EvilBevel

In order to avoid going off topic in the other thread, I decided to open a new one...

Mark talks about ported headers ("Before I went and spent circa £1200 on headers, I'd recommend people port their standard headers. You'll be surprised at the results......") and I suddenly realized I haven't got a clue what it actually means

Could someone explain this a bit further ? What exactly is done, and who can do it ? What is the effect of having it done ?

Thanks.

Richiehash

as i understand it i think he means matching all the holes line up flush with each other on the manifold to header join ie no steps between the two .
using the gasket as a template scribe/draw round it on the manifold flange then do the same on the header flange.
slowly and very carefully open the holes out to match the scribed lines.(use a file cos power tools can rip out too much too quickly unless you are skilled in thier use)
clean everything carefully as iron filings and engines dont mix that well.
reassemble and hey presto smoother airflow to the turbo.
this principle applys to any flange type joint on inlet and exhaust .(good power gains on older tech cars cos of poor matching at the factory )
hope this helps
richie

Adam M

Theo,

without meaning to put loads of work onto him, mail bob rawle on this, as he has done his properly, and knows the way to achieve the right results when playing with the stadard items.

Ported, refers to the ports, or where the headers join onto the up pipe and the block. At these points, I believe there is a mismatch in diameter, and exhaust flow is forced round a step, this creates turbulence, which restricts airflow.

There are problems inside the heawders themselves where the sections are joined, the standard items, are not accurately joined, so that the interior walls of the headers, have steps in them where two castings meet. Each of these steps is a restriction, and people try to remove them also.

There is theory in how these should be removed, it is just a case of smoothing them out. This is all I know on the subject, I hope it helps.

Incidentally, Pat has done this himself also, and maty be able to report on what teh results were too. I believe he may also have a spare set of headers to work on.

EvilBevel

Adam & Richie, tnx for the replies...

So it does involve serious work & knowledge...

Would I be correct in assuming that the replacement headers that are commercially available (equal length or not) would already have this work done ? Or would they still need to be matched to the block ?

Would I also be correct in assuming that I would need to remap the boost targets in my Unichip, because of the more efficient exhaust gasses ? And would that mean the real advantage would be a more efficient/ thermally less stressed system - given that I'm perfectly happy with the boost I am running ? Or would the turbo also need "less load" to start spinning ? (thus having better low down torque)

Sorry for all the questions, just trying to get my head around this one.

Theo

Adam M

Theo,

Porting smooths out the standard manifold. Replacement manifolds are tubular steel (normally) and are smooth in the first place. They are also normally well made so the ports and the heads mate up very well indeed. I believe they can still be ported and smoothed, but it is questionable whether or not this is worth doing.

It does take skill and knowledge and it is possible to do too much and make things worse. You would as I said have to ask bob about this. Not only has he done his own car, but he also knows about these things due to his job.

You should need a remap as the acar should be running leaner with the headers in place.

the results should be exactly the same as removing any other restriction in the exhaust such as cats or a blocked wastegate exit.

In the same way that you should remap with a downpipe because it runs leaner, the headers should be compensated for. more fuel should equate to more power, which is nice.

Personally I dont like the idea of equal length headers. Apart from the loss in sound, the whole point of them is to make the tuned length of each pipe the same. A length of pipe has a resonance frequency which equates to a resonance rpm in an engine. At this point, the scavenging from the pipe will be improved (asw will the noise level). by tuning all the pipes to the same rpm, you will get a high torque peak.

With unequal length headers, you will get four different peaks equating to each pipes individual resonance. These add up to a wider but lower torque plateau.

EvilBevel

Hi Adam

I did not ignore your "ask Bob" statement, but I can imagine he has more things to do than enlighten an already confused Belgian dude

>>the results should be exactly the same as removing any other restriction in the exhaust such as cats or a blocked wastegate exit.

Which brings me to even more questions (oh dear). You often see discussions like "you need backpressure if you're below/on vacuum" versus "but the turbo is already the biggest obstacle providing enough backpressure already" and I never really saw a definite answer to that question. Would a more efficient gas flow provide "less backpressure" in this case ?

>>You should need a remap as the acar should be running leaner with the headers in place.

