North American Turbocoupe Organization

Exhaust manifold porting
Pete D2 Offline
Porting your E6 cast iron manifold can help free up some HP in your TC and improve spool up time because the exhaust side of the system is the biggest initial restriction in the air flow system. There are some real nice headers out there that are going to flow better than any E-6 no matter how well it's ported. They are also going to cost more. If it's a header you want, look at 40Bob's, Stinger, and Rod's offerings. There may be a couple other choices out there also. Expect to pay $300 and up + shipping for an after market header. Don't even think about buying a cheapie off Ebay. You get what you pay for.

What do you need to do it?
First you should make sure you have an uncracked E6. Cracking is not uncommon so it pays to check.
They usually crack along #3 runner as illustrated in the pictures.

In the first picture, the manifold on top has been welded - shiny area. This is the area where they typically crack and the cracks always run up and down. The bottom manifold, in the encircled area marked "1" shows how a crack runs and where.(No real crack in this manifold). I have only seen 1 manifold cracked in the area marked 2, so usually not a problem. The second picture shows a welded manifold. Some people believe welding, done right, is OK, some don't. I discovered that manifold was cracked after I ported it so I decided to try having it welded. I ran that manifold for at least 3 years, including several runs down the strip and no problem.

In checking for cracks it is necessary to get any rust scale off. A wire brush in a drill motor can help. For heavy rust scale, try tapping the area lightly with a hammer first. Wear safety glasses.

Tools: My opinion is that most of the flow gains for an E6 are to be had on the turbo end of the manifold. I have heard of people doing it with a drill motor and grind stones. I wouldn't do it that way but.....
My preference would be some kind of die grinder and a carbide rotary cutter or two, plus some grind stones and sanding rolls for final smoothing.

Die grinder: there are a couple ways to go. You can get some fairly inexpensive ($15-20 and up) air operated die grinders (Harbor Freight). You have to lubricate the air grinders frequently or install an inline lube system. You need a pretty good sized air compressor to keep up. The little 3-3.5 HP single lunger's with 20-25 gallon tanks aren't going to cut it. You will be constantly waiting for it to recharge . A good 2 cylinder and 40-50 gallon tank works but those are major bucks. Air grinders are light weight. What I don't like about air grinders is fighting the air hose, especially for the delicate work in the valve pockets on cylinder heads. All that air really blows around chips and dust too. Speed control can also be an issue.

You can get electric die grinders. They can cost more up front and they will weigh more. The cost range can be significant so look around. However they are useful for other things too. For speed control, I seen some expensive controllers recommended, but I been using a $5 rotary light dimmer switch for years. I mount it in easy reach from my work bench Check Harbor Freight for electric die grinders. I like the Makitas but they are a little upscale and bigger/heavier than some others. Sears may have something also. Stay away from the cheap Makita knockoffs on Ebay. They won't run for 10 minutes. BTDT

Rotary cutters (carbides): Check Harbor Freight and Ebay. Sometimes you can find them at the "tool tents" at bigger car shows and swap meets. You don't need a lot of them or many different shapes. I do 95% of the cast iron work with 3-4 cutters and you need less for exhaust manifold porting.
I've gotten mine at a local Industrial Supply dealer, but there are cheaper places to get them

Here is some pictures of the tools I use and brief comments.

Cutter "A" is a "single cut" barrel type. It has less teeth than the other two "double cut" types, "B" and "C". The double cuts cut significantly faster. It's a personal preference thing but I like B the best and do most of the exhaust manifold and head work with it. Other people seem to like "C". I don't use A for anything as B can do anything it can and more, faster. The cutters you see are about 1" long for the cutting area with shanks that are 2 to 2.5" long. I have one shaped like "B" with a roughly 6-7" shank that I use a little on the corners and transitions for the exhaust manifold. It's "nice to have" but not necessary and not needed for a budget job.

Here is a couple of small cutters beside the "B" cutter in the first picture. I use the ball shaped one for work on the sides around the valve guides on heads. The pointed one is good for doing the corners and knife edging on the lower intake and other fine work.
Here are two aluminum cutters, middle and on the right. You will need an aluminum cutter for the intakes. Regular carbides clog up in aluminum and once they clog they don't cut until cleaned out. You will spend more time cleaning than cutting. And yes I have tried all the tricks to keep carbides from clogging (as fast). Give me a real aluminum cutter any day.

Various grindstones. I use stones mostly on the exhaust manifold to smooth carbide marks. The second and third stones from the bottom, I use to work the pockets on either side of the air diverter web on the turbo end of the exhaust manifold.
These are sanding rolls (cartridges) It's very important to have some of these for porting work. Used for metal removal and smoothing and blending. I've tried different brands and I think Standard Abrasives makes the best. They also make a porters kit that has enough to port two heads (V8).
Here is the deluxe kit;
Here it is through Summit Racing;

Here is a little cheaper kit. option;

Same kit fom Summit Racing;

Here is a less expensive kit from Standard Abrasives;

