Why are 318's low HP and torque?

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Chryslerkid

Chryslerkid

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Hello everyone,
I wanted to figure out why 318 engines are rated so much lower than 340 and 360 engines? Other than the smaller cubic inches, is it only the compression that is lacking in order to wake up the 318 engines? Or is it completely different engineering that made it so much tamer? Just a random curiosity I have and I know y'all can tell me what's up! Thanks everyone.
 
Compression, cam, intake and exhaust. See? Simple.
 
Just what 67Dart273 says. Replace those with 340 parts and comp. and they run surprisingly well.
 
The LACK of 318 performance...boils down to the (3) C's.

Compression
Camshaft
Carberator

Increase those....and 340 performance is doable....with less cubes.
 
67Dart273 said:
Compression, cam, intake and exhaust. See? Simple.
Click to expand...

Yup what he said! Also small displacement on top of that is no bueno, but if you have a nice strong balanced lower end "for some high rpm's" and high compression with a nice flowing set of heads and a good size cam and rev the piss out of it I'm sure they could make 450+hp
 
The gasoline engine is essentially an air pump. Make it move more air through it, the more power it will produce. No one has addressed the efficiency of the cylinder head (size of valves, transitions in passages ,to name two aspects) which makes a big difference in terms of moving air through the engine.
 
I tell you what, I have a stock bottom end 318..I added an Edelbrock Performer RPM cam and lifters, the RPM manifold, a set of RHS heads prepped by Brian @ IMM, 1.5 Hughes roller rockers, a MP windage tray and viscous fan package, and a 650 holley spread bore carburator. FBO ignition equipped as well. This "little" 318 has some power! It pulls and pulls, and revvs to the moon! 6500 RPM's -No Problem! It's in a 68 cuda fastback with a 3.55 sure grip rear, and 24.5" diameter tires. It definitely rips for what it is! I am very impressed with this little engine. Spins the tires with ease, and gets sideways like no ones business. Chirps 2nd gear in my TransGo 2 shifted 904 with a 3000 stall, and will get squirelly too!

Specs of heads: 202/160 stainless valves with 5/16 stems, beehive springs.
Cam: 234/244 Dur @ .050" 488/510 lift 112* lobe sep. 107* centerline

Currently I am probably at 8.7 - 8.8 to 1 compression. Is there more in it? Absolutely! Bump it up to 9.5 to 1, add a custom ground solid roller, fully port the heads, and hang on!!
 
The 318 was the grocery getter, the truck motor, the people mover. It was never meant for high performance use. Even the "police interceptor" 318s were not true high performance engines. They had 360 heads with larger valves and ports to gain flow, but lacked compression. I think Chrysler didn't try to pump it up in part in the late 60s and early 70s, because it could have come really close to the 340 and the 340 WAS Chrysler's performance engine.
 
Small pistons and on top of it! Piston are down in the hole. Also thay put some heads with tiny intake runners and small valves. But all that can change!
 
valentino automotive said:
Small pistons and on top of it! Piston are down in the hole. Also thay put some heads with tiny intake runners and small valves. But all that can change!
Click to expand...

Ma Mopar basically used 273 heads when the teen was born. Now if they would have used 340/360 sized ports and valves and 10.5/1 compression Like the HP 273's and a solid lifter cam spec'd like the D Dart motor there would have been a
350+ HP motor from the factory. Just for fun, in the next few hours, I will put that combo in the ol' Desktop Dyno and see what comes out. I'll report back later. tmm
 
valentino automotive said:
Oh and the 318 has same stroke as a 340 and same rod length just bore is different.
Click to expand...

Well, look

At the risk of .........................


Let's look at the several Chivvy small block combos

283, 301 (we used to call 'em, GM "renamed" it 302!!)

327 (We'll just ignore the 307)

and 350

Mopar 273/318/ 340 all the same stroke at 3.31"

Chivy 265- 283 / 302 stroke is 3"

327 stroke is unique at 3.25 stroke

350 is 3.48 stroke

302, 327, 350, are all 4" bore

So a 318 is not all that much different from a 327, which were pretty much great engines "in their day."

Only difference is, that GM BUILT them with compression, heads, cam, etc, instead of (Mopar) putting them out as a deduned 2bbl family sedan mover

(And don't forget, GM pretty much did the same thing with the 307 as Ma did with 318's)

But if you want to start preaching "bore to stroke" ratio, what about the 305 TA engines which were de-stroked 340's and therefore had a LARGER bore than a 318, with a shorter stroke?

