CIVIC4G.COM  1988-1991 Honda Civic 4th Generation

When I was looking at my ebay header, I noticed the flanges between the upper and lower pieces weren't lined up with the header tubes. In some places there was as much as a quarter inch of overhang. I went ahead and installed the header, got a small gain, and so I just left it.

Today I decided to pull it and grind the flanges so that they are flush with the header tubes. Believe it or not, I did get a very slight gain from doing this. I also removed any rough edges from the factory welds (on the inside), and sanded the flanges to a mirror shine.

Here's a pic of the downpipe (no pic of the upper part):


EDIT: Be sure to wear a dust mask...I didn't and now I'm coughing up bits of metal :roll:

If they were so misaligned then they were creating turbulence aided by the badly made edges. That turbulence although a little, impedes the continuous exhaust flow, aligning and polishing all the edges could really help improve the performance of the header. You should also check the mating surface where it connects to the head and the size of the header openings vs the head exhaust ports, using a rotary tool you may even polish the ports of the header or match them perfectly.

Well whit no disrespect I can say "Made in China" & pls change it

"el_jelly" wrote:If they were so misaligned then they were creating turbulence aided by the badly made edges. That turbulence although a little, impedes the continuous exhaust flow, aligning and polishing all the edges could really help improve the performance of the header. You should also check the mating surface where it connects to the head and the size of the header openings vs the head exhaust ports, using a rotary tool you may even polish the ports of the header or match them perfectly.

Yeah the header openings were fairly good, but I went ahead and grinded/polished them yesterday just like I did on the middle flanges. I also milled all 3 mating surfaces with my orbital sander, measured with my micrometer, and was able to get them pretty well even.

And yes they were badly misaligned, the flange was blocking off 2 tubes over a 1/4in in some places, but in other places it wasn't so bad.

how much did you pay for your ass dyno??? :lol:

"civicjdmb16a" wrote:how much did you pay for your ass dyno??? :lol:

The university lets me use the automotive dyno for free.

that's cool, if they have some flow bench testing facilities drop the header on that and tune it!

"cougar289" wrote:

"civicjdmb16a" wrote:how much did you pay for your ass dyno??? :lol:

The university lets me use the automotive dyno for free.

Nice its a chassis dyno?

Yeah it is, I'm not sure how accurate it is though because it's pretty old and worn out. I think the brand is like Taylor or something, it looks like its from about the 80's.

I wish they had some flow testing tools there, I'd like to see some flow charts of a pm9 head.