# DIY: VR6 Exhaust Manifold and Downpipe Porting (Pic Intensive)



## need_a_VR6 (May 19, 1999)

I wanted to try and document this a bit while it was still fresh in my mind, but I had a race to get to at the end of the week so it's a been a bit since I did it. However, I will do my best to tell you what I did and why. I lost a few pics of the process but I'll describe the best I can what I did that isn't shown.
To start off you'll need these:







Just one I could only find a pic of four of them. Make sure you get the 6" shank as the manifolds are pretty deep. 
You'll also want a decent air compressor and die grinder that can operate at the speed of your bit for extended periods of time. 
Plan to spend between 4-6hrs on this and it's VERY messy. Be sure to wear eye protection as well as some sort of face mask/respirator. The carbon dust is not fun if inhaled.
It's easier to start with the downpipe as it's a little easier to get going and get the feel for things.
Start off by getting the exhaust manifold 'back welded' as seen below:

This will allow you to fully port the inside of the downpipe, but the welding will leave some 'dingleberries' on the inside:

You want to get rid of these, as well as try and smooth the transition to gasket size:
About halfway.

Complete.

You'll notice I didn't quite go to gasket size as my weld wasn't THAT big and the transition would be sharp had I gone bigger. This is personal preference but it works. I cleaned that up with a sanding bit but didn't polish it much more then shown.
Now to the manifolds, these take FOREVER so be patient. Your hands will hurt after a bit, so stop and come back later.
Starting point:

Comparison to gasket:

Ported:


Notice not only the matching of the gasket but also the smooth transitions around the turns. Getting in there deep is where it matters. 
I only finished it with the grinder plus some 80 grit final finishing. Some will argue that full polishing will hold some power as well. I didn't have the time to find out. 
I don't have pics of the manifold where it meets the downpipe but it's ported just a little less then the downpipe so that there's a step up to it, roughly .5mm large. 
I hope that explains some things about porting the manifolds now that we hear so much about it these days.


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## cgeromi (Apr 30, 2006)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (need_a_VR6)*

Can you explain exactly what porting does? Pardon my ignorance I just am not sure exactly why to do this.








Awesome DIY tho. Thanks!


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## need_a_VR6 (May 19, 1999)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (cgeromi)*

In this case you make the exhaust manifold entry larger and smoother, less restrictive and more even across all the cyls.. basically, more power. 
An almost identical setup on my old car made in the neighborhood of 5-7whp over a very expensive aftermarket header at a fraction of the cost.


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## RDSFSU2004 (Jan 24, 2005)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (need_a_VR6)*

Pimp status... Thanks for doing this


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## cgeromi (Apr 30, 2006)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (need_a_VR6)*


_Quote, originally posted by *need_a_VR6* »_In this case you make the exhaust manifold entry larger and smoother, less restrictive and more even across all the cyls.. basically, more power. 
An almost identical setup on my old car made in the neighborhood of 5-7whp over a very expensive aftermarket header at a fraction of the cost.

I figured it would give some HP gain, just wasn't sure how much. It's amazing just by porting those area out you get better HP. Why wouldn't the factory do that from the get go?


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## WeeZFan69 (Aug 3, 2003)

It would require more machining, therefore more expensive. Also it makes things thinner, larger chance of things cracking. 
I'm going to bookmark this though. I'm actually picking up a spare cylinder head to port and polish and I'd like to get some ex. manifolds and a lower intake to port too. Along with some 262's and a chip, I should see a good power gain.


_Modified by WeeZFan69 at 5:21 AM 12-25-2007_


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## TgiRicky (Nov 13, 2006)

*Re: (WeeZFan69)*

Hey paul, did you notice any difference at the track? butt dyno?


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## 708VR6 (May 20, 2006)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (need_a_VR6)*

I did this when I had my CRX and my bone stock 1.6l kept up with my brothers modified ZC 1.6l swap...is a worthwhile mod to do, might consider doing this when the spring comes along or maybe buy a used DP & manifolds and prep them for the spring time...we'll see what happens http://****************.com/smile/emthup.gif


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## Joe Amato (Aug 13, 2007)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (708VR6)*

Nice work, Paul http://****************.com/smile/emthup.gif


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## need_a_VR6 (May 19, 1999)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (Joe Amato)*

At the track it's worth 'about a tenth' which is noticeable, considering most of the time I'm looking for hundredths or thousandths!
I'll do a DIY of the lower intake manifold I did when I get some time this week as well.


