Anyone figured out yet why some headers apparently get rid of the 'torque dip'?

[Hawaiian]

Originally Posted by FirestormFRS

The factory cat or high flow aftermarket cat?

Had a typo there. The redline is the full P&L exhaust with high flow catted header, and catted midpipe. The blue is the same exhaust, just swapping out to an uncatted header.

[Xero-Limit]

The "goofy" longitudinal g chart is a direct representation of the torque curve (upside down) if done proper. I've confirmed this on the dyno many times, and you can clearly tell when the torque dip is gone. I have dozens of dynos and hundreds of datalogs that confirm this....simple math if executed properly. The said header will get dyno'd when we get time.

Now as to why the a proper header gets rid of the dip, it comes down to scavenging and runner lengths. Yes, you do move it to some extent, but when you have good collector, correct primary length/size, you end up making more HP overall so when you move the "dip" to another area, it simply becomes a global increase with the gains focused on the low end. The smoothness here is all important. Opposing runners are bad, and unequal is just fine as long as the runners from each bank are similar lengths.

The tune then becomes all important because the exhaust cam timing is directly calibrated to the scavenging of the stock header. So here we will see how much more we can make on the dyno as the g meter is only good for curves not fine tuning. I suspect it will be quite significant since the stock cam profile "gives up" in the dip, and with proper header that means we have room to shove some more air/fuel in there.

I doubt the cat itself is the issue. At least until you put it on a racetrack and it melts...

[Hawaiian]

Originally Posted by moto-mike

The "goofy" longitudinal g chart is a direct representation of the torque curve (upside down) if done proper. I've confirmed this on the dyno many times, and you can clearly tell when the torque dip is gone. I have dozens of dynos and hundreds of datalogs that confirm this....simple math if executed properly. The said header will get dyno'd when we get time.
...

The goofy comment was not the best choice of phrase. Sure it's great for tuners who know what they are doing, but for the rest of us, it's not as easy to read.

I was simply supporting the fact that the other headers he's making note of have been fully tuned, while I've yet to see a dyno showing the JDL header that has been tuned, so it's comparing apples to oranges, and not an accurate comparison.

[AZFA20]

Originally Posted by wparsons

Unfortunately, that's not correct on these engines. They only have a single cam profile, it's not like VVTiL in a 2ZZ that has a second cam profile.

As for the reason not all headers behave the same, it all comes down to flow and resonance in the header. If you look at the length of the primaries in the nameless long tube they're quite longer than most of the other headers out there. There's simply no room for a cat in the header with the longer primaries, so you need a cat in over pipe if you need one. Diameters, steps, length between steps, etc all play a part as well.

4-2-1 headers also do better with low end torque than 4-1 headers, but typically at the cost of a little bit of power up top.

It's not incorrect per se but rather a bad choice of words to decribe what I am guessing they meant. Low speed "profile" and high speed "profile" should have probably read low speed cam "timing" and high speed cam "timing". In layman terms this would essentially result in different flow characteristics at different speeds hence them using the term "profile". I am only going out on a limb here because I dont know who wrote this but it does sound like they may have understood what they meant but just didn't convey it correctly. The headers do smooth the graphs out but the cam timing does in fact have a role in the dip we see as they transition through cam phasing. In your defence I understand how you interpreted what was written to be incorrrect because there are cam systems out there that literally ramp from one side of the lobe to the other that do essentially have different "profiles". When it comes down to it all these parts work in unison and one change affects them all in some way regardless of how small it may be. The alternative header options allow the engine to exhale a little better which translates to a smoothed out area on a graph. If everyone really wants to combat the dip just force feed it with forced induction

[ngabdala]

JDL FTW

[wparsons]

