273 LA bored .040 change in performance?

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Barracuda 65

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I recently pulled the 273 LA engine out of my '65 Barracuda and found it has been bored .040 and crank and rod journals are .010, how will this effect compression ratio and/or horsepower. What would that do to change the cubic inches of the engine?
It has the stock heads and exhaust manifolds with no obvious changes on those.
Thanks
 
I recently pulled the 273 LA engine out of my '65 Barracuda and found it has been bored .040 and crank and rod journals are .010, how will this effect compression ratio and/or horsepower. What would that do to change the cubic inches of the engine?
It has the stock heads and exhaust manifolds with no obvious changes on those.
Thanks
Why'd you pull the motor out and how did it run before?
 
Won't matter enough to notice really. High compression pistons? That will make a difference. And the cam, and the heads, and the headers and the intake and carb.
 
I've heard if you remove the hood, fenders, and doors, all passengers and seats, they go a LOT faster
 
I was just curious it it made any difference. It had a rattle in the bottom end and we found the #8 Rod bushing was worn and had slack. All the rest looked good and no wear in the cylinders or journals. I'm replacing the hydraulic cam with a Comp cam kit and it has an Edelbrock 1406 four barrel and 75-80's intake(shown in earlier post). It ran strong but the rattle worried me.
I tried taking hood, doors, fenders and back glass out to lighten it but being winter time and snowy I backtracked!! Ha!!
Terry
 
toolmanmike....I like your rebuild info! I had a '66 Dart GT like that when I was 18 and ran the wheels off it drag racing. Had the HP 273 V8 and 4 speed like this Cuda I have now. Bad thing I found out later it was equipped with the factory drag pack that I wasn't knowledgeable enough to know about back then....now it's worth money as a rare setup.
 
65 cam was a solid. .040 overbore is +6 inches, 279. Compression usually stays the same as your bore is bigger and now you have a larger combustion chamber size too.
 
A .040 overbore by itself won't make a difference you can feel - just from the overbore anyway. Returning a worn cylinder to round, a fresh hone and fresh rings can add power through better cylinder sealing, and higher compression pistons can also add power, but the gain from just the overbore, probably 3-4 hp.

Formula for calculating the volume of a cylinder is pi times the square of the radius times height. Pi is rounded off to 3.14159 - or rounded ever further to 3.142. R is for radius. Radius is one half diameter, i.e., one half the bore. Because cubic inches measures piston swept area, H means stroke (not total height of the cylinder). So: pi times the square of one half the bore times stroke. Then multiply that number by however many cylinders you have.

Or - an easier way if you're mathematically challenged is just use this calculator: Calculate Cubic Inch Displacement

At that size motor, a .040 overbore will gain six cubes, as said above. A larger motor will pick up a few more than six cubes from a .040 overbore (a 440 gains eight cubes), smaller motor less.

As also pointed out above, every 1965 273 came stock with a solid lifter cam, just like all 318 poly motors and all slant sixes (until much later). If your 273 had a hydraulic cam when you pulled it apart, it was not original. Also, dunno if your 273 is hi-po or not but when it was bored oversize, it most likely got low compression pistons. That would be a horsepower loss if your 273 originally had 10.5 to one pistons, and the small overbore sure wouldn't make up the difference.
 
toolmanmike....I like your rebuild info! I had a '66 Dart GT like that when I was 18 and ran the wheels off it drag racing. Had the HP 273 V8 and 4 speed like this Cuda I have now. Bad thing I found out later it was equipped with the factory drag pack that I wasn't knowledgeable enough to know about back then....now it's worth money as a rare setup.
If it was a D Dart and you have any info on the car still @ddartdude would be interested in hearing more. We all would.
 
Are they all bored .040. We are on our 4th block. all .040 over. 2 low compression 4bbl motors taken from comando cars . I don't get it . My son ordered the correct pistons from EGGE. we started tearing all Todd's 273's down to find a standard bore block. All .040 over
 
Are they all bored .040. We are on our 4th block. all .040 over. 2 low compression 4bbl motors taken from comando cars . I don't get it . My son ordered the correct pistons from EGGE. we started tearing all Todd's 273's down to find a standard bore block. All .040 over
My 273 was standard when I rebuilt it. I went .030+ with the Egge HP pistons to replace the originals. I have no idea why his 273's would all be .040+.
 
.040 over bore, is just that, an over bore. It's not standard bore, if it was then what would the "undersized" bores be called?
 
With no other changes;
Switching from a solid lifter FT cam, to a FTH hydro with same after-lash .050 numbers, the hydro will loose some bottom end torque, about 1.2 to 1.5 psi per degree later advertised, Ica.
If at the same time you go one size bigger on the intake duration of the FTH cam, you could easily lose enough pressure to make the bottom end noticeably soft. The only cures are more compression ratio or a tighter LSA. The band-aids are a higher stall TC and more TM (Torque Multiplication).
 
Thanks for the input! the block numbers indicate it is a '67 -7 casting and I'm assuming that's why it had the hydraulic lifter set up. The pistons are not the high compression pistons as they have the 4 small dishes on the top. Hopefully I can get all this figured out so it will run strong, but not a race machine.
Thanks,
 
Since it's not original, and you're gonna re-do the motor anyway, swap in a common-as-dirt 318 block. The extra 45 extra cubes will gain more performance than getting (expensive) higher compression pistons for your 273. And everything else you might want to use with your 273 will work with that 318 block.

PS: I know from another thread that 273's have their defenders, theirs run great, blah, blah, blah. And yeah, you can build a decent running 273 if you really want to. But there's a reason people aren't even building 340's and 360's for the street anymore, given how inexpensive stroker cranks are these days. All other things being equal, the large the motor, the more power it will make.

Only reason I might recommend a mild 318 over a something like a 416 stroker to replace a basically stock 273 is that you begin making so much power you overpower everything else you have - trans, rear axle, heads, intake, exhaust, etc - so you end up having to upgrade everything else to make the extra cubes work.
 
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Not all 318 blocks are a straight install in place of a 273. Sometimes the motor mount bracket(s) need to be modified to bolt up properly on some years. Not a big deal, but, something to consider.
 
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