The Truth about 318s

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THE TRUTH ABOUT 318's:

They were never designed or intended to be powerful engines.
They were designed and intended to be "The Peoples Engine".
Make enough torque to move LIGHT DUTY 3000-4000 lb. cars, trucks and vans.

Their weakness is built in.
Their weakest points are:

Camshaft....no production 318 EVER had more lift than .380" Lift.
Compression.....most 318's have a compression ratio beween 8:1-9:1.
Induction......318's almost never got more than a 2 barrel carb.


Now if you look at a 318 from the standpoint that it is JUST an engine....all of those weak factors can be overcome.

Notice how I never said a 3.91 bore is a limiting factor....nor is the 3.31 stroke....the infamous 340 shares the same stroke....but the bore is 4.04".

Like others have stated, there are pistons available to bump the compression into the Hp friendly 9.5 - 10:1 range, and ideally they should be on more peoples list....but I understand that by the time you BUY a set of custom pistons for a 318, you really should have built a 360....but I also understand the reasons people like to build 318's....they are EVERYWHERE....cheap replacement.

To build a hot little 318, there is no better recipe than the one published by HotRod Magazine. 406hp for cheap.

That, is the truth about 318's.
And if you want more truth...a Forced Induction 318 is a great idea...the factory compression is already inline, you just need a camshaft and some induction...if it breaks there is another longblock ready to go (like Hotrod says) on every street corner.

:cheers:
 
All great input here......I just wanted to add that when people compare a 318 to a 327 Chevy (an engine that is considered a legend), I think the 318 shines (I'm sure most average people don't), what with it's longer rods, bigger lifter foot and the fact that you can build it with some 360 heads and a forged crank for cheap (early 273) and it should be ready to scream. Just gotta get that compression up, do the necessary machine work to get rid of those stacked tolerances.
 
All great input here......I just wanted to add that when people compare a 318 to a 327 Chevy (an engine that is considered a legend), I think the 318 shines (I'm sure most average people don't), what with it's longer rods, bigger lifter foot and the fact that you can build it with some 360 heads and a forged crank for cheap (early 273) and it should be ready to scream. Just gotta get that compression up, do the necessary machine work to get rid of those stacked tolerances.


Yup,I agree.

One more area where all mopar engines seem to suffer is heavy bob weight. The large reciprocating mass makes for a slower revving engine initially. Once the mass starts moving ,it might actually be an advantage.

Lighter pistons are a key for changing that. The KB 167 seems to resolve both low compression and weight issues.

A chev buddy once claimed that the 327 he had could beat any 360. I said fine,you build a 327,I'll build a 360 and meet you at the track.

Utter silence followed...
 
8:1 is a good turbo compression motor

You are correct....anything below 10:1 is good for a minimum of 10 psi of boost..(I ran a turbo car with 28psi with 8.8:1 compression)..how long a cast piston lasts with boost is another issue, BUT....I know of a few turbo V-Eight guys with upwards of 600hp on cast pistons.
 
My point with this post was this:

Lots of people are looking at building up their 318 (they've already got it or can get one cheap, whatever).

So they look at the "How to rebuild your Small Block Mopar" or whatever, and think they're getting a picture of what they're up against in terms of trying to build compression etc. but the figures in those books all seem to be off by a large amount. Meaning, its more of an uphill battle than one would expect.

If you go by what the books say, you're going to end up with too big of a cam, or too big heads and kill all your performance.
 
Tif it breaks there is another longblock ready to go (like Hotrod says) on every street corner.

:cheers:

Well, if by "ready to go", you mean, still needs pistons, decked, and cylinder heads, then sure. LOL!
 
You took that out of the wrong context....I wasn't saying Build a 318 because they are plentiful.

I said: if you use one as a Forced Induction Longblock....you can easily replace it IF it breaks....vs. a Heavily Machined, Modified 340-360....LOL.
And for turbo/supercharger duty...you SHOULDN'T HAVE to replace the pistons, heads or deck, or cut ANYTHING.


(Cause I know when a rod breaks and sticks out the side of a block...I would rather lose a 318 block with Stock Internals)

Some people have more money than brains though.
 
A 318 POLY pistons sits right at '0' deck on an LA block.
With an actual cc volume of 67 on a 'J' head, this comes out to a static compression of @ 9.5:1.

Don't dog on the ol' 318 too much, give them the lighter '782 full floating rod, a break in reciprocating weight with a cast crankshaft, and they spin RPMs like crazy.
Don't HAVE to notch the cylinders on a 318 for 2.02 valves, as long as you keep the cam down some, but 1.94s or 1.88s with a wilder cam are plenty.

Of course, a manual trans always makes the experience even more fun. :)

Mark.
 
