Question about Stillen headers...
 

Hi all. To understand my questions, check out this thread:

http://www.the370z.com/intake-exhaus...ders-370z.html

Now, here are my questions:

1) Doesn't the Stillen header look similar to the stock header, with similar diameter piping? What makes the Stillen one better?

2) In the thread posted above, the installer says there is reduced midrange power, which could be helped with new Y-pipes. So, why don't we just get new Y-pipes rather than headers? How much more hp will I get with a new Y-pipe? Finally, are there any Y-pipe vendors?

3) So, if I buy a Stillen exhaust, intakes, Berk HFCs, and a Y-pipe, won't I get close to the same hp gains as if I add the Stillen header?

Thanks in advance...

The major difference is that the stock tubes are not equal length, and the Stillen headers are. I'm really not an expert on these things, but my basic understanding of this issue is that equal-length headers ensure that the exhaust pulses flow into the single pipe (after the headers) in a steadily-timed train that tend to "suck" each other along, whereas with unequal length headers, you get "collisions" of exhaust pulses followed by empty-time where nothing is actively happening. There may be other differences that make it flow better that are more subtle, but I think the equal-length thing is the main factor. I'm sure someone from Stillen could chime in more on this.

The Y-pipe / header issue is mostly conjecture at this point, but basically the stock cat-back exhaust (Y-pipe and everything behind it) is *really* restrictive. I installed headers and cats before I replaced it, and you could really hear how the exhaust was basically free-flowing up to that point and then getting all clogged up at the stock Y-pipe. It sounded very restricted.

Most people aren't going to buy a Y-pipe on its own, but rather a complete tuned cat-back exhaust system, which is the Y-pipe, the mufflers/tips, and everything in-between. You certainly can just buy that first (or only) and see some good gains out of it for minimal effort. I really wouldn't advise headers (or even cats, honestly) without also upgrading the rest of the stock exhaust.

Probably the intakes, HFCs, and exhaust (which includes the Y-pipe) add up to more gains than the headers alone by a long shot. Adding headers on top of all of that should take us even further though, and if you're going to install headers, you're going to have to remove your cats (and disconnect the Y-pipe if it's the stock cats) to do the install, so it makes a small amount of labor- (and gasket-) saving sense to install the headers before everything else, or at the same time.

This is some what true but you are forgetting one thing. You forgot to mention why Nissan developed those headers that way. It was developed that way to give you that tq that people have been missing with these headers. Stillen headers look good and have a very good collector. I believe they should of kept the OEM design 100% along with that improved collector. It's all about tuning for velocity, flow, and of course exhaust pulse. Remember the exhaust itself is not a continuous flow because exhaust valves open and close.

In case of the Y-Pipe issue. It will probably have gains with an aftermarket part but you would have to do a couple of tests. If the y-pipe frees up too much backpressure than you will lose velocity and then you will lose tq and but gain hp. Its very difficult to tune for a happy median.

It would be nice to see the following.
1. baseline dyno, stock headers, y-pipe,
2. baseline dyno, aftermarket headers, y-pipe

You can't loose torque and gain hp as one is a function of the other. I think what you are meaning to say is that you will loose low end torque and gain high end torque which will result in more peak HP at the expense of the low RPM range.

We'll find out soon enough. I just received these headers. Literally got delivered to my door just 10 mins ago.

And I'm going to try to get into a dyno Saturday if I can. There's an apparently pretty reputable place not far from me called Engine Logics that has a Dyno Dynamics. Sounds like they can squeeze me in in the middle of the day after another guy gets his tune done there, but it's one of those "call us that day and we'll see how the timing goes" things.

I strongly suspect this is the case, just based on my driving impressions. I think we are trading low-rpm torque for high-rpm torque with these headers. The car feels less torquey (less "jerk" if you will) at low rpms (idle to 3k -ish). It's actually kinda nice, since the car now drives smoother at grandma speeds in heavy traffic. Again, we'll see once we get some headers on the dyno.

Hopefully they can include the low RPM range in the plot, a lot of the time they start things at 3K.

Semtex needs to dyno the WHOLE thing.... I am not interested in losing low end torque.

I'll paypal you $5 to help with Dyno fees!

Sheesh, why is this all on me??? :p

In all seriousness though, I think this is a bit of a red herring. We're going to lose some low end torque with these headers, because any time you reduce back pressure, you will lose some low end torque. And it doesn't matter if it's headers or HFCs or test pipes or a cat-back exhaust. All of those components reduce back pressure, hence all of those components reduce low-end torque to a degree. Here's the thing. Low end torque is typically anything from 0-2500 rpm. As far as I'm concerned, what happens in that range is virtually inconsequential. I just got home from the grocery store and was deliberately watching my tach. When I upshift from gear to gear, my tach needle doesn't even drop below 3000 rpm. When I launch, I'm past 2500 rpm in less than a second. So unless you deplete low-end torque so badly that you're in danger of stalling at each launch, it's just not relevant. What does matter as far as driveability goes is mid-range torque, typically 2500-6000rpm. And that's why I was alarmed when RelentlessRY said he saw a loss in the mid-range. But the bet right now is that it was because of the factory y-pipe. So I'll be interested to see the torque curve on Wstar's dyno. I, for one, couldn't care less if I lose a little more low-end torque over and above what I've already lost with the HFCs and cat-back exhaust, especially not if I'm gaining hp and torque in the ever-important mid-range. This is also one instance where I'm glad the car has a heavy flywheel, because the mass of the factory flywheel more than offsets any loss in low-end torque, IMO. Plus, I used to drive an S2000. You want to talk about crappy low-end torque? Try driving one of those. Let me put it this way. I had a lightweight JWT flywheel in my 350, and it still had more low-end torque than my S2000 did. I do appreciate the S2000 for one thing tho. That thing really taught me how to manage my available low-end torque well. So much so that I haven't stalled my car even once in over 5 years!

+1. This is my take on it as well. I'm unsurprisedly expecting a drop in torque in the low rpm range vs a stock car, given how free-flowing my exhaust is now, and I could really care less. I actually do drive in that range a fair amount, as this is my primary car and I have to fight Houston traffic sometimes. But I only really care about HP/Torque gains up in the good rpms (4k-ish +), which is where my tach will be staying when I care about performance.