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## FaelinGL (Nov 28, 2004)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (need_a_VR6)*


_Quote, originally posted by *need_a_VR6* »_At the track it's worth 'about a tenth' which is noticeable, considering most of the time I'm looking for hundredths or thousandths!
I'll do a DIY of the lower intake manifold I did when I get some time this week as well.

Have you dyno'd since the port? I'd love to see if you break 200








In addition, did you backweld the exhaust manifold? It doesn't appear to need it.
Mike


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## Northren vr6 (May 29, 2004)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (FaelinGL)*

I did this a few years ago and it SUCKED. 
I ended up using 80 grit flapper wheels to finish the insides, then hit it with some rough polishing compound for a nice shiny interior finish.
At the same time i replaced the stock exhaust with a 2.5" cat back, and a cleaned up downpipe. Net gains was 10 wtq, 7 whp on a car with cams / chip and a few other lil goodies. Ceramic coated by these guys too. 
http://www.nationalcoating.com/body_index.html
Its not a "appearance" enhancer, and it does retain dirt/stains etc but seems to work.








If I had to do this again, I'd pick up a used set and take my time until they were perfect.


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## VR6TUNER (May 2, 2000)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (Northren vr6)*

This is awesome Paul! Exactly what I was looking for. Thank you very much.
Merry Christmas!


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## VW_IS_life (Oct 1, 2004)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (VR6TUNER)*

very nice http://****************.com/smile/emthup.gif really makes me want to do this, unfortunatly no compressor, die grinder or garage for me,,
I did the intake side, but thats aluminum and I used a dremel tool,, any idea if a dremel is powerful enough to do this on cast iron/steel?


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## need_a_VR6 (May 19, 1999)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (VW_IS_life)*

I don't know if a dremel would do it, I was having a rough time with the grinder! Wouldn't hurt to try though.


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## 708VR6 (May 20, 2006)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (need_a_VR6)*


_Quote, originally posted by *need_a_VR6* »_I don't know if a dremel would do it, I was having a rough time with the grinder! Wouldn't hurt to try though.

I used my dremel when I did the CRX manifolds and I used sanding rolls too, it just takes longer, but, is doable...


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## VW_IS_life (Oct 1, 2004)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (708VR6)*

well I had good luck using grinding stones on my intake manifold even though they would gum up quickly due to the aluminum,, i might try this, i'm sure i could find some exhaust manifolds for cheap at a junkyard 


_Modified by VW_IS_life at 11:01 AM 12-26-2007_


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## #1 S T U N N A (Feb 12, 2004)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (need_a_VR6)*

Good info = Pimp Status







keep pouring the knowledge Paul. http://****************.com/smile/emthup.gif


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## kevwithoutacorrado (Jun 9, 2000)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (#1 S T U N N A)*

dremel will work, but it took me probably 6 hours total and was no where near as deep as these pics. a dremel just can't get deep, and the bits are so small diameter that they disappear fast.


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## BIGNICKSGTIS420 (Apr 16, 2006)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (kevwithoutacorrado)*

Nice write up! Nothing better than free hp


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## yellowslc (Aug 29, 2000)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (need_a_VR6)*

http://www.ruffstuff.com is your friend for all porting needs.. 
I've done two sets of these.. my personal set and the other for a friend who begged.. 
Particulate respirators are a MUST. The cast iron/carbon mix will mess up sinuses for quite some time. Pick up a decent inline die-grinder and be prepared to make an utter mess. 
Butt dyno says they helped. 
R


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## need_a_VR6 (May 19, 1999)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (yellowslc)*


_Quote, originally posted by *yellowslc* »_
Particulate respirators are a MUST. The cast iron/carbon mix will mess up sinuses for quite some time.

