[nUcLeArEnVoY]

Ever since I got my '79 400/4-Speed, I've tolerated an obnoxiously massive exhaust leak on the driver side where the manifold meets the head. It's really loud and embarassing, and covers the #1 and #3 spark plugs as well as temp sending unit in soot. So If figured it's time to stop putting this off and fix the darn thing.

Aside from the fact that three of the manifold bolts look nearly original and are fighting me tooth and nail, especially with this horrible access I have to them (better than the passenger side at least), I took off the heat riser valve (which thankfully was easy enough since the studs were new due to a recent exhaust system upgrade several years back) and discovered something rather shocking...






It's stuck closed. Which happens, yes. But then look: there's a booger weld on the mechanism. So somebody welded it CLOSED. What. The. Hell. Has ANYBODY ever seen this before, or can anybody just brainstorm and think WHY somebody would weld the heat riser valve closed????? My ONLY guess is that somebody maybe assumed it was open, which is what it normally is when it's not receiving any vacuum, and so they welded it without realizing it was actually stuck closed; which they're known to do. That's my ONLY guess. I can't think of ANY other reason other than that the car was in the north pole and they needed all the heat they could get... which it wasn't. The ironic part is, the stupid thing still holds vacuum, so there was a possibility it was still functional before "bubba" took the MIG to it.

This means that this whole time, I've been driving my car with a partial restriction. I always assumed it was open and I haven't had the vacuum line hooked up to it ever since I got the car (I don't even have the thermal vacuum switch that regulates it in the intake, anymore). She runs fine. Starts within 4-5 seconds of cranking after one pump of the pedal even after having not run for a week, starts at the flick of a key when hot, spins the tires in first gear, and actually runs a bittoo cool now after the cooling system upgrades I did recently. It's not a complete restriction, there's soot on the driver side exhaust tip so some exhaust makes it past the valve, and technically the exhaust is still going somewhere (across the intake crossover and out the passenger side exhaust), including this massive exhaust leak, so I suppose I should actually be glad it was there... I just can't fathom why somebody would do this. Can any of you all? Lol My setup btw is an aftermarket true dual hooked to the stock manifolds - no catalytic converter.

It does explain a lot. If I start the car on a cold and damp morning, especially if it's been sitting awhile, there is a LOT more condensation and water vapor coming out the driver side than the passenger side, and the built up back pressure could even be what caused this massive exhaust leak in the first place. She will also creep engine temp very slowly but surely on the highway. I haven't driven the car on the highway long enough to see it go past around 180, as the car uses a 160 degree stat, but in city driving or at idle, the needle usually never goes past the first 160 degree tick on the gauge, and I can straight up grip and hold the upper radiator hose and not get burnt even after an hour of driving - point is, the highway was the only time I've ever seen the needle go up to around 180 (and this was only in the daytime at around 85 degrees - the one time I took it 15 or so miles up the road on the highway at night at 75 degrees, the needle stayed right at 160 - both of these occasions were at 55MPH, 2200 RPM), so I'm wondering if that may be because the motor isn't breathing the way it should at those higher sustained RPMs. As designed, the heat riser valve should be opened once the coolant temp reaches around 130-150 degrees, but mine has been closed the entire time because of some idiot. Who knows what other tidbits and driving behaviors this partial restriction has caused, not to mention the performance that has been left on the table!

So anyway, once (or IF) I get this manifold off and replace the gasket, I'm obviously going to just delete this heat riser valve. They don't make a spacer that fits Pontiacs that I can find, so I'll just gut the innards on this one and weld up the hole that the butterfly pin goes through and use it as the spacer. My only concern about deleting it is not so much overall warmup, since I live in South Florida, but rather hot air choke operation. Does anybody still use their hot air choke and heat crossover, but NOT the heat riser valve? If so, does the hot air choke still operate well enough? I went through a lot of trouble sourcing a nice used choke tube set recently and my hot air choke works AMAZINGLY well (no duh, the heat riser valve has been closed the whole time!), I really don't want to go back to electric. The issue is, without the heat riser valve, I'll be depending on exhaust to go back and forth between the intake crossover just from normal turbulence rather than it getting forced from the driver side to the passenger side with the closed heat riser valve, increasing the amount of exhaust the choke tube is exposed to. I can see where that would be problematic for older divorced chokes where the bimetallic spring opens from radiant heat coming off the intake crossover, but my '79 uses an integral choke and the tube that feeds the hot air to the housing goes pretty deep into the passenger side cylinder head, so hopefully it's still exposed to enough heat to operate decently.

Anyway, crazy, right???

[dataway]

Those photos are wider than my whole desk so I can't really see what is going on.

[nUcLeArEnVoY]

Originally Posted by dataway

Those photos are wider than my whole desk so I can't really see what is going on.

That's weird, they should shrink/adjust...

Here are smaller photos:

[goatless]

That seems like it would hurt performance a little bit.

[67Fbird]

oops...welded it too soon!.... car wasn't warmed up yet...lol I'm surprised it even ran AT ALL.

[dataway]

Owner lived in Antarctica.