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Porting A Turbo Exhaust Manifold

Bob’s Dodge Daytona 2.2 factory exhaust manifold will get the performance treatment, as part of the top end treatment. It will be ported to the gasket size, blended back into the ports, then polished.

exhaust manifold final

There are a few obstructions that are above and beyond choke points. These will be addressed. Next, the turbo flange will be machined to ensure a good leak-free seal. Afterwards, the manifold gets sand blasted and coated with Tech Line’s Color Guard Titanium high temperature external thermal coating. The final step is to tap the turbo mounting stud holes and install the new 316 stainless steel studs and nuts.

If you haven’t yet read the article on basic porting, please do so before making one of these manifolds your first attempt at porting. There are a lot of pictures that will help to better understand the steps outlined in this article.

remove studs

Before I begin porting, I like to remove the stock turbo mounting studs. They don’t get in my way while porting, I usually have to mill this surface anyways, plus I install new ones later. Soak them in PB Blaster (or something pretty potent) a day or 2 before trying to remove the studs. I have a stud removal tool that makes it quite easy. The tool pops into a ratchet. There are 3 rollers with offset axles that get tighter the harder you twist.

A used manifold will usually have fairly distinct marks where the old gasket ended around the perimeter of the ports. I have found that various aftermarket gaskets will have different sized port openings than the factory gaskets do. Use the gasket that you will be installing on the engine and see if the marks match up with the new gasket. If they do, then you can skip the next step and go right to porting.

If the marks do not match up with your new gasket, or if the marks are not distinct enough to use for porting, then you'll need to make your own marks. Start by cleaning off the manifold with a Scotchbrite pad in a high speed drill. This will leave you with shiny metal that you can make legible marks on.

Next, use either machinist’s bluing or a magic marker and mark about ¼” around the perimeter of the port opening. Next lay your gasket on and line up the bolt holes. Using a scribe, scratch your new gasket size and shape into the marker/bluing. When porting the head, you want to take the port out to just a tad (1 mm or so) smaller than the gasket (on exhaust ports), and when porting the exhaust manifold, you want to take it out the whole way to the marks.

toolsInstall a good carbide bit into your grinder and take the opening out to your marks. Blend this new size about ½” to ¾” back into the throat of the port. I like a large bit with a short shank for this part. A little grinder’s grease (available through Eastwood) will help your bit last longer and reduce the heat build up on both your manifold and your bit. You can leave a little material on the floor of the port. When I port the Chrysler 2.2/2.5 heads, I don’t lower the floor. The bottom of the port in the head will stick up past the gasket anyways.

Take your marker and mark about ¼” deep around the inside of the ports. I like to do this so that when I'm blending I don’t accidentally open the port more. As long as I can see some of my mark I'm doing alright. If I grind away the mark, then I've just changed the size and shape of the port opening. The marker makes it a little easier not to get distracted and make a mistake.

What you'll find on most manifolds is that there is core shift. One side of the port opening will have a lip around the edge, and the other side will have an indentation, then the rest of the wall will protrude. This can make it challenging to get the port size fairly square. Just remember, the better job you do, the more power you'll make. Cylinders 1, 2, and 4 will be fairly straight forward. Match the gasket size, then blend it as far back into the port as your tools can reach.

ported-manifoldCylinder #3 presents its own challenge. you'll see a large protrusion cast into the manifold. There is a clearance notch for easier access to the nut that holds the manifold to the head. The factory was counting on core shift. So to ensure adequate material in that wall, they put lots of metal into the port. The trick here is to remove as much of that protrusion as possible without getting the wall too thin. Be patient and take as much time as needed. I've personally spent as much as 2.5 hours on a #3 port alone. There is a lot of material there. The more you remove, the more power your engine will make. Just don’t get too thin and end up with a cracked manifold.

One of the tendencies I've noticed in people’s work is for the port to get rounded as the size gets larger. To maximize flow, keep the general shape intact as you enlarge the ports. Don’t let them get too rounded. Go back and square off the corners. This will give you a little more flow without getting too thin.

The photo at right shows the finished top and stock bottom. Notice the bump in the throat and the large protrusion at the top left of the port. Also note the old gasket marks that can be used for new port size.

no bumpIn the back of ports #3 and #4 there are bumps in the ceiling. These are clearance bumps for the turbo mounting studs. You can completely remove them. I have never broken through to the stud hole after porting a couple of dozen of these manifolds. Grind at them until there is no evidence that they ever existed.

Once the ports are sized and shaped, the next task is to size and shape the turbo inlet. Again, you should be able to see a fairly distinct mark showing you where the turbo opening was. Grind out to about 1mm shy of this mark the whole way around the opening. On the top and bottom of the opening, blend this new size into the port.


With the manifold in front of you, turbo mounting flange up, and cylinder #1 on your left and #4 on your right, look at the bottom left corner. This corner is very restrictive and affects 3 of your cylinders. Work the corner back, opening the port up larger. Keep a nice smooth radius as you open it up to take advantage of the Coanda Effect. Leave enough material so the exhaust gasses can make the transition from the log into the turbo inlet smoothly.