Even with the mask I was messed up for a few days. 
Oh and my 198whp pull was done with that manifold on the car. That, a Joe head, ported intake and the modded VGI got 11whp at peak and 15whp+ at 7k, even with the 'small' cams.


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## isault (Mar 3, 2005)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (need_a_VR6)*

would it work for the trottle body?


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## cliffhuxtable (Jun 30, 2004)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (need_a_VR6)*

instead of this mod how bout making proper width gaskets?


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## turbo mike (Dec 8, 2005)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (cliffhuxtable)*


_Quote, originally posted by *cliffhuxtable* »_instead of this mod how bout making proper width gaskets?








youre supposed to port the manifolds to fit the gaskets, which helps in hp. 
are you trying to say just make gaskets that fit the stock size of the ports?
not trying to be a dick, just curious as to what you mean


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## cliffhuxtable (Jun 30, 2004)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (-THROTTLE-)*


_Quote, originally posted by *-THROTTLE-* »_are you trying to say just make gaskets that fit the stock size of the ports?

bingo. why do all that work?
curoius cause i made proper fitting gaskets when putting my new exhaust on.


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## turbo mike (Dec 8, 2005)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (cliffhuxtable)*

got it. reason to do all that work is bc it actually improves flow, and helps gain some power. just adding a correctly matched gasket wont do anything to improve power or flow. if youre an all motor guy looking for every little bit of power then this is a great idea. if youre boosted, theres other things to do prior, but this helps.
we will find out soon enough, i just grabbed a set of manifolds/downpipe and will dyno the car again soon.


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## Shteifen (May 12, 2007)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (-THROTTLE-)*

just clarifying why the exhaust manifold is "back welded" as in the first and second pictures.
is this to add extra strength to the part of the manifold that you are effectively making thinner?
-steve


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## need_a_VR6 (May 19, 1999)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (Shteifen)*

It's just the downpipe, welding the outside lets you grind the inside weld out and not have it come apart.


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## FLATBLACKMK2 (Oct 10, 2003)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (need_a_VR6)*

good write up sir.... http://****************.com/smile/emthup.gif


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## need_a_VR6 (May 19, 1999)

*Re: DIY: VR6 Exhaust Manifold and Downpipe Porting (FLATBLACKMK2)*

Thanks, I have to update some of the pictures the next time I do a downpipe.


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## mwm2 (Oct 8, 2008)

I planning on porting out a downpipe, but is it going to be pointless if I don't do the manifold too?


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## mwm2 (Oct 8, 2008)

mwm2 said:


> I planning on porting out a downpipe, but is it going to be pointless if I don't do the manifold too?


Bump!!! 
Because I need an answer to this before I start taking my exhaust off.


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## need_a_VR6 (May 19, 1999)

I wouldn't bother doing the downpipe unless the manifold is done as well.


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## mwm2 (Oct 8, 2008)

need_a_VR6 said:


> I wouldn't bother doing the downpipe unless the manifold is done as well.


Thanks!


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## cabriosnap (Apr 24, 2009)

great thread:beer:


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## pimS (Jan 7, 2009)

I started working on this over the weekend.
I'm fully gasket matching the head plus the exhaust manifold


First i ported 1 exhaust manifold, then i compared sizes with the head.
sizes are in cm's.

Oval port @ stock head









Oval port @ ported manifold









Round port @ stock head









Round port @ ported manifold










I bought an extra head for 30 euro's, so i took the gamble









Here you can see the difference between a ported vs non ported manifold










I'm planning on rebuilding this head, and swapping it with my stock head, over time.
I think i should wait with putting my 264 catcams in, just to see what gains porting the head and manifolds made.


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## cabriosnap (Apr 24, 2009)

be sure to report how you like the head and manifold port after you get it back together. looks like you took a lotta meat out of those exhaust ports


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## pimS (Jan 7, 2009)

Yeah there's a lot coming of it

I'll be running it on a vrt, but it's likely ill be doing a BTB comparison

turbospool start
max boost
power overall


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## need_a_VR6 (May 19, 1999)

*FV-QR*

I would port more of the exhaust ports, there's more to be done further in.. but you would have had to take the valves out.


