273ci thoughts?

[AJ/FormS]

, good heads a cam and you're set

Waitaminute; are you saying;
It's ok to change the heads and a cam but just don't bag that 273?
In the big picture, how much power do you imagine

good heads a cam

is gonna make on an 8/1, 273
I'll tell ya; Pishta knows; check his sig.
A 318 is 16.5% bigger, runs the same heads and cam in those years but ran 9.0 Scr. There is no contest.
So I say; take the 273 top end and slip the early LA318short under them, for an instant 50horsepower gain, 2bbl for 2bbl. And it idles at 500rpm and scoots with a 1700stall, and pushes 2.76s all day long. Not to dis the 273 too badly but; the 273-2bbl is a factory-rated 180hp base V8 grocery getter engine.There is a very good reason production ended in 1969.
But I just gotta tell ya,Once upon a long long time ago, I tuned up a 273 67 Dart for a guy, who was going on a tour. When he got back he mentioned 30 mpg on the hiway. That's 30 Canadian , so 24US. And it was just a basic tune-up, So hooray for the little engine that could!

 

[66fs]

Waitaminute; are you saying;
It's ok to change the heads and a cam but just don't bag that 273?
In the big picture, how much power do you imagine is gonna make on an 8/1, 273
I'll tell ya; Pishta knows; check his sig.
A 318 is 16.5% bigger, runs the same heads and cam in those years but ran 9.0 Scr. There is no contest.
So I say; take the 273 top end and slip the early LA318short under them, for an instant 50horsepower gain, 2bbl for 2bbl. And it idles at 500rpm and scoots with a 1700stall, and pushes 2.76s all day long. Not to dis the 273 too badly but; the 273-2bbl is a factory-rated 180hp base V8 grocery getter engine.There is a very good reason production ended in 1969.
But I just gotta tell ya,Once upon a long long time ago, I tuned up a 273 67 Dart for a guy, who was going on a tour. When he got back he mentioned 30 mpg on the hiway. That's 30 Canadian , so 24US. And it was just a basic tune-up, So hooray for the little engine that could!

no such thing as an 8:1 273. Never a smog motor. Pistons at the top of the block within .020.

 

[66fs]

If I had a 273 Dart , i would keep the 273 , how often do you see 273 Darts ? people all stick a 360 or 340 in them . 273 is plenty good for a street cruiser , good heads a cam and you're set . Put in somenew torsion bars and good bushings , maybe new rear springs upgrade the brakes and have fun . That car will be fun to drive , and different

273 already has the best flowing small port heads as cast. I'd take a 273 over a 318 any day, just get a small solid cam and be done. Nothing to change or get. 318 2 barrels don't make anywhere near what a 273 Commando or Charger makes. They are down about 50 HP.

 

[nm9stheham]

I have a 67 273 now...you saying go with the sealed power pistons and my stock heads (freshened up of course) would work well?

Also, the 273 vs. 318 crank snout and relationship to my 904 trans...I'd be best running my 273 forged crank in the 318, no?

The Sealed Power pistons will be just under 9:1 compression ratio only if you use the available .028 thick head gaskets. They will make a CR of 8.5:1 if the standard Felpro kit head gaskets is used. So they are low-to-moderate compression at best. They should balance with the 318 or 273 crank as-is .

The other disadvantage is the lack of eyebrows. You will have to stay modest on the cam lift and duration. But you would do anyway if you have that low-moderate compression and want spunky street performance with good low RPM torque.

The KB167 is going to give you a CR that is 0.6 point higher, all else being equal. That will make the engine behave very noticeably more torquey at low to mid RPM's. And now you have eyebrows and the compression to do a bigger cam without hurting the low RPM torque. The disadvantage is that the crank will need to be balanced to the lighter piston.

BTW, all of these CR numbers cited are with the small chambered heads, around 62 cc.

 

[Nat]

It all really depends on your budget. Nothing wrong with a 273 for a cruiser, but probably cheaper/easier to do a 318/360.

You're right but if you want cheaper drive a ford or Chev .

273 already has the best flowing small port heads as cast. I'd take a 273 over a 318 any day, just get a small solid cam and be done. Nothing to change or get. 318 2 barrels don't make anywhere near what a 273 Commando or Charger makes. They are down about 50 HP.

yes my father had a 68 gt 273 4 bbl it would smoke the tires with ease , it was much stronger than the 1972 318 in the Dart he replaced it with .