Originally Posted by AZFA20

It's not incorrect per se but rather a bad choice of words to decribe what I am guessing they meant. Low speed "profile" and high speed "profile" should have probably read low speed cam "timing" and high speed cam "timing". In layman terms this would essentially result in different flow characteristics at different speeds hence them using the term "profile". I am only going out on a limb here because I dont know who wrote this but it does sound like they may have understood what they meant but just didn't convey it correctly. The headers do smooth the graphs out but the cam timing does in fact have a role in the dip we see as they transition through cam phasing. In your defence I understand how you interpreted what was written to be incorrrect because there are cam systems out there that literally ramp from one side of the lobe to the other that do essentially have different "profiles". When it comes down to it all these parts work in unison and one change affects them all in some way regardless of how small it may be. The alternative header options allow the engine to exhale a little better which translates to a smoothed out area on a graph. If everyone really wants to combat the dip just force feed it with forced induction

The cam timing is variable at any RPM, not set to two different "speed" bands. If the dip was purely because of the cam timing, it would've been totally tuned out by now.

What you were describing is definitely two physical cam profiles, like VVTiL or VTEC. You'll never get behavior like that from variable timing alone.

[AZFA20]

Originally Posted by wparsons

The cam timing is variable at any RPM, not set to two different "speed" bands. If the dip was purely because of the cam timing, it would've been totally tuned out by now.

What you were describing is definitely two physical cam profiles, like VVTiL or VTEC. You'll never get behavior like that from variable timing alone.

I think you may be confused on how AVCS works. The cams are advanced and retarded based on load levels and the reason you see the same dips on everyone's dyno is because they are all essentially recreating a constant rather than a variable. The constant is WOT on a dyno (100% load). Yes the cams can advance and retard variably through the RPM based on load but if load is the constant @ 100% on a dyno while pulling WOT the curves will look the same and essentially in the same spot because the cams have to transition through phasing at some point. Tuning advance and retard in the variable cam timing only shifts the same flow characteristics because without a true variable cam lobe profile there is no way to change the way a cam physically opens a valve, only when it opens and closes it. The only true way to get rid of this would be to disable the cam timing and put another set of cams in with a profile that will achieve whatever goals you may have. Cam timing can be tuned for sure but really all you are doing is shifting the same exact flow characteristics around not physically changing them via lift and duration. This is great for tuning emissions and power based on load which in normal driving circumstances is in fact variable but not so much on a dyno @ WOT. Either way I agree with you that this is only part of what is happening and that is why we see a smoothing after a header install. Its still there its just not as apparent.

[Sonolin]

Originally Posted by Hawaiian

We will have to agree to disagree. Here is a dyno of my car, with stock cams... no dip.




The red line is with a cat. It's actually flatter than the blue line (with cat).

That looks sexy

How's the p&l header for daily driving? Is it raspy/load at all? I've heard some negative things about it in the p&l thread noise wise.

[Hawaiian]

Originally Posted by Sonolin

That looks sexy

How's the p&l header for daily driving? Is it raspy/load at all? I've heard some negative things about it in the p&l thread noise wise.

I haven't had it on the car for a while now, but should have it back on friday for various reasons, none of them being sound related.

Initially I took it off to get it coated, then packed it off to Gem for testing/fitment with the vortech kit, had a new one built, went on vacation and couldn't get my car in wile it was out, so I passed on it so P&L could get a few more orders out etc.. I will have it back on the car permanently on friday.

It is a bit louder with an aftermarket exhaust, but it all depends on what exhaust you're running. My car seems quiet compared to @CircuitJerk, but He has the SRT exhaust, and that thing is rowdy as just a catback.

Once the header goes on, I will be doing a little exhaust modification, adding in a larger, or second resonator because I have a low noise tolerance level for my DD cars, however, we do have video of my car with the full P&L exhaust, and will record more once the header goes on. We will also use a DB meter for measurements in, and out. There were a lot of people asking me for that, and I want to make sure they get the information they want.

