Converting 69 sb to 2.5" manifolds

[Martyn T.]

Can anyone tell me the combination of manifolds or a way to add 2.5" factory sb manifolds to my 69 with a 383 and keep the alternator on the driver side ? It has later heads with the 2 3/8" holes I believe would take a later alternator bracket ? I would like to use factory factory ram horns. Also, I would assume the 2.5" front header pipes from a '65 sb would fit in place of the 2- 2.5" pipes I have now ? Just trying to go 2.5 all the way.
Thanks
Marty

[Dan A.]

Re: Converting 69 sb to 2.5" manifolds

I used to have a 69 L46 that a previous owner put 2.5" exhaust manifolds on. The alternator was still on the drivers side but as I recall it there had been some creative alternator bracket configuring that was hard to discern to the casual observer. The car also had A/C and I always had problems finding an A/C belt that would work. It seemed like the bigger exhaust manifold limited the adjustment travel of the compressor which made the belt a pain to install.

[Patrick H.]

Re: Converting 69 sb to 2.5" manifolds

I suspect that you could use an alternator bracket like a 72 and it would work.

You might have to talk to someone like Corvette Central to make you a custom bent piece for each head pipe, but that is likely not too difficult.

[Joe L.]

Re: Converting 69 sb to 2.5" manifolds

Can anyone tell me the combination of manifolds or a way to add 2.5" factory sb manifolds to my 69 with a 383 and keep the alternator on the driver side ? It has later heads with the 2 3/8" holes I believe would take a later alternator bracket ? I would like to use factory factory ram horns. Also, I would assume the 2.5" front header pipes from a '65 sb would fit in place of the 2- 2.5" pipes I have now ? Just trying to go 2.5 all the way.
Thanks
Marty

Marty-------

If you need to retain the AIR (smog) system, you cannot convert to 2-1/2" exhaust manifolds. There was never a 2-1/2" outlet manifold made that was designed to accommodate AIR.

If you are not going to maintain AIR, then you would use manifold GM casting #3846563 for the left side. This manifold has an integral alternator bracket the same as your existing 3872765 but is 2-1/2" outlet.

For the right side you could use a GM casting #3797902 (without choke tube). This manifold will have an alternator bracket on the forward end which will be unused for your application. You could also use a GM casting #3797942 (without choke tube) which has no alternator bracket but these are very hard to find.

Your big problem will be the forward exhaust pipes. None were ever made for a C3 small block with 2-1/2" outlet manifolds. You might be able to use forward pipes with some modifications from a 1965 small block with 2-1/2" manifolds modifications. I can't say with any certainty, though. Otherwise, you'll have to have some custom made.

[Tom P.]

Re: Converting 69 sb to 2.5" manifolds

The 63-65 (and 62) came with 2 1/2in manifolds which are a direct bolt-on fit for 66-later SBs. If I remember correctly, the 63-65 2 1/2in FRONT pipes will be a direct bolt-on fit between the manifolds and the cross member.

There were TWO different left side manifolds for 62-65. The 62-3 manifolds had an alternator mounting bracket with two threaded holes facing the left side. The 64-5 manifolds had a FORWARD facing bracket with two holes.
The right manifold had a bracket with two right facing holes.

Below are comparrisons between 62-3 and 64-5 LEFT side manifolds (the upper manifold is a Chinese copy, which FUNCTIONALLY is quite good).




This is the right side manifold.


There was also a 942 PLAIN manifold with NO bracket which could be used on either side depending on engine configuration (air cond, FI, etc).


A 62-63 style LEFT manifold and alternation brackets can be used if you prefer. Both 63 Vettes and 64-68 Chevelles and Novas used the same type of left side alt bracket as seen below.

[Joe L.]

Re: Converting 69 sb to 2.5" manifolds

The 63-65 (and 62) came with 2 1/2in manifolds which are a direct bolt-on fit for 66-later SBs. If I remember correctly, the 63-65 2 1/2in FRONT pipes will be a direct bolt-on fit between the manifolds and the cross member.

