Back in my drag racing days (Oh, no, not another old story) I used to port and polish my small block Chevy heads using a pattern I got from none other than the famous (late) SMOKEY YUNICK . They were as effective as any of the contemporary heads and the little 327 Chevy would pull hard out of the hole breathe fire on the top end.
So I thought I would try the same with the little Cummins 3.9 litre.
Starting with the stock casting,exhaust gaskets and a high speed grinder equipped with a new carbide tool. Place the gasket on the turbo end as shown and mark out the shape to be made. Then grind and grind and grind and check the sizes and grind and grind and grind some more until the gaskets and the ports match and then enlarge the whole passage until it is the same size and shape.
Lifes just a GRIND!
This may look less impressive but a flow test before and after showed 50% reduction of restriction or 100% more flow! It is a matter of how you do the math. We will start the dyno testing using this cast iron "TRI Y" four into two into one as it enters the turbocharger. It is centred on the ports and very short so should retain more heat than the fabricated headers like the PYTHON 4BTX. The cost with the labour factor of 8 hrs @ $50.=$400.00 is less than the custom fabricated @ $1250.00
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