OK, Here's the pertinent info:

'84 F-150 XL, 351 HO (HAD a Holley 4BBL - been replaced) 4x4.

So I had an exhaust leak pop up on me out of the blue one day that I knew had to be fixed. Not having time to do it myself, I took it to a local shop that does good work. Here's what I found out:

Apparently this had the heat riser valve attached to the bottom of the manifold. The blow out is with that valve (square block between the bottom of the manifold and pipe) and the bolts attaching it to the manifold are completely rusted over. Guy says basically there is no way to remove them without shearing the bolts, which are in the base of the manifold. So, he suggests a new manifold and replacing the pipe from it down to the Y, which I have no problem with.

My question: I see manifolds with and without the ability to add a heat riser valve. Do I need to worry if I DON'T replace it with one that has the heat riser valve on one side? What benefit is the valve and can I get by without it or should I find one with the valve?

I ask strictly because of economics. This is an old beat around truck that I just need to get inspected.

Thanks in advance!

 

My 84/302 had an exhaust leak. It was the heat riser valve itself. I ended up replacing the manifold, and valve. I didn't think the stock Y pipe would fit, unless I replaced the valve.

 

Thanks!

The exhaust shop will custom fit the pipe, I just didn't know if I could get by without the heat riser valve on there. I assume there is one on the other side as well, so I didn't know if having the valve on one side and not the other would cause back pressure issues or if not having the valve would be problematic elsewhere. Pricing this stuff out it appears that the heat riser valve through LMC is more than the manifold!

If I don't need it then I am going to opt for just a manifold and let them do the "pipe work" for me.

 

There is only one heat riser per engine. It blocks the exhaust from going down one side, which forces it to go under the carb to the other side of the engine. There is a exhaust port on each cylinder head that is connected through a passage in the intake.

What this does is warm up the intake and carb quickly to make it run good in cold weather. This along with the original aircleaner and heat stove around the exhaust lets you start the engine cold and pretty much take off.

It depends on your engine setup. If the valve wasn't even hooked up or working in the first place, then I guess you don't need it. If you don't have the valve but still have the original aircleaner with the heat pipe in the snorkel and it all works, I have found that is good enough to prevent the carb from icing up. If you don't have anything on it but a chrome aircleaner, I would keep the valve. If you don't, your engine will be very finicky in cold damp weather. It may be already, I don't know your situation and what you have on it.

 

Thanks Franklin!

Honestly, this thing was so "frankenstiened" before I got my hands on it aside from the "Ford" logo it is almost an entirely new vehicle. Case in point: the original Holley carb had been rebuilt and had parts from another Holley carb added so that not even the fuel filter that was supposed to go on it would fit.

The original air cleaner is still on, but the snorkel isn't attached to anything except at the front of the engine well and it is full of holes anyway. I don't recall seeing anything attached to it that leads down to the exhaust, but I will check tomorrow when I am crawling around in there.

I just replaced the carb with an Edelbrock and also I don't remember seeing anything from the intake down to this valve, but I really wasn't looking either. Being in NC there isn't a lot of cold, damp weather I have to contend with, so I am not too worried about that. I was more concerned with something else going wrong if I didn't put it on there.

If I see something attached to it or something that looks to be part of this setup you are talking about I will post some pictures and make sure before I get a new manifold and leave this off.

Like I said, it is an old work truck that isn't used more than a couple of times a week at most and is never driven outside my county.

 

Sounds like it's probably not working anyway. If it runs ok for your purposes, then save your money. If you run into problems in the winter, you could get the aircleaner thing going again. It doesn't have to be but around 40 degrees and rainy for it to take a fit.

 

I have a similar problem and I found a heat riser on fleabay. it cost $50 but took me a while to find.

 

There's not really anything external that you can see......the exhaust is all directed internally when the valve operates.

That valve on my truck has been welded in the 'open' position by the previous owner......presumably he was trying to avoid reliability problems.

We only have a frost or two a year here, & not having the valve operating doesn't cause any problem; but the hot/cold ducting on the air cleaner is all functional.

 

Everyone I've ever seen was welded open, of course Central and South Texas, don't see alot of cold weather

 

Then I would be shocked if mine ever worked! I confess the last few months I have learned a lot more about these trucks than since the day it was given to me by the MIL. New carb and all kinds of stuff replaced to keep it on the road when the wife's car died and we had to replace the motor. This old girl went from a once in a while to daily driver. She's running better now than ever but this exhaust leak got me today when I had to get an inspection. They wouldn't even look at it until that was fixed.

Anyway, I appreciate the help, I think I am going to go with the cheaper option and be done. Old girl just needs to be kept on the road and no more than I will drive it now that the wife's car is back I think that is the best option.

 

It's been a while ago, but IIRC, my manifold and heat riser came from Rock Auto. A little cheaper.


Good Luck!