273 or NOT 273?

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polyjohn said:
Good thread with lots a different opinions!
My mate has just bought a 273ci 65 Coronet, the engine runs but needs a rebuild.

Firstly my thoughts were ''why bother'' put a 318 in there and save time and money.
Then he says '' 318-LA not available in 65 '' but who actually cares?

I wasn't talking 318-LA I was talking 318-POLY!
He says '' they is more expensive to rebuild than a 273ci '' oops...

So its a 273 versus Poly 318 '' (too expensive) scenario for him.
If its an 65 A-Body then its a 273 every time or don't bother.
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I would take a Poly too. Cool engines as well. I already have a Weiand intake just waiting for a car. :BangHead: :rofl:
 
polyjohn said:
Post 219 almost true for forged cranks.

The 318 forged crank was weighted for 318 pistons.
The 273 forged crank was weighted for 318 pistons.

Whats the difference here?
Monster sized 273 wrist pins to compensate for the imbalance.
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and just in general forged is heavier than cast.
 
The only problem with the 273 is the small bore size.
To make good power you need a 340 bore to make the heads flow properly.
The factory made a good performance engine in the 273 commando, but things have moved on.
Forged crank, fully floating pistons, adjustable valve gear.
Nice closed chamber heads that flow nice with 318 or 360 valves.
 
polyjohn said:
The only problem with the 273 is the small bore size.
To make good power you need a 340 bore to make the heads flow properly.
The factory made a good performance engine in the 273 commando, but things have moved on.
Forged crank, fully floating pistons, adjustable valve gear.
Nice closed chamber heads that flow nice with 318 or 360 valves.
Click to expand...
Cast cranks are much lighter and need external balancing which can be a pain.

From memory the 318 cast crank was still neutral balance so all good there.
Then the 340 got cast cranks in 72 and the external balance thing raised its ugly head.
Then the 318 got the heavier truck rod too and it gets complex in the 70's.

Its the big-blocks that suffer with the external balancing nightmares...:mob:
 
polyjohn said:
The only problem with the 273 is the small bore size.
To make good power you need a 340 bore to make the heads flow properly.
The factory made a good performance engine in the 273 commando, but things have moved on.
Forged crank, fully floating pistons, adjustable valve gear.
Nice closed chamber heads that flow nice with 318 or 360 valves.
Click to expand...
I should have put bigger valves in mine. But then I would really need a bigger cam and headers and................................. I stopped before it got out of hand. The head work came cheap from a friend that took a few die grinders in on trade. I have a few hundred in all the head work.

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Like my Daddy used to say, when push comes to shove, you Can't Beat Cubic Inches. That said, if you you can look away from price and power, a 273 would be a beautiful thing if that was what came in the car from the plant.
 
polyjohn said:
Cast cranks are much lighter and need external balancing which can be a pain.

From memory the 318 cast crank was still neutral balance so all good there.
Then the 340 got cast cranks in 72 and the external balance thing raised its ugly head.
Then the 318 got the heavier truck rod too and it gets complex in the 70's.

Its the big-blocks that suffer with the external balancing nightmares...:mob:
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yes, all LA/Magnum 318's are neutral balanced, and that's a good thing
 
66fs said:
You do not understand. A 318 "all" things being the same, will run very similar to a 273 but at a lower rpm. A 273 was a high performance engine with a forged crankshaft so no matter what you do to a 318, you have to do a lot to catch up. But not much of a price difference when rebuilding an engine, pistons, cam, etc. I also include 340/360 heads, carb, intake, distributor, and exhaust. You don't have to do anything to a Commando/Charger 273, it is all there, maybe a slightly larger cam.
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Thanks
 
ajarofclay said:
Like my Daddy used to say, when push comes to shove, you Can't Beat Cubic Inches. That said, if you you can look away from price and power, a 273 would be a beautiful thing if that was what came in the car from the plant.
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especially if it's the same block, crank, and rods. Bore becomes king
 
ajarofclay said:
Like my Daddy used to say, when push comes to shove, you Can't Beat Cubic Inches. That said, if you you can look away from price and power, a 273 would be a beautiful thing if that was what came in the car from the plant.
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That's why I rebuilt mine in my 66.
 
ajarofclay said:
Like my Daddy used to say, when push comes to shove, you Can't Beat Cubic Inches. That said, if you you can look away from price and power, a 273 would be a beautiful thing if that was what came in the car from the plant.
Click to expand...
Yes displacement of fuel and air (CFM), which Cid VE% Rpm all play a role NA in the amount of CFM your engine can displace, the true displacement of your engine. And CFM amount within a narrow range pretty much equals HP .
 
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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I had a 65 Dart with a 273 Commando engine. I had to have pistons made as i couldn't find any after market ones.
 
It’s all about piston choices for any build. What compression you want and is it a street or strip engine. a
A straight six car would benefit from a 273 as an upgrade, but 318’s are much more common.
Haven’t seen any high compression 273 pistons for many years, so if you have a complete 273 just swap all the parts onto a 318 block with many more piston choices at affordable prices.
The 273 closed chamber head is a wonderful casting and any 318 build would be greatly enhanced.
Keep it Simples…:thumbsup:
 
a 3.0 mercedes td six will easily make over 500hp while doing 40mpg..... just saying.
plus it's sort of in the family, at least these days anyway.
much smaller and lighter than a 6bt cummins too.
 
A 273 definitely a huge step up in performance potential then a /6, most built NA /6 probably don't even make the power of a stock Commando, A well ported /6 head flows like a port on a stock 273 head but a 273 has two more sets of ports nevermind porting and or other sbm heads available plus all the other performance sbm parts available. They maybe somewhat close in displacement but miles apart in potential. But /6 is a kewl little engine glad people hop them up :)
 
Beams said:
@67_Slimer any update based on discussion with your engine builder? I’m with @toolmanmike …I want to see someone build and dyno a hot 273.
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I'm talking to him Saturday. Bringing my 340 block by and he's going to check it out. I will pick his brain but I'm pretty sure he's going to ask why , if my 340 block checks out , I should build that. Lets face it , my current 340 in my car is faster than the 273 I'm looking to build. I think I'm trying to be that different guy but in reality , I'll just build my 340.
 
4eighteener said:
There is definitely an overwhelming interest on this site for a high performance 273 build.
Maybe like toolmanmike says, someone will do it, document it, and dyno it.
With this interest, a go fund me is in order!
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oh?? LOL
 
67_Slimer said:
I'm talking to him Saturday. Bringing my 340 block by and he's going to check it out. I will pick his brain but I'm pretty sure he's going to ask why , if my 340 block checks out , I should build that. Lets face it , my current 340 in my car is faster than the 273 I'm looking to build. I think I'm trying to be that different guy but in reality , I'll just build my 340.
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Hard to argue against a 340.
 
The YT super crew couldnt or didnt do it with a 318 so...I think the caveat that kills them is the notion o f "doing it cheap"
 
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