Identifying Exhaust Manifolds

[harnalien]

I have a question as to the difference b/w 350 and 305 exhaust manifolds (i.e. bolt pattern). It is an '84 chevy shortbed. Before i bought the truck, the 305 was replaced w/ a 350, and it may still have the original 305 manifolds on it. i've heard that the 305 manifolds aren't an exact match to the 350, and that could be the cause of the exhaut leak i'm hearing/feeling. I thought it was bad gaskets. my question is is there any way to visually tell the difference b/w the manifolds. On the other hand, i would like to just get headers, but my truck has that opening on the front of the passenger side manifold that goes to the snorkel coming out of my air cleaner. I never see that opening on headers. is that part of the emissions equipment? if i can get headers, do i need to do anything to protect the opening on the bottom side of the snorkel that the vacuum switch is in?

[Prerunner1982]

there shouldnt be any difference.. and the opening is the hot air "chimney".. it heats the air going into the engine, there is a flapper in your air cleaner assembly that opens and closes, when its closed it sucks hot air off the exhaust.. if you have to do emissions testing, they will check for those, or atleast they have on me in the past. They really arent that necessary for the engine to run, The part that the "chimney" actually attaches to should come off of the manifold and you may be able to adapt it to the headers. But I have never seen anyone do that.. I didnt and dont have a problem at all. Manifolds and Headers are pretty universal.. unless it has angled plugs... they mount to basically any small block.

[piecesparts]

IF, and only IF you want the heat riser chimney on your headers, there are aftermarket risers sold that will clamp onto the header to allow for heated air to go to the air snorkel. Most of us, toss the original air cleaner or hack it up to where the snorkel is laying behind the garage, so we don't use the heat riser.

The exhaust manifolds on the 305 and the 350 are the same (they are both Small Block Chevy motors)

[Slonaker]

The 305 and the 350 have different spacing on the bolts on the exhaust manifold. Look at the bolt holes on the back of the head in the linked pic below. It is a universal replacement engine, so it is drilled for both.

http://www.sdpc2000.com/images/produ...27_2784194.jpg

Also, on all of the later tucks I have seen, the 305s have manifolds that go over the plug. The 350s all have manifolds that go under the plugs.

If your manifolds have all of the bolts in place, you have the right ones for your engine. Either that, or you have a universal engine like the one above or you have adapters that adapt from one bolt pattern to the other. I have some pics of the adapters that a board member had on his truck after he had his original 305 replaced with a 350 if you need to see what they look like.

Small blocks don't use gaskets on the exhaust manifolds unless they leak, usually because of rust. They come without from the factory. If you don't have any, maybe you need to add some. Your manifold could also be cracked. It happens sometimes...

Whenever I get leaks, it is usually at the donut between the manifold and the pipe. I usually check for leaks with my bare hand. You will feel hot exhaust blowing from the source of the leak if you put it near the leak. It only hurts if you accidentally touch something!

Slonaker

[piecesparts]

I changed out my factory 305 in my 84 truck for a 350 and the manifolds were the ones that go under the plugs, so I don't know how much later the manifolds were like described above. The manifolds bolted into the holes without any problem, so I had no problems. SLONAKER is right about the universal head availability on the replacement motors, and it is a great deal for the changeout.

[Slonaker]

Originally Posted by piecesparts

I changed out my factory 305 in my 84 truck for a 350 and the manifolds were the ones that go under the plugs, so I don't know how much later the manifolds were like described above. The manifolds bolted into the holes without any problem, so I had no problems. SLONAKER is right about the universal head availability on the replacement motors, and it is a great deal for the changeout.

I don't know for a fact that all 305s have the manifolds that go over the plugs. It has just been my observation. I am pretty sure my '86 shop manual shows that configuration for that year, though.

The information regarding the bolt pattern came from a friend who is a GM mechanic. He also owned a junkyard specializing in GM trucks back in the 1980s and 1990s, and is an amazing resource for SBC information.

Slonaker

[mhicks]

For a truck that old, you don't need the haot air chimney. At least not in Texas. I live in Weatherford and Parker county is one of the counties that require the emmissions test and they are not required for that year model.

[Prerunner1982]

I dont recall my 350 having those, but i knwo they did reuse my 305 manifolds.. might just be a hit and miss thing.. by over the plug do you mean ram horns?..

[Slonaker]

Originally Posted by Prerunner1982

I dont recall my 350 having those, but i knwo they did reuse my 305 manifolds.. might just be a hit and miss thing.. by over the plug do you mean ram horns?..

Mine go over the plugs like ram's horns, but they are not that style. I wish they were. My first choice would be 2.5" Corvette Ram's horns.

This stuff probably is hit and miss. The trucks we have are pretty old, and have usually been messed with a lot. GM has never been known for consistency either.

