I'm going to be playing with the wagon a bit, so I figured I'd start cheap and see what improvements I can make. I'll be adding a Hedman header in the near future, but I wanted to see what I could do with a stock intake. I picked one up from Fred and promptly disassembled it as soon as I got it home.
First, I'm keeping the stock Holley/Weber so the adapter plate will be staying. When you look at the adapter, you'll notice a couple things. The (for lack of a better name) flow plate on the backside of the adapter has a significant mismatch in the throttle bores. I figure it certainly can't help flow, so I'll start by smoothing the bores.

I've smoothed both bores, but have some finish work to do on it. Smoothing the bores more won't buy any more, but I have to have things a certain way. It'll be perfect. While I was at it, I tapped the EGR hole and plugged it, but if I ever want to put it back on I can.
In the plenum on the intake, the runners have very sharp edges as they enter the plenum. I know air doesn't like to turn corners, and it REALLY doesn't like sharp corners, so I've radiused the port edges to smooth flow into the runners. I'll be doing a quickie port match to the head when I replace the intake, but until then there's not a whole lot more I can do with this intake.
Hopefully these little changes will help not only smooth the flow for more rpm, but help atomization by keeping the air/fuel mixture from breaking down when going from the plenum into the runners. Will it wake it up more when I add the header? We'll see......

 I have a lot of appreciation for guys who work hard to get the most out of existing parts.  I can't pull a head/manifold without taking a grinder to it if even just to clean the sharp edges.  I hope you gain a lot for all your hard work.  All the best.
Tom

Here's the adapter bolted to the carb. The alignment isn't too bad. What DOES concern me is usually I see the thick spacer gaskets between the carb and adapter. This creates a big gap under the carb (between the bores) that may cause flow problems. I have both the spacer type and thin gasket so I'll test both to see if there's any difference performance-wise.

I talked to the Ford enginner in charge of their R&D dyno room in the late 70's about the 2.3 intake manifold, and how to improve it. He told me that it was a bean counter manifold , and made as cheap as possible. Thats why two of the runners are 1/2 the length of the other two. He said that on the dyno, it made no difference in HP reguardless of what carb was bolted on. He said it was the same HP with a stock cab as with a 500 Holley two barrel. He said the flow rate was so poor because of the two short runners, that two runners would run pig rich at all times even when the other two ran lean. LOL.

The 74/75 intakes are the ones all the mini-stock boys use when the rules require a 100% stock intake. Its the one with ribs in the bottom, inplace of the later ones with triangles on the bottom. They can be ported to work better, BUT never as good as an equal length manifold. Even Eslingers oval and d-port intakes are of unequal lengths. Only the Eslinger ARCA intake is close, and it wount fit a stock head.

Well, after having a few beers and staring at the plenum on this manifold, it looks like I need to find a mill and modify the plenum. The primary isn't the problem... it'll feed all 4 runners with little restriction (inefficiently, but relatively speaking). The orange arrows show the flow paths. The problem is the secondary. When the secondary opens, it can flow relatively unrestricted into #2 & 3, but for 1 & 4 it hits the "divider" creating a low pressure area behind it. My understanding of flow dynamics is that the flow hitting the divider will separate the fuel from the air/fuel mixture and create turbulence at the low pressure area behind the divider.  So I'd have #2 and 3 richer that 1 & 4.
My plan is to mill the dividers out of the plenum and round all the runner edges to smooth the flow. In looking at it, it should flow smoother (and more equally) if the flow starts higher instead of moving horizontally in the plenum.  This will require a spacer to lift the carb and extend the plenum higher. The downside is normally adding more plenum (like a tunnel ram) gives you more top end and not necessarily more torque down lower (where I need it).
There's only 1 way to find out...... :surprised:

Interesting read.  what cam are you goin gto be running with this build? or do you have one in mind?  I have a suggestion if you are doing the full build.

