273ci thoughts?

[NC Engine Builder]

One the original poster asked for our "thoughts" on the 273, vs a 318/340/360. That's EXACTLY what we are doing, giving him our thoughts. Nobody mentioned a top fueler at all.

 

[toolmanmike]

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 hp/ cu in.
the 340 has .808 hp/cu in.
Huh, looks like the 273-4 wins that comparison. (even playing field)

9 times out of 10 the larger engine is going to have more power. No reason to compare the two.

If you want to compare something closer to the same than a engine that has XX more cubic inches, compare a 283-2 CHevy or may be a 289-2 Ford to a 273. Those are much closer. I happen to have owned a couple 273-4 and I think they are quite impressive for a factory engine. Don't look down on or make fun of guys that like their 273's. Compared to something bigger, what you own is probably not superior.

 

[273]

I think for 90% of people the are just looking a decent powerplant even if power isn't much of a concern would still be better off with a stock 5.9 Magnum or even the 5.2 version with 4bbl and duals. No one likes a dead car thats why every modern family sedans have a better power to weight ratio than most muscle cars add efi and OD for even better drivablity. And for those that want a bit of performance add cam headers gears and stall. If you got to ask if you should upgrade from a /6 273 or even 318 the answer is probably yes or other wise you'd already be happy and wouldn't of questioned it.

 

[toolmanmike]

I think for 90% of people the are just looking a decent powerplant even if power isn't much of a concern would still be better off with a stock 5.9 Magnum or even the 5.2 version with 4bbl and duals. No one likes a dead car thats why every modern family sedans have a better power to weight ratio than most muscle cars add efi and OD for even better drivablity. And for those that want a bit of performance add cam headers gears and stall. If you got to ask if you should upgrade from a /6 273 or even 318 the answer is probably yes or other wise you'd already be happy and wouldn't of questioned it.

Yep. There's always bigger. (not necessarily better but usually more powerful)

 

[ir3333]

and on the 7th day, God created the 340!

 

[66fs]

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.

I've had them all and built them all every which way. Kept the 273's and 340's. Sold all the 318's and 360's. Don't give a darn about torque, that's what gears are for. It's not high performance if it does not rev to 6k. 273's are a lot different than 260 Fords and 265 Chevy's. 273's have better heads, forged crank, solid cam and adjustable rockers that 318's do not have. Not the same dynamic, but you keep plugging away. I would love to get any 273 at give away prices, just like the "Thermo Bogs", Quadra-Junks, and 71 Air cleaners I used to get.

 

[273]

Yep. There's always bigger. (not necessarily better but usually nore powerful)

I've read your build a few times, and would be a good build for most who want to do a 273 should follow, I know you know if you did similar to a 360 you'd have a lot more power but obviously you're happy with what you done. But for most if they just dropped a good running or a refreshed Magnum between the frame rails would more than enough satisfied with little effort and or thought. Magnums are arguably the most powerful stock small block, with no need for more than highway gears and stock stall and more than enough under 3000 rpm to idle driviblity power.

 

[273]

Don't give a darn about torque, that's what gears are for.

Totally agree

 

[66fs]

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.


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


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.

A good response to you will take a while. Maybe tomorrow morning.

 

[66fs]

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.

Maybe tomorrow morning I'll try to answer your post.

 

[NC Engine Builder]

It would be pretty hard to have a intelligent discussion with anyone who says "he doesn't give a darn about torque" and thinks the requirements for a high performance engine are being able to rev to 6k. Which, by the way, any decent sbm can rev to 6k and beyond, even the lowly 318 two barrel.

 

[nm9stheham]

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.

There ya go..... roger, a flat top piston .070" in the hole cannot match the CR of an eyebrowed piston .012" in the hole. 0.6 points higher with the KB's all else being equal. Plus the piston in the hole can' have quench and won't have the valve clearance. But the 526AP's are a $500-550 + or - cheaper route in the 318, once you factor in the piston cost and balance work for the KB's. (You can do it for < $350 difference with the right local shop and some info.)

 

[ir3333]

Ya but I vote for the underdog.

I never vote for the underdog...unless it's me

 

[pishta]

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.

Debunked here: 273 & 318 Connecting rod weights

273-2 had a helluva piston pin. So much as to make it the same weight as a poly 318's bobweight. 273-4 had a thinner wall pin to offset the taller pistons weight.

 

[RustyRatRod]

The 273 is absolutely worth rebuilding. Personally love to keep classics with their original engine size. They already have a forged crank and with a little head porting or porting in combination with valve size increase and notching cylinders, tailoring cam specs depending on gears and headers plus a good intake manifold matched to heads they are most impressive even a modded non commando lower compression 2bbl setup. Also they love cfms once modded just like all mopar small blocks. Will never be torque monsters so gearing is critical.
Here is video of nasty 273 in my 65 Dart rt. after build began. Had about $3700 in engine build.

I love that! It sounds really good.

