tmaleck

Some may not consider this a major project, but it feels like it to me... :-)
My 330 did not like being submerged so I decided to put in a fresh built 403 I had bought recently. In the MAW spirit, I bought a FITech throttle body fuel injection kit, stand alone Derale trans cooler with fan, and a bunch of other stuff. Not to debate the merits of these, but I bought a set of Thortons 350 manifolds. I have the O2 sensor about 12 inches from the flange on the left side.
My question is would you use gaskets on the manifold to head exhaust ports, or run them without as stock. I've read a lot about how any exhaust leak can cause trouble with theses systems, and a big reason I went this way was starting and driveability issues.

I'm looking to get the engine in and running this weekend, any thoughts are appreciated.
Tim

joe_padavano

Never used a gasket on any stock manifolds (except the welded tubular manifolds on the roller cam 307s, as per factory) and never needed them. I can't speak to the flatness of aftermarket manifolds, as I have zero experience with them.

I will say that I am skeptical of what you've read. The O2 sensor is not active or used during starting, so leaks would have exactly zero impact on starting. Any exhaust leak large enough to cause a driveability issue will also be loud enough to be obvious and annoying.

quaddriver

an exhaust leak large enuf to throw off the o2 sensor will have been busted by the cops long ago for noise.

Where you have the O2S, does it see the output of BOTH banks? It really should seeing as it measures O2 counts per unit time in the ECM, if not both banks, it will consistently read rich. (ignore what I said if this system is capable of reading 1 bank in a dual exhaust situation and just uses 1 O2S - the programming will have this accounted for)