I have noticed people commenting on how race headers are bad for our cars and "you'll lose a bunch of bottom end", "4-1 headers are bad for torque, and 4-2-1 headers are better for the street", "4-1 headers are only good for top-end power, and not the best pic for our long stroke TSX."

Well, I've been modifying Hondas/Acuras since 1989, peaking in 2002 with a 227 whp B18C5 engine in my '92 Civic CX race car.

Regardless, through many years of testing and experimenting with B16's and B18's I've found opening up the intake and exhaust have always helped. I remember running a JDM Spoon header with a 3" back exhaust and had gains EVERYWHERE!
So, taking this info, and applying it to a larger displacement engine I thought opening up the exhaust would be beneficial.

My first race header dyno was with the Weapon R race header, which has a 2.5" collector, see dyno.



I also had a spare Skunk2 header laying around. It is a 4-1 race header with a 2.25" collector.
The results are as follows:


Here we compare the Weapon R header 4-2-1 w/2.5" collector to the Skunk2 Race header 4-1 w/2.25" collector.


Look at that low end torque! It's huge!
Remember the difference between the two is only time and I added a Bilstein B12 suspension kit. Now the question is stick with 2.5" and build a custom 2.5" exhaust, or go with the 2.25" and build that. Not sure yet, we'll see.

Car mods are,
Intake resonator removed, stock paper filter.
Non-Stop tuning pulleys

Suspension:
Bilstein B12

That's all.

 

holy cow at that skunk2 header. i remember reading on the 'other' board that someone got the hondata reflash with the skunk2 and had a huge pop in their hp/torque on the dyno.

cool results, cool comparison.

 

I'd go with the 2.5" collector with a matching high flow cat and exhaust. The gain from the exhaust may not be huge but it's definitely measurable.

 

Here are a couple photos of the Skunk2 race header. I took off the 2.25" merge collector and will be buying a 2.5" merge collector (as JTSo suggested) to put on, then sending it out to get coated.
BTW at the collector the 4 main pipes are 2" in diameter...much larger than I expected, I thought they were gonna be 1 7/8" max.

Notice how the header comes off the head nice and straight, taking advantage of the usable space in the engine bay. Nice header.

 

hmm i wonder if i there will b the some gain with the CT header enlarging the collector to 2.5" ?

 

what about 3in collector?