I really like the little engines. Of all of the smaller small blocks, Chevy 283, Ford 289 and I'll even throw in the Pontiac 326, to me, the 273 has the most potential. We all know how well the Mopar heads flow in comparison. I don't think anyone would be disappointed investing in a good 273 build, as long as it's for a street car. Even a drag car would have a level of coolness with a 273. I like them.

 

[pishta]

I've had them all and built them all every which way. Kept the 273's and 340's. Sold all the 318's and 360's. Don't give a darn about torque, that's what gears are for. It's not high performance if it does not rev to 6k. 273's are a lot different than 260 Fords and 265 Chevy's. 273's have better heads, forged crank, solid cam and adjustable rockers that 318's do not have. Not the same dynamic, but you keep plugging away. I would love to get any 273 at give away prices, just like the "Thermo Bogs", Quadra-Junks, and 71 Air cleaners I used to get.

You missed the part where my 318 had all that: retained all the 273-4 parts, 'cept the pistons and the block. Same heads, same cam, same rockers.....Same everything cept +45 inches. I found the added torque in the increase in displacment and didn't lose a beat in the ability to bounce the needle off 7K on the slow SW tach. Didn't seem to miss the higher compression at all.

 

[273]

It would be pretty hard to have a intelligent discussion with anyone who says "he doesn't give a darn about torque" and thinks the requirements for a high performance engine are being able to rev to 6k. Which, by the way, any decent sbm can rev to 6k and beyond, even the lowly 318 two barrel.

The reason to not give a darn about torque, cause unless your competing over dyno numbers, it what gets to the ground which is more important. Torque is mainly based on size in a NA engine , same with powerband and needed gear which tends to even out if everything is setup optimally . Say an engine needs about 650 cfms of fuel and air to make 400 hp and both engines have a VE of a 100%. A 440 at 5100 rpms will displace 650 cfms of air, a 340 will need 6600 rpm. A 340 is about 3/4 the size of a 440 and a 440 needs 3/4 of rpm than a 340 to displace the same amount of air. "cid x rpm / 3456 = cfm" Most mid built engines will make 1.15-1.25 lbs-ft per cid so say 1.2 per cid. So would give a 340 408 lbs-ft and 440 a 528 lbs-ft.

So say a 400 hp A body does 115 mph in quarter mile and you want to hit peak power at the finish line, a 440 would need a 3.70 gear to turn 5100 rpm and a 340 would need 4.78 to turn 6600 rpm. Again 340 is about a 3/4 of a 440 and 440 needs about a 3/4 as much gear. Now times torque by gear to see whats going to the ground 528 lbs-ft x 3.70 = 1954 lbs-ft for the 440 and 408 lbs-ft x 4.78 = 1950 lbs-ft for 340, Hp is what counts the rest is proportional, if geared right everything tends to equal out.
There's no free lunch, cubic inch don't give bonus power ie. torque.

 

[RustyRatRod]

A 273 has plenty of torque to move an A body. More than a slant six and how many of those were put in A bodies?

 

[Wyrmrider]

street takes torque
you want to rev and row the gears with a low rear end
that's a different build
more of a sports car
Duntov drove a big block vett automatic

 

[RustyRatRod]

street takes torque
you want to rev and row the gears with a low rear end
that's a different build
more of a sports car
Duntov drove a big block vett automatic

He also owned and drove a lot of 265s, 273s and 327s, so get outta here with that nonsense.

 

[rumblefish360]

There's no free lunch, cubic inch don't give bonus power ie. torque.

LMAO!

Yeaaaaaaaaaaaaaa

Oooooooooooooooooo
Kayyyyyyyyyyyyyyyyy

 

[rumblefish360]

A good response to you will take a while. Maybe tomorrow morning.

Well, first things first, I, in no way shape or form will discourage you or anybody from building what they want how they want for what ever purpose there targeting. Also, as mentioned above, I have sat in the passenger seat of some pretty impressive 273’s.

I myself will always take the same stroke engine and move to the larger bore size every time for power production in all areas for all purposes.

 

[nm9stheham]

The reason to not give a darn about torque, cause unless your competing over dyno numbers, it what gets to the ground which is more important. Torque is mainly based on size in a NA engine , same with powerband and needed gear which tends to even out if everything is setup optimally . Say an engine needs about 650 cfms of fuel and air to make 400 hp and both engines have a VE of a 100%. A 440 at 5100 rpms will displace 650 cfms of air, a 340 will need 6600 rpm. A 340 is about 3/4 the size of a 440 and a 440 needs 3/4 of rpm than a 340 to displace the same amount of air. "cid x rpm / 3456 = cfm" Most mid built engines will make 1.15-1.25 lbs-ft per cid so say 1.2 per cid. So would give a 340 408 lbs-ft and 440 a 528 lbs-ft.