Hmmm. Confused again. If I lower the duty cycle of the boost solenoid, thus aiming for the same boost targets, the fuelling itself would not need a remap I think :confused ... I am still using the MAF sensor (Unichip), so the fuelling should be the same if the boost levels are the same ? I think ? Help

>>Personally I dont like the idea of equal length headers. Apart from the loss in sound ...

The sound is lost at low rpm, but it sounds quite astonishing actually above 4000 rpm (WRC type of sound). You do loose the "burble" at low revs though, sounds hair dryer-ish...

>>by tuning all the pipes to the same rpm, you will get a high torque peak.

I seem to remember Pete Croney posting on this board that you can actually "tune" those headers to "low down torque" versus "high up power"... they were still called equal length headers in both cases. Help again

>>With unequal length headers, you will get four different peaks equating to each pipes individual resonance. These add up to a wider but lower torque plateau.

I want torque as wide as it gets :-) Switching to the VF23 robbed me of some low down TD04 grunt already, so I would prefer to get some of that back.

My Powerstation RR figures should be up pretty soon, so maybe we should look at the graph, and see if we can actually improve on it ? (in a pub-talk kind of way, I mean

Thanks Adam.

Theo

MorayMackenzie

RichieHash,

Don't cut the engine ports!

IIRC, the subaru ports tend to be mismatched where the header port is smaller than it really should be, thus blanking off part of the exit and causing unnecessary turbulence in the exhaust gasses. When you pull your (used) subaru headers off the car you can use the soot marks on the header side to guide you in how much material you want to remove.

Moray

Richiehash

moray thanks but was just generalising as from experience on old tackle( mk2 escorts and the like)almost all the way from carb base to tailpipe would be more stepped than an escalator.
just havent pulled the exhausts off yet to have a look at requirements specific to the scooby.
thanks for the concern
richie

dfullerton

My brother did mine made a top end gain

Richiehash

if this is done to a car without an aftermarket ecu will it cause fuelling probs or should the standard ecu cope.
richie

Adam M

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by EvilBevel:
<B>Hi Adam

&gt;&gt;I did not ignore your "ask Bob" statement, but I can imagine he has more things to do than enlighten an already confused Belgian dude

&gt;&gt;&gt;&gt;the results should be exactly the same as removing any other restriction in the exhaust such as cats or a blocked wastegate exit.

&gt;&gt;Which brings me to even more questions (oh dear). You often see discussions like "you need backpressure if you're below/on vacuum" versus "but the turbo is already the biggest obstacle providing enough backpressure already" and I never really saw a definite answer to that question. Would a more efficient gas flow provide "less backpressure" in this case ? [/quote]

Not sure exactly on this one. It sounds reasonable that the turbo is itself a significant restriction and will therefore provide the adequate backpressure required by the engine.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by EvilBevel:
<B>
&gt;&gt;&gt;&gt;You should need a remap as the car should be running leaner with the headers in place.

&gt;&gt;Hmmm. Confused again. If I lower the duty cycle of the boost solenoid, thus aiming for the same boost targets, the fuelling itself would not need a remap I think :confused ... I am still using the MAF sensor (Unichip), so the fuelling should be the same if the boost levels are the same ? I think ? Help [/quote]


Theo, I am not an expert on this, so all I can say is pure reasoned guess work, but I think if you are flowing more exhaust to the turbo at higher speed then it will work more efficiently, in that it will take a lower load to produce the same boost as before. I can only guess that this means it will be "able" to spool up faster and will be able to hold more boost. I assume as you say, that if you dont change the boost targets, it will produce the same boost with the same amount of air, and will therefore not require a remap. It is possible that running more efficiently means it runs cooler therefore the air will be denser, but I think running the standard ecu with the same boost targets as before, the MAF sensor will be abvle to accomodate any extra fuelling if required.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by EvilBevel:
<B>
&gt;&gt;&gt;&gt;Personally I dont like the idea of equal length headers. Apart from the loss in sound ...

