So by all means, I'm not very knowledgeable when it comes to engines as I haven't delved into that subject to much in my personal studies. I asked a couple months ago about boring a 273 to 340 specs and you guys said it couldn't/shouldn't be done due to the webbing between the cylinder walls. Simply, there's not enough meat. However, IIRC, you guys said the 273 and 318 blocks were similar. So theoretically speaking, if I really wanted to, I could buy a 390 stroker kit, bore out the 273, and purchase heads, intake, and carb compatible with the 318 and have myself an engine?

I way back suggested in that thread, I admit now, tongue in cheek, that you bore out the 273 some number like .353?, which would have for all intents and purposes made it a 318 block, never meant to be serious, nor suggest there was enough meat in the block for that overbore, there might be, but without a real complete sonic test, I wouldn't even consider it, and the hidden point I was getting at then, just find a nearly free good running 318. Sorry.

what,s the point of doing this anyway, get the right motor from the start. or just build a radicle 273 with some magnum or after market heads, or boost

As cheap as junkyard 318's and 360's are I would put the money towards one of those before I even considered a 273 build.

I am not going to do this guys. I just asked for curiosities sake.

So, what if someone were to use a 360 cast crank that's been turned down to 318 mains in a 273/318/340? Any real benefit their? Someone just offered one to me on FABO for pretty cheap but states the 6 bolt flange was chipped.

A really nice stock appearing 273 could be fun... maybe work on heads and cam, build/blueprint carefully and make it a hot little engine in the spirit of the original.

If boring, stroking ect. for performance, why not start with a 360/5.9 with a lot more ultimate potential (and save the rare block)?

I got that 273, but not sure where the fun is relative to any of the other suggestions here.

Just because something can be done doesnt mean it makes sense lol. I learned a long time ago that if you're gonna be building an engine and putting a stroker together, they all cost the same in their respective engine family. Stroking a 318 will cost the same as stroking a 340/360 at the end of the day. Same with BB's.

IIRC the small bore of the 273 needs to be notched for bigger valves, and the small bore really kills flow

I picked up a complete 360/727 for $100 locally...too bad you aren't closer, Id probably give it to you

The ANSWER to the OP's question is NO. You cannot bore a 273 to 318 bore size. There is too much difference between the 3.625 and the 3.91. That's taking 0.142 out of each side and most Mopar blocks have minimum wall thicknesses of around 0.140, some have even hit the streets with spots thinner than 0.090. As the minimum non-thrust thickness for an acceptable hot street build is 0.100", you can see why it wouldn't work.

Now on to stroke. I am sure you could put a 3.58" crank in a 273 block, if the crank had the right main size. At stock bore it'd be a 296. It'd run noticeably stronger than a 273 but would have peak hp earlier.

I hear the people screaming "a 318 is still bigger and you can get them for free!" That's true and this is a discussion of THEORY, not in the real world where one has to pay for things.

I'm not sure if a 4.00 crank would work in the 273 block because the bores are so small that the connecting rod could run into the lower edge of the bore somewhere mid-stroke. It'd have to be checked out. A stock bore 3 5/8 x 4 motor would be a 330. It'd have really good low-end torque but would run out of breath early because the small bore limits breathing.

ANY of these theoretical engines would require custom pistons, which would be extremely costly, except for the fact that any high performance 273 piston is also going to be a custom forging. So in reality, in our theoretical world, that part of stroker-vs-non stroker cost washes out.

If anyone was REALLY interested in doing something like this, and again why would you want to, the Toyota 22R motor has the right-sized piston and its 0.866 pin is also one of the NASCAR pin sizes, so it may be possible to use NASCAR rods in this engine.

Those of you who are tempted to pile on with the "take-your-pick engine would be cheaper and more powerful" post, just put a sock in it. Those comments have already been made and aren't the answer to the question in the original post.

I love these paper engine builds, once in a while something real pops up from the study.

R.

I didn't hear anybody screaming anything.

If being theoretical only here, the OP could bore the 273 block out, sleeve it , and make it a 340. I'll put a sock in the qualifiers to such a plan.

Any thing is possible i guess within reason. Small bore could restrict stroke so 3.75 or 3.58 would fit better. Bottom end size is same as the 360. Walls should be thick enough to bore quite a bit, sonic would tell. Chrysler might have used the same block for the 318 so no new casting cores needed(money)then again they might have used the poly block, reason they have weird push rod angles. Like the guy before said pistons are there on the shelf(it don't care what engine it goes in). A $10,000 275 hp engine.