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## pimS (Jan 7, 2009)

need_a_VR6 said:


> I would port more of the exhaust ports, there's more to be done further in.. but you would have had to take the valves out.


The head is stripped, ive got a grocery bag with all the valves etc in it
But my cutter is kinda rough wich makes controling it a lot harder once i get further inside the ports.
i'm allready going in for about 2 inches.

Going in any further at the ovals would greatly increase the risk of f*cking it up though:laugh: seeing that it's my first attempt ever at porting a head


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## pimS (Jan 7, 2009)

Finish the head and the manifolds today

exhaust manifolds



























it'l take some time to collect al the parts + doing the nessesary headwork before i will be able to put it on.


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## der_Architekt (Jul 5, 2005)

pimS said:


> But my cutter is kinda rough wich makes controling it a lot harder once i get further inside the ports.
> i'm allready going in for about 2 inches.
> 
> Going in any further at the ovals would greatly increase the risk of f*cking it up though:laugh: seeing that it's my first attempt ever at porting a head


Are you using an aluminum porting bit?

I dont have experience with that bit but figured Id ask to see how well it works.


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## pimS (Jan 7, 2009)

Yes i am, cost me 25 euro at the local hardware store










really neede to be carefull with this bit, not paying attention could cause serious kraters.
Because its so brutal the finish of the ports is'nt the smoothest ever, but i'm pleased with it.
But it never gets clogged up, and making the ports to the basic shape only took about 5 minutes each. after that i took a couple of hours *perfecting* it


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## JohnStamos (Feb 3, 2010)

*FV-QR*

Sorry to say, but that head is a giant paper weight at this point. 

"Portmatching" is the single worst thing you can do. It kills velocity.



A carbide burr shouldn't touch a head, til you have MANY hours of experience. Start with paper rolls, and just smooth the short side radius, clean up the bowls, ect, all while removing as little material as possible. 

Hogging out the ports isn't the goal here.


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## SlantSix (Apr 16, 2003)

1 Find flowbench
2 Get stock Vr6 head
3 compare those heads
4 post results here


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## pimS (Jan 7, 2009)

Find head for 30 bucks
Try anyway.


well see what it'll do @ 20psi


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## cabriosnap (Apr 24, 2009)

JohnStamos said:


> Sorry to say, but that head is a giant paper weight at this point.
> 
> "Portmatching" is the single worst thing you can do. It kills velocity.
> 
> ...



he said he's going to be boosting, so yeah, he really would want to open up the exhaust side as much as possible. as long as they have an "even" flow and a nice symmetrical polish in all the port's, that head should do fine after bowl blending and a nice valve job...

if he was going to keep it n/a and a semi stock build, then yes you are correct he would of just wanted to use flapper wheels and do a good polish rather then hog the ports out.


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## need_a_VR6 (May 19, 1999)

The flutes on that bit are gigantic. I use a bit for steel and wax to keep the material removal on head ports under control.


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## pimS (Jan 7, 2009)

need_a_VR6 said:


> The flutes on that bit are gigantic. I use a bit for steel and wax to keep the material removal on head ports under control.


But i did manage te keep it under control.
I know it looks a bit rough on the pic.s but irl it's quite smooth, and i decided that while i'm at it i might as well smoothen it out furter with a flapper bit.

At this point i spent more money on bits then on the head, so i was not really lookign forward to getting another(smaller) bit for the fine alu work


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## JohnStamos (Feb 3, 2010)

cabriosnap said:


> he said he's going to be boosting, so yeah, he really would want to open up the exhaust side as much as possible. as long as they have an "even" flow and a nice symmetrical polish in all the port's, that head should do fine after bowl blending and a nice valve job...
> 
> if he was going to keep it n/a and a semi stock build, then yes you are correct he would of just wanted to use flapper wheels and do a good polish rather then hog the ports out.



Sorry, but you don't seem to have any understanding of port work.


You do understand, that both a NA engine, and a FI engine are BOTH under pressure correct?

A NA engine is already under 14.7 PSI of pressure. 


NA/FI port work has the SAME principles. People that think FI needs a different approach to PE are very misguided.

