Original 1969 L-71 3880828 casting Exhaust manifold failed

[Dan M.]

The car is all original numbers matching. Car build date 3/5/69 and motor build date Jan 24th 1969. I'm in need of a replacement exhaust manifold and would like to keep it as original as possible.  Need help on where to buy and or any other advice. Can send PICS but it blew out on the back side of #6 cylinder just past the flange. It looks like a casting flaw as the material is very thin.

Thanks in advance for your help and suggestions.

Dan NCRS 35068

[Joe L.]

Re: Original 1969 L-71 3880828 casting Exhaust manifold failed

The car is all original numbers matching. Car build date 3/5/69 and motor build date Jan 24th 1969. I'm in need of a replacement exhaust manifold and would like to keep it as original as possible.  Need help on where to buy and or any other advice. Can send PICS but it blew out on the back side of #6 cylinder just past the flange. It looks like a casting flaw as the material is very thin.

Thanks in advance for your help and suggestions.

Dan NCRS 35068

Dan------


These manifolds can be found on eBay. You might even be able to find one with a date that's "correct" for your car. However, keep in mind that these dates are on the rear side of the manifold as-installed and are difficult to see.

Reproductions of these manifolds are also available.

Keep in mind that you need the version of the manifold with air injection fittings; not all examples of this casting number are equipped with these.

[Joseph W.]

Re: Original 1969 L-71 3880828 casting Exhaust manifold failed

I would call and email pictures of your manifold to Lock and Stitch in Turlock CA.
They are the world leaders in cast iron repair.
When I picked up my block after repair, I saw many different GM exhaust manifolds being repaired.
Those guys can perform miracles on damaged cast iron.

https://www.locknstitch.com/

[Duke W.]

Re: Original 1969 L-71 3880828 casting Exhaust manifold failed

Casting flaw or not ported vacuum advance and injected air likely accelerated that failure.

Duke

[Joseph W.]

Re: Original 1969 L-71 3880828 casting Exhaust manifold failed

Casting flaw or not ported vacuum advance and injected air likely accelerated that failure.

Duke

Duke,
can you elaborate on the not ported vacuum advance/ injected air comment?
The above mentioned things will slowly erode the cast iron?
Trying to learn and understand. Thanks!

[Mark E.]

Re: Original 1969 L-71 3880828 casting Exhaust manifold failed

I have a Paragon reproduction BB manifold. Looks perfect and sealed up against the head. Got to choose the casting date too.

They're part of Corvette Central now.

[Duke W.]

Re: Original 1969 L-71 3880828 casting Exhaust manifold failed

Duke,
can you elaborate on the not ported vacuum advance/ injected air comment?
The above mentioned things will slowly erode the cast iron?
Trying to learn and understand. Thanks!

Ported vacuum advance along with air injection was part of emission control to oxidize HC and CO. By not allowing vacuum advance to get something close to optimal idle advance, EGT increased to about 900F. With full time vacuum advance EGT would be closer to about 500F.

So hot cast iron plus injected air (oxygen) equalsl much more rapid oxidation of the cast iron than with cooler EGT and no air injection.

Duke

[Joseph W.]

Re: Original 1969 L-71 3880828 casting Exhaust manifold failed

Thank you Duke!
So it may not be repairable.

[Duke W.]

Re: Original 1969 L-71 3880828 casting Exhaust manifold failed

It may be reparable via the method described in post #3, but it may actually be less expensive to buy a serviceable replacement. Also all OE L-72 and L-71 had ported vacuum advance as OE back to '66, and I recommend converting to full time as long as field emission testing is not required.

The OE L-72 12" VAC is okay as it passes the 2" rule (assuming an OE cam), but L-71s will require the 201 15 15.5" OE VAC be replaced with a 12" such as the NAPA VC-1765 or equivalent in another brand.

More in info on this in my tuning seminal, which is attached to the restoration documents thread at the end of the sticky section.

Duke

[Mark F.]

Re: Original 1969 L-71 3880828 casting Exhaust manifold failed

Duke, can you elaborate on the not ported vacuum advance/ injected air comment? The above mentioned things will slowly erode the cast iron? Trying to learn and understand. Thanks!

I believe this is the one Duke is pointing you to in the Database of Restoration Documents [DoRD] Sticky Post

Tuning and Timing

Duke Williams 2012 Nationals tuning seminar.pdf

[Dan M.]

Re: Original 1969 L-71 3880828 casting Exhaust manifold failed

Thanks to all for the advice and input. This is why I love this site its full of knowable people willing to share.

Thanks
Dan