318 carb questions

First off, I apologize for this question and the no doubt countless others in going to ask in the near future. Besides changing spark plugs, filters, and oil, I've never done anything (nor do I know anything) about engines. But I'm excited to learn.

I'm finally getting down to taking apart my 318 to, at the very least, replace some gaskets and the carb, and most likely the heads. I've decided to keep the 318 for the immediate future.

The car (68 Valiant) already has headers and duals. My first instinct is to swap out the 2bbl for a 4bbl, but after searching around it seems like some folks are saying it isn't worth it. So question 1 would be, should I go 4bbl or a newer 2? If I decide to go with 4 do I have to get a new manifold or will the stock one work?

TIA

Welcome to FABO. Yes u will need to change the intake. U will need the 4 barrel linkage and bracket for the tranny that bolts on top of the intake where ur cable bolts on to. A carburetor and an air cleaner. Kim

With a stock longblock, unless the tires spin, the 4bbl will not do much until much later in the game. It really depends on your stall and gears.
If you have one available, yes, bolt it on . But I sure wouldn't fork over big bucks for new stuff, in your situation.
The secondaries usually do not or can not open until the engine vacuum is sufficient to pull them open . Furthermore, the power might only peak at say 15 hp on a stock longblock 318, and it doesn't arrive until maybe 4000rpm. And it doesn't start until whatever rpm your current carb gets to be too small, which might not be until ~3300rpm.
If you have a A904, stock stall, 27" tires;
and 2.73 gears; this might not be until maybe 30mph. But if you have
3.55s and the tires don't spin, then maybe 23mph, but if you have
4.30s and the tires spin, then the secondaries might open just a few feet off the line.
But if you have a 2800stall, then it don't matter what gear you have, the secondaries are gonna jump open. However, just cuz they are open doesn't mean the engine is making power yet .....it just means the engine is ready to make power.
It can't make more power than the current combo,until the rpm starts to rise past whatever the choke point is, with the current carb.
If the engine can only inhale 300cfm at a particular rpm, then it don't matter if it is does with 2bbls, or 4, or 8, it will only inhale 300. And if the engine can only inhale 400cfm no matter what, installing an 850 will not make any more power.
The stock 318 Carter 2bbl, IIRC is rated as a IDK 280cfm or something, on the 2bbl rating, which, doing the math is 198cfm using the 4-bbl rating, which is supposed to go 2150rpm@100% VE..... but your stock engine will never make 100%. If it makes 65%, a stretch, then the 2bbl is good to 3300rpm . In Second gear for passing, with 2.73s, 3300 is about 58mph, so in this situation, the 4bbl is just starting to make power, over the 2bbl.

If you wanna make significantly more power; your engine has to be able to inhale more air, and that usually takes more rpm. The usual way to do this is to extend the rpm with a longer period cam, ...... then the 4 bbl will start to earn it's keep. But along with a bigger cam, might come a requirement for a higher stall convertor, and/or bigger number rear gears, and/or better heads.
If you want the power at low rpm; it usually means more pressure, or a bigger engine. But a short-period solid-lifter cam can help maintain pressure.
If you want the power at a lower roadspeed; this usually means a lower rear gear, a lower first gear, a higher stall TC, or a bigger engine.

I hope that helps.

PS; if you decide to take the plunge, do some time trials with the current combo tuned, and again after the swap. Do not make any other changes between the two tests; just the intake and carb. Then you will know if it was worth it.

IMO; the best bang for the buck at this stage is a higher than stock stall convertor, if you don't already have one. Below, is a curve that can help you see the difference from a stock TC that might stall at 2000rpm, versus say 2800. The power difference on this graph is from ~105 to ~155, so 50hp on the starting line. Realize that this is on a higher-compression 5.2M, which also has better heads. But the end result to you will be a similar result when measured as a percentage. For example, in this engine, 155/105=47.6% increase. If your engine makes 80hp at 2000, you might expect 80x1.476=118, which is plus 38hp; the 4bbl cannot touch this at 2800rpm, on a stock longblock; it will NEVER happen.
=

That helps immensely. I know the rear has non stock gears, I'm going to figure out what they are tomorrow. I'm absolutely not against getting a bigger cam, in fact the car might already have one. I won't know until I get it apart.

