Exhaust manifold collector size?

[Gearhed]

Does anyone know what size the collector is on the stock 318 M-body exhaust manifolds? I know it's a ball and socket style, and the exhaust is 1 7/8 from the cat back, but what size is the pipe right before the primary catalytic converters? Also, anyone know the bolt spacing of the 2 bolts?

Looking at building my own "canadian-style" y pipe

 

[BudW]

I just now saw this post (must of missed it).

Does anyone know what size the collector is on the stock 318 M-body exhaust manifolds?

It depends on the year built and if a HP (police) or not.

- The factory Y-pipe on my '77 318 2-bbl wagon has 2-1/4” down pipes which converts to 2-1/2” after the Y (three pipes welded at one location).
- I have a Y-pipe I swiped off of a '80 wagon with 318 2-bbl – which is 100% 2” pipe. This pipe has two pieces of pipe. The Left side pipe is un-cut with the right side down welded onto it.
- The Y-pipe on my '86 Fifth Ave 318 2-bbl (with pre-cats) has 1-7/8” down pipes which are welded to a 2-1/4” exit (three pipes welded at one location).

I don't have any 318 exhaust manifolds removed to perform manifold exit hole measurements.

Looking at building my own "canadian-style" y pipe

Great!
You might talk to the exhaust shop about making a few, then selling them here. I wouldn't mind buying one, myself.
BudW

 

[Gearhed]

Thanks, budw. That's also the same measurements I got when I measured mine the other day, so now I know I'm on the right track. Mines 2" primaries, 2" into the main cat, 1 7/8 from cat back. I work in auto parts, so i can get any of the Walker crap fairly cheap. Walker's catalog doesn't even list the Canadian y pipe anymore, at least not in the US. I got a y pipe that I'll be modifying, it's for a 318 Dakota, I believe 95-99 with Federal emissions. The ball/socket flares are the right size, and it's a 2" primary, 2.5" after the y. I also bought a random 2" tail pipe to scavenge some bends and straight pieces from. When I get started building I'll make a project thread and try and document the process pretty well.

 

[Gearhed]

Finally starting this project, half a year later. Anyone have any tips on removing the the stock y pipe with the cats? I'd prefer to not cut it up to remove it, so I can use it to pattern the new one after. Bolts on the driver side are turning with the nut, and I cant seem to get a wrench on the manifold side. Can't even figure out how to get anything on the passenger side nuts, the cats are in the way

 

[BudW]

Can't even figure out how to get anything on the passenger side nuts, the cats are in the way

They were rather difficult to remove, even when the cars were new.
Those fasteners are notorious for ends rounding off. Removing a rounded-off bolt (or nut) is rather difficult.

The easiest way is to drop the engine/transmission down along with the K-frame as one big assembly. You have a straight shot at the bolts as well as can add your new Y-pipe (or fabricate one) before installing the assembly back into the car. A bit overkill, yes - but at least it is an option.



Work on the drivers side, first. You most likely will need to cut the old bolts off – which is not a fun job. On the Y that I removed the car (mentioned above), I used a Dremel using fiber reinforced metal cutting blades (and tore up a few of 'em) as well as a Sawzall (with a blade assortment). Even without cats, it was not easy.

If you still can't get to the passenger side fasteners off, and if you have the car up high enough, a person might be able to remove the passenger side exhaust manifold from engine and remove the Y with manifold out from under car...maybe. This is pretty much impossible to do on the drivers side. That said, It will take 3 or 4 hands to man-handle it.
Removing the starter and the oil filter before you start will help, a lot.

Don't plan on reusing the bolts.
BudW

 

[Mikes5thAve]

Try being creative thru the access holes in the fenders with the covers on them. Thats how i got to at least one side. It does make it next to impossible thanks to the pre cats.

 

[Gearhed]

Just to update this, I built the new y pipe, modifying the dakota one was actually pretty easy. I made a thread in the projects section: Custom y-pipe diy (new substitute for the NLA canadian pipe?)