[wparsons]

Originally Posted by AZFA20

I think you may be confused on how AVCS works. The cams are advanced and retarded based on load levels and the reason you see the same dips on everyone's dyno is because they are all essentially recreating a constant rather than a variable. The constant is WOT on a dyno (100% load). Yes the cams can advance and retard variably through the RPM based on load but if load is the constant @ 100% on a dyno while pulling WOT the curves will look the same and essentially in the same spot because the cams have to transition through phasing at some point. Tuning advance and retard in the variable cam timing only shifts the same flow characteristics because without a true variable cam lobe profile there is no way to change the way a cam physically opens a valve, only when it opens and closes it. The only true way to get rid of this would be to disable the cam timing and put another set of cams in with a profile that will achieve whatever goals you may have. Cam timing can be tuned for sure but really all you are doing is shifting the same exact flow characteristics around not physically changing them via lift and duration. This is great for tuning emissions and power based on load which in normal driving circumstances is in fact variable but not so much on a dyno @ WOT. Either way I agree with you that this is only part of what is happening and that is why we see a smoothing after a header install. Its still there its just not as apparent.

I'm not confused about how variable timing works in the slightest... but now you've gone and contradicted yourself.

At first you said it's because there are two cam timing "profiles" (not cam profiles), one for lower engine speeds and one for higher engine speeds which have the ability to change flow characteristics. Now you're saying it's load based (as far as I know, the maps are actually speed and load based) and can't change flow characteristics.

In any case, the cam timing is not to blame for the torque dip, it's all about airflow into and out of the engine. Since Nameless actually totally reversed the dip (they got like 40wtq gain at the worst part of the stock dip) with their long tube header, it's safe to say the header is playing a big part in it.

[AZFA20]

Originally Posted by wparsons

I'm not confused about how variable timing works in the slightest... but now you've gone and contradicted yourself.

At first you said it's because there are two cam timing "profiles" (not cam profiles), one for lower engine speeds and one for higher engine speeds which have the ability to change flow characteristics. Now you're saying it's load based (as far as I know, the maps are actually speed and load based) and can't change flow characteristics.

In any case, the cam timing is not to blame for the torque dip, it's all about airflow into and out of the engine. Since Nameless actually totally reversed the dip (they got like 40wtq gain at the worst part of the stock dip) with their long tube header, it's safe to say the header is playing a big part in it.

Again I am pretty sure you are confused because nowhere did I say it has 2 cam "profiles" or "timing" profiles my first post was exactly directed toward clearing up the difference in "profiles" and "timing". The original person quoted was the one explaining it incorrectly and I was interpreting what I am pretty sure they meant. Please re-read the posts. I agree with you 100% that they are two totally different things. If you want to get into "airflow into and out of the engine" what do you think cam timing does????

[Swift]

Originally Posted by AZFA20

Again I am pretty sure you are confused because nowhere did I say it has 2 cam "profiles" or "timing" profiles my first post was exactly directed toward clearing up the difference in "profiles" and "timing". The original person quoted was the one explaining it incorrectly and I was interpreting what I am pretty sure they meant. Please re-read the posts. I agree with you 100% that they are two totally different things. If you want to get into "airflow into and out of the engine" what do you think cam timing does????

I will stand behind you as well in how cam timing works. What I think is the problem is a combination of the stock exhaust manifold and the physical cam lobes/timing. The header takes away the dip because it may get rid of back pressure causing a pressure wave or some magic unicorn theory. However if you changed the cams without a header it may do the same thing.

[wparsons]

When you see aftermarket cams come out, the dip will look like it's gone because to get high end power it's going to sacrifice low end power, likely all before the dip making it look like a smooth increase instead of a spike/dip/spike.

I still stand by the stock header being the biggest contributing factor to the dip, there's too many dynos of good headers showing drastic improvements to not feel that way. From the nameless header thread, the 4-2-1 prototype with stock cams/heads:

[TOTO_86]

In my opinion, the reason for the torque dip is because the computer is on the motor. I've heard from a Toyota technician that when a car has it's computer on the engine it can cause problems. He suggest to buy a heat shield for it. This is the first time I've read that headers are helping the problem out.