loghead carb adapter idea

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My latest manifold adapter idea. When finished I will find a small foundry to sand cast it and get a couple made. If I can't find one, I have found a place in Washington that will sell me a hobbist furnace and I'll cast it myself.
The carbs are Motorcraft 740's (Weber/Carter models). They are rated at 285cfm. The beauty is they are progressive carbs. The throats measure 33mm each. If these workout well, then I'll replace them with Weber 32/36's and see if there is a difference. I have a new 250 engine build plan. I am starting with the head first. If you have carb location ideas or anyother ideas, please feel free, so far nothing is finalized.
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Sorry, the pictures had too many pixels.

Ken
 
I have no sophistication in flow characteristics so please humor me. But why are the carbs so far apart? I would think - at least with the 3/4 port divider - that you would want them more central to the three intakes. OTOH, I guess I can see that you want to avoid starving out the outermost intakes by placing the carbies a little farther apart.

And why a casting that runs the entire length of the log? Could you get the same effect with a block off plate and two platforms that are secured with countersunk allen screws and 2 U-bolts, similar to the outer ends of the 3 in I head? If it's an alignment thing, you could include a removable bar that mounts to both brackets to keep them in line during assembly.

I'm just playing with your idea here. Props to you for mocking it up and finding someplace to cast it. It still looks good. I've been thinking about something like that for a while.
 
Good one Jackfish!

Ludwig, the reason for the full length is 2 fold, a third carb could be added and second the bellcrank for the linkage will be located on the center of the part. The hold down will be the 2 origional carb mounting screws and at the ends of the log. Where the casting is the thickest. The adapter will be held on by by high temp adhesive then fastened down.
The carb location is no science, I just put the primary's as close to the same location similar to the Offenhauser 3x1 manifold.
I am just a truck driver and have no sophistication in flow characteristics. I am asking for help in this area. But no one else is doing anything like this that I have seen. (There might be a reason for that.... HMMMM) Hell, I can't even post pictures!
Ken
 
8) i think that three two barrel carbs would be a bit much for most small sixes, though a six making around 200hp would benefit from three carbs. a few suggestions;

1: for a two carb system, mount the carbs on either side of the original carb location as that will give you the best mixture distribution.

2: for a three carb system, mount the carbs perpendicular to the log not parallel for best results.

3: use staged carbs, small primary, larger secondary throttle openings, so that you have two or three small primary barrels to run the engine on for normal operation, and then you still have the larger secondaries for maximum power, much like a spread bore four barrel carb.
 
Ken,

I've been kicking the idea around for a long time, but only recently decided to get serious about it. I ordered a couple carbs from Langdon's a couple weeks ago, but just got them Friday, as they were closed during the month of Feb. While there is very little info on the internet about these carbs, I have been able to dig up a little. Some say they are difficult to tune and mileage drops, while others say they work great. Guess I'll find out. I ordered a couple books last night, hoping they'll have some more info on them, but I won't get them until later in the week.

Correct me if I'm wrong, but I think they flow around 180-185 cfm, rather than 285 cfm? I do know that the 32/36 DGV's only flow 270 cfm @ 3", or 200 cfm @ 1.5". All 4V carbs are rated @ 1.5", so two of these would be around 360-370 cfm, while two 32/36 carbs would be 400cfm. I'm currently working on the cylinder head, installing three conversion pads on the log intake. This will let me test a single Weber, twin Weber's, or even triple Weber's if I want. Since the carb base bolt patterns are different, I also had to make three new adaptors for the 32/32 carbs. However I used the same bolt pattern to secure them to the log, so it's an easy swap during testing.

Next, I don't know if you've ever check into the cost of having a pattern, match plates (molds), and castings make up? If not, your in for a shock. Based on what I've done in the past, I'd say it will run between 7-10K, just for the pattern, match plates, and gating. Most of that depends on what the pattern maker charges? Even if it was only 5-6K, you'll certainly want to sell more than one or two castings. That is if you want to recoup some of the money you invested. Personally, I don't think the demand is there, at least not enough to consider casting them, which is why I'm going with conversion plates (direct mount). If you do decided to cast them let me know, as I might be willing to chip in. However I want to see how they perform first, and test them on the dyno. Once I have the dyno results, I'll run a poll to see if there's enough demand for casting them. If not, I'll probably offer a conversion kit. Just depends on how the testing works out.