I think the real answer was in the first few posts --these engines never enjoyed decent compression, cam, or intake and exhaust.

Don't forget most 318's were factory single exhaust, with WORSE exhaust manifolds than the 340/ 360s

Many came with smaller ports, and certainly "undecent" 2bbl carb and intake

Finish it all off with low compression and a camshaft which only accidently opens the valves, and you have..................
 
Hmmm. I see. So a little of everything and I could really wake up my little 318 huh? Well I am building a mostly stock 318 right now. I currently have a street master four barrel intake manifold with a 650 Carter, stock exhaust manifolds... What else would be easy to do without breaking the bank to wake up my 318? Do you guys have pics of your 318 setups to give me some ideas?
 
Chryslerkid said:
Hmmm. I see. So a little of everything and I could really wake up my little 318 huh? Well I am building a mostly stock 318 right now. I currently have a street master four barrel intake manifold with a 650 Carter, stock exhaust manifolds... What else would be easy to do without breaking the bank to wake up my 318? Do you guys have pics of your 318 setups to give me some ideas?
Click to expand...

http://www.summitracing.com/parts/SUM-6900/
 
Mild cam 262ish and headers with duals will wake your up the 318 to 250+ HP, 300+ you'll need more compression 9:1+ so you can go with bigger cam and more head flow. Google 400 HP 318 there's like 5 different builds mostly using stock parts will show doesn't take a lot to make these engines to run strong. P.S. Torque is made by how much fuel and air your engine can ingest and compress for every power stroke that why bigger displacement engines have the advantage. Horsepower how much fuel and air your can use in a given amount of time, heads, cam, intake and exhaust is the major contributors to HP, that's why more RPM's equals more HP more power strokes per minute is more fuel and air per minute.
 
Ever look at the runners in true early 318 heads? Tiny. Better heads and 0 deck they will run strong with a 2bbl.I,ve built 4 and been as fast as 8.0 1/8 mile on the cheap.
 
toolmanmike said:
Ma Mopar basically used 273 heads when the teen was born. Now if they would have used 340/360 sized ports and valves and 10.5/1 compression Like the HP 273's and a solid lifter cam spec'd like the D Dart motor there would have been a
350+ HP motor from the factory. Just for fun, in the next few hours, I will put that combo in the ol' Desktop Dyno and see what comes out. I'll report back later. tmm
Click to expand...

I threw some figures at the computer and came out with 382 hp@ 6000 rpm and 379 tq@ 4500 not bad for bolt on parts and a far cry from the rated 230 hp for the 68' model. (the 77' 318 had only 145 hp.) I used a stock bore 318 with 10.5/1 compression, stock heads with 1.80/1.60 valves, a single plane intake and a 750 cfm carb, and small tube headers, and a 284/495/505 cam. tmm
 
I got a pic for you. 318 bored to 326 Forged pistons cam ported heads and intake headers And a big shot of nitrous!!!
 

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Why are 318's low HP and torque? Because they run forever that way. Just like Ma intended.
 
toolmanmike said:
I threw some figures at the computer and came out with 382 hp@ 6000 rpm and 379 tq@ 4500 not bad for bolt on parts and a far cry from the rated 230 hp for the 68' model. (the 77' 318 had only 145 hp.) I used a stock bore 318 with 10.5/1 compression, stock heads with 1.80/1.60 valves, a single plane intake and a 750 cfm carb, and small tube headers, and a 284/495/505 cam. tmm
Click to expand...

Port the heads and increase the intake valve to 1.94 and gain Hp to 450 and torque to 404. Open the headers up and gain to 469/420. It's only a computer simulation but it proves a point. With the right combination, a teen can be a strong performer. Ma Mopar didn't want a race motor when she built the 318. That's what the 340 was for. Kinda like the 361 or even the 383. A good running motor that would last many miles. Not enough HP to kill itself. tmm
 
Such a cool thread.... I've got a 318 sitting on the floor of my shop.... this thread makes me want to build it into something really special.

I guess the thing is though for the amount of money your gonna spend on building a new motor.(let say you buy new pistons, rods, aluminum heads, intake, headers etc....) adding on a couple of hundred for a 360 core( or maybe a 340 if can find it) most guys are gonna go for the extra cubes.

Still I think a SCEEEEAAMIN 318 would be crazy cool!:finga:
 
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