Making Power 318

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dylantman8

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Hello, I recently just purchased a 1973 Plymouth Duster and it has a 318/727 combo. From what i could tell it's an 87 motor. At the moment it's unbearably slow and I'm looking into modifications to make it faster. I've read about aluminum heads and a cam. The motor already has an Edelbrock performer intake with a 600 cfm carb and from what I can tell just by the sound of the car is a mild cam. I want a way to make more power out of the motor in a cheap way without tearing into rotating assembly. Furthermore, what power could I make simply with heads and no cam? Any help is appreciated, I just want to make the car faster for relatively cheap. Also another random thing about the car is it has a Ford 9" rear end.
 
dylantman8 said:
Hello, I recently just purchased a 1973 Plymouth Duster and it has a 318/727 combo. From what i could tell it's an 87 motor. At the moment it's unbearably slow and I'm looking into modifications to make it faster. I've read about aluminum heads and a cam. The motor already has an Edelbrock performer intake with a 600 cfm carb and from what I can tell just by the sound of the car is a mild cam. I want a way to make more power out of the motor in a cheap way without tearing into rotating assembly. Furthermore, what power could I make simply with heads and no cam? Any help is appreciated, I just want to make the car faster for relatively cheap. Also another random thing about the car is it has a Ford 9" rear end.
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If you don't want to tear into the short block, I'd call Hughes Engines and ask about their Whiplash cam. I don't have any experience with it, but supposedly it's designed to build cylinder pressure in a stock, low compression 318 which should help your performance. Also, what gears are you running? There's a channel on YouTube called 318WillRun that has lots of good info on getting mostly stock 318's to run good, he's also a fairly regular contributor on this forum.
With the rest of your combo, I'm not sure just throwing a set of heads on will help much. First thing before buying any parts would be to do compression and leak down tests to make sure there's nothing going on with the rings or valve job, then check timing.
 
What I would do before I spent ONE RED CENT is to make DAMN SURE what's there is in the top optimum tune for performance. Run a compression test. This will tell you the general condition of the engine. Get out the timing light and see what kind of curve is in the distributor. Make sure the carburetor is tuned correctly. The thing just might be way out of tune.
 
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You can't make power with a 318, they're junk and power is impossible with those. Just kidding! But some guys actually believe that and will convince you to pull the 318 for a 360. That's nonsense, keep the 318 (unless it's bad) and have fun with it.

Before you do anything, listen to Rusty's comment. With a Performer intake and 600 carb it should get down the road just fine, even if it had a stock cam and 318 heads, so you might very well have a tuning issue.

Let's say it's tuned and it has compression and you want more... if you want CHEAP without getting into the rotating assembly, you could get a pair of used Magnum heads and Speedmaster air gap intake. Magnum heads have 1.92" intake valves (318 intake valve is 1.75") and runners that are way bigger than the LA 318 runners. They will also won't hurt compression at all, actually maybe give you a bit more.

Used Magnum heads will be cracked between the valve seats. Don't be alarmed, it won't matter because the cracks don't get into a water jacket and almost never drop a seat because of the cracks. Lots of guys will say that's crazy talk, and maybe it is. But there are tens of thousands of Magnum engines still on the road, many of which have never been apart.

There are 2 caveats with Magnum heads. First, you have to make sure you have lifters that will oil the valvetrain through the pushrods, and hollow pushrods for that same reason. BUT, a 1987 engine would already have a roller cam and roller lifters that allow for pushrod oiling to the valvetrain. You would have to pull a lifter know for sure. I'm not sure if the roller LA engines came with hollow pushrods, but if not just get a set from a Magnum (used, of course).

Second, Magnum heads use a different intake bolt pattern than the LA heads so the Speedmaster air gap makes for a great upgrade at the same time. It is drilled for both the Magnum and LA heads, so if you went back to LA heads you could still use it:

Mopar Chrysler Dodge SB 318 340 360 MidRise Air Intake Manifold Satin
 
I can tell you this. My grandfather's stone stock 71 318 Dart would ROAST the right rear tire on command. Stock 230HP 318 2 barrel. It was actually difficult (for me) to take off without at least chirping the tires. So I would say something is "WRONG" with yours.
 
So many unknowns. Just a couple questions to answer...
  • Is the car performing as it should now ???
  • What kind of performance are you wanting to achieve? A simple chirp from the tires ... or beat your friends Scat Pack 2018 Challenger....
 
That '87 318 should be the 9.2:1 cr Roller cam engine with the 302 closed chamber heads. Should be good with just the 4bbl and intake upgrade on its own.

Now if someone swapped on 360 open chamber heads, then that is going to kill compression and slow it down.
 
as stated above, a bone stock 318 will never be "fast" in many people's eyes but if everything is in good shape then it should at least be able to smoke a tire or be close to that, simple upgrades can be done (carb, intake, re-curve the dist) to get some decent daily driver fun out of it without having to do any major surgery. The first step is first, listen to the above posts and make sure what you already have is in decent condition before you continue, if you find obvious issues, then address those first.
I have a bone stock 360 out of a motorhome and I'm still using the motorhome distributor. Only thing not stock on the engine is intake and headers with a 4bbl edelbrock. It's not "fast" but it's a hell of a lot faster than my jeep and is a boatload of fun. I've tried to maximize what I have before opening up the engine.
 
A Ford 9 inch rear? I'm going to guess it may have ridiculously low gears, and that's what you're perceiving as being "slow"... you may need to get some different gears. Of course, this is after confirming the engine's state of tune.
 
