[andrewT]

My engine has been apart so long I am starting to forget here and not many pictures of engines show the back. Please excuse my ignorance!
Its a street driven 11.3:1 488ci aluminum d-port motor

I can't decide if I should run both passages to the heater core as seen here: http://forums.maxperformanceinc.com/...9&postcount=23
Or run both to the front as seen here: http://forums.maxperformanceinc.com/...66&postcount=4

Or is there another thing guys are doing now? what would you guys suggest? it does get cool here in spring and fall so I wouldn't mind having defog/heater working but no biggie if not. Do guys plug these passages if ever at all?
Does anyone make adapter plugs for these holes so that I can use AN or NPT fittings? I see that fella 67Cruiser had made some but he's suspended so SOL for me there.

Thanks guys

[Goatracer1]

If you want the heater to work you can use just one and plug the other or "T" the 2 together and run one hose to the heater. Use the other hose from the timing cover.

[PONTIAC-ONE]

I "tried" to buy 2 sets of those from 67Cruiser maybe 2 years ago but got nowhere after waiting weeks for PM replys, I guess he didn't want my cash. I never had any issues with any other members and I buy allot of stuff.

I'm going to make my own system soon.

[Ed Fitzgerald]

Andrew let me know what you decide to use and I'll fab you up the plug. Made some for Chris Dale (CNC) in London a few years back out of stainless. Ed.

[HWYSTR455]

Why not run the factory style config?

.

[Old Man Taylor]

The first time I did it I ran it from the back of the head to the water cross over. On the 505 the connection goes directly from the head to the back of the block.

[Blued and Painted]

Originally Posted by HWYSTR455

Why not run the factory style config?

.

with a .250 restrictor @ the head oulet so to not blow heater hoses off at high rpm's.

[Tom Vaught]

Been discussed many times before.

The 64 engine cooling strategy was better than the 65 and later strategy but not as good as the earlier "feed the heads then the block" cooling strategy.

The 64 engine cooling strategy had the water pump feeding the block then the water went to the heads and finally to the water cross-over where some of the water went back to the radiator and some went to the heater core and then back to the timing cover/water pump. So the 64 strategy had the block evenly cooled and the heads evenly cooled.

The 65 and later engine cooling strategy has the water pump feeding the block then the water went to the heads and finally to the water cross-over where some of the water went back to the radiator, like the 64 design. BUT the water for the heater core was taken off of the back side of the passenger head to save some money most likely by a "Bean Counter" and now the driver's side head cools differently vs the passenger side dead. The passenger side head has some of the cooling water diverted so that the passenger head sees less cooling water on the way forward to the water cross-over and radiator.

So if you branch off with nipples off the rear of the heads you can:

1) Even out the water flow going forward thru the heads to the cross-over again

2) Remove potential trapped air in the rear of the heads, cooling the heads a bit more evenly

3) Send the air and the water to the heater core where the air gets trapped in the heater core reducing the effectiveness of the heater core.

4) Send twice as much water to the heater core for a instant (when you go to WOT) thereby blowing out the heater core quicker.

So the .250" restrictor (right before the heater core inlet" is needed under all conditions/plumbing to reduce the slug of water trying to rupture the heater core under WOT.

OMT's water system where the heads get the water first (like the first design engines) and then the water going to the block seems to be the best late model solution for cooling in a race car. race cars do not have heater core robbing water from one or both heads.

Tom V.

[lust4speed]

My way of seeing it. Coolant goes into front of block and travels to the rear with a percentage going up to the head as it goes to the rear. Much of the coolant from the rear of the block travels from the rear of the head forward to the front of the head and finally to the crossover. This coolant traveling through the head picks up additional heat and all coolant is directed to the radiator. Any coolant removed from the rear of the head to the heater or bypassed directly to the crossover is not available to remove additional heat from the head. Worse than that, the heater supply bypasses the radiator and is directly inserted into the water pump and back into the block. Great for those cold mornings for fast interior warmup, not so great for summertime engine cooling. If you have 15% of coolant being recirculated in the heater and engine, that's 15% that is not going through the radiator on a cooling cycle.

The stock Pontiac heater connection was limited to a 1/4" coupling which limited the amount of bypassed coolant to an almost insignificant amount.

I like OMT's block to head hoses. They would provide less restriction and should push more coolant through the heads.

[Blued and Painted]

Not to mention the intake to timing cover bi-pass. I install a plug on the intake side and drill to .250" for street applications.

15 minuets after initial start up and break in, i was able to remove the radiator cap and confirm circulation @ 2200 RPM's.

Note/ check pressure at top hose before removing radiator cap.

[quicksilver97ta]

I blocked both rear outlets from the heads, at least that provides for even LT and RT cooling. Then I used the extra threaded outlet in the water crossover to supply the heater core.

[Tom Vaught]

Originally Posted by quicksilver97ta

I blocked both rear outlets from the heads, at least that provides for even LT and RT cooling. Then I used the extra threaded outlet in the water crossover to supply the heater core.

That is a good set-up for sure.

One question on the .250 restrictor some have mentioned.

In the early 70s every heater core I replaced on a HP GTO was leaking and my Uncle's Head Mechanic had me bend the round inlet tube using duckbill pliers into a square with about a .250"-.300" opening. So when did the factory install this .250" restriction and where was it installed?

Tom V.

ps 80s Hot Rod Mustangs had the same failure mode with their heater cores and Ford used a plastic restriction in the line before the inlet to the core.

[Ben M.]

Originally Posted by Tom Vaught

In the early 70s every heater core I replaced on a HP GTO was leaking and my Uncle's Head Mechanic had me bend the round inlet tube using duckbill pliers into a square with about a .250"-.300" opening. So when did the factory install this .250" restriction and where was it installed?

From what I've read, it was installed in 1965 or so as part of a factory recall bulletin, directions to install it and everything (it was posted in the forums in the past).

I was also told that the heater hose nipple in the block in the 70's had the restriction built in - I've had several engines that it wasn't a straight outlet at the back of the head.

But I've also seen dozens of cars with the crimped inlet tubes as well, so I know that was done by many people. I use a solid 1/2" long plug that I drill a 1/4" hole into on my cars.

Edit: found it and attached it.

[Tom Vaught]

Thanks VERY MUCH for the info on the coolant restrictor/ "one way valve".

I will copy and save in my files. Thanks again.

Tom V.

[andrewT]

Thanks for the replies everyone

Originally Posted by quicksilver97ta

I blocked both rear outlets from the heads, at least that provides for even LT and RT cooling. Then I used the extra threaded outlet in the water crossover to supply the heater core.

does someone make these plugs readily available or are they just a standard size? (My engine is at a shop not near me right now for me to check) thanks

[Tom Vaught]

I believe they are not too common on the size in the parts houses. Not sure of the exact size, sorry.

Tom V.

[andrewT]

Originally Posted by Tom Vaught

I believe they are not too common on the size in the parts houses. Not sure of the exact size, sorry.

Tom V.

anyone else remember or know off hand? can't seem to find it in searches