peejay wrote: ↑Tue Oct 30, 2018 6:41 pm
I'm going to declare the patient cured. Or at least, I feel comfortable that its cooling system is not going to overpressure. (One of the hoses that ruptured had a burst rating of 250psi!!)
The key I think is a combination of an overdriven instead of underdriven water pump pulley (the manufacturer does not offer a larger one, and insists that nobody has ever had this kind of problem before) combined with that Trick Flow intake manifold. The bypass passage on one of these engines is a maybe 2" length of 5/8" hose going straight from the intake to a port in the water pump. In the water pump and in every other Ford manifold I've seen, it is a pressed-in thinwall tube. On this particular water pump the tube had a roughly .550" ID.
The Trick Flow manifold, however, does not have a pressed-in tube, it has a 3/8" NPT female thread, into which was threaded a 3/8" NPT-to-5/8" nipple... which was under .400" ID. Some simple math says that this was about half of the area that it should have been. Opening up that nipple just short of making the threads weak got peak block pressure down to 75psi at about 6000rpm. A restrictor was sized to ensure that the heater core never saw over 30psi. Once the thermostat opens the block pressure never goes over 25-30psi.
Incidentally, I decided to measure block pressure on a 3 liter pushrod Taurus that was available. It would build 45psi at 3000rpm.
The older I get, the more weird sh* I see like this... nothin' you can really do about it but find out exactly what is happening and observe what might be causing it.
Im kind of amazed that a conventional style water pump could generate anything close to 250 psi +. I admit I dont know much about cooling systems (or anything else) but I have always looked at an automotive water pump as more of a coolant circulator than a pressure source. I thought coolant temperature increase was the source of alot of the indicated pressure, as in when a hot engine is off and there is still pressure until the engine cools off.
I have seen a lot of hoses blown off because of extreme coolant temperature , but to see that kind of pressure I would expect to see cylinder pressure leaking into the coolant system.
I used to disable the water pump ( take the belt off, etc.) and fill the radiator full and start the engine, with the cap off and watch the coolant level and for bubbles. If possible load the engine a bit. I found it to be quick test and found a lot of problems that way.
I just cant imagine an automotive water pump generating close to that much pressure even dead headed.
Its very interesting, but I am glad you have it sorted out.
Jeff