63 340HP intake

[Bruce B.]

There is a 63 340 HP intake on Ebay GM PN 3794129, and I could use some opinions about it.
Behind the carb on the passenger side there is usually an undrilled boss on the top of the casting. I read in Nolands restoration book that sometimes there is no cast boss. It also appears that sometimes the boss is drilled and plugged using a threaded plug. Does the situation exist where the casting without the boss is also drilled and plugged?
Ebay item #230250080582 is drilled and plugged but has no boss, could this be a legitimate GM part in it's present configuration?

[Duke W.]

Re: 63 340HP intake

I suspect the answer is no, but need other opinions. My March-built '63 L-76 manifold has the boss/pad, but it is not drilled and taped/plugged.

The other question is what would a drilled and taped boss be used for - something to do with power brakes? Mine are non-power assisted.

Duke

[Clem Z.]

Re: 63 340HP intake

I suspect the answer is no, but need other opinions. My March-built '63 L-76 manifold has the boss/pad, but it is not drilled and taped/plugged.

The other question is what would a drilled and taped boss be used for - something to do with power brakes? Mine are non-power assisted.

Duke

the 64 SHP manifold had the PB fitting in that location. i would guess the 63 would be the same because the PCV system on the 63 would prevent the fitting from being any closer to the carb. JMHO

[Joe L.]

Re: 63 340HP intake

There is a 63 340 HP intake on Ebay GM PN 3794129, and I could use some opinions about it.
Behind the carb on the passenger side there is usually an undrilled boss on the top of the casting. I read in Nolands restoration book that sometimes there is no cast boss. It also appears that sometimes the boss is drilled and plugged using a threaded plug. Does the situation exist where the casting without the boss is also drilled and plugged?
Ebay item #230250080582 is drilled and plugged but has no boss, could this be a legitimate GM part in it's present configuration?

Bruce-----


I HIGHLY doubt that the plug is original to the manifold. I've never known GM to do something like this. In other words, I don't think that they'd tap a hole into an intake runner without a boss being present to support the hole and tapping. On the other hand, drilling and tapping such a hole is just exactly what someone might do needing a vacuum source for some reason. I would say the chance of it being factory is slim to none. Mostly none.

[Duke W.]

Re: 63 340HP intake

the 64 SHP manifold had the PB fitting in that location. i would guess the 63 would be the same because the PCV system on the 63 would prevent the fitting from being any closer to the carb. JMHO

The '63 AIM J-50 section shows the PB brake vacuum source as typically seen. The PCV adapter at the back of the AFB is a tee rather than an elbow. The PB hose routes into the LH side of the tee and the PCV into the RH side.

It could be that a change was in the works, but got superseded by the new '64 casting that was required for the Holley carb.

Is it correct that early '63 L-76 manifolds do not have the pad?

Duke

[Joe L.]

Re: 63 340HP intake

The '63 AIM J-50 section shows the PB brake vacuum source as typically seen. The PCV adapter at the back of the AFB is a tee rather than an elbow. The PB hose routes into the LH side of the tee and the PCV into the RH side.

It could be that a change was in the works, but got superseded by the new '64 casting that was required for the Holley carb.

Is it correct that early '63 L-76 manifolds do not have the pad?

Duke

Duke-----


I don't know whether they had a boss (pad) or not. However, I cannot see GM drilling and tapping a pipe fitting into an intake manifold runner (as is the case with the eBay manifold referenced) without a boss to support said fitting. I can't think of a single case in which I've seen the factory do this sort of thing.

[Bruce B.]

Re: 63 340HP intake

Thanks guys for your input.
Bruce B.

[Stuart F.]

Re: 63 340HP intake

I have a July 63 build 340 hp and it has the boss, but is not drilled or tapped. I agree this one was probably butchered (so to speak), perhaps by some one wanting to use it on a newer engine w/o PCV can (becoming popular nowadays). I have a P.B. tee fitting for the back of my AFB, but never used it. It has the correct sizes for the PCV and a P.B. hose fitting. I intended to use it for a vacuum tap to connect a cockpit gauge. I decided not to install the gauge, but instead use a temporary tee and test gauge in the Vacuum advance line to set idle screws. The smaller orifice in the vacuum advance line fitting seems to dampen the reading a little which makes them easier to adjust.

Stu Fox

[Duke W.]

Re: 63 340HP intake

However, I cannot see GM drilling and tapping a pipe fitting into an intake manifold runner (as is the case with the eBay manifold referenced) without a boss to support said fitting.

I definitely agree. The data on ebay says the casting date is 8-1-62, which would make this a very early production piece. The picture with the casting number is somewhat blurred, but the last digit looks like "8".

I've always been curious what that pad was intended for. It looks like it was added after the original release date, but AFAIK it was never drilled/tapped in production.

The diameter of the pad indicates a rather large hole was intended. That's why I think it might have been intended for the power brake vacuum source. Mixing the PB vacuum source with PCV can cause deterioration of the rubber PB diaphragm (In the seventies GM added a small activated charcoal filter to the PB vacuum hose to absorb HC.)

Duke