There were TWO different left side manifolds for 62-65. The 62-3 manifolds had an alternator mounting bracket with two threaded holes facing the left side. The 64-5 manifolds had a FORWARD facing bracket with two holes.
The right manifold had a bracket with two right facing holes.

Below are comparrisons between 62-3 and 64-5 LEFT side manifolds (the upper manifold is a Chinese copy, which FUNCTIONALLY is quite good).




This is the right side manifold.


There was also a 942 PLAIN manifold with NO bracket which could be used on either side depending on engine configuration (air cond, FI, etc).


A 62-63 style LEFT manifold and alternation brackets can be used if you prefer. Both 63 Vettes and 64-68 Chevelles and Novas used the same type of left side alt bracket as seen below.

Tom------

The manifolds I mentioned in my post are among those you picture. The manifold in your third photo is the GM casting #3797902. As I described in my post above, that can be used on the right side if the unused alternator bracket does not bother one. If it does, the GM casting #3797942 shown in your fourth photo can be used.

The GM casting #3846563, shown in your second photo, can be used for the left side. The integral generator bracket is exactly the same as used on the stock small block, left side manifold used for 1969, so the alternator will mount perfectly using the existing 1969 separate support bracket.

The manifold shown in your first photo would not be of practical use in the conversion which is the subject of this thread.

The bracket shown in your last photo is designed for use for applications with log-type manifolds (as also seen in the photo). I don't think it will work with ram's horn type manifolds. If a separate alternator mounting bracket were to be used, which would require the use of the 3797942 manifold (or the manifold shown in your first photo with the integral bracket oriented towards the rear), a GM #3951337 or 14015539 can be used.

I don't think the forward pipes from a 2-1/2" outlet 63-65 small block application will be a direct bolt-on for a 1969 application. As I mentioned, they might work but I think they'll need at least slight reconfiguration.

[Martyn T.]

Re: Converting 69 sb to 2.5" manifolds

Thanks to all ! That cures the manifold issue. I'll call CC and check if 63-65 front pipes will work. Seems to me that everything under the car is the same ?, but I'll check.
Thanks again to all !
Marty

[Tom P.]

Re: Converting 69 sb to 2.5" manifolds

Joe,
The 63 used the 901 style manifold (first picture) with an alternator mounting setup similar to the last picture (on a Chevelle). I realize that is not what would have been on a 69, but it would seem that the 901 and 63 style alt brackets should work.
Since the original style 563 is no longer available----------------and not even Chinese copies are not made, then a 901 and 63 brackets (which were used on early Chevelles) should work. Now, if he could locate a nice original 563, OR, one of the later GM service replacement 563 manifolds (which were finally discontinued several years ago), that would be even better.

[Joe L.]

Re: Converting 69 sb to 2.5" manifolds

Joe,
The 63 used the 901 style manifold (first picture) with an alternator mounting setup similar to the last picture (on a Chevelle). I realize that is not what would have been on a 69, but it would seem that the 901 and 63 style alt brackets should work.
Since the original style 563 is no longer available----------------and not even Chinese copies are not made, then a 901 and 63 brackets (which were used on early Chevelles) should work. Now, if he could locate a nice original 563, OR, one of the later GM service replacement 563 manifolds (which were finally discontinued several years ago), that would be even better.

Tom-----


The '563' is available in reproduction.

[Tom P.]

Re: Converting 69 sb to 2.5" manifolds

At an astronomical price!

[Joe L.]

Re: Converting 69 sb to 2.5" manifolds

At an astronomical price!

Tom-----


I never said this conversion was going to be cheap. As a matter of fact, I don't think this conversion is worth the cost.

[Martin M.]

Re: Converting 69 sb to 2.5" manifolds

It seems to me I got a mount from Summit/Jegs some time ago that bolted onto the exhaust manifold and had an adjustable sliding part that allowed accurate alignment of the belt. I couldn't see it in their catalogs but it helped me in moving 'Something" from the passenger to the driver's side. That was back in my hot rod days. Actually I still have that car but it is buried.

[Jeff P.]

Re: Converting 69 sb to 2.5" manifolds

Mr Gasket makes Alternator Brkt's that mount to the front two bolts on the exhaust manifold.