Hence why so many people on here pull the "big cam's are bad for FI, SRI's are great for FI and don't need tuned runners to be optimal, ect" even though they have no idea what they are talking about.



You do understand, that port volume/cross section does not dictate flow correct? You know how many heads need WELDED up to decrease port cross section, to increase flow? Alot more then you'd think.


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## JohnStamos (Feb 3, 2010)

pimS said:


> But i did manage te keep it under control.
> I know it looks a bit rough on the pic.s but irl it's quite smooth, and i decided that while i'm at it i might as well smoothen it out furter with a flapper bit.
> 
> At this point i spent more money on bits then on the head, so i was not really lookign forward to getting another(smaller) bit for the fine alu work



I have over $400 into bits/hard parts.

One head takes me over $50 in disposable media.


You can't port a head with just a aluminum flute bit, and expect even remotely decent results, sorry. I VERY rarely need to touch a aluminum bit, as double cut carbides for steel/iron still cut WAY to fast.



I am not trying to bash you in ANY way, I just want you to have the best results possible, and so far it is a step back from stock.


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## need_a_VR6 (May 19, 1999)

*FV-QR*

It would take me forever to port with just abrasives, and it's hard to get the area around the guide right without them.


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## pimS (Jan 7, 2009)

I started off with other bits, an it took forever to make a litlle notch in it.

I'll post pics of the finished head after re-working it


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## Rockinred (Apr 3, 2008)

*Porting*

Just finished... Timing chains, MK4 head gasket, 10lb flywheel+sachs clutch, A/C delete, 2.9intake clone, and gasket matched intake and exhaust. Even with the lightweight flywheel and a/c gone i noticed very little loss of torque off the line. It feels great all through the power-band, i know its no dyno, but i noticed a good difference. I totally agree with you guys on taking it easy, but i don't think you need to worry unless you get the valves out and really do some work. There's still enough back pressure


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## VwDubDriver8 (Dec 22, 2011)

What does it mean to port the exhaust manifolds?


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## need_a_VR6 (May 19, 1999)

Did you look at the pics or google the word "port?"


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## Teh_Chris (Dec 31, 2007)

need_a_VR6 said:


> Did you look at the pics or google the word "port?"


Lols


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## Kahvel (May 6, 2011)

Sorry for bumping,but does someone have ever used aftermarket exhaust header?










Whats the sizes of ports?Is it okay to port exhaust ports and then use this header?Is this header useful?
Thanks guys!


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## need_a_VR6 (May 19, 1999)

I had that one. Spent 6hrs porting welding and re-porting to get it to not potentially suck. I would skip.


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## 00JetVR6mk4 (Jun 18, 2010)

back to life! 

Give me something to waste my time on while my cars sit for months not doing anything :thumbup:


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## vwuberalles2003 (Dec 1, 2004)

JohnStamos said:


> Sorry, but you don't seem to have any understanding of port work.
> 
> 
> You do understand, that both a NA engine, and a FI engine are BOTH under pressure correct?
> ...




LOL been telling people that forever. Try explaining volumetric efficiency to a forum crowd! Officially impressed by Stamos. Hasn't happened since Full house was OG!


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## Jeroentje (Dec 24, 2012)

Kahvel said:


> Sorry for bumping,but does someone have ever used aftermarket exhaust header?
> 
> 
> 
> ...


I have the very same header, professionally 'wrapped' for higher exaust heat output, tied up to a 200 cpsi catalytic converter, the gains are there but not as much as you'd expect. Headers on VR6's generally dont do much unless you tweak the rest of yuor exaust.










It rather saves hood temp alot with this setup


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## need_a_VR6 (May 19, 1999)

Keep those junk headers out of my thread


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## [email protected] (Jul 7, 2006)

Is this just as good as the tt downpipe or is the tt better?


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## need_a_VR6 (May 19, 1999)

TT should be better, but I have never tested both back to back or in any scientific(ish) way.


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## RDM_performance (Nov 22, 2013)

Where did you get your bits from I can't find anywhere that has them


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## need_a_VR6 (May 19, 1999)

I think I got the last set from Eastwood, but you can get them at Summit, Jegs, Speedway, etc normally.


