Ld340 vs ld4b

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FC7VW9

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Hello, I have been a member for a year or so, (since I bought a 70 dart). Several members have been very helpful in selling me parts to put her back together. I am finishing the 340..... .30 over TRW 2332P, J heads large valves, with head gaskets looks like 68cc's, gaskets matched porting, balanced, four speed, 391 post. Headers and TTI exhaust. I am doing the car old school, like mid 70s street racer. I purchased a couple of truck loads of parts and have a LD340 and a LD4B had them stripped (walnut shells). Both are great, which one would fit my dart best? I plan on driving the car once a week or so.
Thanks
 
The LD4B is smaller port (unless it's been hogged out), better for stock 318/273 heads.
 
I agree!

They are both similar and good manifolds. But the LD340 is a little bigger internally and will work well with the extra mods and 4-speed.
 
Ok, sounds good to me. What carb would you recommend? Would the LD4B work on a stroked 318 auto in a 68 barracuda?
 
FC7VW9 said:
Would the LD4B work on a stroked 318 auto in a 68 barracuda?
Click to expand...

That manifold is designed to run on 273's and 318's. It would not be a good choice for a stroker motor. It IS worth some money. I sold a nice one a couple of months ago for $288. Probably enough to buy RPM Air Gap if you shop carefully.
 
Go with the LD340 if you are using the larger port 340/360 heads.

Use the LD4B if you have smaller port 273/318 heads.
 
Another LD340 vote for the already mentioned reason of bigger ports. I have an LD340 and a 4779 750 DP on one of my 340s. Had to fatten up the secondary jets to get rid of a slight hesitation, but now runs great with 72s primary and 84s secondary
 
Thank you for all your responses. I will go with the LD340 on my 70 340. I think the mechanical secondary 4779 would be more streetable? The LD340 does not look like a spread bore app. Still kicking around the 318 stroker with the 920 cast 273 closed chamber heads and the LD4B intake.
Thank you,
This is more helpful than the Maports sight...lol:shock:
 
The 750 3310 vacuum secondary would be more streetable. The 750 4779 double pumper is more of a race carb, tends to run richer and is harder to tune. (Both are square bore.)
 
Hello Locomotion, I think I'm confused with the terminology, what is square bore?
thanks
Ron
 
FC7VW9 said:
Hello Locomotion, I think I'm confused with the terminology, what is square bore?
thanks
Ron
Click to expand...

Hi Ron,
That just means that all 4 barrels of the carb are pretty much the same bore size. A "spread bore" carb is like a Thermoquad or Quadrajet, where the front, primary barrels are a lot smaller than the rear secondaries. They started that for mileage and emissions in the '70's.

Some older Carter carbs have primary and secondary barrels obviously a "little" different, but are probably still considered "square bore".
 
A square bore is just that where the carb bolts to the intake it's square and a spread bore intake is on where back barrels are it is notched out.
 
So the two oval openings on the intake are Square bore....lol. I got in now. I like the thermoquad on my 74 RR. No more Quadajets since 84, when I bought my first Mopar.
Thank you
Ron
 
Yea. Some of the newer aluminum intakes get wider towards the back to clear the larger secondary throttle blades. But usually you can still use a square bore carb on them. It's a compromise. But the 2 you have are strictly for square bore carbs unless you use an adapter (bad idea) or do some custom grinding.
 
Locomotion said:
The 750 3310 vacuum secondary would be more streetable. (Both are square bore.)
Click to expand...


If you run the 3310 vacuum secondary carb. Order the vacuum advance spring assortment and install the shorter yellow spring in the vacuum pod for the carb. It will run real good that way. It's easiest to change before you install the carb.
 
With 3:91s and a 4 speed, no way I would use the vac secondary.... double pumper for sure
 
The LD4B came both ways, FWIW. One had 318 port sizes and the other had 340/360 port sizes. In either case, the LD340 would be the best choice for a stroker.
 
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