ITRCA

im wanting to buy a friends comptech 4-2-1 header, but it is on his 99 civic si. I realize that the header will bolt up to the head, but is this header the correct length and is the o2 sensor bung hole in the correct spot? from looking online, there are different part numbers, but both show a 2" collector. thanks.

It won't fit. The header for a GSR/ITR will fit an Si, but not the other way around. The b16 is shorter overall than the b18, so the Si header will not be long enough to clear the oil pan.

shivers wrote:It won't fit. The header for a GSR/ITR will fit an Si, but not the other way around. The b16 is shorter overall than the b18, so the Si header will not be long enough to clear the oil pan.

I know this is correct for the stock parts, but I'd suggest calling / e-mail comptech they might have made it a tad longer for dual use.

Bbasso wrote:

shivers wrote:It won't fit. The header for a GSR/ITR will fit an Si, but not the other way around. The b16 is shorter overall than the b18, so the Si header will not be long enough to clear the oil pan.

I know this is correct for the stock parts, but I'd suggest calling / e-mail comptech they might have made it a tad longer for dual use.

Good call, Rob.

I called Comptech and stayed on the phone a good while as he was trying to find specs and product information for both headers. The best he could do was guess and tell me that it might be a tight fit and that I would have to use a different cat because one header is longer than the other. Due to his lack of confidence in what he was telling me, I am not about to take his word for it. I guess I will just scratch this header off my list.

just a thought, would it be possible to have a muffler shop custom build a bolt on pipe between the header and the cat?

of course it would, however, if it's going to be a tight fit or rub on the block or oil pan and cause something to crack.... No Thanks.

Bbasso wrote:

thanks. that sums it up very well.
Now I know in case someone asks this question again : )

It's actually the height of the blocks where the difference lies. The b18 blocks are 7mm taller than the b16. The cat converters on the Si and ITR are the same length, so the guy at Comptech sounds a little confused.

shivers wrote:The b18 blocks are 7mm taller than the b16.

Block or head?
I thought block at first... then head, so I put head.

Either way...

Block because of the longer stroke of the b18 (87 vs 77).