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If the info laid out here is going to be truly comparative, I would recommend dropping comparisons to twin scroll. TS vs SS are different turbine technologies and as such have differences in design for optimized performance; offering difference in performance characteristics.
 

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With that said, I designed our headers with the purpose of optimizing the EJ's VE (Volumetric Efficiency) and maximizing the energy (pressure, heat, flow, sound) from exhaust port to turbine.

As far as layout goes, we have intellectual protection of the design for good reason, it works well. We've tried 4-2-1, longer primaries, twin scroll, as well as compared to many other brands. If there were a design that worked better than a symmetrical primary layout like we use, then we'd be doing it :)
I've seen it mentioned a few times that single scroll is believed to be superior to twin scroll on the EJ257. In comparison, the EJ207 responds very well to the OEM twin scroll setup providing more area under the curve despite its displacement disadvantage.

Did your testing provide any insight or theories as to why this may be? Displacement, bore/stroke, head design (ports/cams), turbo manifold length? The EJ207, FA20 & FA24 all have twin scroll setups with varying designs (bore, stroke, displacement, header length, etc.).

I'm curious how the EJ257 might respond to a small-ish, TS, ball bearing turbo setup for a daily driver. Targeting something in the 350-400 whp range with maximum responsiveness and area under the curve.

Obviously manufacturing a twin scroll header would be more involved (and expensive).. while also potentially limiting sales since most US buyers are running a single scroll OEM or aftermarket turbo. It may not be a cost effective option for most consumers.. perhaps the expense and challenges of converting to twin scroll outweigh the benefits.
 

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I purchased a Killer B Holy Header with the SwainTech coating today :D

Here's how I rationalized the "financial investment":
  • It's the only header made of 321 SS with a cast merge collector. While 321 may be considered overkill for a daily driver.. it's stronger & more crack-resistant (added peace of mind) and has a lower thermal conductivity (less energy lost due to heat transfer) compared to 304 & 409. It's made in the USA and has a lifetime warranty if it ever does fail.
  • It's the only header with a symmetrical primary design (tube length & bend geometry) and has the shortest primaries possible. These features reduce header volume, maintain high & consistent exhaust gas velocity, and should improve spool & responsiveness.
  • Available for purchase with the SwainTech White Lightning coating (rather than shipping the header to SwainTech yourself). The coating should reduce radiant heat and help retain more heat in the pipes; lowering under hood temperatures and maximizing exhaust velocity hopefully improving spool & boost response. If you're already spending this much.. why not spend a bit more for the very best results?
  • All of this leads to a header that provides the best gains in VE. That means improved fuel economy and saved money at the pump, right? :LOL:
I'm a fan of over-engineered products. Maybe some of these features are great in theory, but nearly imperceptible compared to other ELHs.. but at least I'll never have buyer's remorse or worry about a sub-par product. Killer B is at the top in terms of quality, engineering & providing support to the Subaru community. How many other companies do you see actively participating in forum discussions? I can only think of a couple.

I'm looking forward to getting rid of the inefficient OEM header and seeing how the KBHH transforms the car.
 

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Discussion Starter #24
If the info laid out here is going to be truly comparative, I would recommend dropping comparisons to twin scroll. TS vs SS are different turbine technologies and as such have differences in design for optimized performance; offering difference in performance characteristics.
Yeah i wasnt planning on comparing to anything twin scroll. I know that is a whole other world in and of itself. This comparison thread is for single scroll sets ups since most of us with the EJ257 are single scroll :)

I purchased a Killer B Holy Header with the SwainTech coating today :D

Here's how I rationalized the "financial investment":
  • It's the only header made of 321 SS with a cast merge collector. While 321 may be considered overkill for a daily driver.. it's stronger & more crack-resistant (added peace of mind) and has a lower thermal conductivity (less energy lost due to heat transfer) compared to 304 & 409. It's made in the USA and has a lifetime warranty if it ever does fail.
  • It's the only header with a symmetrical primary design (tube length & bend geometry) and has the shortest primaries possible. These features reduce header volume, maintain high & consistent exhaust gas velocity, and should improve spool & responsiveness.
  • Available for purchase with the SwainTech White Lightning coating (rather than shipping the header to SwainTech yourself). The coating should reduce radiant heat and help retain more heat in the pipes; lowering under hood temperatures and maximizing exhaust velocity hopefully improving spool & boost response. If you're already spending this much.. why not spend a bit more for the very best results?
  • All of this leads to a header that provides the best gains in VE. That means improved fuel economy and saved money at the pump, right? :LOL:
I'm a fan of over-engineered products. Maybe some of these features are great in theory, but nearly imperceptible compared to other ELHs.. but at least I'll never have buyer's remorse or worry about a sub-par product. Killer B is at the top in terms of quality, engineering & providing support to the Subaru community. How many other companies do you see actively participating in forum discussions? I can only think of a couple.

