Overheating 400

I have a 400 in my 81 TA. Recent rebuild. 10.5:1 compression, Meizre electric water pump, new 4 core rad and 2 electric fans pushing. At highway speed, temp hangs at 160-170. But soon after stopping, or 5 minutes idling after cold start up, temp is at 230 and climbing. Can't get it cool. Used water wetter and no thermostat. Osbournes Pro street in Wisconsin Rapids built it and now I find out they don't know Pontiac's. Is it possible they used a Chevy 400 headgasket?? I'm afraid I'm going to cook the motor. Any ideas??  

Chevy head gaskets will not fit a Pontiac engine at all the Cr worries me as 9.5:1CR is the max. for a iron head Pontiac engine using pump gas.
What is the casting numbers on the heads and what type of pistons did they install in it flat,dish or dome tops.  
professional hi-performance engine builder

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6X heads. Told me he decked the block to bump the CR. Not sure if dish, dome or flat. Can check tomorrow, car is at a friends shop. Have a pair of Catalina? heads. Guys at swap said they were junk, combustion chamber too big. Maybe they'd help lower the CR?? One more thought. Being that the guy's are morons, could they have set the timing 180 off from where it needs to be??

Thanks.........Joe  

Do you know how much they milled off of the block?
What is the secondary casting number on them 4,8 or 11.  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

Don't know how much they milled. Any way to ckeck?? Where do I find the secondary casting number? My guess is between the rocker studs??

Thanks......Joe  

You may be pushing water through the radiator too fast. Try a 160 stat or even a restricker to slow it down. Does the pump run all the time or after some preset temp???? Unless they put domed pistons in it there is no way to be 10.5 to 1 with any 6X head unless they milled the crap out of them. Then they would have to milled the intake to make it fit if the heads were milled much over .030.  

The secondary casting is on the rectangle area on the exhaust boss.
Ya I agree with 65pmdgto1 - Unless they put domed pistons in it there is no way to be 10.5 to 1 with any 6X head unless they milled the crap out of them.
I would go with a 160 std flow thermostat and see if that works.  
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Horsepower sells engines and torque wins races

Numbers I found are 0255, GM2 on drivers side, and D145 GM7 on the passenger side. It's an Edelbrock Performer RMP intake, no mods. I ran a mechanical water pump before and ran hotter than it does now. Have tried 160 thermostat and didn't help. Hoses gets too hot to touch. The electric pump runs constant. Today the air temp is near 90 and on my 20 minute drive home on country roads, the temp gauge never fell below 200. What about a compression test?? Would that give us any ideas?? Any way to test for dome pistons without pulling the head?? Thanks  

Do you have a FACTORY fan shroud in place? Otherwise, the air from those fans will not be directed where it should be going. Also, did you try another gage? My 68 Firebird was doing the same thing, at idle, it went to 230 degrees. i checked it with an infared thermometer (about 30.00 at Sears, Harbor Frieght), and found it was running at 180. I had a bad temp gage.  

Both fans are shrouded pushers. No shroud on back side. Thought about the temp gauge too. Bought a new one, actually reads hotter. Fans are set to come on at 210, otherwise they'd run all the time.  

If it was mine one fan would be running all of the time and the other only when needed the fans not coming on until 210 degrees could be a problem as well as at 210 the engine is already starting to over heat.  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

Did you try to reverse the polarity on the fans to pull instead of push? Or mount it to pull? Are the blades curved? I had mine pushing and it overheated. I have a 400 bored 30 over and stroked. Just some food for thought.  

This is very simple. TO ALL OUT THERE. Electric water pump = restrictor plates. You cannot run thermostats with an electric pump. Never run nothing at all as the water will flow to fast and not spend enough time in the rad to transfer heat. Only when you are at cruising speeds is enough air flowing to pull the heat out. When stopped the air flow to water fow ratio is too low, so it over heats. Go buy 3 sizes of restrictor plates from you local speed shop and start experimenting.  

Also no matter what the brand, electric fans are inefficient at pushing air. Set them up on the other side pulling. Even then you are only moving air through 50% of the fan area (where the blades pull), thus only 30% total area of the rad. The most serious street cars only need one good 3200cmf fan if used with a shroud. A shroud will pull air evenly across 100% of the rad all the time.  

I agree with flynryan. That makes complete sense. Pulling air with the right fan is the way to go.  

Pulling is the way to go always-50% 0f a fans effeciency can be lost otherwise
Wire your fan using a relay so the relay carries the load instead of the switch or wiring