This question comes to my mind but I can't tell which is better. Suppose, I am going to build a S4 NA. I have two choices of combination of irons (below). For either case, irons are used as stock (no porting) and S4 LIM will be port matched.

A. All TII irons
B. S4 NA front/rear irons (no sleeves will be used) + TII center iron

Since it looks 6 port irons have bigger ports and later port closing timing, they might work as well as TII front/rear irons, or even better than TII front/rear irons. However, aux ports have terrible dead-end runner shape, it might not work as well as TII irons.

Any experience or thoughts?

 

Use the T2 irons.

 

t2 and n/a middle irons are the same with the only difference being an extra threaded hole for the LIM, just for reference.

 

Wrong. The TII center iron has a larger port. If you're set on using an NA manifold you are pretty much stuck with NA front and back irons. To properly port match the NA manifold to a TII iron would require welding up the NA manifold and lots of grinding. Otherwise you have lots of intake manifold port that runs into a brick wall when it meets the TII iron.

If you are doing no porting at all use the NA front and rear and TII center irons.

 

The "larger port" on the TII irons is just a larger cutout. The actual casting of the center irons is the same, so if you are doing any porting it's basically irrevelant which center iron you use.

Since this is an NA car, I would stick with FUNCTIONAL port sleeves, and do some basic porting to the 6 port irons. Leave the sleeves in place so you don't have crappy low end due to excess port area.

 

The TII has a larger port. More duration. I believe the original poster said "irons are used as stock (no porting)". In that case the TII center iron would be the choice that provided a larger port.

 

Just reread...no porting...Wonder why? In that case use the TII center iron.

 

imo though i would do as aaron said and stick with the 6 port irons and port them and use the the T2 iron since it won't need any extra porting.

 

For my engine, I went with your combo B, my NA centerplate was cracked and a t2 center was the only thing I could get on short notice.
The t2 center plate has a rectanger port that the S4 NA LIM doesnt have a provision for so youll need to plug up the port, I used high temp epoxy putty. Just not sure how important that port is if you ever wanted to try a S5 manifold swap. Anyone know the answer?

 

Thanks all. I think I get an idea.
I said "no porting" because if I street port them, it is clear that TII irons have advantages, but it will probably be end up with using TII LIM/UIM (more modification and more cost). However, if I use only TII center iron, I thought I get larger primary ports (I have both irons and TII ports are larger) and I could utilize modified NA LIM/UIM (I thought it requires less modification).
So, at this point, it seems using TII irons makes sense with port modification to aim more high end power, using NA+TII irons would be good to go with woking 5/6 port sleeves to keep good low end and maybe a few extra power.

 

good point and a problem i just ran into today on an engine i built with this exact setup described in this thread.

the S4 T2 middle iron has the EGR port under the middle LIM ports, this port runs down to the exhaust manifold which would cause an exhaust leak if left exposed. a temporary solution would be to flip the exhaust manifold gasket to cover the port but a more permanent solution would be to block port in the exhaust manifold.

something you will have to also consider while doing this build.