I notice what sounds like an exhaust leak when I drive my 56 Fairlane with 292. I changed to a 57 B manifold and Autolite carb and it runs good but I hear a pfft pfft pfft when driving it. I don't hear it idling nor when I rev it at a stop. I checked for loose bolts and tightened the few I found but no change. I even plugged the heat line to the choke but no luck. I haven't seen any signs of exhaust soot around the intake nor at the exhaust manifolds. For something so seemingly simple it has me stumped.
Any suggestions where I should concentrate my search? I don't recall hearing the leak when I had the original intake and carb.


~DJ~ AKA "Bleach"
1956 Ford Fairlane Town Sedan 30K original miles

Sound dumb but did you plug both ends of the tube for the choke thru the exhaust crossover heater. On my dual quad manifold I found the rear tube leaked and made the sound your discribing. I had to plug both ends and use the front one for the rear carb which has the choke.

56 Vic, B'Ville 200 MPH Club Member, So Cal.

I had a similar Noise that I couldn't find.  Wasn't there when idling or revved up in Neutral. Only when Engine was under Load. Finally figured out the Gasket between Exhaust Manifold and Head had burned out at lower rear near Firewall. Couldn't see it visually from Top. Only noticeable under Load. The Manifold Flanges on mine are  not flat and won't seal to Head without Aftermarket Gaskets.You might consider that possibility. 

  

there two heat riser holes one on each side of the manifold make sure you plug both, plug may have come out of one. my 56 merc sounded the same found open heat riser hole plug it stoped noise, I now have both sides pluged 

The other hole on the drivers side of the manifold appears plugged but I haven't messed with it since getting it from the guy I bought it from. I did find a few loose exhaust manifold bolts and I went ahead and tightened all of them. The one that was a real pain was the rear passenger bolt. There's no way to get a socket on it yet alone a wrench. I had to alternate between a few different 12 point wrenches to tighten it. Maybe that's where the leak was. It was the loosest bolt of them all.


~DJ~ AKA "Bleach"
1956 Ford Fairlane Town Sedan 30K original miles

I had to take the Rocker Cover off to get a "stubby" 9/16 Wrench on that Bolt. With Cover off its easy. Wouldn't surprise Me if that's your Leak.Tried mine without Gasket before I replaced it and leaked badly because Flange is not Straight. 

  

Oldcar you're right, it would be easier to remove the cover to get to that bolt. I'm not going to mess with it today since it's Sunday. I'll give it another look next Saturday when I have some more time.


~DJ~ AKA "Bleach"
1956 Ford Fairlane Town Sedan 30K original miles

If you want to try the Gaskets I mentioned they install without removing the Manifold. Just back off the Bolts and the Gasket slides in between Head and Manifold. Rock Auto has a very good Price on them I ordered 2 Sets because at some Point I will probably have to replace them again if they burn out. Once every 2-3 Years.

  

I think I'll try the gaskets. It already has gaskets so there must have been a problem before. I found I had some Felpro exhaust gaskets for a Y-block but only one for the manifold. I was surprised they were for a Y-block because I bought the set when I replaced a broken exhaust manifold for my 94 F150 with a 302. I never checked the applications on the box.
Do you have a link for the Rock Auto gaskets?


~DJ~ AKA "Bleach"
1956 Ford Fairlane Town Sedan 30K original miles

Rockauto.com. Select Ford year model engine and click on Exhaust. Listed as Exhaust Manifold Gaskets.Come as a Set of 2 including Pipe to Manifold Gaskets.