1.6Tdci Flexi Down Pipe, Is Bigger; Better?

[Lenny]

Hi all,

After fitting a 2.5" exhaust system to my focus last year, I took it to the guys at souhan exhausts to get it fitted,

They can manufacture any exhaust part for any car or full systems,

My current 2.5" free flow goes from the down pipe flange to tips, as you can see in the image below; its bolted to the standard 1.5" flexi pipe leading from the DPF flange to the exhaust straight.

Here is an image from the internet of the standard 1.6TDCi focus flexi down pipe removed from place,

Now my questions are:

Would the focus benefit further by changing the standard flexi down pipe to a custom built stainless 2.5" flexi?

Would the larger flexi create a louder nose in the drivers and passengers cabin area?

Would the larger pipe help performance or even the DPF?

[FOCA]

Lenny - Now my questions are:

"Would the focus benefit further by changing the standard flexi down pipe to a custom built stainless 2.5" flexi?

FOCA - Yes, The 1.5" pipes will cause a restriction "bottle neck" compared to the 2.5" tubes (or dual tubes) ideally if the exhaust is one 2.5" tube (or larger) from exhaust manifold to tip, it would flow more gas, turbine would spool up quicker etc

if the outlet of the exhaust manifold is 1.5", (or less than 2.5") it needs to have a smooth transition without any "steps" that would cause loss of velocity, it may need a special kind of adapter called a "diffuser tube" that gradually opens up the diameter from the manifold (like a gradual "cone")

Would the larger flexi create a louder nose in the drivers and passengers cabin area?

Possibly- but if it does not much louder - the turbo turbine on its own cuts the noise down a lot and works as a silencer - ive ran a turbo with a completely straight- through exhaust on the road and it was not that loud

Would the larger pipe help performance or even the DPF"

Yes, the turbine would spool up quicker, this would cause a knock-on effect on the compressor, boost would come in quicker, throttle response would be quicker, the engine may rev better at the top end (better breathing/ scavenging) the 0-60mph should be quicker as the turbo & engine revs through the pand quicker

ideally, you want to ditch the CAT and the DPF completely (if fitted) because this will restrict the gas-flow and negate the advantages of the larger exhaust ("bottleneck")

If the DPF is phisically removed, it would have to be electronically deleted, this would normally be done with a specialist remap, its my opinion thnat to get the full potential of the 2.5" exhaust, you need to remove the cats/ dpfs, and have the entire system at 2.5", or more, nose to tail, with no "steps"/ gradual tranitions/ and the silencers need to be the "straight through" type, if you try to make it too quiet, you may compromise the power, its a balance between noise & power, as said the turbine cuts the noise down a fair bit

Removing the "bottlenecks" might finally, release the potential of the 2.5" exhaust, with a big, noticable impprovement in performance, other things, like small injectors, might "hold it back", once they are sorted (with the "deristricted" total 2.5" exhaust fitted) the car might teally "fly" then

You won't lose (engine) back pressure by going bigger, the "tiny" exhaust manifold/ restriction of the turbine blades etc, creates a "massive" back pressure (as "seen" by the engine)

after the turbine the "fatter" and shorter the pipe the better, (quicker turbo spool-up, better scavenging/ breathing/ gas-flow) extreme examples of this are 4" systems on scoobies/ evos and ultra short fat pipes on dragsters, short side pipes on the Maclaren SLR and short side pipes on DTM cars etc - ive experimented with short pipes myself with some success

If you went up to 3", it would have to be nose to tail with no cat/ dpf and a smooth transition out of the manifold, it may help the turbo spool faster by reducing back-pressure post-turbine , as mentioned before it would not loose engine back-pressure because of the restriction of the manifold/ turbine, there may not be any advantage because the relatively small engine may not flow enough gas to justify a 3" pipe, and 2.5" being a better "match" for the engine, the velocity would be lower in the 3" pipe and it would not get as hot as a 2.5", getting the heat into the pipe improves scavenging - so the 2.5" may be the best way to go on your engine (rather than 3") but not nessesarily because the 3" would loose engine back-pressure

You probably don't want to hear this bit but a (larger diameter) single tail pipe will outperform a dual/ twin tailpipe -(on a single turbo with intenal wastegate or VNT ) it flows better because it has a lagger ratio of volume to surface area, its lighter too, the 2/ twin tailpipes are mainly cosmetic , but having the 2 rear silencers can reduce noise without impacting performance too much and the twin pipes can be slimmer/ better packaged

Finally heat-wrapping and/or ceramic- coating your pipes would help too, ive done my decat/ downpipe& flexi - & plan to do the manifold in the future - ceramic- coating is expensive and heat-wrapping is time- consuming

The biggest (wrapping/ exhaust insulation) gains are under the bonnet (manifold/ (de)cat / downpipe) as this reduces undebonnet temps, reducing heat-soak into the inlet/ intercooler/ boost pipes etc, as well as keeping the heat in the exhaust/ turbine

Another "epic" post with me "waffling on", not everyone may agree with my theories/ opinions, much of it is based on actual experience rather than stuff ive read or "googled" etc

I was going to ask do you have a fixed-vane or VNT turbo?

[Lenny]

Yes, The 1.5" pipes will cause a restriction "bottle neck" compared to the 2.5" tubes (or dual tubes) ideally if the exhaust is one 2.5" tube (or larger) from exhaust manifold to tip, it would flow more gas, turbine would spool up quicker etc

if the outlet of the exhaust manifold is 1.5", (or less than 2.5") it needs to have a smooth transition without any "steps" that would cause loss of velocity, it may need a special kind of adapter called a "diffuser tube" that gradually opens up the diameter from the manifold (like a gradual "cone")

I was going to ask do you have a fixed-vane or VNT turbo?

Thanks foca,

Lots of good information there,

If I got the internals of the dpf removed then the dpf chamer could act as a cone or swirl pot from manifold to 2.5" exit

Before purchasing my exhaust I was asking what size sets the best back pressure balance and I found 2.5" to be best for my perticular engine,

The exhaust I have is a single 2.5" pipe until it gets to the other side of the single back box then splits two ways

Much like an exagerated twin back tip,

The place who fitted my exhaust can do dpf and egr removal with electronic delete,

But I want to get the dpf cut on the weld, internals removed and welded back up like it never happend,

So as it will pass any visual inspection on MOT

And I need to fit an egr blanking plate in stainless steel,

2.5" flexi and graguated 1.5"-2.5" dpf down pipe sounds good mate,

This is the dpf down pipe leading to the flexi I can see it would benefit from heat wrap, even the oil sump pan would be subjected to large heat volumes from it,

Some 110cc injectors are on the plan for later in the year, need to research on coding injectors etc. And find out how big the job will be,

But the exhaust plans will be sooner and less expence,

[salsheikh]

go for it Lenny..you know it makes sense!

[Lenny]

go for it Lenny..you know it makes sense!

Sal how did you become the voice inside my head lol

Ok,

As soon as the 16" snow flakes sell, its straight to Souhans for a 2.5" flexi

[salsheikh]

good man...just dont tell the missus!

[Lenny]

good man...just dont tell the missus!

lol too late,

Its all good though, went well..... I think