Rebuilding my stocker '83 302 and the two emission items I'd like opinions on are the heat riser valve located post of the driver's cast iron header and the intake manifold preheater valve located on the passenger side of the stock intake manifold (running stock 2150 electric choke carb). Of the two my heat riser valve is shot and LMC sells it for about 150.00 but the vac valve on the intake manifold was able to work free with a lot of pentrating oil and elbow grease.

My main question: Are these items worth hooking back up? I heard both aid in initial cold weather startups which I have here in Virginia. I also heard both are considered a waste since eventually both with seize with carbon...if the heat riser valve seizes when closed the truck will run like *@#! and if the intake manifold seizes open again we're talking not only poor perforance but to free these items takes some major disassmembly.

If I hook them back up is there maintanence I can do to prevent them from seizing?

If I don't hook them up is there a spacer I can swap with the ol heat riser valve? Thinking I'd leave the intake manifold valve disconnected with the blutterfly in the closed postion?

 

You are absolutely correct that they assist with cold starts. The heat riser will give you the warm air needed to run properly at start. I would look in junk yards for that piece. If frozen, attempt some lube and work it by hand. The intake manifold diverter is hard to come by and I have seen some that are just plain junk after carbon build up. I have attempted to free them with no success, but have also found operational ones in the junk yard. I would leave that for last.

 

You can buy a new exhaust manifold in the store that does not use the heat riser, it's made to bolt right to the y-pipe. Last time I looked they were about $80.

If you disconnect any of this stuff you MUST use the original air cleaner and make sure the vacuum door in the snorkel is working and the hose is hooked to the heat stove on the exhaust manifold. The engine barely makes it with just the aircleaner heat and the restrictors installed in the intake gaskets. If you get rid of the head riser in the exhaust manifold, I would lock the door open on the intake and use the restrictors that come with the gasket kit.

Whatever you choose is going to require some work. The stuff you are working with is froze up, usually the heat stove around the exhaust that goes to the aircleaner is rusted and has fallen off.

If all the heat devices are working, and the choke is properly adjusted, the engine will start and run almost as quickly as fuel injection when the engine is cold. Each thing you get rid of will make it more and more cold natured.

 

I do want it to run well when winter comes. Being a stocker I don't mind some power loss. Where could I find a new heat riser valve (other options beside LMC)? My snorkel valve is toast so any direction here will help for a replacement. Yes the stove is long gone...if anyone has a picture I'm sure I can weld one up. Lastly, the vac lines to my snorkel left with stove...any idea where / how I hook new replacement vac lines to get it to work properly? Loaded questions I know but I'll appreciate any help.

 

The vacuum lines are generally pretty easy to install, post some pictures and ask again when you get to the point of actually installing stuff and trying to make it work.

 

My page on air cleaners (Air Cleaners - Gary's Garagemahal) shows how the vacuum lines should run. You can get bulk vacuum hose from the parts store and cut it to fit.

On the heat riser valve, the majority of the V8's I've been around don't have it nor the valve in the intake manifold. Only the 351HO's and some of the 302's had it. And, as Dave suggested, it takes a different exhaust manifold to do w/o it - or remove the flapper and plug the holes. Anyway, I think the truck might need a jetting change w/o it to drive perfectly, but I'd bet it could be easily done - assuming you have the whole air cleaner setup with the heat stove, et al.

 

Thank you, Gary.

 

Awesome info Gary! Thank you