273 or bigger?

just a question I have a old 273 thinking of using it to drag in a small car maybe a turbo different heads higher compression and a good cam not worth the time or good idea

Never messed with one, but my understanding is the 273's small bore size limits the valve diameter if you install better cylinder heads.

Not worth time and effort. Small bore limits head valve size. Also rebuild kits are a little more expensive.

Buy a 360 block and move forward.

yes if you go like x or heads its stock bore now but I could go bigger I interested in bore and stroke ratio if good to go turbo

Turbo equal more air. Small valve chokes it.

How much over std bore allows 2.02 valves in a 273?

Nonetheless, all the money and effort of a turbo to save $200-400 on a 360 block and crank? If you are making 1hp/1cid (which you should at least) you are theoretically giving up 87 hp picking a 273 vs 360.

makes sense thanks

Sell it to someone that needs one for a restoration.

or who owns a 1966 Dodge D-DART ...

I have a warmed (cam, Alum 4 bbl, Electronic MSD, headers, windage tray, valley tray) over rebuilt 273 that was in a 62 b body I bought. It is strictly a cruiser. I was truly surprised how peppy the car was with a 4 speed. At first i expected to ditch the 273 asap, but soon changed my mind.
Most "think" the 273 motor as high revving, its more a long stroke small bore torgue motor in the LA family, IMO

My suggestion, a 318 can be had for free almost, and you hvce 45 more cubes out of the box. Best bang, is a 360. mods are all the same pretty much on all the LA's. I would consider putting the 273 on the shelf.

There is no replacement for displacement
There are a time and place for all things, the idea of a 273 being built because you have it has not found any place in my mind, step up now to a better starting platform

If you like doing more with less like I do, keep the 273. My '65 Valiant four door went a best of 12.72 ET at 108 MPH with the small valve, stock cylinder heads (port matched to 340 intake/header gaskets).

Later,the same .060 motor was used with 340 cylinder heads (cylinder bores notched for intake valve clearance). With the 340 heads, the vehicle never broke out of the low 13 second bracket. All I could figure is I lost considerable compression after installing the open chamber, bigger valve, 340 cylinder heads.

With the 273, I used a 4.56 sure-grip (super stock springs), Mopar four-speed was launched and shifted at 6000 RPM and trap speed hit 6400 RPM. It did have a bad ass camshaft, the full competition Isky 312 degree (advertised) .580 lift monster. That did not keep me from cruising Main Street on the weekends (Salinas, California).

I had a 273 4bbl in a 63 dart 4 speed really peppy and with a low gear set got off the line well

awesome id like to put it into something light and small and mayby turbo

The 273 cannot by any stretch of the imagination be called "long stroke". It was oversquare, bore 3.625, stroke 3.31. It had exactly the same stroke as the 318 and the 340.

The 273 piston was so light that the factory used special heavy pins to get the bobweight to the same value as a 318 so they could share the 318 crank and rods.

The 273 liked GEARS. Someone mentioned 4.56s, that's what I mean.

It's true, I have been given three 318s over the years. And it has 45 cubic inches more and will rev the same as a 273.

It would be a fun project to turbocharge a stock 273. You could get your tuning experience with a throwaway engine. Then when you'd learned how to turbo an engine, you could move to something bigger.

My dream for a 273 would be 3.58" crank, 30 over for 300 cubic inches. You can easily take 200 grams off each piston/rod combo. If you have to buy custom pistons anyway, then it costs little to stroke it. So maximum 500 gram pistons and 600 gram rods. The smaller bore has less octane requirement so I'd go for 11:1 with a decent aluminum head. I'd use a Perf RPM and 750 Holley, headers and a mechanical lifter cam. The cam doesn't have to be overly large but it does have to rev easily. Bullet has lobes that are designed for this.

Yup, you could do the same thing with a nearly stock 360. And it'd cost a heck of a lot less. But strip out a '68 Dart and add a 5 or 6-speed transmission and it'd be a lot more fun on challenging roads.

It's your money, do what you can afford.

R.

If you're going to build for high HP or turbo, bang for your buck I think a magnum 318 or 360 would be a better buy. Stock magnum heads with a bit of cleanup would be a decent starting point for a turbo build.

I have a CNC ported set of 302 casting 318 heads done by Jeff of modern cylinder head with 1.88 1.60 valves that would be as good as it gets for a 273 head. They are a full SS deal with bronze guides and all never run. If you decide to go 273 PM me about em, Ill make you a great deal.

Aw, a 273 thread. I love those. Nothing wrong with a 273. Good little engines. My buddy who has been a stock racer for years ran 273s back in the 60s in Junior Stock.

There’s a lot of things you can do to a 273. The stock flat top piston with a 920 casting head garnered a respectable 8.8 to 1 CR, factory rated. With a little massaging its easy to get the motor over 9 to 1. Lots of things can be done to lighten the internals to bring up the revs.

As far as valves, the problem with larger valves is shrouding. You can get around that by cutting down a 1.88 valve to 1.82 on a .030 over bore block without the shrouding problem.

As far as heads the 920 is the best flowing head. With the 1.92 valves, stainless of course, some bowl blending and pocket relief the 920 will give the 273 more than enough airflow. Of course there’s the swirl port heads which seem to favor the 273.

As said, th 273 depends on low end torque which means steep gears. On my 273s I found 3.55s to be the gear to run on the street.

Nothing like a 2800 pound Valient with a 273 running a 4 speed and 3.55s.

273s running stock eliminator and super stock hold their own. Ask Paul Wong out of Division 7 and Matt Steen running a 273 in Super Stock that runs in the mid 10s.

Dogdays:"The 273 cannot by any stretch of the imagination be called "long stroke". It was oversquare, bore 3.625, stroke 3.31. It had exactly the same stroke as the 318 and the 340."

You realize I referred to the LA family of motors in regards to the "long stroke" comment. Forget "imagination", using real numbers, It would be accurate to designate the 273 as the least "oversquare" motor of the LA family I believe. In threads here on Moparts for overa decade it is common for members to comment about building a "high revving little 273", and its stroke/bore ratio is the opposite of the usual ratios sought for high revving, especially relative to the other motors in the LA family.

Having messed with Slants for the last 20 years or so, I hear all the time "a 170 will turn more rpm and be better than a 225". Wrong on both counts. Same thing here, when building a little motor from a clean sheet, why start out deeper in a hole than you need to? All you are doing is leaving free power on the table.