In the exhaust thread, before you edited it, you stated, the Delta header is different and you would expect different results from it. But it now seems you are expecting the same results that you had, even though there are vast differences in the parts, just because of one common aspect. The fact that the pipe is reduced to the stock size, for such a short distance, should not negate the other possible benefits the rest of the system as a whole can provide. At worst it would provide the same restriction as the stock header, which you state would perform better, but would still have the same nipple size. So I'm not sure that that makes sense to me. If the whole exhaust is dependent on it's smallest part, the tip is generally it. In this case it's only 1in. But it's not melting my blinkers. .

I really think the results you saw are not a direct comparison to this system, and my setup as a whole, that could stem from multible causes. First off was the DG really designed to be used with stock header, if it's smaller than the FMF that would cause problems, is the midpipe different then the FMF was tuned for. Does the FMF MB with the chamber leading straight into the nipple require the nipple to be large to scavenge correctly/ did the gasket cause extra turbulance in that area hurting flow. How does your MCM effect exhaust needs, and how that plays in to both of our setups. Being that your exhaust and intake timing has been changed it's possible that alone will effect gains or losses that an exhaust system could show. How does the lidless setup effect all this? Does the fact that I'm running a lid setup make that my biggest restriction, making the exhaust more moot for me. Ect...

I do have to admit, that it's possible you are right. But I see plenty of evidence to show that you could be wrong, under these circumstances. I will put back on the stock pipe at some point soon to see if I can notice a difference, one way or another.

 

You're "grasping at straws" when you know darn well you have a simple pipe sizing mismatch that causes a restriction to gas flow at the header bell..And I know what happens to power levels when a performance exhaust system is restricted at the slip joint.. But hey, whatever...

When first advertised, the Delta Trq Header was touted as being longer (thru a longer bend out of the head) than stock and a low RPM TRQ creator. The header they are now showing is not the same - it is a simple step design performance header. Read the Japanese reviews of the header ( I have ! ) , the results of using it are exactly as expected from a stepped performance header. No low trq production, just better mid and high end power. http://www.drcproducts.com/delta/products/torq.html

It seems that Delta does not offer a slipon with the correct nipple size for their header.

 

If it's all about restiriction at the nipple, then why do you think the stock header made more power for you when the whole header is as restricted as the nipple?

The Barker uses a stepped header, and it produces more power everywhere. I feel that is the closest relative comparison to be made. This is a barker exhaust type system, with a 1.25 restriction in the middle of it. I do believe that that will effect upper rpm performance, but I'm not convinced that reducing the whole pipe to 1.25 is going to net more gains.

 

The piece of the puzzle that you don't have is hard to acquire. So if you won't take my word on it, nor my dyno results from a mismatched exhaust system, then I can at least point you to the knowledge you need to make "expert" determinations yourself. Under the subject of performance exhaust system design, pressure wave scavenging and acoustic wave rebound scavenging are the items that are implemented (or intended to be implemented) in a well designed system. During knowledge acquisition, you'll also begin to understand exhaust gas flow characteristics through various header designs, midpipe designs, and silencer designs..

After you've "done your homework" on the subject, and understand what is happening in the header, midpipe, and silencer, you will put back on the stock header or buy a proper-fitting slipon..

 

Honestly I don't know that you have all the pieces, and I'm not sure you haven't lost the dang cover to the box.

But I'm going to explain my thinking.

For those dummys like me here's some basic ideas of what's being discussed. Think of scavanging like siphoning gas from a gas tank, the flow coming out of the hose, continues to suck more gas from the hose. Think of your cams as pinch points on that hose, lift determines how much it opens, duration how long, ramp how quick it opens. The cam timing determines when they open to each other. This creates waves, that are effected by exhaust shape. The idea is to get those waves to suck as much air through as they can while the cam allows the flow. By having a tuned exhaust, you choose where those waves move the most effieciently. Because the rpm of the motor also changes those waves, its very hard to get an exhaust that gives best performance everywhere. Generally a smaller pipe will give better velocity at lower rpm's allowing better scavenging there, giving more power there. A larger will give more flow in the upper rpm's, giving it it's best performance there. But to big and you lose the effect, to small and you just choke it off.

Now for your exhaust to tune those waves think of it as a river bank. As it makes bends and turns or has restrictions, it effects whats going on around it , by slowing it down, speeding it up, or causing turbulance. Turbulance can be a killer , because it basically causes a dead spot, that the exhaust gases then have to flow around. Everyone has seen those dead spots or backflows in rivers, or creeks.

So for my exhaust I have a restriction in the middle of an otherwise straight flowing riverbanks. So that should effect my overall flow rate for sure. The question in my mind is, is it causing a turbulance flow problem there, and I think not. I think it is being allowed to scavenge correctly.

With KLXster's example, in my mind his is a very different setup because he has that chamber, that is right before the restriction. Think of the river bank going big then narrowing, and right where it narrows or soon after, it's going to be flowing it's quickest, you then have that restriction. Because the water/ exhaust gasses are going to be flowing there quickest at the banks and you have that restriction, I could see that causing turbulance, and possibly even sending that turbulance back into the chamber, doing god knows what. Plus I would expect the midpipe to be much more important to the FMF MB as a system because that chamber would be tuned to use that specific pipe to scavenge correctly. So I think the mismatch it this case was being amplified by the specific need of that chambered header, compunded by the turbulance caused at that joint, allowing no scavanging .

And honestly I'm not sure how the different cam timing and intake setups play into the shape of the wave and how the exhaust needs to tune it, but I know ours are different.

