318 top end build

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mawler

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Hi all,

I just purchased a 72 Duster with a 318 and I am looking to get some more oomph out of it without changing the bottom end. Would adding some #302 heads, a new cam, and intake be worth it to get some power or is it not worth it without bottom end mods? I am getting a set of TTI headers too so I have some ground clearance. Current headers are street draggers.

Thanks,

Michael
 
Micahel,

Since you have a low performance 1972 318, no reason to go 'crazy' trying to get
unwanted horsepower, and stick with improved low-end torque.

A good cam, would be the Compu-Cam 'High-Energy 252' (Part #20-208-2) which has
a lift of .425/.425 and 252* Duration, which is excellent for a stock 1972 318. Of course
getting the Cam Kit is highly recommended with (Springs, Lifters and Retainers, etc.)

Note; The 1972 318 (Stock Camshaft Specs = .390/.420 Lift and 242* Duration)

Of course a new timing chain will be required.

A perfect intake would be the Edelbrock Performer #2176 - which is designed for a
street application where you will not be going above 5500 RPM's.

And an Edelbrock Performer #1403 500 CFM Carburetor will give you some good
low and mid range performance, as well as good Gas Mileage.

As for Cylinder Heads, the #4323302 castings would fit nicely, as they have
a swirl-port design and have 63.0 CC chambers which will keep your compression
close to the stock 9.23-1 (1972 #675 Cylinder Heads = 61.00 CC). The #302 Heads
have hardened exhaust seats, so you can probably have a valve job performed and
utlize the current exhaust valves. Intakes, you may have to change to stainless units,
but stay with the stock size (1.78") as bigger valves will 'not' help you in the
low-to-mid power range.

The #302 Cylinder Heads have better 'Volumetric Efficiency', which allows the gas to
hit the chamber better, and dissipates the exhaust much faster.

As for exhaust, TTI units are fantastic, but expensive. You want to take a look at
Accurate Exhaust systems for a performance dual exhaust system, which keeps
a balance back-pressure, which is dynamite for the street.

Paul
 
I would go with a spreadbore or thermoquad if you want milage cause of the tiny primaries and then you get the power when you put your foot into it and open the huge secondaries
TTIs are a great investment and worth every penny
 
TTi Headers,,,,,,,,absolutely the best, but at $623 not sure they are going
to make a difference with a car pushing less than 250 HP.

Even TTi recommends a higher HP minimum for a Header Application.

Accurate has a bolt-on system with 2" piping that expands to 2 1/4" which is
designed for low-to-medium street applications.

On the Carburetor, it would nice to find an old Thermo-Quad #TQ6340, but
the Edelbrock #1403 is designed for efficiency with low-to-medium lift Camshafts.
 
I'm running a 318/904 in the Demon. 69 Cuda 440 has given you a good shopping list. I'm running, 302 heads, a 625 cfm AFB, and a little more cam.

I think the 500 cfm Eddie will work fine. IMHO the key on the carburetor is an air valve secondary. This feature allows the secondaries to open when the engine is ready, reducing bog.

When you're getting gaskets, make sure you get soft, thick intake gaskets. The thin metal ones that come with most gasket kits do not allow the manifold to seal properly resulting in flooding when the radiator is filled.

If you're running a Torqueflite, you'll need to make a provision for kickdown. Lokkar makes a kit that is widely available. If the hot rod look of it puts you off, check out Bouchillon Performance. The install looks very factory under the hood. Works great. I've installed two on different cars with no problems on either.
 
69 Cuda 440 said:
a swirl-port design and have 63.0 CC chambers which will keep your compression close to the stock 9.23-1 (as the 61.0 CC 1972 Cylinder Heads).
Click to expand...

I really like the parts selection you put together, i'd run it myself...........But, if a stock block 72' 318 made that much compression with 63.0cc heads it would be a true gift from Ma Mopar. Stock pistons are just too deep in the hole for those numbers. 8.3/8.5 would be more realistic in my opinion. If it was a true 9.2 to 1, you "could" run a little more aggresive cam if your looking for some extra power upstairs.


P.S. To be fair, i did allow for a little eyebrow volume. If it has true flattops, the numbers i posted above could be a hair low on this application.
 
69 Cuda 440 said:
Micahel,

Since you have a low performance 1972 318, no reason to go 'crazy' trying to get
unwanted horsepower, and stick with improved low-end torque.

A good cam, would be the Compu-Cam 'High-Energy 252' (Part #20-208-2) which has
a lift of .425/.425 and 252* Duration, which is excellent for a stock 1972 318. Of course
getting the Cam Kit is highly recommended with (Springs, Lifters and Retainers, etc.)

Note; The 1972 318 (Stock Camshaft specs + .390/.420 Lift and 242* Duration)

Of course a new timing chain will be required.

