Coolant Flow and S4 NA Center Iron Compatability
 

Quick question for the rotary experts around these parts. I just bought a fairly low mileage S4 NA motor that I am building for a turbo. I am keeping the stock rotors and housings and replacing the 6 port front and rear iron with turbo 4 ports.

My question is regarding the center iron and its compatibility with a turbo setup. I have read that you can use the NA center iron on a turbo motor if you enlarge the port correctly and drill & tap an extra hole for the manifold. This sounds reasonable to me aside from the weird S4 NA canter iron with the EGR cavity that blocks 2 of the main coolant passages near the top on the irons (red arrows in the picture). Since it is only in the intake area, it should be a cooler part of the motor, but I still feel it would reduce the cooling capabilities of my motor.

Has anyone ever had any experience running a S4 NA center iron in a turbo, and if so did you have issues with coolant temps?

https://cimg2.ibsrv.net/gimg/www.rx7...c870f29d87.jpg

I don't have the answer to your question, but I'm also interested in finding out.

Secondary question though in case someone who has tried it sees this; Assuming you don't need EGR functionality, could you block off the port up top and the one on bottom (IIRC) and then drill out the coolant passage areas and grind to match the TII version?

I was in the opposite boat as you, but FWIW here's my experience. I was rebuilding my S4 NA and I found a chip in the coolant seal groove on the center iron. The only iron that was available was a S5 Turbo center iron so my engine is all S4 parts except for the S5 turbo center iron. I noticed the difference in coolant passages too, but I figured that the extra cooling wouldn't hurt my case.

I understand that you might have diminished cooling so I get your concern, but as far as compatibility to whether it will run, you will have no issues. That being said, there are plenty of turbo-NA engines that still use the stock NA irons with the blocked coolant packages from factory. As long as you have good tuning and a good cooling system, I don't think you'll have any cooling issues on the street. Harding racing is another issue though.

Good to know that at least physically, the center iron should work. I will have a well built cooling system to handle turbo heat, but right now I'm just trying to balance being cheap and future-proofing. My car will be primarily a street car with very occasional trips to a track so I might be okay, but I think I am leaning toward getting a real turbo center iron or a S5 NA center iron as cheap insurance.


Unfortunately, they can't be drilled out and filled because the egr cavity would fill with coolant with nowhere to go which leads to additional problems.