273 parts interchange

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nutz

nutz

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so bought this 69 273 for parts for my oe 340 build
just started thinking maybe build a screamer out of it
what makes a 273 is it bore and stroke ....thinking could use left over parts from the 340 (have a set of .020 pistons extra rods ect )
going to tare it down tomorrow see if block/crank ect. is anygood
 

stock 273 bore 3.625
stock 340 bore 4.040 add in that +.020 and i don't think you get there

273 rods are lighter... 273 crank is already forged...
 
so some good heads and a cam 7500 rpms ....could piss off the neighbors
 
most say the short stroke makes a screamer, 273/318 and 340 are the same stroke. however there's plenty of 4" stroker motors spinning real high too so the old 'stroker's are low revving' myth is just that. decent pistons that'll hold together will be expensive for the 273 too. i guess the cheapest way to get to 340 cu in (and use your +20 pistons) is to overbore a 360 block. your 273 forged crank' with bearing spacers would work (if spacers are still available).
neil.
 
mygasser said:
most say the short stroke makes a screamer, 273/318 and 340 are the same stroke. however there's plenty of 4" stroker motors spinning real high too so the old 'stroker's are low revving' myth is just that. decent pistons that'll hold together will be expensive for the 273 too. i guess the cheapest way to get to 340 cu in (and use your +20 pistons) is to overbore a 360 block. your 273 forged crank' with bearing spacers would work (if spacers are still available).
neil.
Click to expand...
True top end (heads) is what makes an engine spin, 273 and 340 have similar air flow per cid compared to 318 and 360, why the former are the revvers of the family. Piston speed (stroke) can play a role but most aren't spinning high enough to matter. But it is a lot easier to feed a 273 to high rpms than a 408 but obviously gonna make less power per rpm though.
 
Yea it would be to just make noise
I bought the motor for the bolts ...
And I might modify the vc to look like 340s
Not even sure what the difference is yet
So they are all the same stroke ...the 340 rods would work that i guess is just free floating wrist pins
 
There is an enormous effective difference between a standard 2bbl 273 and the 4bbl Commando/Charger version. When people think of 273s as high-winders they are thinking about the 4bbl. Check out the different power curves in the right lower corner of this page — 2bbl upper right, 4bbl lower left. It's like a completely different engines.

67_back_cover.jpg
 
mvh said:
There is an enormous effective difference between a standard 2bbl 273 and the 4bbl Commando/Charger version. When people think of 273s as high-winders they are thinking about the 4bbl. Check out the different power curves in the right lower corner of this page — 2bbl upper right, 4bbl lower left. It's like a completely different engines.

View attachment 1716412459
Click to expand...
Yes, but they have the same heads so the same potential. Beside that your talking cam and intake which is an afternoon swap leaving cr as the main difference.

Problem making power (350-450 hp+) with a 273 is it needs lots of rpm (6500-7500 rpm+) to do so, with it's tiny bores limits valve sizes which makes it harder to make those power numbers and stock heads ain't capable. if you want 250-350 hp then that's more in a 273 wheelhouse needed more like (5500-6500 rpm). That's 0.92-1.28 hp per cid.
 
Yeah, all I was saying was, if he was starting with the 2bbl 273, there is nothing about it that is special. It has low compression, small bores, small valves... he could start with any other LA block and be ahead. But the graph shows what a difference compression and a cam makes...
 
mygasser said:
most say the short stroke makes a screamer, 273/318 and 340 are the same stroke. however there's plenty of 4" stroker motors spinning real high too so the old 'stroker's are low revving' myth is just that. decent pistons that'll hold together will be expensive for the 273 too. i guess the cheapest way to get to 340 cu in (and use your +20 pistons) is to overbore a 360 block. your 273 forged crank' with bearing spacers would work (if spacers are still available).
neil.
Click to expand...

If 6500 is revving up then this is true.

Not many 4 inch stroke small block mopars turning 7500 let alone 8500.

No one has the induction to make them run that high.