 

[toolmanmike]

I have a 67 273 now...you saying go with the sealed power pistons and my stock heads (freshened up of course) would work well?

I wonder if @AJ/FormS has done the numbers there? KB-167's or similar or the 85-87 lean burn Sealed power pistons should end up with around that 9:1 compression mark with the 67 closed chambered heads. They are probably #920's and are very similar to the #302's that came on the lean burn engines. Oops, NM9 already commented on that.

 

[ir3333]

built to the same specs the 273 will always fall short of a 318.Having said that, in a light car it can make for a snappy driver...and that's what it's about.
Very few guys actually hit the strip with their cars.

 

[toolmanmike]

built to the same specs the 273 will always fall short of a 318.Having said that, in a light car it can make for a snappy driver...and that's what it's about.
Very few guys actually hit the strip with their cars.

Ya but I vote for the underdog. Bragging rights are huge with a 300 horse 273.

 

[Wyrmrider]

same stroke
why are we forgetting bigger bore is better
I vote for a stroked 340
or 360
does everything a 273 can do easier and better and most likely for less money

 

[66fs]

built to the same specs the 273 will always fall short of a 318.Having said that, in a light car it can make for a snappy driver...and that's what it's about.
Very few guys actually hit the strip with their cars.

They are just different. Hard to explain, without changing everything the 318 will not pull and rev as high as the 273, which for me is the draw for the 273. You can get a 318 to run, but for me, you pretty much make it into a 340 - 22 cu in. It takes a lot more than a cam change, and then you still have a cast crank. A 273 takes a solid cam and valve spring change, a 4 barrel intake and a carb. High Performance Done.

 

[66fs]

... most likely for less money

LOL Add your total, I'll add mine for a quick small block in an A Body.

 

[toolmanmike]

They are just different. Hard to explain, without changing everything the 318 will not pull and rev as high as the 273, which for me is the draw for the 273. You can get a 318 to run, but for me, you pretty much make it into a 340 - 22 cu in. It takes a lot more than a cam change, and then you still have a cast crank. A 273 takes a solid cam and valve spring change, a 4 barrel intake and a carb. High Performance Done.

Damn if that doesn't sound like a HP 273! LOL Ma Mopar did good. And then came the 340.

 

[pishta]

...how much power do you imagine is gonna make on an 8/1, 273
I'll tell ya; Pishta knows; check his sig.
A 318 is 16.5% bigger, runs the same heads and cam in those years but ran 9.0 Scr. There is no contest.

Word...

I swapped a 318 short block under a 273/4 top end and cam and was blown away with new found torque.
with 318 blocks give away cheap, Id not waste time hopping up a 273. For stock power, no problem running a 273. Ford guys dont mess with 260's becasue they have cheap 289/302 motors. We got the same dynamic.

 

[ir3333]

oh oh...this is getting' emotional

 

[leblanc]

My slightly modified 360 develops about 350 HP and I like it a lot. a 3.55 rear gear helps too, makes it more fun to drive. The motor came from a 79 Ramcharger.

 

[NC Engine Builder]

Ya but I vote for the underdog. Bragging rights are huge with a 300 horse 273.

Bragging rights? I dunno if I agree with that. A stone stock, junkyard 5.9 magnum with a carburetor would be a HUGE improvement over a 300 hp 273.

 

[ir3333]

The last car show i was at a guy said to me "You know, every car here is somebodies favourite"
I have seen some fast 273's!

 

[rumblefish360]

They are just different. Hard to explain, without changing everything the 318 will not pull and rev as high as the 273, which for me is the draw for the 273.

I have no idea how you figure that. The 1 and only advantage the 273 has is a lighter piston. (The potential to rev up quicker.) There is absolutely no reason ether engine would haves problem matching rpm for rpm.

You can get a 318 to run, but for me, you pretty much make it into a 340 - 22 cu in.

There would be no reason to do so. The 318 has a 45 CID advantage get the 273. That’s HUGE!

It takes a lot more than a cam change, and then you still have a cast crank. A 273 takes a solid cam and valve spring change, a 4 barrel intake and a carb. High Performance Done.

