(Mods: If this isn't hard enough tech, feel free to move this thread to wherever it belongs)
If I can do it, anybody can!
Here are some pictures of a 200-250 exhaust manifold that I did some very mild porting (gasket-matching) on to show my nephew what I was talking about.
Simply put, you lay the gasket on the sealing surface, mark the inside diameter of the gasket onto the exposed port surface, and then grind away the inside of the port until its opening matches the opening of the gasket (hence the name...) On virtually every engine I've ever seen, the gasket openings are bigger than the head and manifold ports/openings. As long as you leave enough meat to seal (1/8 inch min), you'll be ok.
Racers will often open up both the ports in the head and manifolds, but for a street engine it's usually enough (and better) to only open up the port on the "downstream" side of the gasket, ie; the head side of the intake gasket and the exhaust manifold side of the exhaust gasket. This is because the "ledge" of the 'upstream' part will act like a one-way valve on the flow and reduce what's called reversion (think backwash). Reversion happens because the flow through an engine isn't continuous - valves open and close, and the flow starts/stops, plus there are pressure waves flying up and down the ports, but that's a whole 'nother science. Simply put, on a street engine, leaving the 'upstream' port smaller than the 'downstream' port is the thing to do.
Note: Ford 6 exhaust manifolds are the worst I know of for having itty-bitty port openings that are off-center and even off-square from the gasket and head. Their casting tolerances must have been huge - and there's a LOT to be gained from opening these things up.
ANYWAY:
I like a 3/8" carbide bit in an air die-grinder, usually 45-60 psi spins it fast enough to cut well but not so fast it'll get away from me.
Here's an exhaust port (#5, I think) on a manifold that's been run maybe 30 miles on an engine and then pulled. Note the soot outline around the port - that's where exhaust gasses have "tripped" trying to get out of the head, and that's what we're going to remove. You can see two shades of soot, the darker one is where the manifold is actually in the way of the flow, and the lighter one is out of the direct flow path, but the gasket is holding the manifold off from the head.
Same port with the gasket laid over it. The roof of the passage aligns well, but there's a LOT of material that can be removed from the sides and bottom. Take a scribe and draw a line around the inside of the gasket's opening.
Here I've held the die grinder at a 45-degree angle and gone around the port opening, cutting out to the line I scribed earlier. Makes you wonder how these engines ran at all, doesn't it?
Here I've ground the inside of the port out to about 1/2-inch inside the manifold, trying to smooth any corners in there I could reach, smooth any casting flash/ledges, etc. Note the hump in the floor inside the port, that's where the manifold is cast with a dimple for the bolt to go. If you're going all-out you might reduce it down, but I don't want to weaken the manifold, so I'm just smoothing it as much as possible. Darned sure don't want to break through anywhere! (note I haven't finished reaching the scribed line at all points - but I did before I finished!)
I didn't get a picture of the final smoothing of the port opening, but I used a stone and then an 80-grit sanding tip to smooth the port entry and everything inside the manifold I could reach.
The whole idea is to make it as easy as possible for exhaust gasses to get out of the engine as smoothly as possible, and if there are any ledges/lips, they're facing so that they interrupt flow going backwards.
If I can do it, anybody can!
Here are some pictures of a 200-250 exhaust manifold that I did some very mild porting (gasket-matching) on to show my nephew what I was talking about.
Simply put, you lay the gasket on the sealing surface, mark the inside diameter of the gasket onto the exposed port surface, and then grind away the inside of the port until its opening matches the opening of the gasket (hence the name...) On virtually every engine I've ever seen, the gasket openings are bigger than the head and manifold ports/openings. As long as you leave enough meat to seal (1/8 inch min), you'll be ok.
Racers will often open up both the ports in the head and manifolds, but for a street engine it's usually enough (and better) to only open up the port on the "downstream" side of the gasket, ie; the head side of the intake gasket and the exhaust manifold side of the exhaust gasket. This is because the "ledge" of the 'upstream' part will act like a one-way valve on the flow and reduce what's called reversion (think backwash). Reversion happens because the flow through an engine isn't continuous - valves open and close, and the flow starts/stops, plus there are pressure waves flying up and down the ports, but that's a whole 'nother science. Simply put, on a street engine, leaving the 'upstream' port smaller than the 'downstream' port is the thing to do.
Note: Ford 6 exhaust manifolds are the worst I know of for having itty-bitty port openings that are off-center and even off-square from the gasket and head. Their casting tolerances must have been huge - and there's a LOT to be gained from opening these things up.
ANYWAY:
I like a 3/8" carbide bit in an air die-grinder, usually 45-60 psi spins it fast enough to cut well but not so fast it'll get away from me.
Here's an exhaust port (#5, I think) on a manifold that's been run maybe 30 miles on an engine and then pulled. Note the soot outline around the port - that's where exhaust gasses have "tripped" trying to get out of the head, and that's what we're going to remove. You can see two shades of soot, the darker one is where the manifold is actually in the way of the flow, and the lighter one is out of the direct flow path, but the gasket is holding the manifold off from the head.
Same port with the gasket laid over it. The roof of the passage aligns well, but there's a LOT of material that can be removed from the sides and bottom. Take a scribe and draw a line around the inside of the gasket's opening.
Here I've held the die grinder at a 45-degree angle and gone around the port opening, cutting out to the line I scribed earlier. Makes you wonder how these engines ran at all, doesn't it?
Here I've ground the inside of the port out to about 1/2-inch inside the manifold, trying to smooth any corners in there I could reach, smooth any casting flash/ledges, etc. Note the hump in the floor inside the port, that's where the manifold is cast with a dimple for the bolt to go. If you're going all-out you might reduce it down, but I don't want to weaken the manifold, so I'm just smoothing it as much as possible. Darned sure don't want to break through anywhere! (note I haven't finished reaching the scribed line at all points - but I did before I finished!)
I didn't get a picture of the final smoothing of the port opening, but I used a stone and then an 80-grit sanding tip to smooth the port entry and everything inside the manifold I could reach.
The whole idea is to make it as easy as possible for exhaust gasses to get out of the engine as smoothly as possible, and if there are any ledges/lips, they're facing so that they interrupt flow going backwards.
Seriously, I do. I like my eyes, and want to keep them. Also, I figure breathing is a good thing. If you think likewise, wear goggles and a mask also.
