Intake Manifold Construction for Cadi 500

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cking894

Well-known member
Joined
Jan 22, 2008
Messages
180
Location
Northern California
Norman and I have been considering building an intake manifold for my pickup for some time. The one the criteria is that it has to be something completely different but be fully functional. We started putting the plan into action this past week. Here are some pictures and thoughts as we have been coming up with our design. Any thoughts or critique is welcome. This is a driver and we want it to run rights.

We started with 1/4" intake flanges that a friend of ours had water jetted out in Colorado. The flanges are great and fit the intake ports on the heads perfectly. I had to open up the bolt holes for the flanges because of the angle the bolts go into the heads. I put a big block Chevy rocker arm ball under each bolt that will be welded down to the flanges. The ball will maintain the right angle for the bolt and give even pressure for torquing them down.

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To tie the flanges together we have welded 1/2" X 1" mild steel as a border around the intake valley. The stainless steel that is laying across the valley as pictures will be removable. It will be bolted down onto the valley frame work. Unfortunately my battery died on my phone before I could get a picture of it. I will get one later and post it.

The main portion of the intake from the flanges up are going to be constructed out of stainless steel and tig welded. I started by cutting 2" diameter stainless tube into 6" lengths and then I worked one end of them in the vise to make them rectangular to fit the intake ports. The 2" diameter works out perfectly to make the shape for the intake ports. The stainless steel holds the shape much better than mild steel also so it wasn't much work to make them fit. The 6" length is just a starting point on the height into the plenum.

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We tried mocking up several designs of plenums for the intake. The taller one in the back was our first shot at one but we realized right away that it would end up being way to tall for our application. The shorter one in front was our second shot at it but we determined that it looked too bulky and the intake runners looked to small and out of proportion.

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I guess I haven't mentioned it yet in the post we are planning on running five Rochester two barrel carbs on the intake. We have been collecting the 250 cfm ones at every swap meet for a while so we have a good supply of them. Norm has an eight deuce manifold for his 392 hemi that he is using them on also. Here is a picture of the layout we are going to use. The air cleaners are on there only as an idea for now on what to use.

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Our plan is to run on the center carb as the primary and have them all be setup so that they are fully controllable by progressive linkage. We will probably need to use restricter plates to keep the total cfm at about 850 but we will have to try it and see.

Our third attempt at making a plenum looks about right. The intake runners would be about three inches with it and the proportions look much better. The overall height will work out just about perfect also.

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After looking at it for several days we came up with another idea. Last year I picked up a WWII bomber oxygen take at a swap meet for $20.00. They are make out of stainless steel and it just so happens that my pickup has three of them in the back already. We came up with the idea of using a portion of the tank at the bottom of the plenum and possibly using a portion of it as the top to an air cleaner. Here is a picture of my pickup with the tanks in the back to give you an idea of what they look like.

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We did mock up the plenum and the size and shape look good but I wasn't able to get a picture. I will next time I go up to Norms.

If any of you have any thoughts or see something we missed please speak up. We are in the planning stage and it's easy to adjust something now.

Keith
 
After reviewing some tips on multi carb intakes, I decided to run a large base Rochester for the center primary. It should work better for the Cadi 500 as the single primary. Here are some pictures from several days ago of our progress.

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Keith
 
Here are a few more pictures from yesterday.

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After taking a look at the carburetor stands last night we decided that we are going to shorten them at least an inch.

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Keith
 
You have some clever ideas going on here. I have nothing to add, but I am interested in seeing how this all pans out.:)
 
I understand the concept of the long runners terminating inside the plenum chamber, some early tunnel rams did this, but were quickly changed. longer runners = lower peak torque rpm.

But, the tubes allow raw gasoline to puddle big time in the bottom of the plenum, a very bad thing, as it will sooner or later back fire and blow the top of the manifold into a bunch of lethal shrapnel.