Slonaker

[harnalien]

I've been doing some looking, and i've found a couple on Summit that would work. http://store.summitracing.com/partde...40140+400065+0 http://store.summitracing.com/partde...5&autoview=sku. They are the kits, but i couldn't find any of the heat riser "clamps" referred to earlier. The stock replacements from o'reilly are $134 each. Summit headers would work fine if i could find the clamps.

[Slonaker]

Originally Posted by harnalien

I've been doing some looking, and i've found a couple on Summit that would work. http://store.summitracing.com/partde...40140+400065+0 http://store.summitracing.com/partde...5&autoview=sku. They are the kits, but i couldn't find any of the heat riser "clamps" referred to earlier. The stock replacements from o'reilly are $134 each. Summit headers would work fine if i could find the clamps.

I would be more worried about the air pump stuff than the heat riser clamp thingy. AFAIK, emissions testing is required in Fort Worth, and I assume (maybe incorrectly) that you need the AIR pump installed and working.

Slonaker

[harnalien]

Actually, my truck doesn't have the AIR equipment on it, just the heat riser.

[magnethead]

I believe emmisions only applies vehicle between 2 and 20 years old from build date. So if your truck is a 86 or older, you can trash any/all emmisions stuff i believe.

[harnalien]

The TXDOT website says 2-24 years old, http://www.txdps.state.tx.us/vi/insp.../item_insp.asp , but i don't know if that emissions stuff still needs to be on for visual inspection. i'm getting the truck inspected for the last time in january, then getting the engine swap afterwards, so we'll see. it will be 24 years old in 2008.

[Mooshoo]

305 maifolds run above the plugs, and the big difference is that the 350 oil pan won't allow the dipstick to pass the manifold if you have 305 manifolds on it

[Slonaker]

Originally Posted by Mooshoo

305 maifolds run above the plugs, and the big difference is that the 350 oil pan won't allow the dipstick to pass the manifold if you have 305 manifolds on it

I have a 350 with 305 manifolds. No dipstick problems.

Slonaker

[Jonboy]

Originally Posted by harnalien

The TXDOT website says 2-24 years old, http://www.txdps.state.tx.us/vi/insp.../item_insp.asp , but i don't know if that emissions stuff still needs to be on for visual inspection. i'm getting the truck inspected for the last time in january, then getting the engine swap afterwards, so we'll see. it will be 24 years old in 2008.

My old 87 has passed for the last 3 years with no AIR pump. As long as it will pass the sniffer test they usually will not bust on you too bad.

[MylilBowTie]

Its just two different styles of manifolds over and under. I don't think it makes a difference as to the over under vs 305-350. I have seen both 305's and 350's with both style manifolds. I'm not sure why some of the heads had 7 bolts (305's from what I have noticed) and the majority had 6 (older 305/350's). But there is an adapter flange that will allow 7 bolt manifolds to bolt up with a 6 bolt head. Could be just a transition years with newer 7 bolt heads and phasing out the older 6 bolt heads. With most any aftermarket or newer heads 88+ (I think not positive on year) are 7 bolt. Then in 80-81 the oil dipstick move from the earlier driverside of the block to the passenger side.

So that is where a lot of problems come from with swapping different year parts. With manifolds you have to go with what side your dipstick tube is on. Then if the cylinder heads are 6 or 7 bolt will work along with the manifold. 6 bolt manifolds will bolt on most heads with 6 or 7 bolt. If you have a 7 bolt manifold and 6 bolt head you would most likely need the adapter. This will allow the manifold to seal better than if not using it. If going with headers it makes it much easier to get around swapping different year parts. Most headers are 6 bolt flange and pretty much open so it doesn't matter what side the dipstick is on. You can bend your oil tube a little or get an aftermarket dipstick.

[mySAVIOReigns]

I hate to be too off topic, but what exactly happens when you have an exhaust leak? I've had this problem that people have said sounds like it could be that, but I'm not sure. Any clear symptoms to look for?

[MylilBowTie]

http://video.google.com/videoplay?do...ust+leak&hl=en

That is about the closest thing I can find to what it sounds like.

[harnalien]

that video is pretty close to what mine sounded like before i replaced the gaskets. kind of a raspy tapping sound, especially under acceleration.

[7387chevys]

I think he was thinking 80 up manafolds on 79-back block........least thats what ive always herd wont work.......as far as the exhaust leak most annyoing tapping sound in the world....go with full length headers even if it does get a leak it isnt as noticible because they exit under the cab as opposed to in engine compartment......I fought manafold doughnut gaskets long enough....headers are the only way to go(plus that extra 3 mpg is nice)
Shane

[piecesparts]

Throwing the stock m anifolds away is the way I would go. The headers opens up the free flowing gases and the performance follows. There are ways to m ake headers reliable on sealing. I have had them on my vehicles for years and I seem to have no leaks to speak of.