273 vs 318

[NC Engine Builder]

It's easier to get compression in a larger bore, the small bore diameter hinders that. That's why a 273 requires a dome piston to get above 10 to 1 where a 340 can do the same with a flat top. The smaller bore also slightly limits flow.....the 273 has basically no advantage over a 318

 

[nm9stheham]

What's the wheel bas and track width on an STI?

Food for thought


Edit: WRX is 103/60.2 and a dart is 111or 108/59.6

It's just for the fun of it! But yes, around 100" seems to be the ideal rally wheelbase; too long, and the rotational moment of the car gets too big to snap the car around a series of tight corners, and too short makes it too twitchy on a straight gravel road at 100 MPH.

I started rallying back in the late 70's, and am well past the need to be at the front of the pack. Just getting back out there is the goal for me. (I'm 63. now...) I actually almost got started on a rally A a year ago (I found the candidate car: a well patched rustbelt car), but life and business got in the way. The rear suspension has to go, and be replaced by a 4 link and panhard setup. It would be a popular car.

 

[318willrun]

No secret here..... If you bored a 273 .060 over (but kept the compression the same), would it be capable of more power?? Of course, the answer is yes. You just added about 10 cubic inches.
A 318 is a bored out 273 by the tune of 45 cubic inches. If both have the same cams, intakes, carbs, heads, exhaust, and compression, the 318 is going to out perform it every time.

 

[318willrun]

I'll never figure out why folks like to give up 45 cubes in bore, but still somehow make out like the 273 has an "edge", or somehow the 273 comes in for the win......

Yet........ yet.... these are a lot of times the same folks that will declare "the little teener" is a laugher when compared to the 340, even with same heads, cam, blah blah. The 340 is just a bored out 318. And in this comparison there is only 22 cubes difference in the bore.

So let me get this straight: When you loose 45 cubes in bore only, then they are close. But when you give up 22 cubes in bore, then it isn't even close, in fact, it's bashed, laughed at.
This I find very amusing......

 

[318willrun]

But, the answer to the original question is..... a 273 commando (4bbl, hotter cam & compression) would have the edge on a 318 2bbl. But, that's not much of a fair comparison. Give the 318 the same cam, intake, carb, and compression, and the 318 is in for the win

 

[yellow rose]

I'll never figure out why folks like to give up 45 cubes in bore, but still somehow make out like the 273 has an "edge", or somehow the 273 comes in for the win......

Yet........ yet.... these are a lot of times the same folks that will declare "the little teener" is a laugher when compared to the 340, even with same heads, cam, blah blah. The 340 is just a bored out 318. And in this comparison there is only 22 cubes difference in the bore.

So let me get this straight: When you loose 45 cubes in bore only, then they are close. But when you give up 22 cubes in bore, then it isn't even close, in fact, it's bashed, laughed at.
This I find very amusing......

That's why there are engineering rules of thumb for stuff like bore to stoke ratio, rod to stroke ratios, the percentage of exhaust flow to intake, which has been wrong and known wrong for a while, the percentage of exhaust valve you should be able to see from the port. Stuff like that.

When you have an engine making 1.1-1.2 HP/CID, a 22 CID advantage can be easily overcome by gear ratio and RPM. And then if you figure in weight, that 22 CID can even be less of an advantage. I lost $500.00 USFRN's one Friday night in 1981 to a guy with a 273 in a valiant. His 4.11 gears ate my 3.55 all world gear set. I then went into the army. 4 years later I ran into the same dude. I had updated all my stuff to include 4.56 gears. I got my $500.00 USFRN's back, plus another 500 just because.


That's why combinations win.

In the real world, small gains or losses in displacement rarely affect very much. Sort out the rest of it, and you can make HP with most anything.

 

[Hipo65]

The 318 & 4bbl 273 are close because (for whatever reason) chrysler never hopped up the teener. They share the same valve train & head design. But the 273 got more squeeze & little larger cam. And compaired to the 340 not even same playing feild.larger camshaft yet, bigger valves, bigger ports, bigger better about everything from top to bottom. Now yer correct give the little "Rodney Dangerfield" 318 the same treatment as the 340........ you bet thed be dam close! I chose the 273 mainly because it was the stock motor first off & just like yellow rose mentioned combination is whats key. Not sturing the pot, its all mopar to me! Stock a commando 273 should have an edge on a stock 318. Even the playing feild & well the 318 wins all day!

 

[stroked340]

I'll never figure out why folks like to give up 45 cubes in bore, but still somehow make out like the 273 has an "edge", or somehow the 273 comes in for the win......

Yet........ yet.... these are a lot of times the same folks that will declare "the little teener" is a laugher when compared to the 340, even with same heads, cam, blah blah. The 340 is just a bored out 318. And in this comparison there is only 22 cubes difference in the bore.

So let me get this straight: When you loose 45 cubes in bore only, then they are close. But when you give up 22 cubes in bore, then it isn't even close, in fact, it's bashed, laughed at.
This I find very amusing......

