The debate has gone on since probably the 1980s- can you run a 318 BBD on a slant six? Many people have taken both sides of the debate. Some say they have run a 318 carb with no problems, others say only a true 225 BBD will work properly on a slant. Today, I found a strong reason why you should really try and use a slant six specific BBD.

Before I get to it, I will admit that I am in the camp that says you should try and use the slant six specific carb. First, there is the choke issue. The 318 BBD has a slightly different choke linkage that will not work on the slant six without addition effort. The workaround for that problem can be found HERE.

Second, the big nipple for the PCV hose is oriented differently. This likely won't make that much of a difference, but if you have lots of stuff in the engine bay or if your hoses are short, you might need to run a new hose.

But the difference I found today between the slant six BBD and the 318 BBD is fairly large, and is really a confirmation of something I have been saying for years based off of factory literature.

Over ten years ago, I found on eBay a 1976 Chrysler factory reference book introducing the "new for 1977" slant six BBD carburetor and highlighting the differences between the slant carb and the 318 carb. That factory reference book is included at the back of the BBD carb manual available for free download HERE.

In addition to other differences, on page 1 the 1976 reference book states,
Emphasis added.

I have been referring to this difference for many years as why one should always try and find a slant six specific carb, but today I obtained photographic proof of this large difference.

I happened to be rebuilding a 318 BBD this afternoon with a Super Six BBD also loose on my workbench. Both these carbs were assembled from loose parts I obtained as part of a bulk purchase of various BBD parts. As I reassembled the 318 BBD, I noticed that the venturi cluster had a "6" cast into the top of it. I remembered the internal differences referenced in the 1976 manual, and checked what I knew was a slant six BBD. Sure enough, the slant six BBD had an 8 cast into the venturi cluster. This got me curious so I decide to take the Super Six BBD apart and compare the venturi clusters.

This is what I found ("6" cluster on top in both photos)





As you can see, the hole in the end of the fuel tube inside the venturi is visibly larger on the "8" venturi cluster. Not visible due to the blurriness of the picture is the fact that the hole in the top of the brass tube that pokes up out of the venturi cluster is also smaller on the "6" cluster vs. the "8" cluster. This makes sense since the smaller air flow of the 225 would required a smaller hole to amplify the effective venturi effect and draw the fuel out of the float bowl.

I determined that I must have unknowingly assembled the carbs with the venturi clusters in the wrong one so I swapped the venturi clusters and reassembled both carbs.

I then tried both carbs out on the 225 in my 76 D100. The 318 carb ran OK but was a touch rough at idle and a bit sluggish when revved. The 225 BBD (with the "6" venturi cluster) idled smoother, would idle down to a much lower RPM, and was much more responsive when revved. I didn't do a test drive, but the 225 BBD with the "6" venturi cluster performs better, at least in the driveway.

I believe the 6 and 8 cast into the top of the venturi pack signifies if the venturis are for a 225 or a 318, and that the right venturi pack should be used with the specific engine it is intended for. If anyone has contrary info to this, I would appreciate being set straight.

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Casually looking for a Clifford hyperpak intake for cheap.

Makes sense. Whenever one uses a carb that is not a factory fit for any engine, one should be measure actual AFR through the RPM and load cycles. Just because a carb fits any given application, doesn't mean it's appropriate. Too much fuel and you're looking at wash down, rich fouled plugs etc. Not enough fuel and you're looking at burnt head gaskets, detonation, pinging, etc. Same is true if you use a carb that came with the engine, but you modify the engine with more compression, change timing, bigger valves etc....you should expect the carb will need to be retuned for the application at hand.

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https://tinyurl.com/yynpj4v2

I've been running the "318" BBD (That was what was on the donor car) since I did my restoration almost 15 years ago. I do notice that it runs a tad rich at idle, and the idle speed is about 100 rpm too high when idling in park. Otherwise, compared to the single barrel setup, it's a huge difference. Where would one be able to obtain a proper slant six BBD that hasn't been molested, or contain parts from all over the world?
Thanks for the help in advance.

Junkyard, craigslist, this website, swap meet, eBay, the usual places. You just have to keep a sharp eye and know how to tell a slant BBD from a 318 BBD. Many people don't know the difference.

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Casually looking for a Clifford hyperpak intake for cheap.

I know Mike tested a 318 BBD on his stocker motor on Bogner's dyno and it was actually lean compared to his Slant BBD.

Probably the main reason they tell you to not interchange them is it wouldn't be emissions legal anymore.

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Official Cookie and Mater Tormentor.

Would you be able to see the "6" and "8" on an assembled carb? Like at a swap meet?

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DynoDave
1970 Plymouth Duster
1972 Dodge Charger Rallye
1977 Chrysler Cordoba
WPC # 12304

Casting numbers ,useless. there a 2 and 8

Picture bad but size difference can be seen.

That black line is Diminishing Well Bleed, page 8 in carter bbd manual . Thats a318 thing, most of them any way. White line is slant six no extra well bleed hole. Factory slants did not use them, but they get mixed up at rebuilders. Carbs that used Diminishing Well Bleeds got smaller main system air bleeds because in effect there using an extra bleed.

Uh oh, my "6" and "8" theory has been disproven. So is it safe to say the venturi cluster with the smaller bleed holes is the six cylinder one?

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Casually looking for a Clifford hyperpak intake for cheap.