The Science of Dump Pipes

[Boxer]

Absolutley I research everything I do. But when I do I am the requester of information and not posing as the subject matter expert. If you want to draw on others experience you should be buying a twin pipe from what I read in this thread . I too like the idea of a splitter, but completely understand the reason for Phat not fitting one.
Sorry this post seems so catty - really didn't mean it as offensive

Be careful using those with a vested business interest in the advice they are providing you ( no supplier will bag their own product)

[cpitts]

Hmmm commonsense would dictate that if boost spikes were due to the wastegate not being able to do its job properly with a twin pipe setup - that the phenomenon would be exhibited moreso with the OEM flange plate Subaru serve up. This would pose far more restriction than any turbulent cause from a twin pipe dump.

This is where I'm not sure. Clearly the OEM dump pipe is blocked off, but when the pressure is released, it shoots back across the exhaust port which is the whole thing we're trying to mitigate with these better dumps (agree with you there). But with the twin pipe setup, the gas HAS to flow down the smaller pipe.
I guess my questions are around how easy it is for the gas to get out the wastegate under full load and flowing along the smaller pipe without being restricted to the point it causes feedback into the turbo system.

More likely the boost spikes if apparent are due to faster boost onset and lack of control over the wastegate from the ECU. Again this is evidenced by a tune or EBC fitment being able to fix it.

Agree, stock boost control is crap. Fitting almost any exhaust will lead to the tell-tale spikes @ 3000rpm.

I have not seen Prodrives musings on the subject, so can't comment on their twin pipe opinion.

They don't have musings specifically about twin pipe v's other, more-so their choice to run with a bell mouth and splitter setup for their WRC cars as their preferred choice. Given my tiny power figures that I'm after (compared to any level of race car), this approach seems more than adequate for what I'm after.

But having used CES three times would put a lot of faith in his engineering and performance exhaust knowledge. Still the only guy I have ever seen gain HP from an NA TypeR without changing headers and he did it be reducing pipe size, while everyone else made them bigger.

CES have been producing excellent gear for a long time. I have absolutely no beef with them, their quality of their product. In the same way that I had no beef with Phat and his product. I'm just looking for the best solution to a problem with the right amount of science behind it to show that it's not going to hurt other aspects (and parts) in my car.

It concerns me that when you talk about the split pipe solution, you also talk about component failure and supporting actions required to ensure they don't happen. If I'm looking to do all those supporting things as well (which I am, but others don't) then the solution may not be for everyone. Most people on here are fitting full 3" exhausts, high flow intakes and then belting their cars without any form of boost control or ECU remap to correct fuelling issues that arise. For those people, busted ancilliaries as a result of an exhaust dump would certainly be unwanted.

This is why I research parts before I fit them. And the best way is talking to owners of them (eg: You and the CES pipes. Clearly you're VERY happy with them if you're on your 3rd for 3 cars (I assume)).

PS: Just saw your resp. Not taken as catty.
Agree with the vendor not bagging their product either. I've moved between AVO, MRT, APS, STi, HiTech, CES, BPM, etc in this dump pipe argument and they all love their own products.
And yes, Phat has a VERY valid reason for not putting a splitter in his original pipe. Thickness of the splitter, bending under heat load and wastegate locking are all valid reasons for concern.
SME on this, not really, just had this 'discussion' many times, so trying to rapidly get to the fun stuff. (which is this stuff and physics / fluid dynamics)

[adam]

Is there off the shelf versions of these pipes with splitters? Well, AVO has them but I think they actually weld the splitter in as they adjust length to suit the turbo it's bolting up to, so the term 'off the shelf' is more a case of 'upon request'.

yes craig, there is an off the shelf for our cars with a splitter. i stumbled across the shop that fabricates them for MRT and seen a whole row of them. if i remember correctly though it was kind of like perrins "top section/back section" ie: phats in two bits. (i think?) quality of work to my untrained eye looked really good.

[cpitts]

Thanks Adam, wasn't aware of that one. Will have a look at the MRT and Perrin sites to see what's on offer.

[coyote]

This is really simple.

Cast pipes are inferior when it comes to thermal efficiency. The only reason some vendors use cast pipes is cost. They are cheaper and allow for a greater profit margin. Forget the marketing line about a hot cast pipe keeping gas hot. The pipe (and surrounding vehicle componentry) is only hot because that heat has come from out of the exhaust gas. Unless it magically stops radiating as much heat, it is actually continuing to remove more heat from the gas than a properly coated steel pipe. Simply, the cast iron lump slows gas flow. End of story.

The idea that the twin dumps made by the original designer restrict wastegate flow is also a myth likely dreamed up by competitors trying to sell their own products. I know this because for more than a dozen years I've run CES twin dumps on a variety of wrxs with a variety of turbos (yes, with a variety of splitters. I think we first did one on mine in 1997). The evidence rather suggests that the CES twin dump actually scavenges gas from the wastegate, rather than blocks it as other manufacturers would have us believe. The rip offs may be different.

[cpitts]

Coyote, agree on the losing of energy from exhaust gasses during the heating up phase, but once heated, would you agree that the benefit exist?

Also, as stated earlier, agree on the radiant heat issue. Coating the outside of the cast head and/or wrapping it would significantly help this, also aiding in heating the unit a lot faster.

I'd have to say, a coated steel (not cast steel) dump would be more usuable for daily on/off low throttle trundling around town where you're unlikely to get heat into the dump real fast, but if you're on/off throttle a lot with some good revs in between, surely the cast would assist . . . . the science suggest so.

