Hot Rods 671 Blower & Cooling

I have a SBC engine that I am putting together, with a GMC 671 Blower this setup is for the street only, I also had a custom rad, shroud, and fan made. The intake has two rear ports that go into the water jacket, I read the sbc over heat's because the water in the back of the block can not circulate, If I were tie into those rear water ports' would that help with cooling ? If so could someone help me to tie these into the cooling system. Or is this something that I should not be concern about and just plug the two rear ports...Thanks Mike

 

Been done for many years now.
It helps with the low "flow" areas in the back of the engine, especially the heads. Does it make a big, overall cooling difference at the gauge, not normally, but it does help keep the engine a little more even in temperature, front to rear.
Yea, I'd do it if you have the space for fittings.

Mike

 

Thanks Mike....How would you plum it in..M

 

I'm curious about this. As I understand it, the coolant flows to the back of the block, then up to the heads, and forward. There are a few smaller holes along the way, where a small amount of coolant goes into the heads before it gets to the back.

fwiw, I've never had any issues with a small block chevy overheating the rear cylinders....

 

I've had many SBC with 671's, and never had a issue with overheating. Just used a good radiator and fan setup.
However, a rear crossover has been used for many years on dragsters and race cars. Looks like Edelbrock now
has the rear flanges tapped for fittings, so check them out. Here is a quick photo of how one guy did it, but
not a blower manifold. The idea is the same. Good luck and have fun.

 

Worth a try!

 

Looks to me like those hoses just make the coolant bypass the cylinder head, and prevent the cooling system from working properly.

But what do I know, I'm just a dumb engineer.

 

Yeh, was hoping for input, been sitting on the cart like that for years, only seen dyno time.

 

In street use and most other applications I don't believe that you will see any benefit. The stock car guys started it long ago after data logging exhaust temps and other data and determined that the rear cylinders were a few degrees warmer than the front. So in the search for a few HP this is where they started. And I suppose when you look at the high coolant temps they run keeping everybody close makes sense. My take is 90 % of the ones you see now are just after "the look". Also driven by the smaller cooling passages in most hi po aluminum heads.

 

The blown SBC in my Austin gasser has an old Weiand race blower manifold on it with no provision for a water outlet in the front. It did have the two tapped bosses in the rear so the water exits there and runs through two hoses to a custom fitting and into the radiator. A Jabsco remote belt driven marine pump circulates the coolant. So far it hasn’t overheated but it does belch out some water from the overflow occasionally. Of course I’ve never had the old gasser in heavy traffic on a 100 degree day either.


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I have the same Weiand as @bchctybob but I drilled and tapped the front of the heads for 3/8NPT and ran -8 coolant lines to an Offenhauser divorced thermostat housing.
The coupe is channeled so the Walker radiator is about 4 1/2” shorter than stock, I run a 15 lb cap and an electric fan, no room for a stock fan. On the road to OKC we hit construction traffic, it was backed up for miles. The temp hit 250* at one point but it never boiled over. I think I was sweating it more than that Walker radiator.