Fedex showed up today 
We'll see if the muffler shop is open this Saturday to modify the exhaust

The header was installed Saturday and it's already been off 2 times. First thing about the Hedman header..... it's a 2 piece with a slip-on collector. What does that mean? It'll leak.... if it's assembled as is. I pulled it off as soon as I got home from the shop to see if maybe they overlooked something.... they didn't. I spoke with a neighbor that works for Doug Thorley and he said they all leak unless you use some type of sealant on the slip joint. That brings me to the second time (this morning). I bought some ultra-copper which may seal it for a short period of time (maybe longer). A ceramic sealant was suggested, I just have to find it. Pulling the header really isn't hard or time consuming, but it HAS to be pulled and assembled in 2 pieces as it won't fit past the bellhousing in one piece. No big deal. Here it is after reassembling it with the ultra copper. I need to give it as much time to cure as possible, so I won't know how well it worked until I leave for work tomorrow morning.
 

Here's a pic of the slip joint at the collector



It is nice how well the header tucks up and doesn't reduce ground clearance



If you're contemplating this, keep a couple things in mind.
Remove the battery and spark plugs..... you'll appreciate the extra room.
Clean the slip joint VERY well. I sanded the surface rust and wiped it down with acetone before applying the ultra copper.
As far as any extra power or gas mileage? I don't have any mileage on it yet to test it.... I'll have a better idea tomorrow. 
 

Nice writeup and interesting topic. Thanks for sharing all of this.

Chris

After mocking up the carb on the intake, I chose to go with a 1/2" spacer. The flow plate under the carb is tapered.... a little less than 1/2" on the front, and a little more on the back). 1/2" will make adapting the throttle linkage easier, as well as (hopefully) keeping it under the hood. I ordered the Transdapt 2134 (open center) since I'll be milling the center so the flow plate just goes through the center. This will put the bottom of the flow plate right at the top of the plenum and provide a smoother bend into the runners.

Well, adding the spacer will be delayed as I bought the one Transdapt makes and it won't seal against the rear of the plenum.  The sealing surface at the back of the plenum is MAYBE 1/8" wide, and it also doesn't leave much meat to mill out for the flow plate. Looks like I'll be buying some 1/2" thick billet and making my own....

After spending WAY too much time and money trying to modify a commercial carb spacer, It came down to making one. I bought a piece of 5"x12" .5" aluminum stock, cut it to 5"x6" and started drilling. A mill would have made this go MUCH quicker, but you do with what you have.
This shot shows the carb angle and how the spacer adds 1/2" of plenum and should make the transition into the ports smoother.

I tried to make the plenum hole as close to the flowplate's size as possible to keep the flow as smooth as possible. Theory is that a larger hole would disrupt the flow by creating a reversion (flow trying to go into the hole because of a low pressure area).   

Next is to make a spacer to raise the linkage bracket 1/2" and hope the kickdown rod doesn't need to be modified.

Well, the seat-of-the-pants dyno is getting dialed in, and a few things are becoming evident. First. let me acknowledge one thing..... I know I'm tempting fate doing this to a car with a C3 trans. Ever since I advanced the cam, I couldn't really jump on it from a stop for fear of scattering it. I dialed in the carb and it wants to holeshot a tad better, but the smoothness of the idle is amazing (for a 2.3). Before, it would pull well in the upper rpm's, but when the secondary opened it was less than spectacular. It didn't "bog", but I had to get the rpm up to really feel when the secondary came in.  Now, it pulls a little lower and doesn't bog. Don't get me wrong, it still wants the rpm, but puts a smile on my face when I kick it down a gear, the rpm comes up, and the secondary comes in.
If anyone has some time to play around and make a spacer, I'd consider it time well spent. Granted I haven't seen the gas mileage yet (and playing with it this much may LOWER it), but it has definitely made a difference. I can't help but think it would REALLY wake up a manual trans car. If you have smaller tires than me (225/60-15 on the rear) and a manual trans, this mod should REALLY get your attention!

Good work, I like the play by play! Any thing on mpgs yet?
 
John