Same could be said for those who run "little bitty" 318's when with a 360 your stating with 42 more cubic inches..

 

[273]

Its not the size of your engine its the hp of your engine that matters. Eg 400hp is 400 hp no matter if it comes from a /6, 273 or even a 440 if there all setup for the best quarter mile time they will all do similar.

But bore is the ultimate restriction to power saying that 318/360/340 all have a big enough bore to make enough hp to break the block. 273 is a special case it is really to small. Anything over 300 hp becomes impractical but not impossible. Eg. 1.94 EQ's ported and milled for smallest chamber with domes and a big solid roller with the deepest gears you can get for your rear end probably get you well into the 500's hp wise but the next problem is rpm. A 273 has to rev about 1250 rpm more than a 318 and 1750 rpm more than a 360 to make the same power. And cause of the rpm (/torque) difference the main problem going 273 (or any small displacement) is gearing since a 350 ish hp 360 with 3.55 is basically the standard when it comes to A Body performance a 350 ish hp 273 would have to run about 1 ratio deeper than so about a 4.56 to keep up. Or to put it another way dropping from 3.55 to 2.55 on the 360 would be equal to a 3.55 geared 273. Since many don't want to run anything larger than 3.55 gears it really makes no sense to build anything smaller than a 360 even for a mild build (under 300hp).

To me when it comes to smaller displacement engines "if your willing to gear it build it" if not go bigger.
Your cubic inch should be around 0.9:1-1.1:1 hp:cid for a street car.

 

[318willrun]

Same could be said for those who run "little bitty" 318's when with a 360 your stating with 42 more cubic inches..

Big difference is those folks I know running 318's don't claim them to be as fast (or faster than 340/360's) in pretty much stock/mildly built form. Yes, if somebody wanted a budget 12 second street car and they had the choice of starting with a good running 360 2bbl or a good running 318 2bbl for about the same money, I would always recommend the 360

But I've seen plenty of 318's put spankings on 340's/360's, just like many have seen 273's put spanking's on 318's (340's/360's too, for that matter).

 

[318willrun]

The 318 & 4bbl 273 are close because (for whatever reason) chrysler never hopped up the teener. They share the same valve train & head design. But the 273 got more squeeze & little larger cam. And compaired to the 340 not even same playing feild.larger camshaft yet, bigger valves, bigger ports, bigger better about everything from top to bottom. Now yer correct give the little "Rodney Dangerfield" 318 the same treatment as the 340........ you bet thed be dam close! I chose the 273 mainly because it was the stock motor first off & just like yellow rose mentioned combination is whats key. Not sturing the pot, its all mopar to me! Stock a commando 273 should have an edge on a stock 318. Even the playing feild & well the 318 wins all day!

^^^^this^^^^^ Well written!!
And yes, it is ALL Mopar to me also...

 

[RustyRatRod]

No secret here..... If you bored a 273 .060 over (but kept the compression the same), would it be capable of more power?? Of course, the answer is yes. You just added about 10 cubic inches.
A 318 is a bored out 273 by the tune of 45 cubic inches. If both have the same cams, intakes, carbs, heads, exhaust, and compression, the 318 is going to out perform it every time.

It all depends on the driver.

 

[RustyRatRod]

You're putting words in peoples' mouths, I think. At least mine. I never bashed a dang thing. I am usually the first to jump on board the 318 bandwagon. All my point was, that the 273 can be very formidable same as any other engine with the right parts choices. Sure, it's small, but it's not a piece of ****. The D-Darts weren't slow and they were a factory package that's easily improved upon by modern cam grinds and better flowing heads.

If someone already has a 273 and all they want is a snappy little street engine, there's no reason not to use it.

I'll never figure out why folks like to give up 45 cubes in bore, but still somehow make out like the 273 has an "edge", or somehow the 273 comes in for the win......

Yet........ yet.... these are a lot of times the same folks that will declare "the little teener" is a laugher when compared to the 340, even with same heads, cam, blah blah. The 340 is just a bored out 318. And in this comparison there is only 22 cubes difference in the bore.

So let me get this straight: When you loose 45 cubes in bore only, then they are close. But when you give up 22 cubes in bore, then it isn't even close, in fact, it's bashed, laughed at.
This I find very amusing......

 

[318willrun]

You're putting words in peoples' mouths, I think. At least mine. I never bashed a dang thing. I am usually the first to jump on board the 318 bandwagon. All my point was, that the 273 can be very formidable same as any other engine with the right parts choices. Sure, it's small, but it's not a piece of ****. The D-Darts weren't slow and they were a factory package that's easily improved upon by modern cam grinds and better flowing heads.

If someone already has a 273 and all they want is a snappy little street engine, there's no reason not to use it.

Wasn't at all even thinking of you in my statement. But i wasn't putting anything in anybody's mouth, because they (not all, but many) have sold the 318 short. As I've consistantly stated (not just here, but the last 30 years) that i like all the LA small blocks. I also like the B/RB motors too. I have no problem whatsoever of anyone building any engine they wish. 273 - 408 stroker. If ya have, like it, then build it. I also acknowledge that certain goals can be easier achieved by using a better option for the goal.

