D4B DC mods like the LD340 DC mods?

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go-fish

go-fish

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Would it seem logical that what's good for the LD340 is good for the D48 or LD4B in regards to the Direct Connection plenum mods? I don't know the exact spec but I'm talking about the square notch.

For those that care: 1965 273 2-bbl. Changing to dual point distributor, D4B, Carter AVS 4638SA (1969 340 auto), Commando type cam grind. I will probably keep the 9:1 (?) pistons for now but if it gets opened up you know the 10.5 pistons will go in.

So, from a flow and distribution aspect is what is good for the goose also good for the gander?
 
Not at all. Many differences in the engines, cubic inches, 2bbl pistons, port sizes, etc, etc.

And max flow doesn't make useable power for a street car.

What gears? What trans? Converter? It's about the combination.
 
I've always thought unless you were all out racing, to leave well enough alone.
 
Contact - Rebuilder's Choice I found some .060 over which is a stretch on ebay from rebuilders choice. They are high performance 10 to 1 made from hyperkinetic aluminum with valve reliefs. I contacted builder's choice to get the info for the part number. Ill post the ebay listing in a moment
 
Brooks James said:
FYI
Laster one is LD340 modification



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View attachment 1715924131

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LD340 Direct Connection mods from the manual. This is the modification I'm asking about.


ld340(2).jpg
ld340.jpg

ld340(1).jpg
 
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The notch is cut in to use a thermoquad carburetor. Any way what you are doing is changing it from a dual plane to a single plane, sort of. If your not using a thermoquad carburetor, I wouldn’t do it. I’d use a larger carburetor than an AVS with a dual plane as 4 cylinders only see 1/2 the cfm and the AVS is a small carburetor.
 
Unless you use the AVS2 1412 800 CFM carburetor. I'm pretty sure that a TQ's secondary blades will still require an adapter to fit that manifold. I've always heard that the notch is for the three barrel Holley carburetors that were popular at that time.
 
Check the clearances, run it without and do the mod and run it again. But once you carve it up there's no going back unless you tig it back in and machine it. Let us know how it works. :thumbsup:
 
@go-fish Here’s a pic of my pistons when I was assembling my 273. I used 302 heads that in the final windup had 58 cc’s and 1.88 intake valves. A little massaging, but nothing crazy. I ended up with 9.8 compression wit these pistons. More than enough for what I wanted. Mild hyd. roller cam. I ended up with 260ish HP and 280 lbs. of tq.
88CF58C2-B3B9-4BAC-80D5-1B2580F18677.jpeg
 
@JDMopar The hydraulic rollers intrigue me. I have two LA's that have bushed lifter bores. Needless to say, I like 'em. I wasn't even considering hydraulic rollers with the 273. Are the 273 lifter bores plagued with inconsistent chamfer like the other LA's? What lifters did you use?
 
I had to have mine bushed because one bore was worn out. I never paid any attention to the chamfers. I used Morel lifters. They are the only ones that the oil band on the lifter doesn't come above the top of the lifter bore. The oil band is lower on the lifter body. Some of the big name Mopar builders sell them re-boxed as their brand name lifters...lol. My machinist ordered them thru Bullet Cams. Bullet gets them and tears them down, checks them and squeezes all of them to make sure they are good to go before they leave out the door. Mine will come out with the heads on, but dang they are close! The block will need a little clearance smoothed off too, but it is very little.
 
i would leave it be. keep in mind those modifications were for race applications, or at least very hot street motors with higher lift and duration cams.

the notch will change the signal the carb sees, and for such a mild application i don't see any benefit to doing so.

unless you need it for butterfly clearance, which with a square bore you shouldn't.
 
There was only one reason those old manifolds had the slot cut out of the divider when they were new and it didn't have anything to do with how the manifold ran or reacted. It was so a Holley 3916 or 4604 three barrel carburetor would fit and work. That was it. I've never liked modifying the center divider, because since most people don't have a dyno in their back pocket, you don't know if you are improving or making it worse. The LD340 and LD4B are two very different intakes. They even have runners on opposite sides. So the mods for one will probably not be optimal for the other. Lastly, as was already mentioned, removing the divider does indeed make it pretty much a single plane intake manifold. So there's that.
 
I've got an LD340 that I picked up at a swap meet many moons ago. Someone had attempted the divider mod and spreadbore deal, but it looks like they done it with a bush axe and then used a course thread half inch bolt for a file! :BangHead:
 
JDMopar said:
I've got an LD340 that I picked up at a swap meet many moons ago. Someone had attempted the divider mod and spreadbore deal, but it looks like they done it with a bush axe and then used a course thread half inch bolt for a file! :BangHead:
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I hate it when I see perfectly good parts mutilated by idiots. You think it's savable?
 
I put this one on my H-code Duster. Should I repair the center?

IMG_9659.jpeg


Edit: that might be one I sold. I had 2 of them at one point. I’ll have to check now!
 
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