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Old 01-17-2013, 07:00 PM
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Originally Posted by slownugly View Post
Hey guys,
Im trying to get my motor buttoned up so I can attempt to start it, my question is with the heater hose routing?

I am not running a heater (for now), and I know if your heater core goes out you can loop the system until you fix it. My problem is that to me it doesnt look the best having a big loop of heater hose right on the front of the engine. Can you plug the water pump and intake ports without any adverse affects?

Ive tried to read articles on it and am getting 50/50 answers and cant really pinpoint the answer, so I figured Id just ask the forums.

Also, I am running a performer rpm on a 350 with no bells or whistles and am trying to find a schematic of all the ports and bolt holes on the intake so I can plug what i dont need or bolt up what I do need...anybody have any suggestions? Thanks guys!
Here's the real skinny DON'T! Unless some other criteria, Iíll get to at the end, is met.

There are two major reasons for keeping the large bypass that route's through the heater. The heater is a secondary consideration where the closed thermostat bypass can be used to provide early cabin heat while doing its primary job of protecting the engine's insides. A lot of guys believe that the small bypass hole on the right (passenger side) front is for this purpose, it is not! The small hole is intended to balance flow between the left and right sides because the pump output naturally favors a bit more coolant flow to that side as a result of the direction the pump shaft rotates. This in my opinion this is another case of GM over-engineering something inconsequential to grocery getting driving styles and inadequate to the needs of controlling the problem when racing.

- The first major reason for the thermostat bypass is to prevent the pump from cavitating when there is little to no coolant flow through the engine with the thermostat closed. This froths the coolant trapped in the pump putting bubbles into the coolant passages when flow starts. The other problem is that it vibrates the pump shaft which in-turn bounces the seal and bearing probably shortening their life but this is something that may only be visible in the lab when testing two identical test parts. With the normal variation of quality between production parts I rather doubt that an intelligent ape could point and grunt out that the failure was due to cavitation.

- The second reason is more important, it has to do with controlling nucleate boiling in the very hot spots of the head that occurs without sufficient coolant flow when the thermostat is still closed. The critical areas are around the sparkplug seats and the exhaust valve seats, especially the paired exhausts at the head's center. Without sufficient coolant circulation localized nucleate boiling deprives these spots of coolant, they dry out and super heat. The very hot metal around the seat presses against the colder metal of the outboard head, this results in cracking the casting structure, where buckling occurs between the paired seats the casting releases the head gasket resulting in a compression pressure loss from one cylinder to the other, in extreme cases you get gasket failure. The valve, also, can't make a tight seal on the distorted seat and will leak resulting in miss-fires and possibly burnt valves. Like nobody's ever seen this on an SBC before! Right?

Aluminum heads are more tolerant of the number two situation because even as a casting aluminum is softer, more resilient, is less brittle and transfers heat faster than iron. So if you're using an aluminum head you're somewhat less likely to have these problems but the potential is still there to distort the head enough to lose head gasket seal and sometimes the pressed in hard seat comes out with costly result.

For engines running metering washers instead of thermostats this bypass isn't of concern, but for a street engine set up this way it takes a long time to get the engine to operating temperature which brings a new and nasty host of problems especially if you don't live in the deep south, east or west.

On a Risk Analysis this probably looks to have a low to moderate risk of occurrence, but it has a high risk of consequence. Meaning that it might not happen (largely dependent on how hard the engine gets pushed for power when cold) but has a really high cost to fix if the failure occurs.

That's an engineer's perspective.
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