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Holler: Porting Bob’s Intake

A few weeks ago Allpar featured an interview with Bob O’Neil about making improvements on his ’86 Daytona C/S. The goals were rather modest at 180 horsepower and the ability to average 30+ miles per gallon. Over the next few weeks you get to see what modifications are made to accomplish these goals. This installment covers the modifications to the ‘88+ Turbo I intake manifold to make it compatible with Bob’s Daytona and make it perform to our requirements.

engine porting tools

The first step would be to remove anything that can be screwed off. This would include vacuum nipples, the knock sensor, the throttle body studs, and the ground bolt. These parts are then cleaned up on the wire wheel for painting. Since the knock sensor has a metal base but a plastic body, it gets masked so that only the metal base gets painted. These parts were sprayed with Argent Wheel Paint. After painting, the parts are set aside for reinstallation later.

nub removal

An extra step that I added for this article is to remove the little nubs inside the intake runners. I normally remove them while I do the standard porting, but by squaring off the port first, it is easier to get a more even and consistent port later. The long shank aluminum cutting carbide bit is the best tool for this job.

port size

To size the ports, we will need some marks. In order to see the marks clearly, we need to remove the old gasket material from the surface. A Scotchbrite pad in the drill is the easiest way I know to git ‘er done. With the surface clean, mark around the edges of the port with machinists bluing or magic marker. Place a gasket over the ports, carefully lining up the bolt holes, and scribe around the inside of the gaskets. We want to port right to this line on the intake manifold. When we port the head, we will actually open the port a tad larger so there are no turbulence issues with overhang.

porting the engines

Start by opening the port to the scribed line. You only need to go about ½” to 1” back initially. Once you have the port sized, then blend it back to where the runners neck down. Looking at the back of the intake you can see they start large at the plenum and taper down to the pinch point. Blend back past this pinch point to keep the velocity up going past the injector. Check wall thickness so you don’t break through, as some manifolds might have significant core shift.

After you have the port square and straight, clean up the irregularities with the sanding roll. We aren’t “polishing” the port per se, just removing irregularities.

throttle body

Place the throttle body over the opening in the neck and chances you’ll see a little bit of the intake gasket surface sticking out into the air path. To assist efficient air flow, this little bit of material needs to be removed. Follow the same principles outlined for the runners to clean this area up.


Bob has an 1986 Turbo I car he is converting to 1987 Turbo II electronics and intake manifold. The car came with an air charge temperature (ACT) sensor, but the 1988+ Turbo I intake manifolds have no provisions for this sensor. The 1987 electronics support the sensor, and the Turbo II cars came with one, so we need to add one to this intake. It goes next to the vacuum port on the front (see #15, above, and #16-19 below.)

sensor hole

We start by drilling a pilot hole centered in the cast-in boss. Progressively go with larger drill bits until you have a 9/16” hole. I have a pipe tap reamer for the 3/8” NPT tap that opens the hole to just the right size, and adds the taper the pipe tap likes. After reaming, the tap is run down the hole until about 6-7 threads are still showing. Now we have a place to install an ACT for the conversion.

Bob did claim that he wanted a good looking engine bay. In fact, he’d like to be able to show the car when done. This intake may have a nicer style than the log his Daytona came with, but as you can see by the pictures, it isn’t very attractive as is. A future article will outline the process of blasting and powder coating this ugly chunk of aluminum (as well as a TURBO valve cover) and transforming it into a handsome piece worthy of a show car.

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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