You are correct....anything below 10:1 is good for a minimum of 10 psi of boost..(I ran a turbo car with 28psi with 8.8:1 compression)..how long a cast piston lasts with boost is another issue, BUT....I know of a few turbo V-Eight guys with upwards of 600hp on cast pistons.

There was a guy on moparts who ran a procharger setup on a stock 360 for close to 2 years. He bought it from the wreckers and when it blew up he went and got another for $300.

He was initially runiing 5-6 psi and then cranked it up. Thats when the motor went bang..
 
You are correct....anything below 10:1 is good for a minimum of 10 psi of boost..(I ran a turbo car with 28psi with 8.8:1 compression)..how long a cast piston lasts with boost is another issue, BUT....I know of a few turbo V-Eight guys with upwards of 600hp on cast pistons.


Wow! 600 hp on cast pistons? I am looking in doing a "SRT 4+4" next year, I am looking for turbos now. I am wondering how hypereutic pistons do with boost?
 
i hear hypos and boost are bad. forged IMO are the ones you want to go with.

and i have a motor thats 22:1 and it has a turbo..of course its an old idi..but still..
 
Yup,I agree.

One more area where all mopar engines seem to suffer is heavy bob weight. The large reciprocating mass makes for a slower revving engine initially. Once the mass starts moving ,it might actually be an advantage.

Lighter pistons are a key for changing that. The KB 167 seems to resolve both low compression and weight issues.

A chev buddy once claimed that the 327 he had could beat any 360. I said fine,you build a 327,I'll build a 360 and meet you at the track.

Utter silence followed...
A couple of years ago a good friend of mine was building a V-8 S-10 mini truck,with a 327 & 4 speed, at the same time I was putting together a Ram 50 mini truck with a 318. Merely coincidence. On a few occasions he mentioned that after the trucks were done we needed to line them up & run 'em. Well he finished his a few weeks before me (available kits make this an easy swap) & he took me for a ride, a few weeks later I took him for a ride in mine, It was the last time he ever mentioned anything about a race, haha.

truck 051.jpg
 
hyper pistons shatter

O.K,heres the deal with turbo's and why they dont kill an engine.

Boost occurs when the piston is heading down the bore. This is a compressive load which does not create metal fatigue.Max cylinder pressure occurs 20 degrees after tdc in a turbo engine. The turbo only increases peak pressure about 20% but average pressure over the entire stroke is up and so is power.
What kills a motor and metal in general is tensile load or when it is being stretched.So when the piston is at tdc after coming up is when it and the rod are under the most stress. The other big factor here is heat control. Turbo's build heat so you need to control it in order to have a durable engine.
 
I built a 318 last year for my 71 duster. I built the 318 because it was a low mileage engine but mainly because it was free and anything it better than the slant six. I didn't want to spend much money because I'm building a 528 hemi for my 66 belvedere and I just wanted a driver.
I did a stock rebuild. I was shocked when I saw how far the pistons set down in the block.
To make up for the low compression I advanced the mild cam 2 degrees from DTC. The 318 pulls real hard up thru 5000 and I have out run a stock 5.0. mustang. What more could I ask for from a stock 318 with a mild cam.
The key to making a 318 run decent is use a mild cam around (218 @50) and advance the cam a few degrees to build cylinder pressure at low RPM's.
I plan on building a 360 later but I'm very happy with the little 318 for now.

My car doesn't have power steering which helps the 318.
 
The other big factor here is heat control. Turbo's build heat so you need to control it in order to have a durable engine.

Which is why most current factory turbo cars have Intercoolers and why most older imports have them, too.
It's also the reason there are no untouched 2.2/2.5 turbo heads in good condition, too much uncontrolled heat.
Chrysler bit the big one by not intercooling them.

Mark.
 
The pistons shatter due to detonation. Not the load. With enough horsepower they will break them too. But the main issue comes from poor engine management. Carbureting a turbo or blown engine is just not the best way. In terms of engine development, blow thru carbs are the equivolent of 8 one barrels on a flathead 8. Yes, it looks wicked cool,and it will run. Bu tthere's a much better way to do it with technology. Give them EFI, and set it up properly with the right fuel system, and hypers will live under boost. They will also be fine with 200hp of NO2, but again, you HAVE to be PERFECT on the tune. Hypers are brittle. They cannot absorb the shocks from detonation without failing. Like a cold chisel on a bearing race. They chip instead of flexing.
 
I built a 318 last year for my 71 duster. I built the 318 because it was a low mileage engine but mainly because it was free and anything it better than the slant six. I didn't want to spend much money because I'm building a 528 hemi for my 66 belvedere and I just wanted a driver.
I did a stock rebuild. I was shocked when I saw how far the pistons set down in the block.
To make up for the low compression I advanced the mild cam 2 degrees from DTC. The 318 pulls real hard up thru 5000 and I have out run a stock 5.0. mustang. What more could I ask for from a stock 318 with a mild cam.
The key to making a 318 run decent is use a mild cam around (218 @50) and advance the cam a few degrees to build cylinder pressure at low RPM's.
I plan on building a 360 later but I'm very happy with the little 318 for now.

