Do the Poly 318 blocks have thicker bores than the LA318 blocks.

Generally yes by quite a bit but as usual, confirmation by ultra-sonic measurement is best before committing to a plan for boring.

Thanks, the trouble is I wish to buy a bare block from interstate and I heard once it is possible to fit std 340 pistons into the Poly Blocks. So checking the wall thickness is not possible, probably not worth the risk.

That would be a .130" difference. It is common that Poly's can go .090" over stock and there are likely several that are over .090". It's just not a given you can safely meet your goal without measurement. But, there are many other pistons (and crankshafts) available. A common swap is to use 360 pistons (4" bore versus the 4.04" bore of the 340) and turn the mains on the 360 crankshaft to fit the 318 block.

Not sure what the purpose of this common swap is? Seems like an expensive way to make a 360.

By design, Poly heads offer an obvious performance potential over L/A heads. In fact the current generation Hemi engines are closer to the Poly valve configuration than to an earlier Hemi.

I'm doubtful about that after reading the Poly book...IIRC, valve & port size aren't large enough to make a lot of HP.
I think our own "Polyspheric" wrote that book ?
Mine seemed to run well at lower RPM - torque - but when I thought about taking one to 408", the heads seemed they'd really limit power.
I'd be happy to be proven wrong...

I have yet to see a Poly head that will outflow even the W-2's let alone a W-8!

A friend has the cast iron W-2's on his stroker 340 and makes an easy 600+ horsepower. Show me the Poly head that does that!

One of the guys that wrote an article for Chrysler Power pimps 500 horsepower Polys. When you drill down you find out it takes lots of custom machine work, special parts and your final price is going to be about $15k!

You're comparing apples to oranges as expected. I'm talking factory-stock heads as a benchmark. The prices you mentioned are purely based on the builder, their build plan and their parts sources. Building a poly is all about making something perform what was never meant as a performance engine. I have the same amount of $ in my Poly block and heads as most would have in their LA block and heads. No "drilling down" needed.

Thicker than my early 360?

Better to have bore thickness for ring seal than boring something out the outer edges of usability. Simply boring one out to a 340 is not going to make it significantly more powerful all by itself I don't think.

Years ago some guy built a 402 out of Poly 318 and it did ok for what it was. I think he made it a 4" bore and used 360 pistons? That article was once easy to locate, but it escapes me at the moment. People have posted it on here numerous times over the years, myself included.

Earlymopar, please share the info on your Poly and its output.
I'd love to have a Poly that'd surprise people, but I'm under the impression that a W2 LA is a better unit.
My own little 368" W2 (Batten heads) drag-race motor made 640 HP for reference's sake.

Poly motors are something like the Y-block Ford or the 348 Chevy, not the best nor the most powerful but really cool! If I live long enough one of my goals is to build a stroker poly with 2-4's.

Did more than bore it out to get a 402 out of it. Stroked it too. My math shows a 4" stroke with 4" bore to get a 402.

According to this guy, 450 hp out of a set of ported poly heads is doable. If course he'd building a 390 stroker version.

https://poly318.com/poly-318-cylinder-head-porting/

Stock poly heads flow 187 intake, 146 exhaust at .50" lift. No way this head will support lots of HP, stock. I don't care what you chamber is, you still need air and fuel in to make HP out.

Here's a 402 build with lots of head work. 405 hp, 442 tq. A stock magnum 360 with a cam and intake change will almost beat that, 380hp/410 tq. A 360 based 402 with Edlebrocks will beat it. Port those Edelbrock to similar levels and it will destroy it.

https://www.motortrend.com/how-to/mopp-0110-how-to-give-a-318-poly-engine-more-power/

Is it cool to have an off beat engine powering your ride, you bet. I am build a 230 based flathead with hot rod goodies because it's not a belly button engine. But I have realistic expectations of it's output, 150 hp if I am lucky, lol. Is it cost effective, not even close. Sometimes it's about other things than max output. If I was worried about that I'd swap a Hellcrate in.

Don't discount the Y-block. It has done well and even won some engine masters challenges. Do a google search.