Stock 340 intakes

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dodge freak

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How good are those old cast iron 340 intakes. I have a 1969 one in great shape but never used it. Its so heavy but cheap-since I already have it.

Right now am using a Holley Street Dominator intake. Motor runs fine at all speeds but thought a dual plane intake may help my gas mileage a bit. Rest of my combo is not for mileage so not looking for a lot but 1 or 2 MPG would help out.

Was also looking at the RPM and Weiand Stealth but those are over $200 but are light weight, the old LD 340 go for $150+ now on E-bay, thats too much for a 40 year old intake which the Stealth looks like for just $50 more-E-bay shipping fees are higher than Summit.
 
Is this a daily driver? If not, I don't know if I would even go to the trouble of considering the swap (especially if the rest of your engine was not built for economy). What are the specs on your motor? What converter/gears are you running?
 
Well it has 3.91 gears, 27 " tires., stall converter is a higher stall "police special", trans guy said. I think its like 1800, it was cheap, under $100 and gas was too back then.

Headers, a 268 comp cam HE, my carb right now is a holley 750 but found a Carter 600 for it-scare gas is going over $4 this spring.

My mileage has been stuck at 10 mpg, I do drive it hard but also hear of some 340's getting 13-15 mpg, if I could just get 12 mpg that be 20% better than now

Its not my daily driver but like to drive it, when gas was cheap-under $2- I could put a 100 miles on it in 1 day.
 
They are very good intakes. Not on par with an LD340, RPM or RPM air gap, but very good. You can put a 4 hole 1 inch spacer on them and they work nice on a hopped up 340.
 
If it's not a daily driver and you wan to get an extra 1-2 MPG out of it and you drive it hard ... I say you lighten up on it and I bet you will get your 1 MPG as is. That way, if all your components are working for you (performance-wise), you will have that power on tap when you need it. If you can't keep your foot out of it, perhaps a dual plane and a 600 VS might give you the results you want (again, will be better if you practice keeping the pedal from the metal). Also, consider exhaust mods (I don't know what you are running), ignition mods, fuel type, etc. Also, simple things like correct tire pressure really make a difference. BTW: I agree with crackedback about the factory 340 manifold with a spacer (especially if you were not going to buy an aftermarket dual plane manifold).
 
That LD340 is a kick *** intake and will stand toe to toe with a RPM up to a point. Your in that zone where it will perform right along side the others.

The 340 cast iron intake is not a bad intake. It is limited in RPM and max power output by compare to the other aftermarket intakes. But not all of them.

Some things to help mileage;

K&N or equal filter, an extreme top is a nice add on.
Take the time to really tune the 600.
4 hole spacer
multi spark ignition
(I've added Rhodes lifters to an engine once and found more torque and a slight increase of mileage. But thats rather extreme to do, it was I think $100 for the lifters and then gaskets and time, though everything here is only a little bit to each mod. When it adds up is the goal to reach for. The MSD is the best mileage mod I ever did, minus the Jacobs which was better.
The intake change could very well add alittle mileage.)
 
I have the $$$ in the motor.

MSD 7al-it really does work better than the 6a box.

Exhaust is good and I am getting some of those eddy mufflers that are on sale right now.

Open k&N filter, 3" by 14"

Timing is set for around 35 total, all in by 2000 rpm, no vacuum advance--I know maybe this spring I try it again.


Motor makes good power, I can drive it quick without opening the secondary's, yes its a dp. I do open them but I have tried to take it "easy" and still get like the same mileage-but not babying it, driving too slow, taking off too slow--is not a safe way to drive IMO

So those aftermarket intakes are noticeable enough to tell the diff. from the stock intake. Hmm, it would be easier to install-my back is not always feeling the best.

Thanks guys
 
There should be a power gain with a better intake. Along with power and torque increase's, you should get a increase in mileage. It's part of the package. Tuned up well of course. It's now breathing better and leaner.

However, it may be a very very minimal increase.

Anytime you make the engine more efficent, it should show in power, torque and mileage. Tuning will eek out a tad more.
The vacuum advance is a must for mileage. Hook that baby back up and regain what you lost! You should get that 1 or 2 mpg's back easy.
 
I noticethe comment concerning a 340 stock cast iron intake as being limited by RPM and flow!! in the world of stock eliminator, the cast iron intake will and does make power. most 340 stockers are pulling 7000 +RPM in the traps.
the motors doen't seem to be laying over either. so if it's that bad, then 5500 RPM would be the limit. granted ,after market aluminum should work better?
 
With the cam I have in it now 6200 rpms is max, maybe 6000. Not getting valve float, just it stops pulling good by then.

Cranking compression is 160 psi, a little low for a 340 but it has the lower compression pistons with milled heads. 63cc chambers. The heads are the newer high swirl port 576 castings with the 2.02 valves and no air holes in the exhaust ports.

Drove it today, streets are still salt free, only low 30's outside and very windy. It runs great, idles good and low @ 700 in gear, pulls great but gas cost me $3.20 a gallon for the 87 stuff, which it likes as much as the 93, I can't tell a diff.
 
It would be nice to increase both mileage & performance but, if you're willing to sacrifice some performance, maybe a gear change is in order. Not necessarily cheap, but I know gas isn't cheap either. When I switched my car from 3.23's to 3.91's, my mileage went from about 17 on the highway to about 12, IIRC.
 
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