motorcraft 2150 using stock manifold

Hi, have '69 AMC Rambler with 232. Wondering if anyone with experience in swapping to motorcraft 2100 carb using stock 2-bbl aluminum intake can offer guidance. So far, I haven't found any discussion of this topic on the forum.

The carb adapter plate (small 2 bbl to large 2 bbl) and the mc 2100 are larger than the bored holes in the stock manifold. If no grinding/blending on the manifold is done at all, it would leave a horizontal 1/8" perimeter shelf or lip, as well as the center divider between the bored holes, that would seem to be a significant flow disrupting restriction. Sorry if that's not clearly worded, but if you've seen the swap, you will recognize the issue. Something like this looking down, the outer lines are the adapter plate opening, the inner is the manifold bores.
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(OO)

I see two options, one is to fully machine the manifold to the same dimensions as the adapter plate (a larger oblong opening, rather than the two bored holes), and the other would be to just remove enough material from the manifold at the mating surface to blend/match the opening to eliminate the sharp transition, but leave the manifold's bored holes mostly as they are - a bit smaller cross section than the carb's barrels.

BTW, I am installing a high-lift, longer duration cam and having work done on the ports to increase flow, so I think it will be able to make use of better flow from the carb. Thanks,

Tim

Thanks Mr. Ed, sorry your experience was bad, I hope my goes better.

I've tried to find as much as I can via google and forum searches, and while I've found a lot of discussion, and reports from people who've done it, especially on the Jeep stuff, I haven't found any discussion of this issue. I'm leaning to opening it up as the probably the best approach.

Tim

Thanks. Yes on 80's manifold. It uses the adapter commonly sold for this, Mr. Gasket, Gronk on ebay, and at least one other adapter seller that are often referred to in these discussions. I got the Mr. Gasket one first, it fit, but the quality was too poor and so I'm throwing it away. Unless someone wants it.

I'm not having problems with assembly of the components, sorry if something I said led you to think otherwise. My question was about an optional extra step to better blend (by ginding, machining) the manifold's stock two-hole opening as it mates to the adapter opening to remove restriction/improve gas flow. I could just bolt it up and it should work fine, I'm wondering if performance could be improved further if some machining work were done to blend the manifold opening to better match the adapter opening. Possibly no one has thought it worth doing, or maybe even detrimental. I'm trying to get a gauge on that.

Seems a very common swap, I've seen several write-ups with pictures, and you-tube videos of the swap, and they all just bolt up the adapter and carb without remarking on the difference in the respective opening cross sections between the manifold (which is smaller w/ two bored circular holes that match the size and location of OEM carb barrels) and the adapter (larger w/ single oblong hole that matches the MC 2100). The MC 2100 has larger barrels and their centers are spread apart further than the stock manifold opening, and so is the adapter plate (the butterflies open into the oblong space in the adapter - they would not open if bolted straight to the manifold, or if the adapter plate were much thinner than it is), so there is going to be a mis-match in the mating and so some fuel/air flow disturbance if I just bolt up the adapter and carb.

In the several times you've done it, have you noticed the difference in openings' sizes and shapes, and have you felt it wasn't worth doing any blending to better match the openings?

Depends on the MC2100 you have. Bores are anywhere from 0.98" to 1.33" in diameter. The general CFM ratings are as follows:
.98 = 190
1.01 = 240
1.02 = 245
1.08 = 287
1.14 = 300
1.21 = 351
1.23 = 356
1.33 = 424

Most people use 1.08" bore models for the 258, but any will work depending on the mods to the engine. I wouldn't run any bigger than the 1.14" with a stock cam. The 1.08" is about the same cfm rating as the BBD 2V -- 280 cfm -- the 1.14 just a bit more.

The 2150 was only made in two sizes -- 1.08" and 1.21" (287 and 351 cfm).  The 1.08" was used on some AMC 304s.

Here is an article where a Jeeper used the adapter as you are using. Didn't do any machine work or blending. No report on how well it ran, just that it did.  If you plan on leaving that carb on I'd at least blend the bore with the adapter. Won't hurt, though it probably won't help much. The "ledge" in the intake will create turbulence. While that may hinder smooth flow, it will also keep the fuel and air mixed. You need a little turbulence in a wet intake.

http://www.inajeep.com/motorcraftcarb/

I didn't think about the butterflies being the same size, but should have. The venturii are what determine flow, nit the butterflies. Carter did the same with the BBD -- the Chrysler 318 version has larger venturri than the AMC 258 version, but the butterflies in the base are the same size. The base itself is a bit different though (I think the bolt pattern is the same, but connections/arms are different) and many AMCers take the center bowl section from the Chrysler and mate it to the AMC base and top.

I've seen 280 cfm tossed around for the BBD on the 258, but I think that's an Internet error -- the Chrysler 318 version is 280 cfm. I have an old Jeep manual that lists the AMC 258 BBD as 195 cfm. I think the AMC versions are all 195 cfm. The Chrysler 318 version bores are at least 1/16" larger, might be as much as 1/8" -- I forget!! The 318 BBDs are supposedly 285 cfm. Chrysler used 220 cfm  BBDs on the 225 slant six in cars, the 285 on truck engines, and a 260 cfm version on export model cars. Many assume the AMC BBD is the same as the Chrysler slant six model, since the AMC six is a bit larger. It's possible that the Jeeps used a slightly smaller carb than the cars to get a little better low end torque, but I don't think so. Researching carb numbers might solve that (Jeep and cars using same model carb).