This is what I started with. You still need at least one carbide for the heavy metal removal. It's also nice to have longer mandrels for mounting the cartridge rolls, but they can be hard to find. Look around on the web, you may find better prices. Let me say that I have tried a variety of brands of cartridge rolls. I haven't found anything that lasts as long as the SA product. Forget that crap that gets sold by the tool tents. You get what you pay for.
These are tools for holding the sanding rolls. The 3 darker ones were purchased (see Standard Abrasives). I think I got one at a swap meet. The two light colored ones were made by a friend (thanks Jeff G.)
These are extensions for holding stones or sanding rolls for real deep work, like the runners in the lower intakes. These are available at Lowe's and Home Depot .
Safety: There is going to be a lot of chips flying around. Safety goggles are the minimum requirement, the kind that seal around the eyes. A full face shield in addition isn't a bad idea. For exhaust manifolds and cylinder heads there can be a lot of carbon dust until you get to bear metal. A dust mask if a good idea. One guy I know got a metal chip in his eye when it washed out of his hair in the shower. I use a cheap shower cap for that reason.
Other stuff: A shop vacuum. Some kind of vice to hold manifolds, I'm lucky enough to have a wood vice built in to a work table.
The Exhaust Manifold:
If you are going to clean it up any, like sandblast or wire brush it, consider doing that first. It is easier to work on the turbo flange if the studs are removed, but not absolutely necessary. Removing the studs can be a real hassle and could get expensive. The studs usually require a dedicated stud removal tool and a lot of heat (as in more heat than the little propane cylinder torch is going to produce) If a stud breaks you are looking at $10-20 minimum to have a shop take it out. If you break one, take it to a shop first. The shop will only charge you more to remove the "easy out" you are going to break if you try to use one to get the broken stud out. Ask me how I know that!?
If the turbo flange is really marked up from rust or the old gasket, get it resurfaced after the porting is finished, in which case the studs have to come out. See the Part Number's forum for source for the new studs and nuts.

The next thing to do is to scribe the turbo flange to mark the limits of where metal will be removed. Use a new type gasket for this:
I used an old gasket in this picture but it is one with the bigger opening. Note the black ink underneath it. You can color that area with a marker or bluing ink if you are going to scribe (next picture) Or just use a fine tipped marker and draw around the hole of the gasket.
Gasket #'s:

This is the scribe mark. You are going to remove metal inside the mark to open the flange up. Do not go all the way to the scribe mark. Leave a few thousandths metal all the way around. This will protect the gasket in use. NOTE the web at the bottom center, inside the manifold. That is the air diverter web. More on that later.

Start by removing metal up and down the long walls, working your way out toward the scribe lines. Try to keep the walls relatively straight, as opposed to significantly tapering them in at the bottom of the log. Do the same on the short walls and also try to round the top edges that transition from the flange area into the log. I usually take a little metal out of the top of the log and then try to round those corners. It's easier if the ceiling is raised. Any rounding you can accomplish is better than a sharp edge or corner.

Here is a finished manifold. There are a couple places where I got too close to the scribe line. Resist the urge to over port. Notice how the pockets on either side of the diverter web have be en worked to deepen and shape them just little for better diversion. This web is what helps the exhaust flow to turn the corner into the turbo.

You want to work as deep into the log as your tooling can reach. Try to work on the corners where the individual runners turn into the log. I use the "B" carbide as well as sanding rolls to try to smooth the corner. A fair amount of metal can be removed from the corners for runners #3 and 4. See the first two pictures below. In the first pictures, note how you can see through from the flange to the #4 runner port. You should be able to get similar results through to the #3 runner. It will require working from the flange and from the runners. Where to work is illustrated in the second picture. Minimize metal removal in the area marked "A", just round it as much as possible. You can take a fair amount of metal up out of the "B" corner to get the straight through from flange to runner for #4 runner. You may not be able to get that much for #3 runner but you should see some daylight with proper work. Always keep an eye on wall thickness. Don't try to take too much metal out. Before doing any porting try to look through to the turbo flange from #3 and 4 runners and from the flange toward #3 & 4 runners. See any direct daylight either way (use a flashlight) Probably not.


Porting the runners.
I'm going to suggest that unless you are going to use a ported head, you do very little to enlarge the runners. The manifold runners are already bigger than the exhaust ports in the head. Any time the size of the air flow path changes, ie big into little or little into big, something is lost, either flow or velocity. If you aren't porting the head, then just do smoothing, take off the flash and try to smooth transitions and projections. If you have a ported head then do any enlargement of the exhaust runner in the top half as would be with the manifold mounted on the engine. The upper half of the runner in the head is where you would port. Otherwise, the idea is minimal metal removal. Try to smooth off the casting skin as deep into the runner as you can reach, using sanding rolls. The projections into the runner from the reliefs from the bolt boss can be smoothed and shaped a little. Do not try to take much metal off the projection's height or the walls will be too thin. See the next pictures. The areas circled as "A" and "B", be careful not to get the walls too thin in those areas. Just smooth the leading face and around the ends for cleaner flow over and around them.

Try to smooth/round the corners where the runner meets the log. This will take a carbide mounted in some kind of extension or a long shank carbide. Then smooth with sanding rolls.

You will not be able to reach all areas of the log. Se 'la 'vie. Do what you can to smooth the transition from the runners into the log on the
downstream side.

Always use the sanding rolls last, to smooth out divots and dips from the carbides and stone marks from the grindstones. Remember to resist the urge to over port. Think in terms of smoothing and blending.

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