Improving turbo performance with equal length headers?

[Blacktree]

Originally Posted by 116HDi

I heard a lot of contradicting claims concerning equal length headers used in turbo engines.

Some say the equally spaced exhaust pulses will get the turbo to spool up faster and improve efficiency, others say the heat loss over the longer headers will lead to less exhaust energy to reach the turbine wheel.

People like to "armchair quarterback" stuff like this. I would be wary of any claim anyone makes, one way or the other, unless they have data to back it up.

That said, the effect of either of those things is probably going to be pretty minor. And packaging might dictate one method over the other, anyway.

[Joggernot]

Originally Posted by Blacktree

People like to "armchair quarterback" stuff like this. I would be wary of any claim anyone makes, one way or the other, unless they have data to back it up.

That said, the effect of either of those things is probably going to be pretty minor. And packaging might dictate one method over the other, anyway.

"Engine Masters" did a show on headers and header length. Don't know if they evaluated equal length headers. This show is on either MAVTV or Motortrend TV, but I can't find which one right now (cable problems). You can probably see a video on their web site.

[cRiPpLe_rOoStEr]

Originally Posted by Blacktree

And packaging might dictate one method over the other, anyway.

Even though most cars nowadays feature a transverse engine, and so do some commercial vans, the difference to the engine bay sizes is noticeable between vehicles of different classes which may share an engine.

And when it comes to the Peugeot/Citroën DV6 engine, it was fitted from some austere econoboxes to mid-size vans for instance.

[Isaac Zachary]

The little I know about exhaust headers is that if they are not equal length then there's a chance one pulse is still creating pressure when another exhaust valve opens essencially creating more back pressure on the piston.

This is also a reason why it could be more efficient to turbo a 3 cylinder (or 3 cylinders per bank) rather than a 4 cylinder (or 4 cylinders per bank on a flat plane crank) because the pulses are more separate from each other and therefore do not affect each other. For the same reason cross plane cranks aren't the best idea when it comes to turbo charging.

Another thing is that different lengths could affect exhaust scavenging, although I'm not quite sure how that is affected with the addition of a turbo.

As far as a diesel goes, wraping the exhaust to insulate it is always a good idea. It keeps exhaust temps hot for the turbo and if you have any emissions equipment it helps keep that warm enough to do it's job too. With SCR it should help reduce the need to burn fuel in the exhaust as well.

[cRiPpLe_rOoStEr]

Originally Posted by Isaac Zachary

With SCR it should help reduce the need to burn fuel in the exhaust as well.

SCR relies on DEF. It's the particulate filter that burns fuel in the exhaust while it's on regen.

[Isaac Zachary]

Originally Posted by cRiPpLe_rOoStEr

SCR relies on DEF. It's the particulate filter that burns fuel in the exhaust while it's on regen.

Older systems used diesel fuel and didn't use any DEF for SCR. Do DEF systems not need any unburnt fuel to do the same?

[cRiPpLe_rOoStEr]

Originally Posted by Isaac Zachary

Older systems used diesel fuel and didn't use any DEF for SCR.

Older systems which didn't feature SCR, so there was no need for DEF.

Do DEF systems not need any unburnt fuel to do the same?

Are you sure we're talking about the same system. DPF which is the particulate filter does use fuel. DEF is that urea-based exhaust fluid, sprayed into the exhaust to decrease NOx emissions. The housing of the DPF core might be the same spot where the DEF is applied, but it doesn't imply the SCR would require fuel to work.

[Isaac Zachary]

I'm certain there were engines fitted with this kind of SCR, now referred to as HC-SCR (hydrocarbon selective catalyst reduction). The idea is the same as with urea injection, except fuel is used as the reduction agent instead of urea.

I just wasn't sure if urea injection systems still used at least some fuel for reduction.

From what I understand, this is basically what led to the VW diesel scandal. The NOx trap needed fuel to be sprayed into the exhaust to reduce NOx without the need for urea injection. Of course spraying fuel into the exhaust made the vehicles get worse fuel mileage too. So the emissions cheat was to only spray the fuel into the exhaust during testing but didn't do it while driving.

[cRiPpLe_rOoStEr]

Originally Posted by Isaac Zachary

I'm certain there were engines fitted with this kind of SCR, now referred to as HC-SCR (hydrocarbon selective catalyst reduction). The idea is the same as with urea injection, except fuel is used as the reduction agent instead of urea.

AFAIK the HC-SCR was meant to use ethanol.

[Isaac Zachary]

https://portal.research.lu.se/en/pub...sel-exhaust-af

Several principal aspects and components of an advanced catalytic exhaust after-treatment system for NO, reduction on a heavy-duty diesel truck engine have been systematically examined and evaluated. The after-treatment system consists of de-NO, catalysts, injection of a reducing agent (diesel fuel),

The main reason for using diesel fueled HC-SCR is it means you only have to fill up (or fuel up) with one kind of liquid making it more convenient.

https://www.cataler.co.jp/en/aee2018/diesel/hc-scr.php