I wish to modify my B16 DC header to house a 2.5" collector. I might just cut the existing 2" collector, move it up back a bit and weld a 2.5" pipe. Has anyone done this before? Do you think its a good idea or would i waste good engineering of a well designed header?

 

anyone?

 

Go for it. You wont know till you try. I'll be doing this to my stock exhaust manifold soon.

 

I put a 2.5" collector on my Greddy 4-2-1 recently. Here's what I did.

* I bought a 2" to 2.5" transition from burns stainless.

* cut off stock collector right where the 2-1 merged.



* put the small end of the transition in a vise to oval it out a bit.

* welded it on


*added flexpipe and flange (not pictured)



I know you have a 4-1, but maybe this will give you some ideas..

yes, I know my welds suck. first time welding..

 

Looks good how you gonna hook up the exhaust? weld it?

 

sorry for hijacking your thread....but unless its the bigger size all the way from the merge to the tip, it will do nothing for you, and in fact will probably hurt performance. qall your doing is taking all the exhaust from all the cylinders, forcing them through a 2 inch outlet, then they just expand into a 2.5 inch outlet. unless its 2.5 all the way back, that exhaust still has to go through that 2 inch collector. therefore, while the exhaust is in the 2.5 inch tubing...it only has the quantity to fill up a 2 inch pipe, since thats what it orignally came from. this is also a common misconception when it comes to cylinder heads....again sorry for hijacking your thread, just wanted to give you a heads up.
kyle

 

It's 2.5" all the way back, and I know it may not be the best way to do it, but the header had the collector broken off when I got it anyways, so it wasn't even on my car before. Plus, I needed a way to make it merge into my 2.5" exhaust. As for the question on how its connected, I attached a 3-bolt flange on the flex-pipe and on my cat.

Anyways, it was a huge improvement over my 91 teg LS 4-1 shorty stock manifold.


Modified by Mr_CRX at 10:15 PM 6/1/2005

 

Thats true. So i was thinking cutting the header from where the 2" pipe starts and replace it with a 2.5". If the JDM 4-1 is an exact replica of the DC4-1 except for the 2.5" collector, then this modification shouldnt harm the design.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by blueoval557 &raquo;</TD></TR><TR><TD CLASS="quote">sorry for hijacking your thread....but unless its the bigger size all the way from the merge to the tip, it will do nothing for you, and in fact will probably hurt performance. qall your doing is taking all the exhaust from all the cylinders, forcing them through a 2 inch outlet, then they just expand into a 2.5 inch outlet. unless its 2.5 all the way back, that exhaust still has to go through that 2 inch collector. therefore, while the exhaust is in the 2.5 inch tubing...it only has the quantity to fill up a 2 inch pipe, since thats what it orignally came from. this is also a common misconception when it comes to cylinder heads....again sorry for hijacking your thread, just wanted to give you a heads up.
kyle</TD></TR></TABLE>

It'll improve velocity.

 

it will improve velocity past that point... before the restriction is just backpressure

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mr_CRX &raquo;</TD></TR><TR><TD CLASS="quote">It's 2.5" all the way back, and I know it may not be the best way to do it, but the header had the collector broken off when I got it anyways, so it wasn't even on my car before. Plus, I needed a way to make it merge into my 2.5" exhaust. As for the question on how its connected, I attached a 3-bolt flange on the flex-pipe and on my cat.

Anyways, it was a huge improvement over my 91 teg LS 4-1 shorty stock manifold.


Modified by Mr_CRX at 10:15 PM 6/1/2005</TD></TR></TABLE>
i think what's he trying to say its that the your added piece is still 2" where it meets that header,so it's really no different than having the old size collector,then stepping up to 2.5".i'd think to see any real gain,you'd need 2.5" for that entire piece-maybe cut further back where the two merged pipes have a larger diameter,then oval out a straight piece of 2.5" pipe,then weld it on like you did.
either way,it turned out well,and looks good.
Chris

 

i've been thinking of exactly the same idea for my DC 4-1 with tiny collector. i wanted to just take a band saw or something and cut the marge area where the area is the same as a 2.5" circle, then bend the end of a 2.5" piece of tubing to fit it and weld it on. then weld a 2.5" flange on the end and slap it back together.

 

.

 

This is my TSX DC header that I used on my EG K20 swap, I cut off the stock collector (only 2") and welded on a 2.5" pipe.

 

I did this mod. a few years ago and it made good power..
Below is my setup.. Made 207 whp and 140.5 tq
https://honda-tech.com/zerothread?id=1263436

Here is the 1st one made with my old banged up DC header...


This is the 2nd one made with a brand new DC header I bought for cheap...



Stock collector..

 

Damn. Good job! Might just do that

 

cool