I'm looking forward to getting rid of the inefficient OEM header and seeing how the KBHH transforms the car.
Congrats on a very nice piece! Let us know what you think after you've installed and tune the car for the KB ELH.
 

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I've seen it mentioned a few times that single scroll is believed to be superior to twin scroll on the EJ257. In comparison, the EJ207 responds very well to the OEM twin scroll setup providing more area under the curve despite its displacement disadvantage.
I can only respond to SS vs TS in regards to the EJ25 and FA20 (WRX). I've honestly never run an EJ20. We've seen them on our dyno several times; they perform well, with less response and torque as you'd expect from 25% less displacement. The flip side is that, the lower torque and response tends to be nicer on rod bearings so there are reliability benefits... Way OT though :)

Did your testing provide any insight or theories as to why this may be? Displacement, bore/stroke, head design (ports/cams), turbo manifold length? The EJ207, FA20 & FA24 all have twin scroll setups with varying designs (bore, stroke, displacement, header length, etc.).
Physics is really the underlying reason for which turbo tech is best suited for the engine. If you read the books on this stuff, it comes down to VE, flow capabilities, bore, stroke, etc, and so on. What may work best on one engine, may not on another type. The FA20 for example, REALLY naturally makes best power in the mid-range and TS technology really is ideal for taking advantage of where the engine wants to make power. The EJ25 makes better power with SS. Now when we did testing, we wanted to reduce header/up-pipe losses as much as possible so all of our testing was on our low mount turbo setup, which further amplified these differences.

I'm curious how the EJ257 might respond to a small-ish, TS, ball bearing turbo setup for a daily driver. Targeting something in the 350-400 whp range with maximum responsiveness and area under the curve.
Very well for daily driving. Keep in mind TS technology was developed as displacement trended smaller, fuel efficiency needs increased, and a desire for reducing the effects of turbocharging (lag) became more important. TS fills those checkboxes. Partial throttle boost response, TS all the way. Best MPG, TS. Once you start expecting to add performance benefits and mid-high RPM power to the mix, that's when things tend to get messy. The short of it is if you have the same exact setups; TS vs SS, the SS will walk all over the TS EVERY time in a drag race by a good amount too. Some kit suppliers compensate for the high flow rate choke with TS by using a larger turbine housing, but you start loosing the benefit of TS when you do that. To the point where a more simple SS version makes more sense.

Obviously manufacturing a twin scroll header would be more involved (and expensive).. while also potentially limiting sales since most US buyers are running a single scroll OEM or aftermarket turbo. It may not be a cost effective option for most consumers.. perhaps the expense and challenges of converting to twin scroll outweigh the benefits.
I can only speak to the testing we've done, which supports SS technology for the EJ25. We've done it multiple times with multiple builds/turbos. From our own testing when we considered making a TS manifold; with the EJ just makes best power when using SS.
 

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I have a full-race twin scroll manifold on my car, it once put down 490whp at 35psi on nothing more then 93 octane and it did all of that at 3900 rpm which should help give an indication on spool up. It was turned down since then for health reasons as an engine would not last under those circumstances. I really like the manifold and see no reason on changing it in the future. But looking at the power my car makes at the boost level does have me believe a single scroll option would make more power at the same psi. I am no expert on the topic but I believe the distance between our cyl heads to turbo has something to do with the single scroll vs twin scroll debate. The further the exhaust gasses have to travel separated in a twin scroll manifold the more they lose their efficiency on making power. And when those exhaust gasses travel through a single scroll manifold they have an advantage as they are kept together allowing them to pack a better punch on the turbo wheel. I think its something unique to our cars as most turbo applications run turbos directly off the head (closer the better), not in our cars where it is remote mounted with multiple feet of exhaust tubing to get there.
 

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But looking at the power my car makes at the boost level does have me believe a single scroll option would make more power at the same psi.
Absolutely true; it take more boost to make the same power. On a 500whp car we lost 40whp running the same boost. Some of this has to do with the TS volutes being more restrictive and less optimized. Essentially you have two smaller openings to the turbine wheel and neither is exactly in the sweet spot. With SS, you have one wide opening perfectly lined up to optimized location on the turbine wheel. This is what you typically have losses up high with TS; we saw power taper +500RPM sooner with TS.

