Log modification question

[Anonymous]

I made an appointment for Thursday to have my log head worked on at my local machine shop.

I'm going to have them mill the cylinder head .050" and mill flat the one barrel intake "bump". This way if my idea below doesn't work out, then I can just put on a single 2 barrel carburetor and go. But...

I've been seriously contemplating the adaptation of (2) two barrel carburetors operating together as one unit but seperated, of course, by location.

Can this be done without physically dividing the log head?

Any ideas would be appreciated. Like I said I plan on having the work doen so that I can mount the carbs. by this coming weekend.


-Chris

 

[rbohm]

8) you can mod the log to use two 1bbl carbs, you need to center them between the runner pairs. have the machine shop mill that area flat, and then bore a hole 1 1/2" in diameter. then using a carb gasket, supply them with a carb as well, have them locate and drill and tap the mounting holes.

 

[CZLN6]

Howdy chris

Certainly it can be done. The challenge is not in fabricating a mounting system on a milled log head, although that's the beginning. And yes, you can use dual carbs simultaniously, but again the devil is in the details. You will be better able to tune each carb if you limit the connecting logs diameter. You do not need to block it completely, just be able to vary the size of the connecting log. If you don't it is very difficult to isolate the effect you are having on the carb you are tuning. For example if you lean the front one, the rear will compensate to some extent. This would be particularly true with the idle/high vacuum circuits and the choking/cold start systems.

Once you have both carbs fairly well tuned and balanced, there may be some advantage to having a larger diameter log connection for WOT, high speed work.

Linkage, air cleaners and carb heat will be other issues that will need to be addressed. If this is a street rig and driven year round carb heat may be necessary.

What carbs are you planning on using? Smaller is better in this scenario. My brother Dennis is currently working on a flat-topped log head, with the log top milled off completely, for thorough porting, and a flat plate affixed to the top for mounting two progressive Carter/Webers. It will have a baffle seperating the front three cylinders from the back three. The baffle will be interchangeable for a larger or smaller connection between the two halves.

Most, who have tried multi carbs on our engines, find a loss of vacuum for the distributor vacuum advance. A hotter cam adds to this problem. Another detail to address.

Careful planning and part selection will help the tuning process. Enjoy the trip.

Adios, David

 

[Anonymous]

Thanks for the information guys. Most of what David said was more or less what I had already thought of but needed an expert to confirm my thoughts and ideas.

I originally thought about using two carburetors simply because of the physical limits the log possess - bare in mind I don't want to chop up the log. I want to stay within those limitations. Keep it clean.

So, again, my thinking was the use of (2) two barrel Motorcraft carburetors (1.21 stamping). Sure the linkage and air cleaners would be a little tricky but that's half the fun!

But - brainstorming again - if I can use a four barrel carburetor mounted to an adapter plate (4 to 2) then I would most definantly prefer this route. Would this work well? Would there be any benefits for this particular setup?


-Chris

 

[CobraSix]

Chris,

Same problem as running a 2V with a 1V adaptor. You can flow more air, but you still are sucking it through the same size straw. 4V is nicer because of a better vacuum signal though, but still putting it threw a bottle neck.

Slade

 

[CZLN6]

Howdy back Chris:

An Autolite 1.21 is almost too much carb for a 200. One 1.14 or the later 1.08 is more in the right ball park for a street performance 200. The 1.14 has a little more CFM, but the real advantage over a 1.08 is a richer idle circuitry. The 1.08 is rated to flow 287 cfm, the 1.14 is rated at 300 cfm and the 1.21 is rated at 351 cfm, comparible to a Holley 500 using 6 cylinder rating. I'm about to try a 1.21 on my much modified 250 and will compare to the 1.08 currently on it.

Two of these carbs used together would be awful as a street driver. They are way too big for low speed air flow velocity. They would screem at 5 grand and up. If you're determined to use 2 #2100 Autolites consider the .98s used on early 221 V8 Fairlanes.

A four barrels biggest advantage is its primary and secondary design. A small 4 barrel would be a great idea, BUT- it will have to be offset to clear the valve cover. Using an adaptor has advantages, linkage and aircleaner, but may limit max flow because of the funnel effect. Hood clearance is also a concern. If you can make it work, I'd sure like to hear about it.

Adios, David

 

[Soldmy66]

As a prior owner of a 66 Mustang w/ a 200, dual 2 barrels is something I thought about a lot. Does anyone know what other 2 barrel carb choices would make sense? Years ago, I thought about two small Dellortos/other carbs used in eiethr VW or 240Z applications. Are there any baby Webers or other carbs that are sized right? Also, rather than milling the carb holes on top of the manifold, has anyone tried milling the openings on the side, and using side drafts?

This is something I'll never use personally (I now have a 57 Chevy Wagon). But I do read the forum daily - and jump on the manifold/carb postings whenever I see them.

 

[xctasy]

See this:-http://www.inlinepages.com/~inlinefever/inline_6_carburation.html

Can you all say MG?MG is GM backwards, is this a coincedence?

This is 1 of my 2 setup's that I have been working on. It is a 1978 U.S. head that features 2 Carter YF 1 Bbl's that are rated at 193 cfm's a piece.
I am not running it at this time, being it needs some more R&D work. I plan on reinstalling it sometime next summer.

The Chrysler guys have a manifold, there are a few around for 300 I6's, and the "MG-Special" is another way you can convert your log head into a well-flowing piece of equipment. Two stock 32/36 Webers or 5200 Holley Webers, or 38DGAS Webers will do okay.