Dumb questions #23 and #24

[DJ Dep]

#23 On the big block intake manifold....the threaded holes. I know the ones on the front of the manifold are all 1/2 inch pipe thread. What size is the one on the top of the manifold in the rear? I think it's a vacuum port for the power brake booster (which I no longer have a use for).

#24. On the front of the manifold is a hole that is used for a "bypass hose" from the water pump to the manifold. What is the purpose of this hose and can it be blocked off? BTW...I am not using a heater core at all.

 

[TimAT]

#23- If my memory is still working, both of those threaded ports are 1/2" NPT. The manifold I have only has one in the rear. I'm using it for the brake booster and the headlight vacuum system. PCV comes off the front of the carb.

#24- NO. The hole in the front is the bypass. A SBC has a bypass hole in the water pump and the block on the right mounting leg. A BBC pump does not. Heater or not, you need that little hose. The top of the water pump has a corresponding hole.

 

[mrvette]

#23- If my memory is still working, both of those threaded ports are 1/2" NPT. The manifold I have only has one in the rear. I'm using it for the brake booster and the headlight vacuum system. PCV comes off the front of the carb.

#24- NO. The hole in the front is the bypass. A SBC has a bypass hole in the water pump and the block on the right mounting leg. A BBC pump does not. Heater or not, you need that little hose. The top of the water pump has a corresponding hole.

The old Pontiacs had that built into the water pump/housing setup, the question is.....why?? i'ts like drilling holes in the thermostat flange the way I look at it.... gotta be something I missing....

 

[DJ Dep]

#23- If my memory is still working, both of those threaded ports are 1/2" NPT. The manifold I have only has one in the rear. I'm using it for the brake booster and the headlight vacuum system. PCV comes off the front of the carb.

#24- NO. The hole in the front is the bypass. A SBC has a bypass hole in the water pump and the block on the right mounting leg. A BBC pump does not. Heater or not, you need that little hose. The top of the water pump has a corresponding hole.

#23 Here is the hole I am talking about:



It's that hole in the intake runner in the center of the picture. I know it's a vacuum hole, I just need to know what thread size so I can plug it.

#24 I know the hose is a bypass hose. But a bypass to or for what????? And why would it harm anything to block it? The manifold is getting water from the thermostat via the upper radiator hose. WHAT does it bypass???? And why can't I just plug up BOTH holes on the manifold and water pump. The less hot water getting into the manifold, the better (for my uses).

 

[mrvette]

#24 I know the hose is a bypass hose. But a bypass to or for what????? And why would it harm anything to block it? The manifold is getting water from the thermostat via the upper radiator hose. WHAT does it bypass???? And why can't I just plug up BOTH holes on the manifold and water pump. The less hot water getting into the manifold, the better (for my uses).[/QUOTE]

IIRC it has to do with internal block cooling evenly on warmup, and so to keep water circulating between block and heads (hot spot) when stat opens of course I have so ASSume it's not all that necessary....:gurney:

 

[DJ Dep]

#24 I know the hose is a bypass hose. But a bypass to or for what????? And why would it harm anything to block it? The manifold is getting water from the thermostat via the upper radiator hose. WHAT does it bypass???? And why can't I just plug up BOTH holes on the manifold and water pump. The less hot water getting into the manifold, the better (for my uses).

IIRC it has to do with internal block cooling evenly on warmup, and so to keep water circulating between block and heads (hot spot) when stat opens of course I have so ASSume it's not all that necessary....:gurney:[/QUOTE]

Thanks Gene. Answered my question perfectly. :thumbs:
Now if I can just get the size of that rear vacuum hole, I'll be all set.

 

[010752]

If you try and measure the root of the female thread or the widest part the tap cut, then,

Close to:

3/8” it is 1/8” npt

½” it is ¼” npt

5/8” it is 3/8” npt

¾” it is ½” npt

1” it is ¾” npt

Those aren't exact, but will get you close enough.

 

[DJ Dep]

If you try and measure the root of the female thread or the widest part the tap cut, then,

Close to:

3/8” it is 1/8” npt

½” it is ¼” npt

5/8” it is 3/8” npt

¾” it is ½” npt

1” it is ¾” npt

Those aren't exact, but will get you close enough.

Hmmmm...I will give that a try. I realy don't want to drag the whole manifold into Ace Hardware to try out the fittings :sweat:

 

[mrvette]

If you try and measure the root of the female thread or the widest part the tap cut, then,

Close to:

3/8” it is 1/8” npt

½” it is ¼” npt

5/8” it is 3/8” npt

¾” it is ½” npt

1” it is ¾” npt

Those aren't exact, but will get you close enough.

Hmmmm...I will give that a try. I realy don't want to drag the whole manifold into Ace Hardware to try out the fittings :sweat:

Hell, I have dragged tons of shit into HD/Lowes, you lazy woose....:harhar::beer:

 

[DJ Dep]

If you try and measure the root of the female thread or the widest part the tap cut, then,

Close to:

3/8” it is 1/8” npt

½” it is ¼” npt

5/8” it is 3/8” npt

¾” it is ½” npt

1” it is ¾” npt

Those aren't exact, but will get you close enough.