This makes nearly 90% ZERO sense.
Dependent on the year 318 you start with.......
We will assume both engines are 2bbl.
If you stand by the 273 as a start with a 4bbl., then mentioning it above as a add on should not have been done but I’ll go there and explain it below.

Example! My ‘67, 318 (forged crank years right?) started life with a 9.0-1 listed/advertised compression ratio. Not bad. A 1 point increase is about, at best, at this low power level, 3% on a good day. If your lucky.

As you said, add a cam and matching springs, 4bbl. carb & intake, HP mod’s done at a 45 cube advantage.

If someone starts with a mid ‘70’s to late 80’s 318, the additional money spent on milling the heads and intake for the cheap route to go from 7.8-1 to 9.0-1 is a worthy expense. Late 340’s also suffered with low ratios as well as always with the 360.

Truly, all of this is about a 99% wash because nearly any as build completely stock engine from the days gone last will need a total over haul.

At least there are off the shelf forged or Hyperutecic pistons or the 318 available in flat top or some as well as various dish depths and numbered valve reliefs. That can not be said for the 273.

OH! You crap on a cast crank even though there known to handle 500 hp/tq easy. Are you going for a 273 @ plus 2hp per cube for 546+ HP?

From a durability stand point, I have never seen a crank last long no matter what the material is being used when the engine is beat on and/or suffers from a lack of oil pressure. Every crank dies when that happens.
There is no dispute on stronger materials lasting longer.

It is to bad you can not (for the most part I have seen! LOL!) turn a 318 into a 340. Even going to a 4.00 bore size is dicey. Possible? Maybe. But at what cost to the thickness and integrity of the cylinder wall? if I can take one safely to .060 (327 cubes is it?) I’ll go there, if the cylinder walls need to go that far and can still have sufficient eat left over.

The ability to “Rev” an engine “High” has a few elements to it. IMO, it starts with proper valve control with the right spring.

 

[NC Engine Builder]

Not to mention that tiny cylinder bore in a 273 limits airflow, and requires a DOME to even get anywhere near the compression ratio you can achieve in a flat top 318.

 

[toolmanmike]

Bragging rights? I dunno if I agree with that. A stone stock, junkyard 5.9 magnum with a carburetor would be a HUGE improvement over a 300 hp 273.

Oh sure it would and that's comparing apples to oranges. Around 90 cubes bigger and 80 lb/ft more torque? The MF better be a big improvement.

 

[toolmanmike]

Not to mention that tiny cylinder bore in a 273 limits airflow, and requires a DOME to even get anywhere near the compression ratio you can achieve in a flat top 318.

WTF are you talking about? The 273-2 barrel engines were rated at 9.1. As much as the 318's were.

 

[273]

The reason 273 and for that matter 340 are considered the revving small blocks is cause they both have the higher head cfm per cid than 318 and 360, 340 have the heaviest pistons compared to the other 3. You would need a set of 360 heads on a 318 and ported 2.02 heads on a 360 to make them all have similar cfm per cid.

I don't consider 273 to be an hp underdog unless we're talking 500-600 + hp NA, A set of stock Magnums on a notched block would give enough flow for almost all 273 builds.

The main problem is gearing, since most don't want to run more than 3.55, most moderate built engines will produce about 1.15 lbs-ft per cid so a 360 will be 414 lbs-ft and 273 will be 314 lbs-ft in first gear 2.45 times 3.55 times lbs-ft you get 3600 lbs-ft to the ground for 360 and 2730 lbs-ft for 273 huge difference even if both are making the same power. The 273 would need a 4.68 gear to put 3600 lbs-ft to the ground. Even worse if up against a 440, with 4400 lbs-ft to the ground the 273 would need 5.72 rear gears.

If willing to gear it build it if not go bigger, but obviously some have different criteria like /6 guys, I get it sometimes I think about pulling my 360 for 273 or even a built /6 or sometime 500+, just be informed of the plus and negatives .
Generally the old saying no replacement for displacement hold true, even more rpm and power adders are just another form of increased displacement.

 

[AJ/FormS]

oh oh...this is getting' emotional

I knew it would; 273 guys all come out of the woodwork when you dis their little motors, just like the BB boys scorn the SBMers..
By 273ers thinking it seems a 383 would would outpower a 440 in same configuration. I mean it's the same plus 16.5% displacement.

