[79 Phoenix]

I just installed a 76 400 in my 71 GT-37 with 3 speed manual. As near as I can tell this manifold originally came from a 73 Firebird. Most recently the engine came out of a 71 Firebird.

I am planning on using a local exhaust shop to do the exhaust. The can do custom bending.

The clearance to the frame is pretty close (approx 1/2") but I think the flange and dowpipe should go on okay allowing the pipe to be routed correctly to the rear.
(Note: Last picture is from to view)

ANY THOUGHTS? IS THERE ANYTHING I'M MISSING OR NOT CONSIDERING? Thanks.

[steve25]

The motor is going to rock to that side, so I don’t think that 1/2” will be enough.

You need to consider that the frame is going to move some when driving also.

Maybe you can move the motor mount frame brackets up a bit higher .
The action of spreading them a part will lower the motor.

[Schurkey]

Originally Posted by 79 Phoenix

I am planning on using a local exhaust shop to do the exhaust. The can do custom bending.

EVERY "exhaust shop" can do custom bending.

99% of them are doing crush-bends. Very few have the capacity to do mandrel bends. Crush-bends are a waste of potential on any performance-oriented vehicle.

There isn't enough clearance. There's numerous "fixes" for that, starting with--but not limited to--getting a different exhaust manifold.

[79 Phoenix]

Originally Posted by Schurkey

EVERY "exhaust shop" can do custom bending.

99% of them are doing crush-bends. Very few have the capacity to do mandrel bends. Crush-bends are a waste of potential on any performance-oriented vehicle.

There isn't enough clearance. There's numerous "fixes" for that, starting with--but not limited to--getting a different exhaust manifold.

Any idea how I can determine which left side manifold will give enough clearance on my 71 GT-37? The 6X heads have 6 bolt holes. Unlike the left side which has minimal clearance, the right side manifold leaves plenty of clearance., As near as I can tell, right side manifold was originally from a 65 GTO. Number is 9779328.

[steve25]

Any drivers side A body exh manifold that has a casting date of 1968 to 1972 will work with out question, and there may be many more but I can’t get into my parts info until later today.

[79 Phoenix]

Originally Posted by steve25

Any drivers side A body exh manifold that has a casting date of 1968 to 1972 will work with out question, and there may be many more but I can’t get into my parts info until later today.

Okay, thanks. Could the 4 bolt manifolds off the original 350 possibly work?

[unruhjonny]

350 manifolds will work - they are the same castings used on the 400 & 455.

[79 Phoenix]

Thanks! That is good news because I have the original manifolds which should line up perfectly clearance-wise. Now I just need to get them off the 350. I doubt if they have ever been off.

It won't be the end of the world if I snap the bolts because I'm not using the engine. I will try to be careful though. I'm thinking heat the bolts and then low torque impact back and forth till they crack.

The bolts currently on the 400 are brass so hopefully they will come off fairly easy... Not sure if I should heat the brass or not.

[79 Phoenix]

I guess all 400s and 455s have 6 bolt holes? So even though my 6X heads on my 400 have 6 bolt holes, manifolds from my 350 with only 4 bolts will work?

[b-man]

Yes, the 4 bolt and six bolt manifolds use the same bolt pattern.

At one point the factory decided to use only 4 bolts no matter what engine size.

Even some 6 bolt manifolds were bolted on using only the middle 4 straight out of the factory, 1965 would be one example.

[79 Phoenix]

When I put the original manifold on from the 350, I found that the clearance was the same as the 73 Firebird manifold . So, since the passages are bigger, I used the Firebird manifold with the 6 bolts. Thanks for your input.