273 to 360 exhaust

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Sreyno

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I'm trying to use the 273 manifolds on my 66 cuda. When I put the mufflers on
It leaks from the bottom of the drivers side. The engine is a 76 360 . I closed the smog holes in the heads. But I'm wondering if the 273 manifolds are too small fort the ports in the 360 heads. Maybe not as the right side isn't leaking. Only the left side. Any info would be appreciated.:banghead:
 
Check the head side of the exhaust manifold for warpage.What gaskets did you use?
 
Good gaskets.Fire the car up. Get your hand close to each exhaust port,feel for pulsation of warm air. Double check the head pipe/ gasket connection as well. After that,check the manifold,for warpage. Hopefully ,others chime in as well.
 
Years ago I had the same issue. The 360 head has a raised boss at the air injection port, and the 273 manifold wraps in very close to the head. I had to grind the edge off the boss to get the manifold to sit flat. I guess you could grind the manifold, but I don't know if there's enough material there, and I didn't want to risk it.
 
It seems to me the center ports would be the problem the two end ones would have enough clearance I will check that tomorrow. This engine swap has been a real learning experience! Like putting a square peg in a round hole.
 
If the center gasket is isolated, from the outer 1 and 7 ports,hit it with some hi temp red RTV.Let it dry overnight. I been lucky,a few times.
 
I had the same problem on a 318 build. The leg that wraps under the steering arm was resting on the block and not sealing. I grinded a little of the back of the manifold to let it sit flush. It also seals up with double stacked gaskets.
 
When I tried to put 360 manifolds on my '69 318 I found that the 360 exhaust ports (at the head) were humungous. Of course I was using the '92 Magnum truck manifolds. There just wasn't enough surface for the 360 manifolds to seal against. Turns out I had to swap my heads for the 302 casting which are a little newer and have more surface to seal on. Look at these pics and you'll see why???
In the pics the 318 gasket is painted blue, the 360 gasket is the long (one piece) gasket. When you overlap them the 318 gasket is almost swallowed by the 360. There's almost no overlap at the bottom and this is the area where 302 casting and newer 360 heads have more flat surface.
Hope this helps??

treblig
 

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Treblig said:
When I tried to put 360 manifolds on my '69 318 I found that the 360 exhaust ports (at the head) were humungous. Of course I was using the '92 Magnum truck manifolds. There just wasn't enough surface for the 360 manifolds to seal against. Turns out I had to swap my heads for the 302 casting which are a little newer and have more surface to seal on. Look at these pics and you'll see why???
In the pics the 318 gasket is painted blue, the 360 gasket is the long (one piece) gasket. When you overlap them the 318 gasket is almost swallowed by the 360. There's almost no overlap at the bottom and this is the area where 302 casting and newer 360 heads have more flat surface.
Hope this helps??

treblig
Click to expand...

interesting,,,learn some thing new every day,,wonder what magnum manifolds i have sittting for a future project,,,they may go on a 318,,,so im assuming if there 360 magnum manifolds they will not seal ???
 
The down pipe on the 273 drivers side manifold hits the head causing the #7 port to leak.
 
fstfish66, I'm not saying that you wouldn't be able to get them to seal like "Sreyno" says but you can see the gaskets for your self. I had read many stories about the 360 manifolds leaking so I didn't take any chances, I drive this car around town a lot and hate the smell of exhaust!! The bolt holes are also bigger so the manifold won't center-up on the ports very well. So I got some thin wall pipe/tubing 5/16" ID and cut pieces to put into the bolt holes to help center-up the manifolds. You'll also need to rotate your 90 degree filter. Otherwise it fit perfect. The best thing about it is that now that I'm going to build a 318 stroker with 360 heads the manifolds will be perfect because they are 360 manifolds.

When you have 2 1/2" exhaust pipes it doesn't help at all if the exhaust has to pass through a 1 7/8 restriction on the way to the 2 1/2" pipes. Gas flow is determined by the smallest diameter in your exhaust system.


Treblig
 

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I had to use a mounting flange that my dad cut off of the old fenderwell headers I used to have so the stock DS 273 manifold would fit. The PS manifold is what come with the '73 360 from a Dodge Monaco and it fit nice.

Can't wait to win the lottery so I can afford the headers that are so F'ing expensive....just because they can be for bent exhaust tubing......:banghead:
 
I used air injection smog heads on my 70 Dart with stock manifolds. I carefully ground the boss on the head and the offending part of the exhaust manifold. I use no gaskets just exhaust sealer. No leaks.
 
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