I'm just trying to figure out where to start on a project where I have no clue what I'm doing, haha. Carb/ manifold seemed like a good, get your feet wet project but I could be wrong.

Btw the purpose of this car is just a fun, semi fast street rig.

AJ is right. You can't just change one part and expect big gains. A 318 with a 2bbl isn't that bad for a car early in your motorhead adventure. It has pretty good throttle response and will keep up with traffic OK. I'd go for a set of dual exhausts so you can get a bit of a psychological boost. If, in the future, you build the motor or swap, the pipes will already be in place.

Whoopsie said:

First off, I apologize for this question and the no doubt countless others in going to ask in the near future. Besides changing spark plugs, filters, and oil, I've never done anything (nor do I know anything) about engines. But I'm excited to learn.

I'm finally getting down to taking apart my 318 to, at the very least, replace some gaskets and the carb, and most likely the heads. I've decided to keep the 318 for the immediate future.

The car (68 Valiant) already has headers and duals. My first instinct is to swap out the 2bbl for a 4bbl, but after searching around it seems like some folks are saying it isn't worth it. So question 1 would be, should I go 4bbl or a newer 2? If I decide to go with 4 do I have to get a new manifold or will the stock one work?

TIA

Click to expand...

First thing to do to a 318 is dual exhaust which you already have...

Next thing is to REPLACE THE TIMING CHAIN... The stock single row timing chain and nylon dipped gears are junk... The nylon chips off the gears when it gets old and brittle, and the chains stretch too easily...

Get a stock 340 double roller timing chain minimum... Here's a great one that I've run over 150,000 miles:

Edelbrock

Then swap a Wiand Stealth intake manifold:

Weiand Stealth Intake Manifold


And a Holley 600 vacuum secondary with electric choke:

Holley 4160 Aluminum Street Carburetor


With this carb gasket, nice and thick to keep fuel from boiling:

Edelbrock Heat Insulator Gasket


The stock 68 318 is a great engine... 9.0 compression and stock 240 HP...

You won't make a top-fueller out of your 318, but it will drive much better with a 4bbl. Those 2 bbl's were never very good. Get a nice small runner intake (stock 273 iron, or SP2P/LD4B aluminum) and a small cfm 4bbl carb (Holley 600 max, or Carter/Edelbrock 500).

I would agree with the timing chain recommendation, see post #6. I'd always run a 4 barrel over a 2 barrel, even on a 273. If you don't get better power and even mpg you did something wrong. If stock, the 68 318 is the best 318 to start with, but not even close to advertised horsepower. Any stock 4 barrel intake will work as well as aftermarket. Look for a dual plane, 68-69 stock 340, Edelbrock Performer, or Weiand Stealth. A small single plane, Holley Street Dominator or stock 273 should also work well with your combination. As for a carb, you can use any 273 AFB or a 68 to 70 340 AVS. For a new carb, I'd skip the Holley and look for a Edelbrock AFB, AVS, or a Holley Street Demon (won't work with any of the stock intake manifolds). Assuming you have an automatic transmission, the transmission kickdown linkage is a must, see post #2. You will also need a new air cleaner to fit the 4 barrel opening and also fit under your hood.

Instead of mechanical carb linkage, you can use Lokar cables instead. Cheap and easy to install.

Whoopsie said:

First off, I apologize for this question and the no doubt countless others in going to ask in the near future. Besides changing spark plugs, filters, and oil, I've never done anything (nor do I know anything) about engines. But I'm excited to learn.

I'm finally getting down to taking apart my 318 to, at the very least, replace some gaskets and the carb, and most likely the heads. I've decided to keep the 318 for the immediate future.

The car (68 Valiant) already has headers and duals. My first instinct is to swap out the 2bbl for a 4bbl, but after searching around it seems like some folks are saying it isn't worth it. So question 1 would be, should I go 4bbl or a newer 2? If I decide to go with 4 do I have to get a new manifold or will the stock one work?

