atb

I was going to put a block off plate in place of the heater core feed spigot on the back of the right head (track car motor) but then I wondered if I need to leave it and feed it back to the front of the motor. Is flow through the head required or can I block it off? SBC heads have a balance tube in the intake manifold to connect the water jackets in the heads, any advantage to running a high pressure hose or hard line from one block off plate to the other?

atb

Based on this diagram it looks like the block off plate is fine. Does anyone else get the feeling that Porsche was overly optimistic on getting even cooling with this set up?

Our cylinders aren't siamesed, so I don't follow how the rear cylinder towers get any where near the circulation of the front towers.

Rob Edwards

Here's a bit of a Blair Witch Project-style shaky video of the bleeder hoses on the back of the Zombie motor, I have to confess that I'm not 100% clear why Mark decided he needed two bleeder ports on the 5-8 head but they join together and along with the 1-4 bleeder run back to T into the coolant bleeder hose to the reservoir.




Still view:

atb

I wonder if the heads tend to over pressurize (what would be the weak link in that scenario?) or maybe form air pockets in the back that need the rear exit to purge with extended high revs? The overall " flow through" design does make some sense to me.

Rob Edwards

Here's a more complete walkaround if any of this helps with thinking about plumbing:

dr bob

Perhaps the bleed line from the back of the head makes sure that you don't leave an air pocket there when filling the coolant system. Hence the guidance to open the heater valve during refills. It not only drains old coolant out of the heater core and loop, but makes refilling the back of the head easier. Otherwise, a block-off plate does the same thing as driving with a (good) heater valve closed. For a race car, I'd put a block-of plate there to eliminate any possible leakage from the hoses and plumbing. I might also put a bleeder valve there to purge the end of the head. It can't be a lot and probably self-purges anyway, as the left side head does now.


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The cross-over "balancing" passage under the intake in SBC's is a relic of the past, when carburetors needed some help under cold-start conditions. Fuel would gather on the floor of the intake when the engine was cold, making cold starting a bit of a chore. Heat the manifold a bit, and fuel would vaporize more easily and stay in suspension in the air going into the cylinders. Hot-rodders would regularly block that passage, or at least put a flow restrictor there so that the charge density wouldn't suffer after the engine was warmed up. Fuel injectors directly over the intake valves, and now direct injection make the habit of heating the intake all but obsolete in performance applications.

James Bailey

The old very brown 1980....Greg Brown made an aluminum plug to block off the rerouted hose( no longer goes to heater core) BUT drilled a very small hole so it can vent and flow.
also the very early 78-79 cars had the odd heated breather hose (NLA) which effectively vented air/ coolant off the left head as well....

mark kibort

i dont know if this is the reason my track car runs so cool, but i just connected the point where it goes to the heater core, to the place where it comes out of the heater core. no block of plate.

mark kibort

I thought the zombi motor had a rod coming through the pan, No?

looks good ! when are we installing that back in the zombi! ???

Rob Edwards

Look carefully at 0:46. Doesn't look so good now, does it....

New motor is coming together, slowly but surely. Crank is out getting tweaked, rods are in hand, block is done, heads are ready to assemble, figured out the desired compression ratio and Greg ordered pistons 2 weeks ago. .

mark kibort

i cant see anything, but maybe a small 1" hole from the #1 cylinder rod?

atb

I'm wondering what affect it has to pull some of the water out before it has a chance to go back through the heads (and collect heat off the exhaust valves), by bypassing the trip through the heads and dumping it right back at the water bridge like the stock heater core route would. Are we losing cooling capacity by not forcing all the water through the heads? Or is there enough capacity to deviate some around the heads and keep the overall temps going into the rad lower for a net gain?

Basically, the water gets pushed into the front of the common water jacket and is forced to the back where it gets pushed / sucked up into the rear of the head and is circulated forward to the water bridge. (Photo courtesy of 928MS - let me know if you want me to pull it Carl).

Rob Edwards

Yeah.