 

NIce metaphors.. And fairly accurate.. Please stop trying to analyze the MegaBomb as it has nothing to do with the problems created when a restriction is introduced into an exhaust system - My tests/system was simply an example of what happens when you add a restriction to ANY exhaust system.

So lets do this...Just inertia scavenging, leaving acoustic wave rebound scavenging for another time..

The initial pulse (exhaust valve moves off seat during combustion downstroke) travels through the length of the exhaust system. Behind the pulse is low pressure.
Metaphor: The pulse acts like a piston traveling the length of the exhaust system, creating "suction" behind it as it travels. This suction "starts the ball rolling" for evacuating the exhaust gases.

During the exhaust stroke, the 'slug" of exhaust gases follows the pulse down the system. Like with the pulse, the slug creates low pressure (suction) behind it, which comes into play during the last few degrees of exhaust valve opening. The exhaust valve stays open/unseated past the exhaust stroke and into the intake stroke, which is the point where the low pressure behind the slug causes additional scavenging of the combustion chamber - this is the crucial moment in time (performance wise) where a proper exhaust system can provide suction to the chamber while BOTH intake and exhaust valves are unseated - evacuating remaining exhaust gases while also "sucking" the new air/fuel from the unseated intake valve..

Anything that impedes the smooth traversal of the initial pulse and the slug through the entire exhuast system, defeats Pressure Wave Scavenging by limiting (or killing) the low pressure (suction) that creates scavenging.

Exhaust systems use various methods (pipe sizing, pipe dimensional changes, etc) to change the RPM range at which maximum Pressure Wave Scavenging is achieved. I won't go "off" on that subject too much except to say that smaller piping creates max scavenging in the lower RPM ranges, and larger do the opposite.

Now lets talk about the effects of restrictions in more detail.
The initial pressure wave, and the slug of gases that follow, must have a clear, unobstructed, path to travel. BUT the path must ALSO be free of any lingering pressure from the last combustion.
Metaphor: as the initial pressure wave "piston" starts to travel the exhaust system, you don't want the piston running into "bunched up gases" from the previous combustion event that are still lingering in the exhaust system. Same is true for the slug of gasses being pushed out, by the piston, on the exhaust stroke..

When a restriction is introduced somewhere in the exhaust system, the gases will "bunch up" from the point of restriction, all the way back down to the exhaust valve ! Technically speaking, higher pressure will linger in the section of the system, from the restriction point to the exhaust valve.
Example: Cut a 1/2" hole through a potato, stuff it into your tailpipe/stinger/endcap, and feel the pain of a total loss of Pressure Wave Scavenging !

We all good ?

 

How about I analyze what I want, and you analyze what you want. Then we can both draw our own conclusions , that will help keep us all good. Especially as you're using your analysis from it as the basis of comparison to this.

We're close to saying the same thing, but we might have to agree to disagree on the fine points. I think there are points you are greatly underestimating, and things you are assuming from your system that don't apply across the board. As I stated earlier there are guys who do this their whole lifes, and nothing but this, and they can't exactly agree, if 2 amateurs on the internet knew it all we'd be doing it ourselves, not playing around here. So I'm good with stopping that conversation here.

I will concede that no nipple would be better, and thats the only time I will ever say that.

With that said, as I stated earlier, I do think there is reason to try the stock header for me and I'm willing to swap it back and try. Even though the stock header is more of a restriction and will still pass through the same restrictive nipple I do think it's possible it could scavange better through the lower RPM's, which is most important to me. I've ordered a new gasket to do the swap, actually 2 in case I want to swap back. I'm also debating on flaring the slip on to the bigger size, a $20 tool gets it done.

Since I started the thread, my KDX snorkel is installed, made no perceivable difference to not running one, but gives me a warm fuzzy feeling of some protection to keeping the creek crossing out of the intake.

 

Like tuners at tuning shops, "guys that do exhaust their whole lives" does not in any way assure competence. Rarely do any of them have degrees in thermodynamics, computational fluid dynamics, and specialized focus in combustion dynamics - (those guys work in the industry for the big bucks) - BUT almost all of them want to sell services or components. They usually do the same-o-same-o, year after year, because somewhere along the line, they found something they think works, or was told what others had found to work..

Again, my own testing is only an example of one exhaust system failure due to midpipe restriction, but the reasons for the failure are not limited to just that system - all systems will fail given the same restriction.

This stuff (exhaust design) is mathematical - in a way that's impossible for Joe Sixpack to understand . Gas flow rates within pressure and temp gradients, etc etc etc... When the (digital) system is supported by the "math" , you build it and test it...

I can't help everyone - but I try..

Good luck !

 

Installed the stock header today and got some running in. I have a 1 mile woods loop near my house that I've done 100's of laps on, so little variences in power are easily notable. I also had done some lower rpm hills on the street, acceleration from 30 in 4th going up hill between mailboxes, the Delta was at 34, the stock at 32. I'm kinda surprised, but so far it seems to me the Delta header made more power everywhere. The stock header has a more obvious power band from around 5500-8000,which I also thought fully stock, where the Delta is much more linear from low RPM's. Coming out of corners and needing a little extra twist, not being able to stay in 2nd as much without shifting to first, not bouncing the rev limiter as hard in first, all seemed evident with the stock header. I don't think it really amounted to huge power losses, and it would be hard to perceive without good points of reference, but that's my take. I'm going to run it a few more times, and see if my take changes.

I'm really thinking about cutting off the nipple and welding in a 1.5 piece of stainless before reinstalling the Delta. That would technically give me the final piece to this puzzle, of what difference does the nipple make, for this combo. I do think it would be more beneficial when I do the BB and MCM, in comparison to my current setup.