Let's go to 1969, and examine these 2bbl engines;
>The 2bbl 273 was advertised to make peak torque at 2400IIRC. And I think the 318-2bbl was at same.
>The 273 was advertised to be a 9.0 engine and the 318 was 9.2
>They both used the same heads, same cam, and same spec rods.
>The 318 pistons come in 43 gms heavier at 592, versus 549 to the 273
> in 69 all SBMs had steel cranks
SO,
lemmee get this right;
in 1969, the only differences were;
45 more cubes for the 318, and
0.2 point more compression for the 318 ..........
But somehow the 273 was the better engine?

I think what the 273 guys miss, is that in comparison, at low rpm, like you would find with 2.76s that most most of these cars were saddled with, and at same weight,and with the same TCs, the 318 can torque away with these, whereas the 273 couldn't torque it's way out of a wet paper bag.

One more; at 140ps cranking pressure, the 273 piston is applying 1450 pounds of force to the crank.
Whereas at same pressure, the 318 is pushing with 1681; there is that plus 16% again...
It doesn't matter what you do to a 273, labor wise it costs exactly the same to do it to a 318, and parts wise it costs MORE for the 273, and the bottom line is always
you just give up the cubes.
That makes no sense to me whatsoever. That will cost you more cam, more gear, and more stall... just to play catchup in third gear.

 

[toolmanmike]

I knew it would; 273 guys all come out of the woodwork when you dis their little motors, just like the BB boys scorn the SBMers..
By their thinking it seems a 383 would would outpower a 440 in same configuration. I mean it's the same plus 16.5% displacement.

Let's go to 1969, and examine these 2bbl engines;
>The 2bbl 273 was advertised to make peak torque at 2400IIRC. And I think the 318-2bbl was at same.
>The 273 was advertised to be a 9.0 engine and the 318 was 9.2
>They both used the same heads, same cam, and same spec rods.
>The 318 pistons come in 43 gms heavier at 592, versus 549 to the 273
> in 69 all SBMs had steel cranks
SO,
lemmee get this right;
in 1969, the only differences were;
45 more cubes for the 318, and
0.2 point more compression for the 318 ..........
But somehow the 273 was the better engine?

I think what the 273 guys miss, is that in comparison, at low rpm, like you would find with 2.76s that most most of these cars were saddled with, and at same weight,and with the same TCs, the 318 can torque away with these, whereas the 273 couldn't torque it's way out of a wet paper bag.

One more; at 140ps cranking pressure, the 273 piston is applying 1450 pounds of force to the crank.
Whereas at same pressure, the 318 is pushing with 1681; there is that plus 16% again...

Aj, I see you are comparing the 2 barrel 273 to the 318. That's ok.
The 273-2 has .657 hp/cu in.
The 273-4 has .860 hp/cu in. where
the 318-2 has .723 per cu/in.
Now we are on the same playing field.
To all you big cube small block guys in this thread, I don't remember anyone saying the 273 was the best engine, the most powerful or any of the like. It does well for it's size and it's limits. Heck, there is no stopping with the comparisons until you get to maybe a 800 horse late model Hemi and there are many power plants larger and of course more powerful. The OP has a nice Dart with a 273 and wanted to know if he should keep the 273. There's always somebody out there that thinks bigger is the way to go. He just wants a street cruiser. He didn't ask how to build a top fueler.

 

[NC Engine Builder]

Aj, I see you are comparing the 2 barrel 273 to the 318. That's ok.
The 273-2 has .657 hp/cu in.
The 273-4 has .860 hp/cu in. where
the 318-2 has .723 per cu/in.

To all you big cube small block guys in this thread, I don't remember anyone saying the 273 was the best engine, the most powerful or any of the like. It does well for it's size and it's limits. Heck, there is no stopping with the comparisons until you get to maybe a 800 horse late model Hemi and there are many power plants larger and of course more powerful. The OP has a nice Dart with a 273 and wanted to know if he should keep the 273. There's always somebody out there that thinks bigger is the way to go. He just wants a street cruiser. He didn't ask how to build a top fueler.

By your own logic, you cant compare the 4 barrel 273 to the 2 barrel 318 either. Apples to oranges. The 273 was the "performance" engine until the 340 showed up, maybe it would be more fair to compare those 2? There is NO magic in a 273, despite some of the emotional driven responses. Decent economy engine, more expensive and more difficult to make power compared to ANY of the other mopar small blocks.