cooling system
Once upon a time, when I was going to the big school, I met some grad students that were doing a project on a small one cylinder engine. I've forgotten what the original expierment was because things rapidly went wrong. We discovered that the cooling system and how good or not good it is, has a big impact on power production. We found that there is a optium temp in a engine and lack of uniform temp control through the engine can and does cost power. The expierment ended up persuing that end.
With summer and hence, hotter weather, just around the corner and if anyone is going to build a all out engine such as has been hashed around in this column, the cooling system needs some upgrades.
The basic operation of the str8 cooling system is out the bottom of the radiator, through the water pump, out through the dog leg pipe and into the left front of the block, somewhat acrossthe block to the right side, then quickly drifts back to the left side to the back of the block and up into the head via the big hole at the left rear of the block in the deck. It then flows to the front of the head where the thermostat housing is, as this is the location of the systems pressure differential. By the time it gets here, it's HOT, providing little cooling, and the head is the place that needs it the most.
I've run my buick through some hot places and I've found it likes cool weather better than hot. I'll bet that most are that way. So what could be wrong with the cooling system? Look at the size of the radiator!!! And the guage hardly ever shows hot!? Well, 1st problem is the dog leg port. It puts the cool water right into the side of #1 cylinder. If the cooling system is nice and clean and in good order, it will cool that cylinder so well that it will distort the bore in that cylinder. Then the flow is mostly down the left side, leaving the right side hotter. The cylinders need to be cooled but the head needs it more. The 248 has no coolant transfer holes in the deck, except at the rear of the block. The 320 may be the same, I'm not sure, I don't recall. The later heads have holes in them for this, early heads may not, I've never had the opertunity to check. Head gaskets are punched for the holes. 263's have got the transfer holes in both the deck and head. I suspect that the head being poorly cooled, particulary in the exhaust port side, has a lot to do with all the destroyed rings&pistons I've found in all the str8's I've ripped down. The biggest problem is the big (1") hole in the rear of the deck. Water follows the path of least restance. That big hole is the least restant path, all those other smaller holes will get little flow. The hottest point in the head is the exhaust side and all the exhaust ports are side by side except front & rear. A odd thing happens when these sites get really hot, which is most of the time, the heat causes the coolant to burst into little steam bubbles on the surface of the metal. These little bubbles remove heat pretty good, unless they get togather and form pockets of steam, then things get really hot and things get bad. You can't hear this and the guage sender is in the wrong place to ever show it. The passage between the exhaust ports needs to flow. The stock system won't do this.
How do we fix this? All the holes at the rear of the block with the exception of the two holes at the very rear, need to be pluged. If the block is on the stand and bare, idealy, get a 3/4 internal hex pipe plug, thread the hole and crank it in. The 3 remaining smaller holes will take a SBC front oil galley plug, 1/4 pipe, I think, thread the holes and crank em in. Some of the plug should stick up. The block will have to be decked. This is the best way. If the engine is togather, put the plugs in the head. If you have a different way, go ahead, just plug em. Next, using the head gasket as a template, drill a 3/8 hole through the deck between the exhaust ports, if you have a early head and it does not have the holes in it, drill it as well. On the right side of the deck, opposite the just drilled holes, drill 1/4 holes. There diffinatly won't be holes in the head, so matching holes must be drilled as well. At this point we have now got a flow from the cooler bottom of the block between the hottest spots in the engine, the exhaust ports. This goes a LONG way towards equlizing temps in the engine, and its diffinatly ok at this point, but one more change makes it excellent. Eliminate the dog leg pipe. Make a block off plate for the port on the block. Fab up a pipe going from the water pump to the middle freeze plug port. I did this out of stainless steel bathroom grab rails. I put a little "jog" in the pipe just aft of the water pump exit, in order run it close to the block, machined up a o-ringed bung that plugs into the freeze plug port, drilled 3 holes in the boss, theres more than enough meat, a little silicone, and "bingo" the best cooling system ever. What this does is put the coolant through the widest cylinder spacing, over to the right of the block and front and rear split, pulling back across, up into the head, flushing the exhaust port space with a good steady stream. Excellent temp controll. alleycat