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## RDM_performance (Nov 22, 2013)

I was hoping I could find them local but I'll have to order them I guess


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## need_a_VR6 (May 19, 1999)

RDM_performance said:


> I was hoping I could find them local but I'll have to order them I guess


Might be somewhere you can get them, might want to try a local welding supply.


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## veersixxx (Aug 3, 2006)

Ported stock cast uppers mated to techtonics "tt" no not audi... 2" down pipe
































































Vs.

S2 metalwerks


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## ticketed2much (Feb 18, 2012)

veersixxx said:


> Ported stock cast uppers mated to techtonics "tt" no not audi... 2" down pipe
> Vs.
> 
> S2 metalwerks



Nice comparison! What other mods does the engine have?


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## crannky (Jun 24, 2006)

Nice. Good to see the S2 makes some power and that a good port job is right there too. :beer:


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## MahTrek=] (Nov 6, 2008)

Sorry to bump an old thread guys, but am I understanding this correctly? Ported stock manifolds mated to the TT downpipe makes almost identical gains as the S2 header?


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## need_a_VR6 (May 19, 1999)

MahTrek=] said:


> Sorry to bump an old thread guys, but am I understanding this correctly? Ported stock manifolds mated to the TT downpipe makes almost identical gains as the S2 header?


Based on the dyno above, that would seem to be true.


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## MahTrek=] (Nov 6, 2008)

I'm surprised that I had a hard time with that concept...

I worry myself sometimes. Thanks Paul


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## Alingarhs (Dec 2, 2010)

need_a_VR6 said:


> I wanted to try and document this a bit while it was still fresh in my mind, but I had a race to get to at the end of the week so it's a been a bit since I did it. However, I will do my best to tell you what I did and why. I lost a few pics of the process but I'll describe the best I can what I did that isn't shown.
> To start off you'll need these:
> 
> 
> ...


Which one of those burrs would be the best to do this with? I understand having a varity is best, but I only want to buy one burr to do the downpipe and manifolds.


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## JohnStamos (Feb 3, 2010)

Alingarhs said:


> Which one of those burrs would be the best to do this with? I understand having a varity is best, but I only want to buy one burr to do the downpipe and manifolds.


If you only want to spring for one, buy a 1/2" flame tip double cut burr. It will do everything, just not ideal in all situations and you can't make large flat cuts.  A good one will set you back $30


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## Alingarhs (Dec 2, 2010)

Awesome, thank you for the info.


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## need_a_VR6 (May 19, 1999)

Yep, the second one from left. Glad people still care!


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## carsluTT (Dec 31, 2004)

i remember seeing this post back in the day and walking into my garage the next evening to do exactly what paul posted!..... good times and great info!


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## Redlineman (Dec 1, 2015)

Just an FYI;

There is a very good reason that factory tube manifolds/downpipes are "back-welded." This seems to allow a lot more heat expansion and helps to minimize resultant cracking, ESPECIALLY on turbo cars with their far higher EGTs. Using the stock iron manifolds on cars that have them will reduce this cracking potential, since the back welded downpipe is removed from the direct heat source. Backwelded downpipes might work just fine because of this.

The reason is likely that the internally welded flanges have a much slower return to ambient temperature because of the longer heat retention of the thick flange, and its proximity to the head if it is a manifold. Less long term heat stress because it cools much slower and therefore stresses the weld root (base of the weld bead) much less. It would be interesting to do a study of out-welded heat wrapped headers -vs non wrapped versions.

Ask anyone who thought they were improving their stock 944 Turbo manifolds by externally welding the flanges. Ask ME, as I learned this a long time ago fixing them. They all crack eventually, but out-welded flanges might as well be thrown on the scrap pile. With badly cracked examples, I have "spot-out-welded" them, with some success.


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## need_a_VR6 (May 19, 1999)

I have done a lot of sets for people and have never had one crack.


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## Redlineman (Dec 1, 2015)

need_a_VR6 said:


> I have done a lot of sets for people and have never had one crack.