And 99.999% don’t want to go past 6500.
 
nutz said:
so bought this 69 273 for parts for my oe 340 build
just started thinking maybe build a screamer out of it
what makes a 273 is it bore and stroke ....thinking could use left over parts from the 340 (have a set of .020 pistons extra rods ect )
going to tare it down tomorrow see if block/crank ect. is anygood
Click to expand...
A 340 crank and rods will fit and work, but, overkill IMO unless you're trying to build a killer drag motor for some reason. Even then, I'd go with a billet crank and light weight rods for that application. Maybe if you were running some sort of special class car it would justify the expense, but, I just can't see it.
 
Yea it's rusty inside
Just going to junk it
Ill post parts..when I get pics
 
nutz said:
so bought this 69 273 for parts for my oe 340 build
just started thinking maybe build a screamer out of it
what makes a 273 is it bore and stroke ....thinking could use left over parts from the 340 (have a set of .020 pistons extra rods ect )
going to tare it down tomorrow see if block/crank ect. is anygood
Click to expand...
To get the .020 over 340 pistons in your 273 block, that's a .435" overbore. Yeah. Do that.
 
I couple of other things I need are the fuel pump drive and the cam plate
Are they the same as 340
I bought a timing cover so can sell that
And the oil filter "90" mine was supposed to be for a 340 are they the same
Is anything special about the heads or block intake
Or should I scrap them
Dont need extra junk around
 
nutz said:
I couple of other things I need are the fuel pump drive and the cam plate
Are they the same as 340
I bought a timing cover so can sell that
And the oil filter "90" mine was supposed to be for a 340 are they the same
Is anything special about the heads or block intake
Or should I scrap them
Dont need extra junk around
Click to expand...
the pump eccentric, thrust plate and all that jazz under the cover is the same.

(cue the arguments about the drilled bolt, tab dripper and timing chain oiling)

the 90's are the same, unless you want the "correct" part number.
 
Not that crazy...
Just stuff I didn't have ...
So stuff i need to save
 
There's a slight difference in the 90 degree filter adapters. The one on the right is from an early A body V8 car, 64-66. It is a true 90 degree adapter. The one on the left is from later motors. If you use either one in a 67 and up A body, it will work. If you use the one on the left in a 64-66 A body, the end of the filter will hit the frame rail because it is not a true 90. Not sure what car you're working on, just wanted to give you a heads up.

Post a pic of the .020 340 pistons if you can. Curious if they are factory or aftermarket.
90 degree adapters - SBM.jpg
 
69 dart 340 swap oe build
So the one on the 69 273 would be correct
I left the pistons with my machinist...
Trying to make as correct as I can for factory look
 
Either one will work on a 69 Dart 340. I have a 69 Dart GT convertible that is all numbers matching and has a 273. Motor has never been out or apart, and it has the early style, true 90 degree adapter on it. I guess the factory was using all those up before they started with the slightly tilted ones.
 
marksmopars said:
My machinist wants $100 per hole to bore and sleeve, maybe a build your own 340.
Click to expand...
i have a 69 340 block,heads,intake ,exhaust ect.didn't have any bolts,and a couple of small parts
block came with crank couple if sets of rods and pistons ..but has rust pitting in one cylinder ...not sure how much over it will have to go
if its too much or only one might sleave ....still collecting parts now ....but list is getting short ..v/c is the last only 340 i need ..not sure what is differnet then the 273 one i just got i know 69 is one year only
 
nutz said:
i have a 69 340 block,heads,intake ,exhaust ect.didn't have any bolts,and a couple of small parts
block came with crank couple if sets of rods and pistons ..but has rust pitting in one cylinder ...not sure how much over it will have to go
if its too much or only one might sleave ....still collecting parts now ....but list is getting short ..v/c is the last only 340 i need ..not sure what is differnet then the 273 one i just got i know 69 is one year only
Click to expand...
Not sure what your asking seem like you want know the differences ?

273 318 340 all have the same stroke 3.31" the bore is what gives the different displacement 3.625" vs 3.91" vs 4.04" other than pistons most parts can be swapped around.

2bbl 273 and 318 basically are very similar equipped engines besides bore, 340 is a performance only engine, came with better heads rods intake cam etc.. later 360 used a lot of these parts.

There is other differences, what do you want to use from the 273 ?
 
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