Hmmmm...I will give that a try. I realy don't want to drag the whole manifold into Ace Hardware to try out the fittings :sweat:

Hell, I have dragged tons of shit into HD/Lowes, you lazy woose....:harhar::beer:

Yeah, but I live in a far left hippy/socialist/liberal/Communist town and they would freak out and call the KGB on me. They would think the manifold is some kind of bomb. The manifold isn't heavy. It's aluminum. I'm not THAT feeble

 

[mrvette]

If you try and measure the root of the female thread or the widest part the tap cut, then,

Close to:

3/8” it is 1/8” npt

½” it is ¼” npt

5/8” it is 3/8” npt

¾” it is ½” npt

1” it is ¾” npt

Those aren't exact, but will get you close enough.

Hmmmm...I will give that a try. I realy don't want to drag the whole manifold into Ace Hardware to try out the fittings :sweat:

Hell, I have dragged tons of shit into HD/Lowes, you lazy woose....:harhar::beer:

Yeah, but I live in a far left hippy/socialist/liberal/Communist town and they would freak out and call the KGB on me. They would think the manifold is some kind of bomb. The manifold isn't heavy. It's aluminum. I'm not THAT feeble

It's early yet, but thanks for the best laugh of the AM....:harhar::amused:

 

[Sam Cogley]

If you try and measure the root of the female thread or the widest part the tap cut, then,

Close to:

3/8” it is 1/8” npt

½” it is ¼” npt

5/8” it is 3/8” npt

¾” it is ½” npt

1” it is ¾” npt

Those aren't exact, but will get you close enough.

Hmmmm...I will give that a try. I realy don't want to drag the whole manifold into Ace Hardware to try out the fittings :sweat:

I do that kind of stuff all the time. Even when I lived in a hippie liberal college town. No one ever cared. Any ACE hardware near me gets used to seeing me drag weird things in to match hardware.

 

[DJ Dep]

If you try and measure the root of the female thread or the widest part the tap cut, then,

Close to:

3/8” it is 1/8” npt

½” it is ¼” npt

5/8” it is 3/8” npt

¾” it is ½” npt

1” it is ¾” npt

Those aren't exact, but will get you close enough.

Hmmmm...I will give that a try. I realy don't want to drag the whole manifold into Ace Hardware to try out the fittings :sweat:

I do that kind of stuff all the time. Even when I lived in a hippie liberal college town. No one ever cared. Any ACE hardware near me gets used to seeing me drag weird things in to match hardware.

Well I may just "man-up" and take it in. LOL...my wife will roll her eyes into the back of her head. Maybe I'll wear my Tea Party t-shirt for added effect.

 

[TimAT]

1/2 NPT. Unless someone stripped and retapped yours. I've got that same hole with a T in it for headlight and brake vacuum.

The bypass is for before the thermostat opens- lets water circulate so you don't get a hot spot and/or a steam pocket.

 

[JPhil]

You also need a bypass for the water pump so that when the t-stat is closed and there's no circulation through the engine, the pump will still have water to move. Otherwise it will cavitate and self-destruct.
True for any medium moving pump, air or fluid. (Fans don't 'cavitate' but they overspeed from lack of resistance and burn up from lack of cooling air movement.)

 

[DJ Dep]

1/2 NPT. Unless someone stripped and retapped yours. I've got that same hole with a T in it for headlight and brake vacuum.

The bypass is for before the thermostat opens- lets water circulate so you don't get a hot spot and/or a steam pocket.

Nope. That's the brass plug I have and it isn't even close. Gotta be 1 or 2 sizes smaller. 1/2 inch NPT fits all the front fitting holes on the manifold, though.

 

[DJ Dep]

Okay, I went out to my storage locker and checked all three of my intake manifolds. The 1/2 inch NPT plug didn't fit any of them. But it does fit the front threaded water passages in all of them. Two of the manifolds are brand new and one is used. No helicoils in the used one except for 3 of the carb mounting holes.
So I came back home and checked the Assembly Manual. I found that the fitting that goes in this hole has two spigots on it. One goes to the auto transmission modualtor, and one goes to the vacuum storage tank.

 

[TimAT]

I would have lost that bet.. Sorry.

GM didn't use any funny sizes that I remember. If I was home I'd go pull the fitting and tell you what it is for sure. I'll be there Friday if it's any help.

 

[SmokinBBC]

I measured the thread on my fitting that is sticking up from the mani...best I can see it is .670....which would be 3/8 NPT.

I have a 1/2 plug and a 1/4 plug...1/2 too large and 1/4 too small.

Funny....i don't have any 3/8NPT plugs:huh:

My bet is 3/8.

 

[mrvette]

All these decades, all I have ever done is fish through the stores and find the fitting that fit....and when it did it was a fine fitting fit for a flitting fairy....

:bounce::bounce::clobbered:

come on guyz, gimme a A for dramatic poetry, anyway....

:nuts: