Is there a simple/easy way to ID a 273 engine vs 318?

[67Dart273]

...........And please,...........PLEASE.........do not call a "poly" engine a "wide block."

 

[cosgig]

To get more air into engine bay…my dad street raced it so I guess he thought it needs more air

Is that really the most distinctive difference between the two? (I already know the answer, but I have to ask)

You asked for a quick and easy way to determine if it’s a poly or an LA motor. If you want to know the displacement of the motor, I already posted to look at the front of the motor below the head on the drivers side. It will have a letter year stamp along with the displacement.

If you want more quick and easy clues, after 1965, the intake bolts take a 9/16” wrench, 64/65 and possibly earlier polys use a 1/2” wrench.

 

[AJ/FormS]

For stock SBMs equipped with autos;
Measure out about 220 yards, then, step on the gas.
If watching grass grow is more exciting, that would be a 273 2bbl.
If you can measure how long it takes with a sundial,
it's a 273-4bbl or smog-era 318
If the car manages this in less than half a minute,
then it's an early hi-compression 318 or a 2bbl 360.
If you actually need a stopwatch, it's a 340, or a 4bbl 360.
If it burns both 295s all the way;
it's a 360 and a daymn fine one

Yes I'm kidding;
I gave the 273 far more credit than was due........ lol.

 

[RustyRatRod]

Is that really the most distinctive difference between the two? (I already know the answer, but I have to ask)

Not really. Not by a long shot. The heads are totally different and much wider. That's one reason people incorrectly call them a "big block 318", which of course they never made. I've also heard them referred to as a "wide block" 318, which is somewhat accurate, since the heads do make the engine appear wider, but the LA and Poly blocks are basically identical in size and shape. When an LA and Poly are side by side, the differences really stand out. But yes, by far the quickest way to ID the difference is the number of valve cover bolts and shape of the valve covers, but as I said earlier, those are hardly the only differences.

 

[cudamark]

I'm looking at a '67 Windsor-built car that the VIN says had a 318 (which means it would have been a polysphere).

The current owner (who to me has an unknown level of familiarity with vintage Mopar mech/tech) says the car has a 273. Maybe someone told him that, and he doesn't know any better. I don't know.

I haven't been to the car, it's a bit of a drive for me.

Is there an easy way to know if it's a 273 vs 318? I have an LA318 in one of my cars and I know it's impossible to see any block stampings with the exhaust manifold in the way.

A vs LA engine, easy. Look at the shape of the valve covers, or, have the seller send you photos. LA273 vs LA318 not as easy. You need to look at numbers.....both casting and year/size stamped codes. You've already been advised to scrape the top of the driver's side block in the front just below the head gasket seam. That will usually give you the year and engine size. The block casting above the starter is another good indication of engine size, or, at least a number to look up to find out. Later (as in '69 and newer) will usually have a year and partial VIN on a machined pad on the passenger side down by the pan rail and about in the middle. If it isn't the original engine, why worry about which it has in the purchase? Is it a make or break deal if it doesn't have the one you want? If it's a good enough body, put in the engine you want.

 

[cudamark]

My 66 273 doesn't have "273" by the casting number but the casting number tells the story. This # is for 64-66 273 only. There was also a #2806130 for some 65's and up to 69 when 273 production ended. I don't see any LA 318's that share the same casting numbers.

View attachment 1716188738

The '68-9 273's I've seen have the -273 after the casting number. As you mentioned, the earlier ones don't. Easy enough to look up though.

 

[toolmanmike]

I'm out. If the op hasn't figured it out by now, I can't be of much help.

 

[J-c-c]

As to the story of this car, who in their right mind would replace a 318 with a 273 in a C-body? A convert C-body at that? Even if that happened 30 years ago, where would you get a 273 from? It would have been a no-brainer to replace it with an LA318 if anything (but a 383 would naturally been more logical).

I over a decade back bought from Spokane a 1962 Polara 500. The car came OEM with one engine option, a 361 4bbl with a 727. I bought the car sight unseen on Ebay. The car had a slightly warmed over 273 4bbl with a 4 speed. That lack of originality I believed depressed its desirability on Ebay, No problem for me a 440 would drop in fine. Except when car arrived, I was surprised how peppy the car was, so I kept it and bought another to hot rod, studying all the supplied original owner's receipts, he made the swap right at the time of the 2nd US/world gas crisis in 1980, and I suspect that is the motivation for the swap. Guy was a bigshot? with Coors I believe.

 

[stillrunners]

Yep....a picture from the owner might help.....as far as a LA273 and a LA318 a quick look at the intake which will be almost flat on a 273 and a 318 will have more of a rise....if you can't see any #'s.....

 

[16richard]

For what it's worth I have a 67 LA 318 out of a 67 Canadian rag top monaco (orginally painted red ) replacing the orginal 273 .
In 68 they started painting them blue. Picture ?