A perfect intake would be the Edelbrock Performer #2176 - which is designed for a
street application where you will not be going above 5500 RPM's.

And an Edelbrock Performer #1403 500 CFM Carburetor will give you some good
low and mid range performance, as well as good Gas Mileage.

As for Cylinder Heads, the #4323302 castings would fit nicely, as they have
a swirl-port design and have 63.0 CC chambers which will keep your compression
close to the stock 9.23-1 (as the 61.0 CC 1972 Cylinder Heads). The #302 Heads
have hardened exhaust seats, so you can probably have a valve job performed and
utlize the current exhaust valves. Intakes, you may have to change to stainless units,
but stay with the stock size (1.78") as bigger valves will 'not' help you in the
low-to-mid power range.

The #302 Cylinder Heads have better 'Volumetric Efficiency', which allows the gas to
hit the chamber better, and dissipates the exhaust much faster.

As for exhaust, TTI units are fantastic, but expensive. You want to take a look at
Accurate Exhaust systems for a performance dual exhaust system, which keeps
a balance back-pressure, which is dynamite for the street.

Paul
Click to expand...

69 Cuda 440 said:
TTi Headers,,,,,,,,absolutely the best, but at $623 not sure they are going
to make a difference with a car pushing less than 250 HP.

Even TTi recommends a higher HP minimum for a Header Application.

Accurate has a bolt-on system with 2" piping that expands to 2 1/4" which is
designed for low-to-medium street applications.

On the Carburetor, it would nice to find an old Thermo-Quad #TQ6340, but
the Edelbrock #1403 is designed for efficiency with low-to-medium lift Camshafts.
Click to expand...

My thoughts on that...

Dont bother with thermoquads , '72 heads had 68cc heads, heads by themselves cannot have "better volumetric efficiency", an the only hardening to the seats was induction hardening which its effectivness is gone after a valve grind...and headers will help make more torque and milage btw.
 
Lets Help the Guy, not 'nit-pick'

The 1972 318 was listed as having 9.23 to 1 Compression with 61.00 CC (#2843675)
Cylinder Heads, an .o36" thickness head gasket and with the piston below the
deck (.056).

The #2843675 Cylinder Head came from the factory with a CC range between
61.00 and 66.00, with most on the high range.

A #302 Casting Head (Milled and CC'd) to a minimum of 63.00 would give him at least
nearly the same compression. If the piston is too deep in the cylinder, taking an additional
.010 off the Cylinder Head will be accetable, and will take an additional 2 CC out of the chamber.

Always go to 'two' Professional Machine Shops to discuss procedures.
 
I'm currently working on an upper half rebuild, myself for efficiency and more torque.

This is what I have going to wake up the '73 318 in the Scamp-

Pre-magnum 302 cast heads

302 cast heads are a run above the stock, open chamber heads on an early '70's head. That is a good suggestion as mentioned above. The reason these heads work so well has to do with the porting, moving air around the valves and helping fuel atomization and having heart shaped chambers changes the propagation pattern and bumps the compression .5 to .75 above your existing actual compression.

-Edelbrock LD4B intake

This intake mic's at the same port sizes as the true 318 port size. This intake is widely regarded as the best flowing runner design for a mild performance 318, to keep velocity up. The higher velocity of the intake is exactly what the 302 head swirl porting banks on to work correctly, so this manifold would really help a 302 head.

The Performer suggested above is a great intake as well. The difference is in the actual port size measurements, along with the wat er neck being offset for A/C compressor clearance, you may need a different molded hose for it to work right with your current setup or a flex hose from the upper passage on the radiator. The port size on the Performer is directly between the 273/318 heads and the 340/360 head port size. It's a good mid-range intake for all of the LA engines, but if you could keep the runner size down, it would help velocity and keep from having a step between the head port and intake port for the air to catch turbulence through.

The problem with an Edelbrock LD4B is that they aren't always available, like the performer, but Holley makes a carbon copy of this intake that measures the same as the true 318 port size, which is closer than the Edelbrock Performer. The Holley intake that has the same runner design is the Weiand Stealth 8022 and the dual carb pattern version is called the Action Plus 8007 that works for both spread and square bore carbs.

The carburetor I would suggest is the latest creation by Demon Carburetion, which was recently acquired by Holley from Barry Grant, called the Street Demon.

This carburetor is a reverse engineered version of the Carter ThermoQuad, only the jetting and metering rods, as well as step-up springs aren't difficult to obtain 2nd hand.

The nice thing about this carburetor is that it has three primary boosters for atomization instead of one, per barrel, but it still retains the 1 3/8" primary throttle bores, so it has great throttle response from idle and excellent vacuum index. The secondary system, much like the ThermoQuad is an air door type, only it's on a tight square bore plane and is technically a 3 barrel carburetor with a new goggle valve design that bridges the secondary valves. This helps with fuel delivery in the intake and keeps CFM up when you want it, without killing your torque with an adjustable air door for primary to secondary blending.

