just matched up my Holley Airmass header (for a 91 Civic Si) to the new ZC exhaust manifold gasket to see how much port-matching
would be needed, which is not much. Basically, the port on the ZC is a little higher than that of the D16A6, so I will need to grind out
some of the area above the port opening on the header flange. This isn't too bad, but I am concerned about the corresponding area
below the port which will be left void; specifically, will it cause turbulence in the exhaust port?

Anyways, does anyone know of a better solution? I have heard of using the top half of a 87-89 Integra header with the bottom of a 88-91
Civic/CRX Si header, but that sounds expensive.

any info appreciated

 

so are you saying that there will be a "low pressure" area on the bottom of the opening of each runner? If so that would cause a vacuum. Which would help evacuate exhaust gases, idk, I'm tired and might not be understanding what you are saying?

 

hmmmn, I'm no engineer, but I would think that a slight mismatch between the exhaust port and the header flange/runners (leaving
a void at the bottom of the header flange) would not be able to create enough of a vacuum to overcome backpressure. What I am
concerned about is creating turbulence in the exhaust port, because that would decrease efficiency.

What I really need to know is what header is available that matches to the stock DOHC ZC head, and will fit in the engine bay of an 88-91 Civic.

anybody????

 

I may be wrong here, but any header made for the USDM 88-91 si motor should fit the zc, but you will have to grind it out always, becouse the ports are shifted.

I finally got around to getting the stock ZC manifold a while ago. Im pretty happy with it. Looking at this thing, its pretty damn good. Looks like it probally flows about as much air as the DC header for this car did. So if you can get your hands on one, I would highly recomend it. If not, just get a header made for the 91 civic si (DC or whatever else you like) and port it out a little.

 

Oh yeah, and as for using the teg upper and civic lower, not sure how that would work. May be great, may not, someone here must have done it before. But as for being expensive, I cant imagine your local wrecker charging more than 25 bucks for a stock manifold.

 

gregv, I used a 'ported out' Neuspeed 91 Civic Si header on my ZC. I don't know how much of a problem the opening under the port would cause, but I can tell you that there is a noticable gain with the ported header. You won't be loosing any power. I know that doesn't tell you much, but if you were worried about a power loss over stock, you won't see that.

You can use an 89 integra upper with a Civic lower, but its pricey, and doubtfully worth it on a basically stock motor. I would guess that the difference based on any turbulance in from the mismatched ports would be unmeasurable.

I think you can also use an 89 integra complete header, you just have to extend or shorten either the down pipe, or the B-pipe. I'm about 25% sure of this though, so tripple check. I really don't know for sure, but I wanted to throw that out there.

 

Hey Greg,
The port mismatch is not the best, but I doubt you'll notice any adverse effects performance wise. Does this mean the swap is in progress?

 

That will prevent some reversion. If you still don't like it, port match the exhaust port to the header.

 

Kamikaze bolts right up - no porting necessary. Simple.

 

I had the DC one before I went FI.....it was.....ok. couldn't notice much of a difference to tell you the truth.

 

thanks dudes; sounds like I'll be doing some porting today.

Oh yeah, swap finally underway