LD340 / RPM comparison pic's

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1wild&crazyguy

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Now I put a few rpm's on friend's cars and they worked good but I always wanted to do a side by side of the Ld340 / eddy rpm.
So recently I picked up a eddy rpm and was able to put it side by side with my LD340 I already had and was able to look at it.

It looks like the LD has more runner/plenum volume.
Also turned the LD to show the difference in runner width at the bends.
The rpm has a narrower plenum below the flange.
The mixture grooves on the plenum floor are different directions netween te 2 intakes as well.
You can see a pic with the LD & rpm's no. 5 runner and how they shape different at the turn and their openings from the plenum all together.
There are plenty of lil diff's between, you can point them out

Photo 515.jpg


Photo 514.jpg


Photo 513.jpg


Photo 517.jpg


Photo 520.jpg


Photo 521.jpg
 
I have both intakes as well and the plenum of the LD is less than the RPM since the RPM is taller. The LD is wider and T-Q adaptable while the RPM is not.

The RPM has thinner runners to keep velocity up and strong while the LD relies on the older addage of bigger is better. Which is great for High RPM 340's or 360's bored bigger for street strip duties.
I noticed the LD has port sizes darn near equal in size to the Fel-Pro intake to head gasket.

This is where the constant comparo questions come in and it depends on what your doing with what size engine.

The RPM is a better intake while the LD is old, it can perform very well if used correctly and not haphazzardly. (Hummm,spellllling!?!?!?!?!)

Seeing how the LD can be picked up, most times, at a reasonable price and modded for a T-Q easy, for a probable price of intake, carb, rebuild kit and install gaskets under $150 installed and running, it can be a great deal for a street or street strip ride.
 
There is only a 1/8 of an inch difference between the 2.

The shallow side of the plenum is 2 1/8 on both.fwiw

The depth of the RPM on the deep side of the plenum is 4 1/4, thats only 1 side.
The depth of the deep side of the plenum on the LD340 is 3 7/8 but if you look at all the area around the plenum of the LD compared to the RPM you'd see why I believe the rpm wouldn't work as well as the LD on a stroker [not to say the ld is the best choice for ultimate HP, it's not]

Now edelbrock did they're test but has anyone else?
They tell you on the phone,'if you already have an LD340 then don't bother buying an rpm'.
They quit making the LD along time ago and everyone wanted a better dual plane than the performer, so they borrowed the design from their chevy manifold..at least thats what it looks like.jmo
 
Myron and I shot the breeze one day on this topic and I posted alot of pictures and measurements between the 2 intakes. (I never got around to CCing the intakes)

The differences are small but add up. I wrote down all the measurements somewhere around here. And how........
 
rumblefish360 said:
Myron and I shot the breeze one day on this topic and I posted alot of pictures and measurements between the 2 intakes. (I never got around to CCing the intakes)

The differences are small but add up. I wrote down all the measurements somewhere around here. And how........
Click to expand...

Good idea:cheers:, I'll cc them both.
 
Hey! Thanks.........cooooool!

Myron was wonering about the runner CC amount IIRC. Also plenum, but that's alot of work.
 
Track would tell, yes.

The rpm will be easier to cc than the LD, especially the runners.

I'll halfta get some sponge and clay, or cc all at once then lop off runners and make molds of them to cc over again. Or the old block the exits and fill and turn fill and turn after each one dries.
 
and if you have the stock 1971, 2100 cast iron intake you will not gain much if any at all going to a LD, just lighter weight.
 
Sure, you can get into the 10s with a "stock" LD340 intake, as long as you've got mega worked $$$ "stock" heads, custom pistons, coatings everywhere, are willing to try 100 different custom cams, $1500 oil pan, $$$$ custom headers, a $1000 Thermoquad, 60% rear weigh bias, etc.

I wonder why they spend all that money on heads and intakes when they have to be "stock"? LOL
 
rumblefish360 said:
Hey! Thanks.........cooooool!

Myron was wonering about the runner CC amount IIRC. Also plenum, but that's alot of work.
Click to expand...

That's the downside of learning things. But in the end, it can pay off. Knowledge is power. ( :p pun intended) I wish I had more time to learn more myself.
 
This is as good a place as any to make my first post! Sorry its a little old.
Well since were taking about LD340 manifolds, here's my TQ hacked up one.................

DSCN1331.jpg


DSCN1332.jpg
 
THPHHHHH

Once the carb is on top, no one will ever know, unless it's the T-Q.

How did you like the plenum mod?
Also, the remote choke spring, what linkage part did you use. I'm just about to do that myself on my LD340.
 
rumblefish360 said:
THPHHHHH

Once the carb is on top, no one will ever know, unless it's the T-Q.

How did you like the plenum mod?
Also, the remote choke spring, what linkage part did you use. I'm just about to do that myself on my LD340.
Click to expand...

This was 15 years a go so it's really haze.

I don't have any comparability, as i cut it up and then put it in with my BADLY ported heads, so it really hard to say.

I never used the choke on the TQ. had it wired open........that choke spring is on the wrong side any ways.......isn't it???

When i get these previously ported head, ported again, with 2.02 in it. I will be testing this LD manifold as well as the single plain Weiand 7545, that is currantly on my 340, with my flow bench to see which one likes my heads better.
 
$100 - $150 condition dependent.

Cudafever said:
I never used the choke on the TQ. had it wired open........that choke spring is on the wrong side any ways.......isn't it???

I will be testing this LD manifold as well as the single plain Weiand 7545, that is currantly on my 340, with my flow bench to see which one likes my heads better.
Click to expand...

Choke is on the correct side.
Good idea for a test between the two intakes. Engines are a funny thing sometimes on what they like and don't.
 
It probably won't be until spring, but i will chime in with my results!:read2:
My even do some velocity probbing.........as I'm still trying to bring back some of the bottom end i lost in the beginning, on these head.

long learning curve still ahead:clock:
 
Ya know...it go's 6500+rpm on my 410 stroker which is good for 40 something year old intake...
Thats with just a 750cfm carb, I ponder the 'top out' with a 850-1050cfm carb..
But what do g stock'rs turn, 8k?? & with econoquad cfm of like 930? on iron ..
makes sense to me..

time for the flow bench.
 
Whatta mean "Top out?"

Grinding the intake or divider?

Before you do so, let me know, I'll save ya some time and trouble.
But going to a bigger carb.... I think the engine would like it on the big end for sure.
 
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