Port Matching

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swanny

swanny

Senior Member
I just picked up a stainless OBX 4-2-1 header for my 95 GSR and I was wondering if anyone had experience port matching. Any advise or specs on what it should be bored to? Thanks
 
Well usually people take some of the extra welding out of the jdm ITR 4-1 header since there is welding that can be taken off, chances are your header is flush with no extra welding.
 
im refering to the flange that bolts to the head. the ports on the flange are not the same diameter of the tubing on the exhaust, there smaller. so i figure boring those out to the width of the tubing would increase flow.
 
you could open it up a little, but gains are going to be literally nothing, so really it's not worth the time, and bits..
 
Ok let me try to re-phrase this. I am trying to bore out the flange on the header that bolts to the head since the diameter of the flange is approximately 4mm smaller than that of the exhaust tubing in hopes of some increased flow\ hp gain.

Other things I would like to know:

-Are the holes in the exhaust gasket are the same diameter as the exhaust ports on the head?

-And since I haven’t already looked, how many O2 sensors are there and where are they located?
Again, this is on a 95 GSR sedan
Any knowledgeable replies appreciated, thanks
 
you should just try a test fit of that header first since its obx.

since your obd1 you have 1 o2 sensor. and you should just leave your exhaust ports alone, they are supposed to be stepped like that so the shockwave in the exhaust tubing has a harder time getting back into your head.
 
I thought 95 was the first year of OBD2? :shrug2:
 
just to ad to what Saturn_Boy already mentioned.

-the O2 sensor should be on your collector, it's where the header and cat meet

-the exhaust gasket should be fitted to your head.
 
Any more input? its all going on tomorrow.
 
ya dont use a gasket to port. Gasket makes just make somthing that seals and dont research ideal port sizes. second as saturn said some poeple belive in the step method others dont it really your choice and is usally based on which works better for which aplication.
 
don't port your exhaust ports on the head, you can clean the shit off of it but I wouldn't go ou and buy a dremel and go to town on the head..
 
Originally posted by JDMilan@Sep 29 2003, 12:41 PM
don't port your exhaust ports on the head, you can clean the shit off of it but I wouldn't go ou and buy a dremel and go to town on the head..
Click to expand...

i was thinking of boring the flange on the headER not the head. if all goes well it'll be in tonight, the parts didnt come in until friday afternoon so i had to hold off til tonight.
 
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