Since i don't think anyone has run both setups that I'm looking at I'm really only looking for opinions, tell me what you think.

So I'm looking at either the J's Racing header or the Weapon R Race header, I'm looking for maximum mid-high end power, since that's usually the powerband that i'm in during "spirited" driving.

So first off here's the two dyno graphs that i have for each.

J's Racing




Weapon R

So just looking at the numbers the Weapon R looks better, it makes more power and more torque, however the base graph on the Weapon R dyno is with WR intake and intake manifold installed and then the power gains are with WR race header and "unknown" cat back exhaust, so basically a full header back exhaust so eventhough the WR dyno says it makes more power, it's making more power with more mods.

Now if you look at the top of each dyno chart they say that they are both corrected to at the flywheel, which means that drivetrain loss has been calculated out of the graph, so they both should really be making less power than stated at the wheels, but if you look at this WR dyno (dyno is stock vs. WR intake) which is supposedly corrected at the flywheel the baseline hp is 91.8 which is what everybody on this site is getting for baseline hp numbers so are they really corrected at the flywheel.



Ok, so the tuner in me really wants to believe in the WR race header it's a superior design vs. the J's Racing which still bolts up to the stock cat, but it seems almost stupidly obvious how superior the WR header should be. I'm jacking the pic from vafitfreak's post just to show the differences (note header next to WR is actually Megan racing, but the general size of the header is the same as J's)



Now in his post he said that the gains of the WR header were "amazing" which at first got my blood pumping.

But then I saw that predestyned said that the Megan header only had a little more umph AFTER 5500rpm's, so it shouldn't really be surprising that in this case the WR header felt a lot better.

And then I read 805fitsport say that if a header flows TOO much then adding a cat delete pipe would only make you lose more power.

I guess what it comes down to is do i trust my gut and intuition and everything i think i know about tuning and get the WR for its superior design or do I trust the numbers and get the J's Racing header.

What do you guys think I want as many opinions as possible.

 

there s nothing superior about WR's design, it's a simple matter of 4-1 vs 4-2-1(donno if J's were bolt to a test pipe or not). But in general, 4-1 puts out the highest peak hp, while the 4-2-1 puts out slightly lower hp in exchange for better torque. So 4-2-1 is generally more practical, but it all comes down to a personal preferences.

 

That's only true though if both header have the same length tubing, but because the WR has longer tubing it's better suited for higher peak hp, whereas the J's should be better for low end torque since all the pipes come together sooner on the J's than on the WR.

Here's another example, whenever you see a standard race header they almost always enlarge the header so that it replaces the stock header and stock cat (check out Buddy Club's race headers), they do it so that the header flows better for high rpm high horsepower gains(i don't know enough about exhaust flow physics).

Now on the other side of things whenever you see a turbo manifold it almost always has really short header pipes, they do this to increase back pressure, which increases exhaust velocity, which increases torque, which spools the turbo faster.

 

no one wants to increase back pressure, and everyone wants to increase exhaust velocity. Just thought I'd clear that. The trick is to create a balance between the least back pressure and highest exhaust velocity.

and you are right about the length issue, in this case, the WR's race header would flow more which = more peak hp.

 

I understand that no one wants to increase back pressure, but the thing with turbo's.....you know what let me explain a different way.

In a normal race header that has long tubing before the tubes start connecting together, at low rpms because there isn't much exhaust pumping you get "vacuums" of space between each "portion" of exhaust, normal 4-2-1 header get better torque because they fill these vacuums which increases exhaust velocity at lower rpms, but by doing so they overload the header at higher rpms because there's too much exhaust flowing in a smaller space which slows down exhaust flow resulting in less top end power. Which is why normally race headers with longer tubing make more top end power and less low end power because at low rpm's there's vacuums of space in the exhaust which slows down exhaust flow resulting in less power, but at high rpms the exhaust flows just right without overloading the header resulting in more power.

So a turbo manifold has short tubing so that aren't any vacuum's in the exhaust flow at low rpms so that the turbo spools faster, but it's ok because at higher rpms the turbo will have spooled up and actually pulls the exhaust out of the cylinder head, meaning no back pressure

The other possibility is that the WR header may be too much for the little Fit engine, so the J's header may be better for a normally aspirated Fit whereas the WR header may be better for a supercharged Fit.