I am no expert on the topic but I believe the distance between our cyl heads to turbo has something to do with the single scroll vs twin scroll debate. The further the exhaust gasses have to travel separated in a twin scroll manifold the more they lose their efficiency on making power. And when those exhaust gasses travel through a single scroll manifold they have an advantage as they are kept together allowing them to pack a better punch on the turbo wheel. I think its something unique to our cars as most turbo applications run turbos directly off the head (closer the better), not in our cars where it is remote mounted with multiple feet of exhaust tubing to get there.
Some of what you're referring to comes down to manifold design. Either way there are losses, but more bends and length comes more loss. I don't believe the location is what cases the difference in SS vs TS though. It's just not an ideal location either way. The other trick tot he equation is the pulse spacing you mentioned. That's managed through header design as well, but with TS, it's one of the main reasons you have better low end characteristics because there's less (exhaust) manifold backpressure to create some positive manifold pressure. This is why tip-in, partial throttle (transient) response and MPG is better with TS. Essentially the cylinders evacuate gasses more completely if there's less backpressure with TS. So at 1psi of boost you make more power with TS. As gas flow increases the advantage becomes a disadvantage. With SS, you don't want to choke things down too much as it starts to effect performance Everywhere. For example, some will want a 3582 capable of 700whp and run a tiny turbine housing in hopes of reducing lag. What happens is you choke through the exhaust terribly. With SS if the turbine A/R is too small you will see power taper a lot, and if you keep upping the boost, you'll start to make less power as the combustion gasses have nowhere to go and heavily pollute the next intake stroke. You see the same issues with TS, which is one of the reasons they make less power up top.
 

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Jay and Nick,

Thank you for starting a genuine conversation and for Killer B for the insightful comments.

Something I want you to understand that hasn't been stated before is that at least in my anecdotal issues almost all if not all of these headers may eventually fail. They fail in that the vibration caused by the engine and the lack of a a vibration dampening flex pipe will cause this. For this reason I suggest something with a lifetime warranty. I have personally had experience with Killer B and the warranty experience was awesome.

This is something that I feel you need to take into account when deciding on a purchase.

Sparky
 

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Good point KillerB; you reminded me of something Ive always thought was funny my car has been on single scroll setups and twin scroll setups. I noticed when getting tuned my single scroll tunes have always looked like a typical bigger turbo sti where things have more of a top end. And my twin scroll tunes seem to resemble a stock turbo sti with more midrange and things tend to fall of up top.

Just to be clear I think its a matter of opinion, where one offers the option of increased spool and the other offers higher power. Sure my twin scroll setup doesn't make peak power but I do like the response. For example when my car was on my last single scroll set up and I would rip turns I would get on the throttle sooner in the corner to help things get spolled up and by corner exit I would have all of the boost under my foot. The first time I rounded a corner on my TS setup I almost spun out because It spooled during mid turn instantly. The car feels much more like a na car on the TS manifold as most of the lag is gone, all of the boost and power are under my foot at all times which I enjoy. While driving fast I dont have to pre plan as much with the turbo which lets me focus on driving.
 

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Discussion Starter #30
Jay and Nick,

Thank you for starting a genuine conversation and for Killer B for the insightful comments.

Something I want you to understand that hasn't been stated before is that at least in my anecdotal issues almost all if not all of these headers may eventually fail. They fail in that the vibration caused by the engine and the lack of a a vibration dampening flex pipe will cause this. For this reason I suggest something with a lifetime warranty. I have personally had experience with Killer B and the warranty experience was awesome.

This is something that I feel you need to take into account when deciding on a purchase.

Sparky
You're welcome, this thread has turned out to be very informative and educational.

As for the failures of aftermarket manifolds, i mean anything failing is a possibility.. I think manifold failures are sometimes blown out of proportion and there are so many reasons as to why a component fails regardless if its ELH or UELH. Lets also keep in mind that most users running these aftermarket manifolds are using them for the purpose of making more power than the car came with from the factory. Yes components like exhaust manifolds are designed to take the abuse, heat, and punishment. Somethings are just still unpredictable.

I do agree, if you are going to make the investment when purchasing and ELH then warranty should be something to consider. Another thing to consider should be how you will be using your ELH. If you are going to just be daily driving the car with some fun on the side then you may not necessarily need the most expensive header. If you are someone chasing numbers whether its on the dyno, track, or street then yes you may want be best possible ELH out there to handle the abuse.

One could also flip this logic the other way around too Lol ^^^ You could have someone getting the best possible ELH for a daily driver and then have the race car with the cheapest ELH running it until it breaks. I guess what im trying to get at here is that the failures are just so unpredictable lol.
 
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