Here is a simple one for you. Have someone sit in the car and floor it.(Not running) And you check and make sure the carburetor is opening all the way up.
 
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If somebody installed a cam, they may have put it in retarded instead of straight up or advanced, that would lose bottom end.
This is a 88 stock 318 with factory throttle body and computer, just no emission crap.
392 sure grip gears and 295-50-15s.
 
RustyRatRod said:
I can tell you this. My grandfather's stone stock 71 318 Dart would ROAST the right rear tire on command. Stock 230HP 318 2 barrel. It was actually difficult (for me) to take off without at least chirping the tires. So I would say something is "WRONG" with yours.
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Your grandpa sounds like mine, except for mine had a Chevelle with a 307 2 barrel that would roast'em. I always wondered how.
 
RustyRatRod said:
What I would do before I spent ONE RED CENT is to make DAMN SURE what's there is in the top optimum tune for performance. Run a compression test. This will tell you the general condition of the engine. Get out the timing light and see what kind of curve is in the distributor. Make sure the carburetor is tuned correctly. The thing just might be way out of tune.
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THIS!!!

What is your feel for general engine condition? Does it "blow" oil smoke or use lots of oil? You MUST ^^as suggested^^ run a compression / leakdown test. Get/ borrow a timing light and see what the timing is doing. CHECK throttle is the carb fully opening, is the choke fully opening when warm?

Do you have a tach? Do you know at what RPM it shifts?

Also someone mentioned the rear axle. Determine the gear ratio, and post up your rear tire size. To determine the ratio, safely block the tires, jack up ONE rear, and put transmission in neutral, parking brake released. Attempt to turn the tire. If it will turn, you have NO limited slip. Turn the tire TWO exact turns, while counting the turns on the drive shaft. If it turns "lets say" 3 1/2 turns + a tiny bit more, you have 3.55 etc

If the tire will NOT turn you have a limited slip rear. Jack up BOTH rear tires and verify that they both turn with each other. Now turn either tire exactly ONE turn while counting the driveshaft.

There are MANY variables to performance let me give you an example.

When I had my 67 together, I obtained what turned out to be a VERY VERY low miles 318. VERY low miles. I could tell my looking at the cam/ lifters/ nylon timing sprocket. All I did was install a little larger cam, headers, 4bbl. The thing was VERY impressive even with stock heads and low compression. I admit I do have 3.7x gears which adds a bit of snap.
 
Are you certain it has a 9 inch ford and not a chrysler 8-3/4? Run a compression test, and tell us what those numbers are as the type of spark plugs and their numbers. I've seen the temperature range set 2 steps higher than stock (Champion JYC14 instead of JYC12) on a 318 kill the performance even with everything else set where it should be.
 
First thing to is what Rusty said. Make sure it is healthy with compression check etc. Next crawl under and see if the rear axle has the ratio tag on it. If not spin the wheel and count the yoke revolutions (lots of youtube videos on figuring out axle ratio). There is a good chance that has a 2.76 or higher gear (I know someone with that has a 8.25" axel and around a 2.46 ratio!) They were looking for low RPMs for fuel mileage back then. If you have one of these tall gear it will feel like a dog if you are expecting it to run like a hot rod!
 
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So here is what I found on the motor. It’s casting number is 4387560-31827. Also it is 100% a ford 9 inch with open 3.0-3.25 gears (just guesstimating). Its got 255 radials on 15x7 cragars. I’m going to assume motor isn’t tuned correctly because it does not have the pep that people above are describing. Attatched are photos of the car and motor.

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is the throttle pressure/kickdown linkage hooked up and adjusted properly?
 
I'm not trying to argue, but the Ford 9" and Chrysler 8 3/4 look almost identical. I would endeavor to get a casting number off the center chunk. That's a nice looking foundation!
 
The lack of a kickdown leaves the clutch packs with insufficient pressure, continued use in this condition can cook your clutches, and it could feel "doggy" since the clutches are slipping all the time now- plus the fact that there is no kickdown when you get on it. All this is under the assumption that the trans wasn't rebuilt with a manual valve body...
In addition to the lack of kickdown linkage, if that 727 is the like year to the motor ('87?) it could be a lock up convertor; and depending how the swap was done, convertor could be stuck in "lockup" mode?
Need additional info on the whole setup.
 
Garrett Ellison said:
Are you certain it has a 9 inch ford and not a chrysler 8-3/4? Run a compression test, and tell us what those numbers are as the type of spark plugs and their numbers. I've seen the temperature range set 2 steps higher than stock (Champion JYC14 instead of JYC12) on a 318 kill the performance even with everything else set where it should be.
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If you have "J" plugs in a 318 that could castrate it a bit as they are the short thread ones, the 318s (except I believe the old poly ones) take an "N" plug if using champions.
And I e used RN12s and RN 14s back to back in the same engine (sometimes based on what was in stock when I needed a set of plugs) with no appreciate difference in power) many times over the years.
And even though when you subtract 12 from 14 the answer is 2, in Champion plug numbers that is only 1 step not 2, I don't think they made an "N" or "RN" 13 heat range though I've seen other series of champions in a 13 heat range.
If going from a 12 to a 14 heat range (or vise versa) makes that big of difference in how your engine runs you got a bad batch of whichever ones made it run bad. .or else the ones that made it run bad were just plum wore out.
 
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