Mikuni intake manifold runner size

[madkaw]

I broke out my Mikunis to look them over for the future install on my Z. I wanted to check out jet sizes and such to get my base line for future tweeks. I went thru great trouble to gasket match my SU's to my e88 before install and thought I would do the same for the Mikuni set-up. But WOW, i couldn't believe what I saw when I layed an extra intake gasket against the manifold. Am I missing something here or is this right? That is a huge difference-not sure what to do here guys, I just seem baffled over this. These are 40phhs by the way.

Comments please.....

[Phred]

Does the gasket fit the port face of the head? If so, measure the I.D. of the Int. port in the head, and the I.D. of your man. at the flange where it contacts the head. Whats the difference? Two things coud be at work here. If the int. man. is new, the I.D. could be on the small side. Which is good. Or if the head has been hogged out too much at the flange, causing the difference in size/fit. It's ok to dump a small int. man. into a larger head port, but not the other way around. In fact, unless its a race car, you will probably loose perf. by opening up the int man. to match a large int. head/port. The key for a street car, is to maintain port velocity, and this is lost when a port is inlarged too much.

Phred

[madkaw]

The head ports are basically stock, all I did was gasket match for the SU manifold. It was suggested that this manifold was supplied for many applications including the l20, so the runner port was kept smaller. I understand what your saying but I can't believe it would be better to leave that much of a size difference. I am also looking ahead to possibly a blow thru set up, so I would want a good gasket match on the intake to head ports.

[240ZGL]

Yes it's normal. Mikuni manifolds are like that.