TIA

Click to expand...

• Yes, a 4bbl/intake swap will add horsepower, especially since you already have dual exhaust and headers. You'll feel the difference by the seat of your pants.
• Your 2bbl linkage will work fine, you'll just have to slightly modify it to work. I have video on my UTube channel showing this. I've done it many times without issue
• The suggestion of the timing chain is a very good one. I have you Video of timing chain replacement on a 318 as well.
• You are correct to look at the heads. Fresh heads and valves that seal are where gas mileage, smooth running, and horsepower are found.
• I've also included a video of a recent 2bbl to 4bbl swap I did on a 318

Mopar 2 bbl linkage on 4 bbl carburator - YouTube
Basic Install Timing Chain '77 Dodge Van 318 - YouTube
2 bbl to 4 bbl intake swap 318 Mopar *Drag Truck part 5 - YouTube

Thanks for all the replies. I am not looking at this first step as a way to make this engine something everyone talks about, I know gains will be minimal. But I will be building this project for the next few years so I don't want to have to rebuild a 2bbl when I should have gotten a 4 to begin with. This car is never gong to run 13s, probably never be put on a dyno. I just want a semi punchy little fun cruiser . It'll never be driven more than 100 miles round trip I'd assume

Whoopsie said:

First off, I apologize for this question and the no doubt countless others in going to ask in the near future. Besides changing spark plugs, filters, and oil, I've never done anything (nor do I know anything) about engines. But I'm excited to learn.

I'm finally getting down to taking apart my 318 to, at the very least, replace some gaskets and the carb, and most likely the heads. I've decided to keep the 318 for the immediate future.

The car (68 Valiant) already has headers and duals. My first instinct is to swap out the 2bbl for a 4bbl, but after searching around it seems like some folks are saying it isn't worth it. So question 1 would be, should I go 4bbl or a newer 2? If I decide to go with 4 do I have to get a new manifold or will the stock one work?

TIA

Click to expand...

A 500 eddy works well on a stock 318.
As does a 390 holley . You can make bigger carbs work.. but they won't be as ideal at rpm you do most of your driving at.
When you change all the gaskets, drill extra holes in the oil filter plate for flow.
Use permatack 'in the can' on the timing cover, water pump, oil filter plate gasket,gasket to oil pan ,intake gasket to heads with/and Black rtv at water cross overs and rear main seal. Copper rtv on exhaust/header gaskets.
Good luck and use a torque wrench on things like heads,rods,mains. Torque by feel the rest. Once its together, use a dead blow to smack tight the crank bolt. A few good smacks works.

Whoopsie said:

I just want a semi punchy little fun cruiser . It'll never be driven more than 100 miles round trip I'd assume

Click to expand...

In that case
spend your money where it does the most good, namely bottom end stuff, like; see post #3.

AJ/FormS said:

If you wanna make significantly more power; your engine has to be able to inhale more air, and that usually takes more rpm. The usual way to do this is to extend the rpm with a longer period cam, ...... then the 4 bbl will start to earn it's keep. But along with a bigger cam, might come a requirement for a higher stall convertor, and/or bigger number rear gears, and/or better heads.
If you want the power at low rpm; it usually means more pressure, or a bigger engine. But a short-period solid-lifter cam can help maintain pressure.
If you want the power at a lower roadspeed; this usually means a lower rear gear, a lower first gear, a higher stall TC, or a bigger engine.

Click to expand...

If your 318 is an 8/1 compression LA
and you are thinking about a cam change, think hard. A bigger hydraulic cam will most certainly make more power at a higher rpm (about 200rpm per 7*intake duration); but with no other changes, the later-closing intake valve, will drop about 5psi of cylinder pressure per cam size, and that takes away the snap from the low-rpm.There are only two ways to get it back, namely;
the right way is a higher compression ratio, and the other way
is more TM(Torque Multiplication); which could be stall or gears.
If the Cr is to stay the same, then the better option is a Solid-lifter cam, which opens/closes the valves faster ,and so can maintain the cylinder pressure higher for longer.