tinypic.com/43w4f1t.jpg
stock headers < X-51 headers < aftermarket headers (Not by a large margin)

I think better is relative to what your looking for. Depending on the design of the headers, one could offer better top end while another provides a better mid range. If you look at the 997/997S product information guide meant for the sales staff, the guide specifically states;

"Compared to the standard manifold of the 3.6 litre engine, the new high performance manifold of the 3.8 litre engine permits better mixing and hence better preconditioning of the raw emissions before they are passed on to the catalytic converter."

I believe the diameter difference in between the 997S header and the X51 header is 43mm vs 48mm. It's also interesting to note that the 997 header looks similar to the X51 but with smaller tubing and the 997S header looks similar to the GT3 header. I don't know what the diameter of the GT3 header is though. There is a good picture of the header in this thread;

http://www.rennteam.com/showflat.php...ge=0&fpart=all

I would love to see someone compare all of the different OEM headers on a dyno vs those of the aftermarket.

hi guys,thanks for all ur responses...i think i understand it abit better now..thanks again:)

The X51 does have a advantage over aftermarket headers imho. First they are available for a 1/3 to 1/2 the price of a aftermarket header for very similar results, and 2nd they are OEM and they have better ground clearance than aftermarket headers. If you look at the AWE dynos (all I had to go by) the race cats and mufflers added the most hp. When they did the headers last they gained 5rwhp over the "crappy" stock S header. When I saw this...I thought spend the money on mufflers and cats and go the X51 route as far as headers are concerned.

Dave

The performance of a normally aspirated engine is affected by how much backpressure it has ( intake and exhaust both)

The Porsche engineers designed the different headers and air intakes on different engines for a good reason . To achieve (what they believe ) is a good compromise between lower end torque and high end hp.

If you just exchange the headers on a 997 S for instance, you should not expect a lot , in fact, you may not like losing the extra torque at the lower end (how much driving do you do above 6000 rpm?)

99.9 % of the time.

Sorry man that just isn't true...that is an old wives tale. With the advant of variable cam technology and not to mention header tubing size has a more affect on powerband than back pressure. The fact that hp is a product of tq (tq = (hp x 5250) / rpm ) and vice versa leads you to the conclusion that more tq means more hp just maybe at a somewhat higher powerband. You don't lose tq, you just move it elsewhere in the powerband. So if you move the powerband up a few hundred rpm you have to ask yourself how often are you below 3500rpm?

The perfect example to this was my M3...the car made 279rwhp stock, with a full Supersprint exhaust it did 302rwhp, but more importantly it made more tq at 700rpm less than stock. Stock the car made 236 ft/lbs of tq @5400rpm, after 248 ft/lbs @4700rpm. What will effect low end torque is if you go to big on the primaries, as this will cause an over scavenge on the exhaust and kill velocity out of the motor. Velocity aids scavenging, you can over scavenge as well literally sucking the AF charge out of the combustion chamber.

Dave

your M3 made 302whp with just full SS exhaust? those are some impressive numbers. Most people I know cant even hit 300whp with full exhaust, chip, pulley, intake, and even some with cams.

Yep, with just SS headers, 100cpi cats, Borla muffler and 94 octane my car did 302rwhp @7600rpm and 248 ft/lbs @4700rpm. This same day 2 stock M3's dyno'd 268rwhp and 272rwhp. The car had no CAI nor software and the OEM midpipe.

Dave

I recently replaced my X51 headers with AWE headers. I actually prefer the sound from the stock X51 headers (deeper sound). I notice ZERO difference in power at any RPM level.

I was told when I bought them that the real difference is in the cats. I will soon replace the PSE and cats with AWE and hope to see some improvement.

Let us know how the cats work out (sound improvement, power gain,..etc.)
I am thinking about changing out my stock cats aswell, I have the X-51 headers and Fabspeed muffler bypass pipes right now.

X-51 vs after market. No comparison, after market is better, The whole purpose of a complete exhaust system(headers, free flo mufflers, sport cats or by-pass cats) is to let the engine breathe better. The more air it can take in combined with increase fuel produces more horspower & torque and subsequently the gas-air mixture (exhuast) needs to leave with the least amount of restrictions. The stock 997 headers are junk, the X-51 is a great improvement but after market headers are better. Why-beacause they have equal length tubing, bigger diameter and merge into one collector vs the X-51. You have better airflow balance with after market with less retrictions.
Ask the boys at EVOMS how well their SC works with a complete system. they wouldn't recommend a SC setup if you ran with stock exhaust.
I've have the complete Fabspeed setup and I am very pleased with the results. Throttle response is better,engine revs more freely, definite hp & torque gain, almost Plus 2 miles more/gal, 28 lbs lighter & sounds great!
Please do it right, X-51's might sound good & cost less but remember-performance has a price