So say a 400 hp A body does 115 mph in quarter mile and you want to hit peak power at the finish line, a 440 would need a 3.70 gear to turn 5100 rpm and a 340 would need 4.78 to turn 6600 rpm. Again 340 is about a 3/4 of a 440 and 440 needs about a 3/4 as much gear. Now times torque by gear to see whats going to the ground 528 lbs-ft x 3.70 = 1954 lbs-ft for the 440 and 408 lbs-ft x 4.78 = 1950 lbs-ft for 340, Hp is what counts the rest is proportional, if geared right everything tends to equal out.
There's no free lunch, cubic inch don't give bonus power ie. torque.

Not trying to be personally critical, 273, so please don't take this to heart as an insult; just trying to work this out. The above is a false argument; the only thing that this says is that the example 340 and 440 engines are equally efficient at the same airflow, which is the case since you picked the flows and power per ci to be equal. It is a meaningless argument as to the effect of displacement.

Real world, the airflow will not be equal at all; we work to make the airflow adequate to support the cubes. So torque/HP output will not be equal vs cubes. A quick look at BB vs SB port flows will tell the story.

Can't agree on the thought that considerations of torque are not important. In some racing forms, it is a far, far better measure of overall performance than peak HP. Peak HP for 4 stoke engines like we typically build here is a convenient and direct indicator of 1/4 mile performance, so is useful as a measure of performance in the drag race world.

 

[66fs]

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.


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


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.

First, I'm not talking theoretical mumbo jumbo. My brother and I ran 273 Barracuda's and put 500,000 miles on them. He still has his and my 64 was replaced with the 66 only because of accidents. I have had a 71 340 Duster and a 73 318 Dart. Still have the 273 Commando Formula S. If one is starting with a nice A body with a 273, imho there is no need to swap motors. All one needs to do is freshen it up, get some 340 valve springs, a solid cam (260-268 and .425-270 lift) from Isky, Racer Brown, etc and it will make an instant high revving 260 HP engine with 2 barrel pistons. Nice street manners and good mpg. No extra motor, no new transmission, no new rear end, no headers.

What are the chances of finding a 67 318 in good condition? The only one with a forged crank and the good 273 heads and decent compression. Most are very low compression absolute dogs, but that can be remedied with pistons anyway. I don't like Hypereutectic pistons. When they fail they take your whole engine out. MOPAR cast cranks are not a problem as you know. It is just a plus.

To turn a 318 into a 340 is easy, used to do it all the time. No need now, as for the most part, I don't do work for anyone and I have 340's. You simply put the good stuff: 360 heads; intake; carb; cam; valve springs; high pressure oil pump spring; windage tray; and double roller timing setup on a 318 with at least 9.0:1 pistons and good rings. Just like they did to the 360 when they retired the 340. Bore the block as little as possible, .005 .020? Bore size is not as important as head flow.

 

[rumblefish360]

First, I'm nor talking theoretical mumbo jumbo. My brother and I ran 273 Barracuda's and put 500,000 miles on them. He still has his and my 64 was replaced with the 66 only because of accidents. I have had a 71 340 Duster and a 73 318 Dart. Still have the 273 Commando Formula S. If one is starting with an nice A body with a 273, imho there is no need to swap motors. All one needs to do is freshen it up, get some 340 valve springs, a solid cam (260-268 and .425-270 lift) from Isky Racer Brown etc and it will make an instant high revving 260 HP engine with 2 barrel pistons. Nice street manners and good mpg. No extra motor, no new transmission, no new rear end, no headers.

Sorry 273, I see a lot of mumbo jumbo.
Bottom line, an extra 45 cubes due to bore size will make for a more powerful engine in HP and TQ across the board when otherwise equally equipped. What ever you do to the 273, I get to do to the 318. The 318 wins.

What are the chances of finding a 67 318 in good condition? The only one with a forged crank and the good 273 heads. Most are very low compression absolute dogs, but that can be remedied with pistons anyway. I don't like Hypereutectic pistons. When they fail they take your whole engine out. MOPAR cast cranks are not a problem as you know. It is just a plus.

The chances? I’d call it even. And that chance I’d call piss poor. That is a 52 year old engine. I stated that the low compression of the 318 can be fixed by a low dollar head killing which is worth the cost of indeed you “NEED” that extra compression.

To turn a 318 into a 340 is easy, used to do it all the time. No need now, as for the most part, I don't do work for anyone and I have 340's. You simply put the good stuff: 360 heads; intake; carb; cam; valve springs; high pressure oil pump spring; windage tray; and double roller timing setup on a 318 with at least 9.0:1 pistons and good rings. Just like they did to the 360 when they retired the 340. Bore the block as little as possible, .005 .020? Bore size is not as important as head flow.

You can turn a 318 into a 340 easy?
Oh please due tell! I have yet myself find a 318 able to accept a over boring of .130. Is it possible? I just haven’t seen it.

Now about head flow. I agree. How that enters in the cubic inch engine vs. engine discussion when basically, from where I stand, they use the same head. The particulars of the exact head castings used on the engines throughout there run years and the flow rates of these heads I don’t have known in my head or even bother to keep on paper/lap top/ stone carvings.. LOL!
As I said, “Basically there the same head.”

Do you have a reliable chart that YOU personally flowed? A trusted friend? Some wacko internet source?