My car doesn't have power steering which helps the 318.

Back when my 1970 318 Dart was on the road,I swapped a mild elgin cam in and later I bolted down a 360 4bbl intake and carter afb with an adaptor plate.The car had a stock single exhaust and otherwise stock driverain. I took it for a spin and the power compared to the 5.0 mustang 5 speed i had previously owned blew me away. That thing would have eaten my Mustang..

I never could get that AFB to idle right ( even with a rebuild)and ended up going back to the stock 2bbl which was all I could afford at the time.
 
the R blocks came out in 89 as a replacement for racers on the right bank it should have an R cast into it right behind the alternator just below the deck and next time you have the timing chain cover off check the water inlets if they are round its just a plain jane block but if they are half moons you really have a pricey item on your hands
Thank you for the reply 1qwikScamp, I am sorry it has taken a while for me to read this thread again, been constantly working on the wifes 67 318 referenced.
The number "GM 318 R" is stamped on a flat surface under valve cover behind/above power stering pump on drivers side. The 1970 referenced # I found cast into the block on passenger side ie: 4 / 1 7 / 7 0. I have just finished replacing water pump inlet holes on it were square like with rounded corners. This must have been a rebuilt engine of some sort due to beeing dipped but not painted. The car also was original 273 cammando, proper vin, badges on fenders, 10" breaks, etc. I wonder where that motor went? So you think this 70 block, rebuilt in 1989 or after>? with the 273 commando taken for one of the FABO members cars about 15 years ago! LOL
But really what do you think?
 
THE TRUTH ABOUT 318's:

They were never designed or intended to be powerful engines.
They were designed and intended to be "The Peoples Engine".
Make enough torque to move LIGHT DUTY 3000-4000 lb. cars, trucks and vans.

Their weakness is built in.
Their weakest points are:

Camshaft....no production 318 EVER had more lift than .380" Lift.
Compression.....most 318's have a compression ratio beween 8:1-9:1.
Induction......318's almost never got more than a 2 barrel carb.


Now if you look at a 318 from the standpoint that it is JUST an engine....all of those weak factors can be overcome.

Notice how I never said a 3.91 bore is a limiting factor....nor is the 3.31 stroke....the infamous 340 shares the same stroke....but the bore is 4.04".

Like others have stated, there are pistons available to bump the compression into the Hp friendly 9.5 - 10:1 range, and ideally they should be on more peoples list....but I understand that by the time you BUY a set of custom pistons for a 318, you really should have built a 360....but I also understand the reasons people like to build 318's....they are EVERYWHERE....cheap replacement.

To build a hot little 318, there is no better recipe than the one published by HotRod Magazine. 406hp for cheap.

That, is the truth about 318's.
And if you want more truth...a Forced Induction 318 is a great idea...the factory compression is already inline, you just need a camshaft and some induction...if it breaks there is another longblock ready to go (like Hotrod says) on every street corner.

:cheers:
Hi Prine, I noticed you really know your stuff & down to earth logic! I was wondering if you could answer a quick question. Just got water pump, carb, etc. went on test drive and popped drivers side motor mount again (just replaced Dec 08 1st night home popped in driveway and almost ran me in the back of the garage. Anyway, when replacing the first time I noticed not flush mounted when engine lowered. Had to go back and loosen everything even metal brackets on block, & holes not lined up perfect. All pulled together after tightening. The previous owners butchered this car. Is there a bracket/mount swap from 1967 Dart 273 commando to 1970 318? Wrong brackets cause mount bushing to pop? Please advise. Thank You!!
 
Hi Prine, I noticed you really know your stuff & down to earth logic! I was wondering if you could answer a quick question. Just got water pump, carb, etc. went on test drive and popped drivers side motor mount again (just replaced Dec 08 1st night home popped in driveway and almost ran me in the back of the garage. Anyway, when replacing the first time I noticed not flush mounted when engine lowered. Had to go back and loosen everything even metal brackets on block, & holes not lined up perfect. All pulled together after tightening. The previous owners butchered this car. Is there a bracket/mount swap from 1967 Dart 273 commando to 1970 318? Wrong brackets cause mount bushing to pop? Please advise. Thank You!!

273 and 318 mounts are the same the 340and 360s have difrent ones than the 273 318
 
273 and 318 mounts are the same the 340and 360s have difrent ones than the 273 318
Hey thanks 1qwikscamp! I just ordered 2 of the same drivers side mounts. That will give me an extra & they are lifetime garantee. I'll make em wish they didn't garantee!
Do you have any more thoughts on the broken mounts every 6 months?
Were the engine numbers referenced above still add up to what you said about thr R Blocks? Thanks Again!!:notworth:
 
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