All Small Six Which cylinder head?

[Otto]

Hey All,

I'm new here but have spent a lot of time poking around the site. I see/hear a lot of mixed terminology for describing parts and wanted clarity. I have a couple of late 70s 200 cylinder heads; one is on my vintage Econoline and the other is on a core engine in the corner. They both have a number cast into the intake: D8BE 6090 BA. One of them has a "X" cast into it. I've discovered that these are referred to as a "large log" head, but have heard/read about octagonal, round and flat "large log" heads.

Q: which do I have and is either a good candidate for the 2V conversion? Would like to get away without brazing on the head.
I'm hoping the one with the X contains some magic!

Thanks

 

[TrickSix]

Greetings. All varieties of the large log head have the 1-3/4" carb inlet. You have a couple of the flat top variety with the bigger 1.75" intake valves and hardened seats. Good heads. I'm not sure what that X signifies. Anyway, they are usually regarded as the best for the 2V conversion, but will still require a lot of machining and probably some brazing. There are some smaller 2V carb models that require a smaller adapter with a little less machining. The 2V carb is most useful for adding power at higher RPMs though. In your van a wound out screamer might not be the best match for how you drive it. It would be a lot simpler and cheaper to add a 2V carb on an adapter to the 1V intake. With the large log's big 1-3/4" inlet and wide flange, you can elongate and enlarge the opening in the adapter and inlet until it's almost as big as a real 2V opening. Should give you a noticible mid-range boost where you'll actually drive the thing without costing nearly as much. Some people more knowledgeable than me will be posting soon. It's good that you want to do some research and make your choices from an informed position. Good luck.

 

[bmbm40]

There is much interest just recently with direct mounting a small base Rochester 2V carb to the existing carb base. Also the large base Rochester carb and Carter BBD 2V. I will find a link and send to you. In the meantime:

 

[bmbm40]

All Small Six - Carburation

I’m building a 200 cubic inch.short block is a 1976 - 30 over-head is a 1979 big log competition type valve job and milled 60.. Howard’s 2800280 cam- stainless headers- pertronics distributor- . My question is which carburetor should I use- I don’t particularly like a Weber. I like the...

fordsix.com

 

[drag-200stang]

Those are the first of the largest of the large logs and they are hex heads or oct. if you want.
They are harder to do than the flat tops but it can be done.

 

[TrickSix]

Maybe that is a hex log. The one I have has a much more distinctive and angular hex shape to it than in the OP’s pic.

 

[Otto]

Thanks for the replies, it sounds like I have a "hex" log.
Some background on what I want to do. Right now my van is sporting the Holley 1940 carb that was on the 170 engine the van came to me with. It runs the engine, but not very well. I have some 2G carbs and the one I want to use is the black one in the photo:



This is the carburetor (left) I bought from Ebay. It’s referred to as a Mercarb and similar to a Rochester 2G, but has some differences. This is the smaller unit for the 120/140 Hp engines as evidenced by the smaller throttle bores. You can see there is only one idle mixture screw vs. two for the 2G; Mercarbs usually have a black coating too so they’re easily identified. The other 2Gs were cheap swap meet items but too large for my use.
I bought these for my jeep that runs a 3.0L Mercruiser engine; this Mercarb is what Mercury Marine equips the 3.0L with as OE. The jeep's EFI is working much better now, so this carb could be used on the van.
I'm very intrigued by this photo, and the fact that the "mill & fill" procedure could be avoided.

Does the carb sit at an angle, or is this accommodated by the adapter?

 

[TrickSix]

Yes, the adapter makes the carb sit square. This is what I had mentioned, the bottom of the aftermarket 2 into 1 adaptor is enlarged to fit the ovaled out hole in the intake manifold. Not quite maximum high rpm performance, but greatly reduced hassle and cost. The pic above is a rather conservative enlargement of the opening, I've seen pics of some that left an even narrower flange.

 

[Otto]

For now, I’m going to try this:

It’s combining two 1.4” holes into one 1.75” orifice. The original carb hole is still an hourglass for the 2 barrel and is probably a restriction for the engine; it’s the difference between 2.4 sq/in and just a bit over 3 sq/in.

I installed the adapter and carburetor on the van’s engine today and gave it a try. I was pleasantly surprised at how well this worked out of the box. Very responsive and it idled down nicely; I see some promise here. I may get a wide band AFR meter and install that to dial it in even more.

 

[bmbm40]

Looks good! That small base Rochester is what I want for my 250 powered Bronco because as you stated I don't want the mill and fill procedure.
Where did you get the adapter?

 

[Otto]

Where did you get the adapter?

bmbm40,
As most of the things I find interesting are outside the mainstream, I can't just buy stuff I want or need. I fabricated the adapter over the weekend.

I had concerns about heat from the head migrating up through the adapter to the carb. But when the engine is running, the aluminum is like an ice cube.

 

[bmbm40]

Nice work on the adapter it looks great and blocking the heat is an added benefit. Looking forward to hearing driving impressions with the Rochester. That's a clean and tidy engine bay.

 

[TrickSix]

I like the wrinkle finish on the valve cover.

 

[Frank]

bmbm40,
As most of the things I find interesting are outside the mainstream, I can't just buy stuff I want or need. I fabricated the adapter over the weekend.

I had concerns about heat from the head migrating up through the adapter to the carb. But when the engine is running, the aluminum is like an ice cube.

Nice fabrication, and good carb choice. Rochester engineering is second to none, and when it's tweaked you should see at least the same, or (I predict) better economy to go with the added power.
Nice rig!

 

[Otto]

Nice fabrication, and good carb choice. Rochester engineering is second to none, and when it's tweaked you should see at least the same, or (I predict) better economy to go with the added power.
Nice rig!

Thank you.
I'm looking forward to more power and fuel economy!

 

[Otto]

I got a throttle cable working on the van and tried a short test drive on the little gravel road I live on. My first driving impression was that there was a bit more "go" than before. I stepped into it a little in second gear and was pleasantly surprised!

We're into the wet season here so test drives are a bit challenging, but I'm encouraged. Next weekend I'll start on the AFR meter install.

 

[Otto]

Installed the AFR meter in the van. Now it’s got a wide-band O2 sensor in the exhaust and a meter below the dash. It should help with dialing in the Mercarb and hopefully save some time and money using science. I’ve found that Mercarb jets do not interchange with Rochester 2G jets according to Mike’s Carburetors in Chehalis, WA. You can buy alternative jets as boat parts, but hang on to your wallet! A jet change could cost 40 -50 dollars if you can’t find them locally.


At idle.

I’m hoping I can find some other metric jets that may work from something else.

This is my first experience with an AFR meter, is there some guidance on how to interpret the data and make changes? Between the vacuum gauge and the AFR it should tell some sort of story right? I get that 14.7 is just right and below that is rich and above is lean, but I'm hardly a mechanic.

 

[pmuller9]

Tell us what you are seeing at idle, at cruising down the road with a light gas pedal and at Wide Open Throttle.
Idle can be any where around 13.5, cruise at 14.7 to 15.5 and 12.5 at WOT.

 

[Frank]

That's curious that the jets don't match a 2G. I would question that, but if Mike at Mikes' Carbs said so, I'll say no more.

 

[Otto]

Struck me as odd too. The next time I have both carbs apart, I'll compare and see for sure.