The

CIS Intake Manifold Fabrication

Fabricating manifolds was quite a challenge. The manifolds I'm using for my engine are the stock dual 32/34 PDSIT carb manifolds which are cast steel. Interestingly enough, these manifolds have small bosses already cast into them. These bosses are, however, too small and shallow to actually be usable in stock form. You must add a larger boss so that the injectors can be in the correct position.

First I needed to get a good idea as to where the injectors were to be aimed. To accomplish this, I cut the center out of an old junk head and mounted the manifold to it. With the help of this fixture, I could better get a visual on where to aim the injector. The push rod in the photos is being used to see where the injector is statically aimed.

Since I planned to use 1" thick steel blocks to extend the injector bosses, it was important for me to get the original cast in bosses exactly perpendicular to the aiming point of the injectors. If I could get those just right, I wouldn't have to do any fancy machine work to true the aim. I would only have to machine straight down from the flat top.

The bolts on the tops of the injector boss (on the left) are for the set screws for the injector hold-down brackets which will be used to hold the injectors once installed. In this series of photos, I've bolted the injector bosses to the manifolds through the pilot holes and original vacuum port. This is only temporary until I have the bosses permanently welded in place. You'll note that I used a piece of 1/8" flat stock to keep the two bosses true and flat one to another. This will help ensure they are uniform making the injector easier to aim later.

Below are a couple shots that I've added lines as reference points so that you can see easier the critical angles used in setting up the manifolds for the injectors.

Here's a couple shots of the welded manifolds ready for final machining.

The final step for the manifolds was to do the final machining. The injector bore was machined to 3/8" which is approximately .020" oversized. Doing this would allow for a few degrees of adjustment later if needed. I also had to spot-face the tops of the bores so that the injector seals have plenty of support and a snug fit. These were machined to 5/8" in diameter and were stepped in .150". The seal fit was really good; nice and snug but not too tight.

Here's a couple shots of the static aiming of the injectors. The first photo is just like looking down the barrel of a gun. You can just see the fuzzy top of the valve guide at the base of the bore. That is just where I was hoping to get them aimed!

To ensure each injector would stay put, I made 4 of these injector hold-down brackets (one for each injector). These are held in place by the set screws at the top of each boss.

NOTE: Just in case anyone out there is thinking I'm going to actually use those rusty injectors, I want to assure you that these are ONLY for mocking up the manifolds. :-)

Cost break-down:

Stock Manifolds - $25 a pair

Injector Boss Blocks - FREE (scrap from the machine shop recycle bin)

Welding - $40 (OUCH!!)

All Machine Work - FREE (a buddy of mine is a machinist) :-)

TOTAL - $65

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