273 or NOT 273?

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67_Slimer

67_Slimer

Real Hot Rods don't shift themselves.
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So I'm a huge small block mopar fan , but overall like small blocks in any hot rods. High revving fun. Anyway currently have a pretty well built 340 in my dart and am looking to build another stock stroke 340 for future use , hopefully not needed anytime soon. So , Because the car is a 67 , I always had the thought of building a 12/1 high revving buzz saw 273 to mate with my 4 speed. Would want a low 12 second street car with my current setup (4 speed , 4.56s , 3200 lbs) Before I even think about this , I'm sure I will get talked out of it and that's what I'm looking for , well basically....Can it be done? If so , will it cost more than a 340 build? And how available are aftermarket internals? (Pistons) Basically , is it a waste of time?
 
I am a huge fan of the 273 but it will be a waste of time with those goals. You can spin a 340 as tight as a 273. That's a myth. They just sound like they are doing 8,000 rpm.
 
toolmanmike said:
I am a huge fan of the 273 but it will be a waste of time with those goals. You can spin a 340 as tight as a 273. That's a myth. They just sound like they are doing 8,000 rpm.
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That's what I'm thinking , same stroke , bigger bore , bigger valves. I'm just seeing if I was missing something.
 
67_Slimer said:
So I'm a huge small block mopar fan , but overall like small blocks in any hot rods. High revving fun. Anyway currently have a pretty well built 340 in my dart and am looking to build another stock stroke 340 for future use , hopefully not needed anytime soon. So , Because the car is a 67 , I always had the thought of building a 12/1 high revving buzz saw 273 to mate with my 4 speed. Would want a low 12 second street car with my current setup (4 speed , 4.56s , 3200 lbs) Before I even think about this , I'm sure I will get talked out of it and that's what I'm looking for , well basically....Can it be done? If so , will it cost more than a 340 build? And how available are aftermarket internals? (Pistons) Basically , is it a waste of time?
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Matt Steen's valiant with a 273 runs in the 11's but it is a purpose built race car. SS/KA index is 11.25. There;s a lot of 340 cars that don't run low 11's. Can you make 350-400 horse with a 273? You might be able to but why?
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4spdragtop said:
Do what you want but it's a proven fact, $$ per hp, the 273 is waayyyy more costly than a 340. 273 limitations is cubes and pistons.
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Yes sir, and with that small bore, stuffing big valves in there takes some carving.
 
You could always build a 318. Use 273 rotating assembly and high compression after market pistons. FWIW 65
 
The fun of building a 273 for horsepower is the mere fact you are using a 273. The Mopar small block that is the underdog. Building one makes a builder be creative to make more horsepower while trying to save money on the build. If you are a guy that wants a power plant that is indigenous to the car make model and year that makes it all the more satisfying to beef up the underdog.
 
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jeff alder said:
The fun of building a 273 for horsepower is the mere fact you are using a 273. The Mopar small block that is the underdog. Building one makes a builder be creative to make more horsepower while saving money on the build. If you are a guy that wants a power plant that is indigenous to the car make model and year that makes it all the more satisfying to beef up the underdog.
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Believe me , I want to build one just to say , Yeah , It's "only" a 273 , but I think the cost would be a lot more than a 340.
 
I imagine if i were to do it Id want the solid cam HiPo 273 version but I also am not one to make things difficult for myself and call it a "challenge" work smarter not harder...
 
We are building a 273 12-1 engine right now for an original 273 HP. customers car. Pistons are available through egge Egge Machinery Company | Pistons Mfg | Water Pump Mfg we bought a set of .040 over.

273's cost a little more to make Horse power due to small valve heads. If you want to use big valve heads the bores will have to be notched for the valves. . 273 forged cranks do not have the journals drilled due to the light duty rods. Use a 318 if you can't find a 340 block near you. Less machine work and more cubes right from the start. It will rev to any RPM you build it for.
 
toolmanmike said:
Matt Steen's valiant with a 273 runs in the 11's but it is a purpose built race car. SS/KA index is 11.25. There;s a lot of 340 cars that don't run low 11's. Can you make 350-400 horse with a 273? You might be able to but why? View attachment 1716334470
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NHRA super stock is a whole different world. He probably has huge money in the engine. Like 20-$30,000! And a $5000 transmission with light weight parts and bearings throughout. And the rest of the car is well sorted out to run those amazing times.

Not much similar to a bracket car or weekend hotrod.
 
I don't think it would be crazy hard to build a low 12 273, what's that 380-400 hp ?

First main obstacle is cylinder heads and valve size, well good thing 400 hp doesn't need that much of a head to get there. 66fs runs 1.88 valves no problem in a 273 bore with a little notching probably fit magnum valves size. So choices are port one of 273/318 heads with 1.78-1.92 valves or run 360/5.9 heads. I'd probably mildly port out a set of aftermarket replacement magnum heads.

Besides possible custom pistons, the rest is a fairly straight forward build cam gearing and stall choices are gonna make or break the build.

Ballpark say a 282 making about 1.2 lbs-ft per cid, = 340 lbs-ft peak say making about 90% of that at peak hp (306 lbs-ft).

400 hp x 5252 / 306 lbs-ft = 6,865 rpm, 400 hp @ 6,865 rpm and 340 lbs-ft @ 5500-6000 rpms. Obviously the better the torque (VE%, CR etc,,) the less rpm needed or vice versa.

Question is, is that what you want ? Combo wise it shouldn't be much different than any other 400 hp build.
 
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67_Slimer said:
Believe me , I want to build one just to say , Yeah , It's "only" a 273 , but I think the cost would be a lot more than a 340.
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Could always find a decent 273 short block milling and notch the block add lapped magnum heads, cam her up and see what she'll do, if you like the results then think of a full build.
Kind of what I think I want to try.
 
FYI, matt steins 273 runs 10.05 @ 131.78, with stock volume ports and stock size valves, stock carburetor, also its a light car. true its a good piece. also , theres a 65 b'cuda in stock, runs 12.20, and a 65 valiant in stock, runs low 12 sec passes. just food for thought.
 
perfacar said:
FYI, matt steins 273 runs 10.05 @ 131.78, with stock volume ports and stock size valves, stock carburetor, also its a light car. true its a good piece. also , theres a 65 b'cuda in stock, runs 12.20, and a 65 valiant in stock, runs low 12 sec passes. just food for thought.
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Completely irrelevant to the typical hotrodder street engine build. Matt Steins engine would take 40-50k to duplicate. And running 12s in the 1/4 mile these days is pathetic.
 
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