 

[318willrun]

It all depends on the driver.

and traction, and gears, and weight of car..... but the comparison is between the two engines, all else being equal

 

[trebor75]

I'm quite attached to my 273 commando. In Sweden it's hard to find 340 and 360's. I choose this 273 over a 318, but mostly because it was fresh and already ran great. I have since done upgrades gradually. It's a fun car to drive, I like it. Converter and gearing is really important though. But it's probably wiser to go with a 318 because there are more parts around, and it would be cheaper to build it up. Having said that, I would like to build me a 360 sometime

 

[stroked340]

But I've seen plenty of 318's put spankings on 340's/360's, just like many have seen 273's put spanking's on 318's (340's/360's too, for that matter).

LMFAO.. I'd like to see that..NEVER have..

 

[318willrun]

LMFAO.. I'd like to see that..NEVER have..

you don't get out much.....

 

[the wall]

I agree......and I can count, too. lol A 318 decked out with all the 340 goodies would spank a 340 if the 340 guy wasn't just right off the line.

Also, don't forget, with the 273, it has the lighter crank and rods. That can and will make a difference.

273 has a steel forged crank.some early318s have the same these cranks are almost exactly the same weight...273 rods are nice light weight with floating wrist pins and so are318 till some were in71 year the rod weigh identical. Later318 rods are 360 castings same as340 minis floating wrist pins. 273s have a very heavy piston wrist pin combo from the factory therefore the factory 273 has very little weight advantage over the318 in stock configuration. You probably new this already but this is for those that don't.

 

[273]

273 has a steel forged crank.some early318s have the same these cranks are almost exactly the same weight...273 rods are nice light weight with floating wrist pins and so are318 till some were in71 year the rod weigh identical. Later318 rods are 360 castings same as340 minis floating wrist pins. 273s have a very heavy piston wrist pin combo from the factory therefore the factory 273 has very little weight advantage over the318 in stock configuration. You probably new this already but this is for those that don't.

From what I remember 273 318 and 360 have similar bobweight the 340 the olny one being a lot heavier.
And the 340 is a capable revver just like the 273 and thats cause both have similar head flow to cid ratio.
The 360 and 318 are way under headed cfm wise about 30-40 cfm.

 

[stroked340]

you don't get out much.....

Sure do i'm at the track all the time..never seen any of those there fast 318's you speak of

 

[Max1196]

It's all in the number! The 273 and the 340 have been labeled as the cool engine to have. And sadly the 318 and 360 are looked upon as just an engine. All can be a winner, it's just the "yap" factor that goes along with saying the CID!

 

[the wall]

From what I remember 273 318 and 360 have similar bobweight the 340 the only one being a lot heavier.
And the 340 is a capable revves just like the 273 and thats cause both have similar head flow to cid ratio.
The 360 and 318 are way under headed cfm wise about 30-40 cfm.

basically agreed here but with one exception, the 360 head (non magnum)head flow is a very small number off on stock 340 head. the main diff in these heads is the intake valve, 202 for 340 till 72 were it was changed to 188, 360 heads were 188. 1970 340 head actually have 360 cast on them on the intake runner were 68-69 had 340. the casting number were the same. not sure but i believe T/A heads have the same casting number but a diff part number. the flow numbers between 202 and 188 heads are a diff of 5-10 cfm difference give or take. the good news for the later smog 360 heads is that the exhaust has a slightly raised floor because of air injection and these port flow higher then 340 heads

 

[the wall]

It's all in the number! The 273 and the 340 have been labeled as the cool engine to have. And sadly the 318 and 360 are looked upon as just an engine. All can be a winner, it's just the "yap" factor that goes along with saying the CID!

i think there is only 1 reason anymore to put a 340 in a car. your restoring a original muscle car that came with one. 340 is a great factory piece with all the great numbers to produce high factory power with tons of flexibility. 360 is the bigger brother of 340 with all the smog. heads up numbers with 340 360 wins. every body new in the hobby look at the number that were published buy the factory see those big numbers and say i want one of those. 340s hall *** and then ad mods and look out. then they tell there friend, 360 is the same beast only 20 cid bigger. (theirs no replacement for displacement) if you find your dream engine and it needs a rebuild it cost the same. putting 202 valves in 360 heads is a easy mod for a good shop to do and if it needs a rebuild the cost for valves that your to replace anyway is the same. one more thing 340 for sale arm and a leg. 360 for sale thank here a few bucks. there still every were.

 

[cosgig]

Since nobody has touched on what I consider the major difference between a 273 and a 318, I guess I will! The register on the rear of the crank of the 273 is a major limiting factor when it comes to finding compatible equipment, and thus will be overlooked by the knowing Mopar public! Unfortunately, not everybody knows of this and will just throw in a 318 in place of a 273 and go racing!! That is until the front pump wallers out after just a couple miles and renders the trans useless!! Now, try coupling that 273 with a 68 and later trans!!!....not gonna happen!!