http://carcraft.com/tipstricks/3027/index3.html

"Chevy Water Pump Bypass Mod

As a last resort on hot-running vehicles not equipped with a heater-water shut-off valve, restrict the small-block Chevy water pump bypass (arrow) by tapping it 1/8 NPT. Install a 1/8 NPT Allen-head pipe-plug, then drill a 1/4-inch hole in the plug to maintain some necessary bypass flow. This improves cooling by forcing more coolant through the radiator after the thermostat opens.

If the heater-hose fitting is at the rear of the engine near the distributor, you should also modify the thermostat to provide sufficient bypass circulation by drilling two 1/8- or 3/16-inch holes in the thermostat."

NOTE that it says only do this if you have a full flow heater that does not shut off water flow. Remember all the water going through that heater is NOT going through the radiator to be cooled. Early Chevys had 1/4 inch restrictors inside the heater hoses to prevent excess flow and to prevent blowing up the heater core at high rpms. X

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Looks like your link got mangled somehow. It shows info on AFB carbs.
JA

Ooo.. how embarrassing xntrik..

http://carcraft.com/tipstricks/3027/index3.html




NOTE that it says only do this if you have a full flow heater that does not shut off water flow. Remember all the water going through that heater is NOT going through the radiator to be cooled. Early Chevys had 1/4 inch restrictors inside the heater hoses to prevent excess flow and to prevent blowing up the heater core at high rpms. X

Not just early Chevies... my LT1 '94 Impala SS has a restrictor in the heater hose too.

Thanks, I didn't know that.

Back in the late 50s and 60s mechanics threw them away not realizing they were in the hoses, or in an attempt to get more heat out of the heater (I was raised way up there, -20* below) then in the summer lots of the cars would overheat. We just stuck in 195* thermostats.

Some genius came up with the idea of putting flow restrictors at the thermostat housing thinking that the water was going through the radiators too rapidly and did not have a chance to cool off. I think that this was the origin of the "old wives tale" about too fast of flow through a radiator.

Same thing happened to Fords, but lots of Fords used a restrictor orifice built into the manifold outlet fitting. I even saw geniuses drill those out larger. LOL.

Here's what it tools like, from the Advance Auto Parts web site: Flow Control

Thanks.

The old ones looked like a piece of 5/8 rod stock cut off 1/2 inch long with a hole drilled in the middle. Then it was inserted in the hose at the engine outlet. Should be installed on any hot rod to prevent heater core blowouts.