For exhaust, I'm currently using rear exit dodge truck 360 manifolds, because they aren't as expensive or difficult to manage spark plugs in, compared to stock 318 manifolds or a 340 manifold. They don't clear power steering boxes without some grinding, but I managed to modify the driver's side manifold and the steering gearbox slightly to gain clearance.

These manifolds, especially if you are willing to use a manual steering box or make grinding modifications, have a 2 1/8" outlet and a more open design than the 318 manifolds and will help with driveability on a street car.

I've debated headers on my car and I know that fuel scavenging is better in equal length tubes, but the practicality and maintenance of headers can be more high maintenance than they are worth on a mild performance car and it's nearly impossible to get an equal length header on an A body without some other body/ chassis/ steering/ suspension modification.

The 302 head, Street Demon, Edelbrock LD4B/ Weiand 8022 Stealth combination is matched for high velocity/ vacuum index/ throttle response/ torque in the low end of the RPM range and more importantly, will help make power with good fuel usage, efficiently. This is the combination that I am using on a factory camshaft, but will work with other camshaft sets.

Hughes Engines cuts their camshafts on the wider Chrysler lobe measurements and has a different lift rate for their sets than most other companies cutting from CWC blanks. Check their selection out online or give them a call for some options, before selecting a cam. They make quality parts.

I'll be posting the results of this build on another thread, but I would suggest it to anyone building a mild performance street driven 318
 
To be honest there's not a lot you can do to make a motor perform better if you're not willing to change pistons and camshaft to match each other.

I would suggest get a RPM performer intake, edelbrock AVS650 carb and some headers and save the rest of your money until you're ready to build a motor from scratch.
 
302 heads will only give you about a .5 bump in compression ratio and flow the same, really no gain in power, the only advantage since your not building a quench engine is closed chambers would need to be milled about .020" less to get get the same CR than open chamber. If you can get a low mileage set dirt cheap and mill and port them might be worth the swap but if you have to put too much into them, EQ's would be better choice. I'd go stock longblock high lift 262ish cam, headers and 4bbl.
 
Touch up ports on stock heads (free),summit 340 cam (126 bucks),touch up ports on stock manifolds,any aluminum intake on Craigslist (75 bucks),carb 600 off Craigslist 75 and ur in it for less then 400 bucks and u will be happy for what it is u don't need headers unless u take motorout and go with better piston and heads.just do the cheap stuff and save for a nice motor and rear and tranny convertor....have fun and hope u don't spend too much money bud
 
DaveBonds,

Excellent information.

I would recommend the LD4B as the #1 Intake also, but it is tough to locate.
Luckily, I have '3' in my shop/garage.

Correct on the #302 Cylinder Heads, as they are worth the small investment. Since
(Mawler) wants a little more 'V-Room', a little 'gasket-match porting' to the heads
would be wise.

Like you, hate to see anybody spend $$$ for Headers when they don't need them.

Better off with a decent set of 'used' exhaust manifolds which you can pick up cheap,
and install a proper dual-exhaust pipe system.

The following suggestions (I listed) are what we did to the 1971 Duster Twister '318' that we
restored for a customer, except for Intake and Carburetor.

We found a cast iron Intake and Carter AVS (625 CFM) off of a 1969 340 Dart (automatic) for $15.00.

We cleaned and blasted the Intake. Rebuilt the Carter AVS and installed it on the restored
1971 318 Duster. Damn thing ran like a top, and got better gas mileage than the previous 2-Barrel.

Even used a 1971 340 Air Cleaner, and had a 'pie-tin' engine call-out plate made for the air-cleaner
top with '318 Four Barrel'

Confuses everybody who see's it...........'Plymouth didn't make a 318 4-Barrel in 1971'

Yea,,,,,,,,,we know........

Remember Them,,,,,Duster Twister

B4026-2.jpg
 
Thanks for the advice everyone. The car is not stock right now. I don't pick it up until Tuesday so I'm not sure exactly what is on it. I couldn't take it apart in the guy's garage and he wasn't sure what it has. He was just selling it. I know it has a 4 bbl and an aluminum intake. The previous owner had installed headers and a full 3" exhaust. The headers have to go since they are killing ground clearance and the 3" pipe is killing my torque. Once I get the car home I will see what carb and intake are on it now. I'm also thinking of just doing a cam for now and swapping the gear to 3.23. That might be enough to keep me happy until I replace the entire drivetrain and drop in a 360. I might be good on intake and carb but i'm not sure. Thanks for all the help.
 
Good Job Mr. Mawler,

But save the money, and wait to install the Camshaft when you swap to the #302
Cylinder Heads if you're keeping the 318.

Correct, the 3" exhaust pipes have to go.
 
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