&gt;&gt;The sound is lost at low rpm, but it sounds quite astonishing actually above 4000 rpm (WRC type of sound). You do loose the "burble" at low revs though, sounds hair dryer-ish... [/quote]

This is true but the shape of the torque curve makes the engine peaky, that combined with the loss of "character" fro the sound means I would never consider it, when there are great alternatives.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by EvilBevel:
<B>
&gt;&gt;&gt;&gt;by tuning all the pipes to the same rpm, you will get a high torque peak.

&gt;&gt;I seem to remember Pete Croney posting on this board that you can actually "tune" those headers to "low down torque" versus "high up power"... they were still called equal length headers in both cases. Help again [/quote]

I mentioned that the torque peak comes from the resonance frequency of the pipes, this is related to the length of the pipes (normally the wavelength of the sound is twice the length of the pipe). ie. the torque peak can be made to come it at a point related to rpm. By changing the length of all of the pipes (still equal length), you can move the point at which the torque peak occurs.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by EvilBevel:
<B>
&gt;&gt;&gt;&gt;With unequal length headers, you will get four different peaks equating to each pipes individual resonance. These add up to a wider but lower torque plateau.

&gt;&gt;I want torque as wide as it gets :-) Switching to the VF23 robbed me of some low down TD04 grunt already, so I would prefer to get some of that back. [/quote]

You could get equal length headers tuned to give low down torque, but as I said, I would stick with unequal length for all the reasons I stated. I believe most of the gains come from the use of smooth tubes which dont represent major restrictions in the same way as the standard headers.

Money and performanxce wise, there is a lot to be said for porting the standard set-up.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by EvilBevel:
<B>
&gt;&gt;My Powerstation RR figures should be up pretty soon, so maybe we should look at the graph, and see if we can actually improve on it ? (in a pub-talk kind of way, I mean
[/quote]
If it makes you happy, go for it. Who am I toargue with a big man?
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by EvilBevel:
<B>
&gt;&gt;Thanks Adam.
[/quote]
No problem, just remember, this has all been an eductaed guess. I was hoping someone truly in the know might be able to offer something too, but no one has tried yet




[This message has been edited by Adam M (edited 17 July 2001).]

MorayMackenzie

Hi RichieHash,

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by Richiehash:
<B>moray thanks but was just generalising as from experience on old tackle( mk2 escorts and the like)almost all the way from carb base to tailpipe would be more stepped than an escalator.
just havent pulled the exhausts off yet to have a look at requirements specific to the scooby.
thanks for the concern
richie[/quote]

I could tell you were posting general info about porting, but you did post a series of instructions that may well have been taken out of context by someone else, EvilBevils original post was asking about porting for the subaru, afterall.

Cheers,

Moray

Adam M

Theo,

having read pats response to a similar question on the other thread

EvilBevel

Moray, thanks for the concern, but with my two left hands I didn't exactly have the spanners at the ready Good warning for the more able DIY tuners though ...

Adam,

&gt;&gt;If it makes you happy, go for it. Who am I toargue with a big man?



I wish my wife would have your wisdom

&gt;&gt;No problem, just remember, this has all been an eductaed guess.

That is a given... Understood & appreciated. I won't make the mistake of taking everything that's written here as gospel, but I enjoy the thought process behind it all. And non-equal length smooth headers may be just what I need though

&gt;&gt;forget the length, there is good stuff in there.

One of the reasons I like his contributions very very much is because it goes way beyond oneliners. Pat is favorite reading material... even with my attention span of a banana fly

But mission accomplished ... when people talk about "ported headers", I will at least have a clue about where those are situated.

Oh well, on to the "gas flowed jobbiemagooks" now

Theo

DHX

The more I read of Adam M's comments the more I am convinced that this man is one of the most informed guys on the BBS and we should all be thankful that he posts here.
(he has a degree in Physics and works on the cutting edge of engine design)

Andy Tang

iTrader: (3)

DHX,

Stop kissing ****, he's only human (with knowledgeable friends)!!

Andy

PS - Not a dig at Adam, as we only do that face to face!!!

Adam M

I think dhx is actually moray taking the **** and boosting my fragile ego after certain people rattled my cage.

The cutting edge thing was a joke, although it is partially true.

There is no way anyone could read dhx's post without pure sarcasm in mind.

If it is genuine, then thanks, but I am convinced it is one of my friends.