Information on the 273

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as for heads, has to be original 920 or 302, not sure if edelbrock aluminum is allowed. port volumes and chamber volumes have to be same as stock, also valve sizes. heads can be ported , welded , epoxyed, must retain stock volumes.
 
The blocks are identical PN and dimensions, whether the regular 2 bbl or the 4 bbl Hi-Po version. I think that includes the crank and connecting rods. Only the pistons varied. You can buy special Hi-Po pistons today (Egge?), to give higher compression. The 1964-65 heads have bolt angles ~16 deg off vertical (rough guess), which requires special manifolds (factory or old after-market, no new offerings). In 1966, they changed to 45 deg like 318-360 small blocks, so regular intake manifolds will bolt up, though some have taller intake ports. Magnum heads will bolt to all SB blocks, but have vertical bolt holes for their beer-keg intake, though I think you can get aftermarket Magnum heads with 45 deg bolts or regular intakes w/ vertical holes for Magnum heads. So, might bolt any combination of heads and intakes to a 273 block, if the valves will clear the smaller bore of a 273 (some even file the block for clearance). 273 heads are preferred even for a 360 block since their closed-chamber design gives higher compression.

I think all SB blocks, incl Magnums, can use the same head gaskets. But, those will have a too-big hole in a 273. Some people buy NOS 273 gaskets or custom-made ones for the ideal hole. May not be a problem if carbon fills the space over time to get rid of the gap volume, and the gaskets fire-ring will definitely be better protected from flame. You could even make a 273 into a cheap MPFI engine by bolting on intake and beer-keg intake, and add the Magnum flex-plate w/ "toner ring". You cut a hole in the transmission bell-chamber to fit the crank sensor on a bracket (search photos). Could also bolt on a Magnum transmission, which gets overdrive, but must reform the trans tunnel for clearance. Most people have just bolted in an entire Magnum engine and transmission. The Magnum distributor should drop into the block. The engine controller is fairly stand-alone, requiring just a few wires from the car. But, wouldn't give the proper open-loop fuel flow for a 273, so better to use an aftermarket controller or perhaps booger with the Pman signal to fake it for lower fuel flow.
 
The development of the 273.

They took many off the shelf parts from the A engine Poly 318 to save money. They modified the block casting a bit. They made new heads for the 273. They used the same Poly 318 Dizzy, timing chain cover, oil pan, forged crank and forged rods but for the simple fact the 273 piston was so much smaller and lighter, they had to add some 'BOB' weight to the piston.
So they put in some THICK wall connecting rod pins (Wrist pin) to bob weight the pistons the same as a Poly 318s piston. From memory, I do not think a 5/8's drill bit will fit inside the 273 wrist pin, its that big.

Put some modern tech light con rods in the piston and shave 5 pounds off the crankshaft. NOW TALK ABOUT A REV MONSTER! With proper valve springs you have a 8,000 to 10,000 RPM engine.

Bore it 0.040" and put a 4 inch stroke crank and have a 340 Ci

Rumors back in the 70's was you could not put a hyd cam in the 1964/65 273. WRONG!

Edited for Wrist pin.
 
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With the factory stock 273 cylinder heads (1965) I would find some traces of coolant under the hood once in awhile at the drag strip (Fremont Raceway circa 1973-1976). I later found (when refreshing the motor) a hairline crack in one of the cylinder heads. Not sure if that was a common problem back then. Converted to 340 cylinder heads but ran slower in the quarter mile than when had been using the factory 273 heads (I guess the open chamber 340 heads resulted in a massive loss of compression, even with the 273 domed four-barrel pistons).

65 Valiant moter head on shot.jpg
 
I tuned one once in a 69 Dart. it ran close to 30 mpgsUS.
But you know, the best part of the 273, is that in metric, it is a 4.474 liter, so you can legitimately call it a ........ Four-Fourty-Seven...... lol
 
BillGrissom said:
You could even make a 273 into a cheap MPFI engine by bolting on intake and beer-keg intake, and add the Magnum flex-plate w/ "toner ring". You cut a hole in the transmission bell-chamber to fit the crank sensor on a bracket (search photos). Could also bolt on a Magnum transmission, which gets overdrive, but must reform the trans tunnel for clearance.
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You'd have to swap cranks or modify the (early) 273's crank flange to fit the later OD transmission- remember, all pre-'68 engines had the smaller register for the convertor snout.
 
They are fantastic engines. Not a thing wrong with them. The only drawback is, the correct head gaskets are hard to get. Probably need to have them custom made through Cometic. The standard small block head gasket will work and seal fine, but the gasket bore is pretty large for the small bore 273 and you lose some compression through the head gasket volume.
 
ethan santin said:
Hey there,

Ive gone and done some reaserch and have read some articles about the 273 already but I am very intrested in what anyone who has owned or owns a car with a 273 in it has to say about them. What makes them diffrent from other mopar small blocks? What kind of issues do they have? I would love to hear any general information about them if your willing to share. I personally dont own one, but ive seen and worked on a lot of mopars but haven never seen or worked on a 273 so I am just genrally curious about them.

Thanks for reading.
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There’s some things you can do to make the 273 a little screamer.
 
I used a 4.56 rear end ratio in my 273 bracket racer, launched and power-shifted the four-speed at 6,000 rpm and the trap speed on a good run was 6,400 rpm and still climbing. Looking back on it now, the way it was still roaring and accelerating at the quarter-mile mark, I believe the vehicle would have benefited more from a 4.88 or even a 5.12 rear end ratio. As it was, we had best of 108 mph at 12.72 elapsed time with the four-barrel 600 CFM Holley double pumper.

65 Valiant1 edited.jpg
 
dart4forte said:
There’s some things you can do to make the 273 a little screamer.
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Good thing about 273 is if you like rpm I don't take much to get a larger engine to spin takes serious head flow with 273 a mild prepped 360 head is all you need.
 
My 273 short block awaiting the heads. Heads will have stainless 1.84 valves cut down from 1.88s, stock stainless exhaust valves. Comp valve springs to match the E4 Isky grind.

The forged pistons are cut down so I can keep the CR reasonable for the crappy gas we have.

53CCEC08-F6B3-495B-A105-83C5BB3765F5.jpeg
 
a 3 angle valve grind on a 360 head will make a lot more flow over a prepped 273 head, the 188 valve does fit, in the bores, last time i flow tested difference was bout 25 cfm per port.
 
perfacar said:
a 3 angle valve grind on a 360 head will make a lot more flow over a prepped 273 head, the 188 valve does fit, in the bores, last time i flow tested difference was bout 25 cfm per port.
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Just should not do it with a low compression 2bbl 273 or you will have a dog. and you must use a 340/360 head gasket or the fire ring will be in the chamber. Even lower compression....

I had a 1965 Dart GT, 273 0.040" over with the TRW piston crown 0.075" above deck.
We bowl worked and ported a set of closed chamber 273 heads and put back cut 1.88 intakes and a back cut 1.50 ex valve in. With a Carter 625 CFM AFB, 340 resto cam, a set of modified 340 A body iron ex manifolds to fit the 883 trans and 3.23 in a 8 3/4 SG.
Did not have the cash to have them flowed back in 1975 but the 'Butt Dyno' said it was quicker. Daily driver till 1985 when I traded it in for a 1984 Shelby Charger in Augusta GA.

I would kick my friends 1984 Z28 5.0L 5 speed's butt all day long. He had headers and was chipped.
 
thats why, we measure chamber volumes and surface heads, to know what compression will be,
 
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