The lower right corner can be cleaned up in a similar fashion, though you won’t need to remove near as much material off the #4 corner as you did from the #1-3 corner. Go back around the entire perimeter of the turbo inlet and radius all of the edges. You want the transition into the turbo to be smooth with no abrupt edges.

After everything is sized and shaped correctly, you can install a sanding roll in your grinder and go back over everything and add polish. It has been proven that this step really doesn’t add performance, but I do it for the manifolds I ship just to make them “look” like they perform better.

About 75% of the manifolds I port have a deteriorated turbo mounting flange. Chances are the turbo will leak exhaust gasses at this flange if it isn’t cleaned up, especially since no gasket is used. After I'm done with the porting, I clamp the manifold down on the mill and drill and resurface this flange. Since most of you don’t have a mill & drill in your garage, you'll probably have to have a machine shop perform this task for you. Use your judgement. About a quarter of the manifolds I port are fine and require no machining. Of the 75% that I do machine, about half would probably seal okay.

milling flange

After all of the porting and machining is done, I like to put the manifold in the oven at 400 degrees for about a half hour. This bakes out the oils and greases that a used manifold will have, and the machining oils I put on it while machining it. After it bakes, just turn the oven off and let it cool slowly. This prevents warpage. Just a note, I have an oven in my garage I use for coatings. If you use your kitchen oven, you might taint any food you bake in it thereafter. It would probably be better to work it with the parts cleaner and Brakleen to get the oils off than to ruin your oven.

Next it’s time to sand blast off all of the rust and scale, baked on grease and oil, and whatever else has become one with the manifold over the last couple of decades. I not only blast the outside, but get inside as best as I can. This will remove any carbon that might get loose and fly through your turbo.

After blasting, I blow as much of the sand dust off as I can with compressed air. Then I’ll clean it with Brakleen to remove the last of the residue; water will rust the manifold before you even have a chance to coat it. It usually takes three or four cleanings to get everything out of the ports. Blow it off with compressed air between cleanings. When there are no streaks from dirty Brakleen left on the manifold, it is clean.

Tech Line’s Color Guard coatings require a touch up sprayer to apply. Shake vigorously before pouring into your sprayer. Air pressure should be between 50 and 60 psi. I lay the manifold on the oven rack to spray it to keep the coating from getting smeared before it has a chance to dry. Coat the whole manifold until you have a consistent color. I hit the flanges when I spray to keep them from rusting. I used to coat the inside with Tech Line’s Cermit ceramic thermal barrier coating.

Chris at Turbos Unleashed asked me not to coat the insides of the manifolds I do for him because he’s afraid of a piece peeling off and going into the turbo, so I decided not to coat the insides at all unless specifically requested.

After the manifold has dried for about ten minutes, place it in the oven at 500°F. Again, don’t do this with your kitchen oven as it will taint the food. Used ovens are cheap or free.

It should bake for at least a half hour. Full curing temperature is 750 degrees, so all you’re accomplishing is a “half cure”. At least it won’t chip easily as you install it. In lieu of the oven, just let it air dry and let it cure when you start the engine.

The turbo mounting stud holes are 10 mm X 1.50. I tap these holes and install 316 stainless steel studs in place of the factory steel studs. They won’t sieze to the manifold or to the retaining nuts. For stock housings, I found stainless steel replacement nuts, but they have a 17 mm head. The larger nut head won’t clear the .63 A/R housings, and many other performance turbos. In these cases I just reuse the stock nuts. Of course, I chase them with a tap before reinstalling them.

Although Bob didn’t want an EGT port, I added one to another manifold to show you how to do it just in case you wanted one on yours. The port will go on the turbo mounting flange right above #4 port. Start by drilling a relatively small hole where you want your port to go. Be super careful as it is too easy to snap off a bit in the thick cast iron. Go progressively larger until you have the hole sized for your probe. The most common sizes are 1/8” NPT and ¼” NPT. For 1/8” NPT, drill to a letter “R” drill bit. That is close to 11/32”. For a ¼” NPT port, drill to 7/16”. Tap the hole with the appropriate tap and you’re ready to mount the probe.


At this point we have a finished manifold that will seriously outperform the choked stocker.

We now have both intake and exhaust manifolds ported. Check back for articles on the head porting. It’s sure to be an eye opener (and controversial).

Mike Holler, known on Allpar forums as mpgmike, also contributes to He has contributed many columns to Allpar:
Interiors Budget interior restoration: making the inside of your car look like new again
Red carpet treatment: Installing new carpet in an old car
Headliner repair
Porting Porting heads for performance: step by step
Head porting example, part 1 | part 2
Intake manifold porting
Exhaust manifold porting (turbo)
Poly Quad heads: porting revisited

Turbochargers Turbochargers - all you need to know (interview)
Turbocharging the slant six for power and economy • Revisiting the turbocharged slant six
Budget turbocharger rebuilding (and Turbo Rebirth)
Installing a boost gauge

Other Powder-coating for a brilliant, durable finish
Custom pistons: roll your own!
Prepping valves for performance: grinding and polishing
Old cars: an opinion
Discuss Mike’s articles! (if you are not registered for the forums, register first )

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