bullet1

had a exhaust leak so crawled under her today to find that both exhaust manifolds cracked!anyone have a good line on a set?
thanks

Oldsmaniac

Strange that you would have 2 cracked manifolds, I think Thornton Reproductions sells repro manifolds. Sometimes they turn up on Ebay but condition of flange would be questionable.

bullet1

drivers side cracked near rear bolt and passenger side looks cracked in the middle?i can get these out without pulling motor?
thanks

72 cutlass455

The problem with the cast manifolds is the they become very brittle with age so a repro set is better than one that cracks when you tighten it on. Also might be a good time for a exhaust upgrade to headers if originality is not a problem.

joe_padavano

Thornton sells repro W/Z manifolds, which are correct for 1969-1972 BBO A-body cars. These will work on a 1968 (and will improve exhaust flow) but will not be correct. The 1968 cars used X/Y manifolds, a combo that is unique to that year. These are not the divided runner manifolds like the W/Z manifolds.

bullet1

thought about headers but not sure what to do yet?can anyone tell me of a good fitting set of headers for the 68?
thanks

joe_padavano

Kooks (now sold by Dick Miller) are the best, and priced accordingly (roughly 3X the price of lesser headers).

J-(Chicago)

I have a set of 66 dynamic 88 A/T manifolds if you'd like to try them.
$40 for the pair+ ship.

joe_padavano

Be aware that A/T manifolds are for the full size cars with rear steer and single exhaust and will not work in an A-body car. The LH "A" manifold is center dump, which absolutely will not work on a 1968 442. The RH "T" manifold is a "two flange" design like the SBO RH manifolds and while you can run a cap, it is also not correct for an A-body and may not even clear.

Again, if you want an exact replacement, you need an X/Y set. If you want readily available replacements, the repro W/Z manifolds will work and will slightly improve flow.

bullet1

looks like i will pick up pair of repros not to worried about factory ones.car will be a driver.have a 68 455 to install someday?

Oldsmaniac

Yep, here is what Thornton sells....

High quality GM licensed and approved reproduction part. They are visually and functionally correct. They are NOS quality without the NOS price. Correct replacement for 1965-67 442, Cutlass or any Oldsmobile with a big block. Eliminate hassles and costly repairs for rust pits, cracks and broken exhaust flange bolts. No need for resurfacing the cylinder head to manifold flange. Eliminates exhaust leaks which occur with original used manifolds.
They are the correct GM "X" and "W" manifold for 1965-67 Oldsmobile big blocks with the correct functioning damper. For 1968 the left hand manifold is correct. The right hand manifold for 1968 is the "Y" manifold but it can be replaced with our "W" manifold. It is the same shape and contour and will fit and function properly.

Will fit any 1965-76 big block Oldsmobile but are correct for 1965-67 (1968 LH only).

joe_padavano

Thanks, I was not aware that Thornton also repopped the X/W manifolds. Note that the 65-67 W manifold is NOT the 69-72 W manifold. The 65-67 W is casting no. 389268 and is a RH manifold. The 69-72 W is casting no. 402295 and is a LH manifold.

Of course this means you could run W/W manifolds...

J-(Chicago)

Thanks for the clarification Joe.

Run to Rund

With a mild cam, street use, the branched 69 up manifolds are good. The more cam, the more gain you will get from reducing restriction. for example, Pypes stainless downpipes are 2.25" at the flange, open to 2.5" and are mandrel bent. Stock is 2.25" (some years the left is 2", don't recall which ones) and ordinary restrictive bends that squash the pipes. Even cheap headers are an improvement especially with aggressive camshafts. The biggest problems with headers for street use regard poor fit with some, necessitating massaging them with a hammer, and restricted access to the starter and oil filter (in some cases). If you use either manifolds or headers with header gaskets, retighten the bolts several times over a few weeks until they stabilize. I have tried a number of header gaskets. Some are cheap, like Mr. Gasket 453, others are expensive, Remflex (graphite) and copper. At this point, for long term use without tear downs maybe copper is worth it. I just bought some 453s because they are cheap and seem to work OK for a while. The center divider may burn out (you can wrap it in aluminum foil to extend its life) in a couple years; more likely to happen with headers than the branched manifolds.