[coyote]

Coyote, agree on the losing of energy from exhaust gasses during the heating up phase, but once heated, would you agree that the benefit exist?

No, for reasons explained twice above.

Also, as stated earlier, agree on the radiant heat issue. Coating the outside of the cast head and/or wrapping it would significantly help this, also aiding in heating the unit a lot faster.

You are polishing a turd. Better to select the superior manufactured item in the first place.

I'd have to say, a coated steel (not cast steel) dump would be more usuable for daily on/off low throttle trundling around town where you're unlikely to get heat into the dump real fast, but if you're on/off throttle a lot with some good revs in between, surely the cast would assist . . . . the science suggest so.

No, the AVO marketing suggests so. As Boxer alluded, there is a difference.


One design keeps more heat in the gas, hence is superior. End of discussion.

[GTSPECB STI]

I love how a metre of bent pipe can cause three pages of replys so quickly! Gets the popcorn out

[cpitts]

One design keeps more heat in the gas, hence is superior.

I think this bit helps the penny drop.
Loss of energy is loss of energy which reduces air speed and contracts the gasses. Clearly not ideal that close to the turbo.

Happy to take your lead on that one.

Have you done any dyno work comparing these solutions directly? I assume yes from your passion here.

As you said in the last post too, this does kind of close the original posters request.

I'd be interested in discussing the whole twin pipe v's split v's open bell mouth design though, but I might shoot you a PM on that one.

[PHAT GT]

POP QUIZ
to help understand the temp Cpits is talking about

with out doing GOOGLE search answer these question regarding a liberty or WRX dump pipe with a cat mounted at the top as most do on exhaust temps

all at normal driving

1: how hot does the gas get in the dump pipe before the cat?

2: how hot is the gas just after the cat ?

3: how long do you think it takes to get to this temp ?

...............................................................................

my take on AVO and other similar styles of colectors

1:radius is to tight
2:the bend is to close to the turbo
3:they are not as large as they should be, with all being smaller than 3" interaly
4:no where near a smooth as a split or bell mouth on the inside
5:lacking in flow compaired to a 3" split or bell mouth

................................................................

and on the coating side of things regarding my pipes i J coat in and out to help with heat and flow and reduce carbon build up

..........................................................

with over 15 years of building high performance street cars (about 40+) i have learnt 1 or 2 things along the way and aquired may skills and a vast aray of tools and testing equipment and made many friend in the high end of the performance world as most people who know me closely can tell you.i am not claiming to be a rocket seientist or anythink close as i learn every day along with many others

i am not like most other vendors who only sell parts, i make and customize alot of things car related and do alot of hands on

this is not ment to affend or knock anybody down but!

i could make the biggest piece of SH*t dump pipe and put it up against the best out there and you would'nt feel the differance at the level most of you will go with your car. now that dont help me out in any way saying this but its true

but in saying this you are better of buying good quailty over some basic rubbish as it will work better and be more reliable in years to come (as the old saying goes do it once do it right)

we are not talking a 6 second 500+thousand dollar drag or race car here trying to gain a tenth of a second .ITS A STREET CAR!!!!! with about 200KW in most cases so i see very little point in this thread debating. loss of energy , radiant heat , the science , thermal efficiency and so on

[coyote]

1: how hot does the gas get in the dump pipe before the cat?

2: how hot is the gas just after the cat?

3: how long do you think it takes to get to this temp?

I can answer 1 and 3, but wouldn't have a clue about 2.

How about 4: How hot does the gas get just cruising down the highway in closed loop mode when you think everything is running cool?

Or 5: What is the temperature of the seat leather after farting on the way home from an Indian restaurant?

As for the performance difference, there would not be much (probably only marginally more than the gains to be had from silicone intake pipes) and if a POS cast dump cost $500 less than a good one ... then I'd probably go that way.

[Boxer]

am not claiming to be a rocket seientist or anythink close

I'll say !! Your spelling is woeful .

Agree everything above is poofteenths, but I suspect many others are like me and want good gear regardless(which is good for you as people appreciate your workmanship). Oh and thhe temps q's above I could have a good guess without reffering to literature, considering the temps at which a cat needs to operate efficiently. I'd argue that similar to your sentiments on spliting hairs for street cars, that knowing the raw figures when considering the cause and effect of different materials and their effects on gas flow, velocity and expansion, may not truely be neccessary at this level. Interesting nonetheless

[Spec B Wgn]

dont run a cat...simple.

[GTBR46]

Thanks guys. I think my question is answered.

My takeaway:.....cast is cheaper to make (though not cheaper to buy from AVO!), and offers no performance advantage, but does significantly add to the risk of radiant heat damage to other nearby components in the car.

So, Phat....can i please have a 6mt dump pipe?

[PHAT GT]

am not claiming to be a rocket seientist or anythink close

I'll say !! Your spelling is woeful .

Agree everything above is poofteenths, but I suspect many others are like me and want good gear regardless(which is good for you as people appreciate your workmanship). Oh and thhe temps q's above I could have a good guess without reffering to literature, considering the temps at which a cat needs to operate efficiently. I'd argue that similar to your sentiments on spliting hairs for street cars, that knowing the raw figures when considering the cause and effect of different materials and their effects on gas flow, velocity and expansion, may not truely be neccessary at this level. Interesting nonetheless

arr yes i must go and spell check all that, but thats what you get at midnight