I hope to have the log head ready to go by the end of next week, as the short block is already done and ready to go. Should be fun..... :wink:
 
Hey Mike,
I was told they flowed 285 cfm, I just assumed I was told correctly.
As far as casting costs go, no I haven't been educated there yet, but I am looking at making my own core and green sand casting myself. Then finishing off the adapter by machining.
I divided the manifold in two, then measured the distance from runners 1-3 and 4-6. (The 2 and 5 ports and located such that they will probably be rich at full throttle.) I divided that distance by 2 and that is where I put the primary on the carb. Now that just happens to be 6" from the center of the manifold for both carbs. Yes the carb's are facing each other so I'll need to add a bell crank in the center of the manifold to activate both linkages.
You will be miles ahead of me, I won't be working on this project for another month. Post your results, I'd sure be interested in your numbers.
Ken
 
Well done Ken for taking the initiative and trying to come up with something.

I think just about every carb setup one could imagine has been done to our little sixes, from six one barrel sidedraft carbs to one Holley 4bbl and to multi port fuel injection.

If you wanted to get your own furnace and do your own castings it seems simple enough to be sand casted.

I do agree that the carb pads should probably be moved a wee bit closer together.
 
Thanks for your carb location input. My question is, I am no fluid dynamisist, how would moving the primaries closer together help the 1 & 6 cylinders? My thinking is if the primaries are in between the 1 and 3 and 4 and 6 ports, this would even out the flow considerably. As I said I have no experience is this field.
Cutting the model up and moving the pads is no problem and really doesn't bother me.

Thanks,
Ken
 
Ken Thompson":25d67bmx said:
Thanks for your carb location input. My question is, I am no fluid dynamisist, how would moving the primaries closer together help the 1 & 6 cylinders? My thinking is if the primaries are in between the 1 and 3 and 4 and 6 ports, this would even out the flow considerably. As I said I have no experience is this field.
Cutting the model up and moving the pads is no problem and really doesn't bother me.

Thanks,
Ken
Click to expand...

I agree...since the ports aren't placed exactly equal in relation to the head centerline, it would make the most sense to me to center the carbs over each group of ports, and not align them with the center of the head.
 
Ken Thompson":2xpjf6di said:
Thanks for your carb location input. My question is, I am no fluid dynamisist, how would moving the primaries closer together help the 1 & 6 cylinders? My thinking is if the primaries are in between the 1 and 3 and 4 and 6 ports, this would even out the flow considerably. As I said I have no experience is this field.
Cutting the model up and moving the pads is no problem and really doesn't bother me.

Thanks,
Ken
Click to expand...

8) dont forget that you are still feeding six ports, just with two carbs rather than one. if oyu push the two carbs further apart like you want, then the center cylinders will tend to run lean while the front and rear ones will tend to run rich. what you are shooting for is an even fuel mixture across all cylinders, and with the carbs closer together you get a more even fuel mixture. remember that the log head isnt the best flowing head around.
 
Over the years I've seen a few photographs of dual, two barrel, direct mount carbs on log manifolds. I would think this would be a very good approach, especially if the block off plate mounted to the original carb mounting included a tab extending into the manifold - effectively to yield two manifolds; one for each set of three cylinders.
 
'like to hear more on Carter/Webers' multi carb use. I was led to believe they are OEM smaller CFM/displacement than most Holley/Webers - or typical H/W 5200 - 32/36 type are higher CFM ... Three progressive Carter/Webers -even on 2X1 adapters on an Offy 3X1 sounds about right for a thirsty six setup that you actually drive. May not physically fit though..

Two progressive 2Bbls sounds more reasonable for 200/250 performance application. The Holley/Weber progressive works well in single and an efficient intake with two would be less tuning challenge than most 3X1 setups. Also tried non-prog. 2300 series/7448 350 CFM 2 Bbl into 2X1 adapter on Offy center position on built 250. Had good low speed and mid throttle, WOT was good but 3X1 singles with carb runners dumping into ports really kick the 250 at WOT. Also have a 4412 - 500 CFM version to try but haven't got back to it yet. The 2300 350/500 2Bbl series is some kind of race spec and is widely available.

Have Fun

H/W's
H-W5200TWO.jpg



7448



 
Soldmy66,
I have done a search looking for info on dividing off the log as you suggested. I would be interested in this idea. I do not remember who pointed out notching a divider to allow for a pressure balance. How big of a notch and where would it be located, top, bottom of divider. I'll keep searching to try to find some info dealing with a divider..
Maybe someone that has tried this can add some insite.
Ken
 
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