Hey everyone, So since I cant justify spending over $800 for a quality header for my car, me and my friend are going to make one. He has fabricated a few headers before, including some tubular manifolds for evo's and sti exhausts. So Im going to give him an exhaust manifold gasket so he can cnc machine the flange. As for as the runners go, what size would you guys reccomend and same with when it funnels down from 4-1. what size should that be too? Im going to be running catless with a resonator. I already have an invidia catback. Also if anyone has any suggestions, let me know. We might possibly start to produce these as an afforable solution with good quality.

 

why bother ? just modifie the oem manifold

just my 2 cents

 

I would run a little wider than the ports for the primaries then get a 2.5" collector so you have no change in diameter when connecting to the exhaust. I didnt measure the port width when I had the head off so you might want to look into that.

 

I have a custom header 4-1 with high flow car & 2.5" collector on my MINI. It was around 8hours of work. Total cost: 1150$ CND.

http://www.rawtekinc.com/Mathieu%27s...ooper%20S.html

I don't think you can't go cheap with custom work if you want quality, service and reliability.

 

$1150 with the exhaust? If so thats pretty good. Header alone thats some expensive gains but it does look nice

 

Nah, the exhaust was an another 1200$ CND more. There is a 12 hours work on the exhaust. All the header and exhaust are in stainless steel 2.5" and 2" for rear mufflers pipes. I have a Hushpower II as main resonator (it was Vibrant resonator on the picture, it was too loud). So, total cost is around 2400$ CND... but, I have an unique deep sound. I wouldn't never go back!

 

Yeah exactly. Like my buddy knows what he is doing when it comes to fabricating, he says it will only take him about one day to make. I will post up pics when its all done.

2mD-How exactly do you modify the oem manifold?

 

Dont bother modding the OEM manifold. The guy might be talking about removing the cat for a straight pipe. A lot of restriction is in the short runners and abrupt collector not to mention the small diameter of the primaries

 

When people talk about modding the oem manifold, they're usually mean gutting the innards of the pre-cat only,
which helps flow some and usually doesn't throw CEL codes.

 

While I'm all for DIY projects, I think you need to spend some time defining primary pipe length and diameter for the target torque peak rpms. My experience with header design is on (normally aspirated) motorcycles, so perhaps a forced induction application is less sensitive to these variables. If you are considering trying to sell these as a sideline venture, I would highly recommend that you do independent, 3rd party dyno testing before and after to document any performance gains.

Regards,

--Rich

 

Another friend of mine has a dyno that I am able to use basically 24/7. So I will definately have results.

Im not really worried about check engine lights, I can always just get o2 spacers or a simulator even.

 

most of the after market headers have way to big primaries
that might be good if you want peak power on high rpm, but most of us dont rev past ~7k


the most basic way: just empty the pre cat ( like cristo wrote )
only that, usualay gives you approximately +5-10Nm from low rpm till red line and +5-10hp. ( while still looking stock )

the better way to do it is to remove the whole pre cat housing and use pipe: no changes in diameter -> less turbulence ( in the picture i did that to the one below, but fitted the housing over the pipe to make it look stock the one above is stock, except the flex joint )

exchanging the part between the pre cat and the flex joint with some pipe helps too ( again: no changes is diameter )



the collector can also be improved...



increasing the ports ( so that they match the cylinder head ) is also not a bad idea

its pretty simple: just think about what would be in your way if you where the exhaust gas

one observation: i ran a 100cpi High flow cat for some time ( installed it in combination with various other parts )... after a while it simply was way too loud, after i got rid of it and fittet the original, i found that i didnt loose any torque or power at all.
seems to me like getting rid of the small pre cat is WAY more important then changing the main cat...


just my 2 cents

 

this thread is hilarious coming from any other car land (JDM, domestic), the stock exhaust is actually engineered, VS just routed any old way to the back of the car... Guess I'm just impressed by the stock system seeing it off the car, but the small improvements to it should flow better by all means. Great reference thread

 

Modified OEM examples.

https://www.northamericanmotoring.co...m/DSCN1086.JPG
https://www.northamericanmotoring.co...m/DSCN1353.JPG


Custom non-comercial example.

https://www.northamericanmotoring.co...m/DSCN0915.JPG

 

I am going to be putting another resonator in my exhaust, Like a glasspack or cherrybomb muffler to help quiet it up a little.

 

A five inch Magnaflow will attenuate high notes creating a rich tone.