I was test fitting my flipped exhaust manifolds for my twin t3 setup, and I ran into a pretty strange issue. As far as i've been told, they are from a fullsize van, late 80s/early 90s. I had been under the impression that exhaust manifold bolt spacing on a SBC has been the same for years. Im not talking ls1, lt1 or anythign; i mean a gen 1 small block. I know the rear-most bolt (i forget which side) has 2 possible positions, one moved about 1.5" away from the port.

My problem is that the middle 3 bolts will line up, but the back and the front bolt are about 1/8" too far back and forward, repsectively. Heres some pics:







My questions are: Why is this bolt spacing different? And will I be ok to elongate the bolt hole, or just grind away the whole edge, leaving a U shaped hole?

TIA

 

Which lines up with the bolt holes on the actual cylinder head, the exhaust manifold or the gasket? If you grind the exhaust manifold bolt hole open wider, it will line up with the gasket but it still wont line up with the cylinder head if the headers are what is different.

 

Im not sure how well the ports line up, it was pretty late and i didnt bother checking it out. The gasket is from the old headers. I'll have to check on that before i go any further with this.

Any info about why the ports/bolts would be in different locations?

 

I have never heard of different styles, the only thing I can think of is the exhaust manifold has warped from being heat cycled (doubtful because that is a lot of warpage) or the gasket isnt right.

 

I run into this problem everyday, the manifolds "move" you need a manifold spreader, available from most tool guys, snap-on, matco, etc. You install the center two bolts loosely, then the spreader goes between the ports & as you turn the tool it pushes the end port over to line up the holes, then you move to the other port & do the same. It is not a really big deal its just a used manifold.

 

Hmm. Ive never heard of that. I'll have to ask around and see who has one. Is the "spread" permanent or just until you take the bolts out again?

I guess heat-warpage is not unreasonable. A small amount of movement at the bottom of the manifold would translate into a lot of movement at the top, since the flanges arent tied together.

 

Pretty common with 'vette headers and truck manifolds since there is some space between the body of the things and the flanges.

 

[QUOTE]Originally posted by slickrock55
[B]Hmm. Ive never heard of that. I'll have to ask around and see who has one. Is the "spread" permanent or just until you take the bolts out again?

The spreader is only temporary to allow intstallation, once you remove the bolts, it "relaxes" to where ever it desires. It works well. Before I bought the tool, I threw away many manifolds because one bolt or another just wouldn't line up.

 

I guess i've only ever played around with L98-ish manifolds, and those wouldnt experience that problem to this degree.

 

https://www.thirdgen.org/techbb2/sho...73#post2245773

 

This turned out to be an issue of the manifold warping pretty badly. I made a manifold "spreader" with some flat bars and big threaded rod. Had to crank it quite a bit to get them to line up, but i got it bolted to a junk head i had, and welded some 1/2" or so rod between the two places that were warping. I left the spreader in until the welding was complete. Now they bolt on and and come of with the greatest of ease.

Couldnt find a pic of the tool i made, but here is the amount of warpage im talking about:


Thanks for the reply anyway.

 

huh... what manifold is that? Is that a truck manifold or something else?

 

most of those I have ever seen were cracked along the long portions

 

Basically i went to a junkyard and drew a little sketch of what i wanted (both manifolds needed to look like the one above. most i found had the drivers side outlet between the 5 and 7 port). I believe they told me it was from a fullsize 350 van.