george landis

Will 400 exhaust manifolds (X&Y's) work and fit on a 68 olds 350?


Thanks

olds 307 and 403

Unfortunately, no.

joe_padavano

The taller deck height of the BBO allows the manifolds to be taller as well. Putting these BBO manifolds on an SBO usually results in problems with the manifolds hitting the oil filter mount, motor mounts, etc. If you are doing this because you want the looks of true "dual" exhaust manifolds, don't waste your time. The X/Y manifolds are open plenum designs, just like the SBO manifolds. There is no performance benefit over simply using a cap on the SBO manifold, like the factory did.

The real BBO W/Z manifolds have individual runners and do improve performance. Those do NOT fit on an SBO. The aftermarket alleged "W/Z-like" manifolds for SBOs do not have the individual runners that the BBO versions do, and thus do not flow any better.

george landis

Thanks for the replies. Was trying to use my original 400E manifolds so I could just bolt up the existing exhaust pipes. Trip to the muffler shop for refit.


George

joe_padavano

The X/Y manifolds are not as large as the W/Z manifolds and might actually fit on an SBO (I have not tried this), but even if they do, the lower deck height will put the outlets in a different place than on the original motor, so pipes may not align anyway.

george landis

Installed a 68 SBO 350 into my 67 442. Interestingly the passenger side SBO manifold ( has the number 4 on it) aligned right up with the original 400E exhaust pipe. The flare and two bolt flange plate fit great. The drivers side SBO manifold (has a number 1 on it) has two studs with brass nuts just like the passenger side did. However the drivers side SBO manifolds two studs are narrower than either the passenger side manifold or the original 400E W&X manifolds. The original drivers side BBO manifold (X) two studs are 3.65" center to center. The SBO drivers side manifold (1) two studs are 3.45" apart center to center. Even though the SBO drivers side manifold did align nicely with the original 400E exhaust up pipe. The two hole flange plate was too wide. So I put the 400E X exhaust manifold on. Thinking the wider studs would then line up with the original two holed flange plate. Which they would have. However the 400E X exhaust manifold being down further laid against the starter solenoid. Making it impossible to slide the two hole flange plate up to the studs. Time to go to the muffler shop for the correct two hole flange plate for the drivers side.


Thanks again for everyone's inputs. I learn something's today.


George

young olds

the drivers side manifold for single exhaust has a smaller outlet and bolt pattern for the crossover pipe. i had a sbo in a car with exhaust built for a big block, which it had at one point, although i got the pipes to bolt to the manifolds i always had exhaust leaks cause the angle that they mated at wasnt quite right.

joe_padavano

This is correct, but just to restate so there's no confusion, the LH manifold on a 350 is the same for both single and dual exhaust applications (as worded one could misinterpret the statement to mean it applied to single exhaust applications only). The SBO manifold outlet is smaller than the one on the O.P.'s 400 manifold, thus the fitment problems.