Ok, I'm might be daring (or stupid) enough to rebuild my 318 Polysphere motor out of my 1966 Dodge D-100. It runs, the valve train is spotless...and yet I have no clue how many miles are on it. I bought the truck with no dials...thats why. But anyway, I've heard alot of information on guys boring those out to .090 over bore, putting in a 4inch stroke 360 crank, grinding the 360 mains to a standard 318 bearing size. One...is it safe to bore that engine that far...two, if it is safe, that does bring it up to 360 CID's, but does that also mean it has the same bore as a standard 360 L.A. block? Three, if not, then where or who makes a piston and ring set that size? Four, with the crank being ground to that point as well, if it safe to run it at high RPM? If anyone has an answer, please respond. Thanks.  

I am pretty sure the poly 318's had the same bore and stroke as the LA and A versions, so if you bored it out .090 over (4 inch bore) and added a 4 inch stroke, that would bring you out to 402 cubic inches. Diamond Pistons make custom pistons that will work with a 318 and a 4 inch stroke crank, and I'm sure they make rings for them too.

thanks, but i found out with my math there if i bore it over .090 it just turns the bore into a 360 std bore. So i can just use 360 pistons and rings (i hope).  

wont you be running kind of thin? im not to familiar with a poly 318, but i know for a fact that the non-thin wall small blocks should be bored more than .060 over

From what i've heard and read, the poly engines (most) can be bored up to .090 or over. I don't know (yet) if i have thick enough walls right know. If i don't then it's just getting a .060 over bore. If it is a thick walled block, then the .090 bore.  

ok cool. not to familiar with them, but if that's what they say, that's what they say.

You should have your block sonic checked then you will know for sure how much can be safely removed.  

I was thinking of that, but what i was also trying to figure out is that, i was looking in my 2002 Mopar Performance parts catolog and i saw that they have a stock 360 stroke for a 318 bearing size. I know the 318/340/and the 360 all used the 6.123 length rod for stock. Now i was thinking of a .060 over bore and 318 pistons on the 6.123 rods. But what i'm trying to figure out, is that since it would be stroked, just a bit, would there still be plenty of clearence between the piston skirt and the crank rod with that stroke?  

that would have to be measured and if at all the blovk would have to be clearance. you might actually have to put the rotating assembly to gether and roll it by hand, then get the block clearanced

I was kinda hoping i wouldn't have to do that (clearance the block). I'll still check if i have too, otherwise that might be a costly corner cut. If anyone has done this to a poly or any 318 block, could you give me some advice?

You won't be able to run 318 pistons if you run a stroker crank your compression hight will be to high. ( the top of the piston  will stick up above the block deck )  You will have to order piston for a stroker. If you will order Mopars engine book a read it you will help yourself a great deal when building your engine, I have the big block B/RB book and even though I have been a machanic for well over 15 years it has been a real help when building high performance engines. 

Thanks. Then i guess, i gotta get custom pistons then huh?  

If you bore .090 over, and put in one of the new Mopar Performance 4" cranks, you'll have a 402" stroker, that'll be putting out about 450-500hp and torque numbers similar (with headers, good cam, etc...).

Check out these webpages for some help...
http://www.dodgepolara.com/318hotrod.html

http://www.1962to1965mopar.ornocar.com/poly318.html

Have fun!

Andy

You may find these links helpful...

The Polyspherical Engine association (there's a list of places to find parts & info):
http://www.geocities.com/polyman64/

At the top of that page you'll find the following links.

The 318 Poly Yahoo Group (which is where we all are (ask us ANYTHING):
http://autos.groups.yahoo.com/group/318poly/

And the Poly Forum, where we'll all lurkers, and casual posters:
http://www.diamondbackengines.com/forums/index.php/board,6.0.html

More info at the sites above...

~Jason