A "V" shaped plenum mating with the runners with the sides of the runners closest to each other terminating at the bottom of the "V" would be more efficient, that way any puddles will run down a runner, and while not burning efficiently will at least not cause an explosion.

to get longer runners combined with low height, would require a cross ram type design.

or a dual tube design with a cross pipe for the center carb, like maybe 3" tubing in the form of an "H" when viewed from above.

rectangular runners mated to rectangular ports will flow more air as it discourages swirling in the runner which hinders the amount of air flowing through the port.

Watch water going down a round drain, it forms an eddy in the flow which in water is a shaft of air going down the drain. now imagine this eddy in the round intake runner, the center will be like the eye of a hurricane (dead calm) no air/fuel flow, less power.

I'm all for creative thinking, but I like to see every one live long and have fun.
 

In keeping with what BlueNorther described, on my slant 6 I radiused the union between the plenum and the tubes. To prevent fuel puddling the "v" at the bottom of the plenum was filled with epoxy up to the bottom edge of the tubes.
 
BN and Bob are correct.....

You guys know your stuff......I've seen a fabbed intake explode....big boom and flying metal....wasn't pretty...digging the set up 894....:D pay heed to the advise...coming from some knowledgeable guys...
 
Thanks for the information BlueNorther. We had thought about that and that's why we tried to keep the runners at the bottom of the plenum. If it looks like it's going to be a problem we will build a pop off plate on the front of the plenum. That way if it back fires there is some place for it to go.

We were in Bakersfield a couple years ago and my buddy had an eight deuce manifold on his 392 Hemi. It didn't have a blow of plate and it back fired as he started it. I was parked next to him and heard the back fire. When I looked over it looked like confetti falling all over the place. The back fire blow out the top gasket and cracked the top plate a couple inches. We were four hundred miles away from home so we ended up making a new top gasket. Using JB Weld to fill the crack and used a welding clam to pull the back of the top cover into place. Fortunately it got us home. He added a pop off plate to the intake now.

Keith
 
That should be one trick manifold when you're done.[cl Dry manifolds like the Caddys sure make custom fab easier. Here's one I made a few years ago from aluminum. One thing I've picked up about multi carb manifolds like this is that the plenum size should be made as small a possible or it will really hurt bottom end power and cause a major bog when you hammer it off idle. After all, you're not going to be running these engines at 6000 RPM too much.
 

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We got a little more progress done this week. The runners are all welded in and the top is welded on along with the back of the plenum. We are working on making the pop off valve for the front of the plenum.

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Keith
 
Bluenorther, that was pointed out to me on the Cadillac forum. We ended up welded up an oval tube and welded it to the bottom of the plenum to reduce the size. It still should have pretty good air flow.

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Keith
 
We made more progress tonight. You can see in the picture the slot on the front of the manifold for the pop off. We got the four outside carb plates lined up and tacked into place. A few more hours of grinding and welding and it should be done.

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Keith
 
Ok, it's finished and ready to be bolted on. We are going to give it a shot today. We may only be able to get the center carburetor hooked up to test it. We have a local car show this weekend that we want to have it on for that. The four on the corners may just be bolted on. We will have to see. I haven't had time to rebuild them and kill the idle circuits in them yet.

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Keith
 
We got the intake on the truck and fired it up Wednesday night at about 11:00 pm. We got the throttle linkage hooked up to the center primary carburetor yesterday and took it for a test drive. It runs great with good throttle response. We have our local car show here tomorrow so we didn't get the other four carburetors rebuilt yet. We just put block off plates under them and bolted them on. There's no linkage or fuel lines hooked to them yet.

Here's a video of it running.

http://www.flickr.com/photos/five_wide_club/9685403477/

Keith
 
Ok here's an update after having some time to drive it. The engine has never run so good. With the old stock intake on there it was all it would do to rev past 4000 rpms. It must be breathing really well because now it revs a lot faster and pulls right up to 6000 rpms. So far I will have to say it was a successful build. I have two weeks to get the outside four carbs rebuilt and the linkage hooked up. We are going to Billetproof in Antioch on September 21st with it and I want it all hooked up.

I entered the truck in the car show yesterday and there were a lot of people scratching their heads over it. And not one person has said that they have seen a five deuce manifold before.

Keith
 

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