As I mentioned;

It may work on the VW downpipe because it is not getting immediate heat direct from the port, and is insulated somewhat by the manifold. The iron block may have something to do with it as well, it likely being more "stable" than a 944 alloy block. The long length of the primaries, and the expansion joint in many of them (not sure when this came online) seals the success, no doubt. Expansion forces in the 944s even crack the tube version manifolds on NAs, although far less frequently than turbos.

Regarding porting & polishing, I'm going to offer that the porting part best be dropped from the equation here. Airflow dynamics are a very complicated and often counter intuitive realm, and unless you have a verifiable process for determining success, you are pissing in the wind. In the old days, casting of less sophisticated method and parts of less refined design could generally be made better by simply making the ports bigger (porting) as well as cleaner (polishing). I don't think that is the case anymore, especially with a head presenting such compromises in flow rate by its very nature, if not its production quality, as this one does.

Even if you had access to expensive modern modelling software that would relieve you of the drudgery of cutting, hogging, welding, and ultimately ruining a pile of heads before figuring out the best parameters, it would still be a highly time consuming and expensive process that still required actual testing to verify. It sounds like Bildon was well on their way to this point, but fizzled before they reached the summit. Even with the knowledge that they did seem to possess, they were scrapping a fair number of heads getting to where they... never got.

"Port matching" might better be left at matching the manifold shape - on either end - to the existing port in the head, so that there are no overlaps or mis-alignments that would disrupt flow. The ones I just did on my engine were extremely close already. Aimlessly hogging out head ports to match haphazardly stamped out gaskets - using the simple-minded bigger is better mantra - is more likely to kill flow velocity than increase it. The well chronicled lack of success that most if not all header makers had in improving performance on these engines should reinforce this notion of multi layered complexity quite clearly.


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## JF_T (Aug 1, 2019)

This is such a good thread with valuable info, to me its one of the best bang for your buck. I can't believe this has been buried for 7 years... This thread was about downpipe and exhaust manifolds and it got deviated with heads talk and what not... 

I've just complied my manifolds and downpipe, I have to say I loved doing it. I got them hot tanked first. I don't have pro tools and I invested about a $100 this was my first porting job too. Spent about 8 hours on them. I read everything Paul said and followed it to the T. Thank you Paul for sharing the knowledge. 
Cheers JF


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## need_a_VR6 (May 19, 1999)

Looks good from here!!


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## boozy (Jun 20, 2007)

JF_T said:


> This is such a good thread with valuable info, to me its one of the best bang for your buck. I can't believe this has been buried for 7 years... This thread was about downpipe and exhaust manifolds and it got deviated with heads talk and what not...
> 
> I've just complied my manifolds and downpipe, I have to say I loved doing it. I got them hot tanked first. I don't have pro tools and I invested about a $100 this was my first porting job too. Spent about 8 hours on them. I read everything Paul said and followed it to the T. Thank you Paul for sharing the knowledge.
> Cheers JF


What did you end up using to port?


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## JF_T (Aug 1, 2019)

I've used a good mix of what's in the picture. Short porting bit around openings, mainly used the same bit but 6" long to reach all around deep. Got them on Amazon, both I paid $30 CAD. Even if they are cheap, I was surprised as they were completely straight, no wobble with my fixed speed Makita 25 000 rpm (which is the speed recommend for the bits). I did the rough with one and when it started to not cut as much because it was dull, I've used it all over again to smooth things out. The Flex-hone in 1" was perfect to make the bends and long reach. The bends are the hardest since the bit is straight. I didn't "just" port where the gasket meets to ramp it up but I tried to make a slow progression towards it from the deepest I could. I finished by the gasket match, not started with it. I finished all of it with a Dremel (bought the flex shaft extension) with 80 grit drums and cones for the bends. I hope it makes sense... Cheers

YUFU-6" (152.4mm) Extened Extra Long length Double Cut Carbide Burr File (1/2" cutter Dia X 1"Cutter Length) with 1/4 shank dia Cylinder Shape With Radius End SC-5L6 ,Pack of 1 : Amazon.ca: Tools & Home Improvement



Amazon.ca


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