360 with 4.04 pistons?

[PlumCrazy26]

Recently I've been looking into building a 318 on a budget for dirt track purposes. I figured I go .030 over with a decked block and some 302 heads and I can run a relatively high comp. somewhat racey motor that will just squeeze under the 200 psi cylinder limit. However after talking with my dad I've become interested in the idea of the 360 bore'd down to 4.04 (340 piston size) where you can get the 360 torque with the bigger 340 pistons. I would love to build a 340 but they're few and far between up here in Alaska. SOOO without any further guff I'm curious what year 360 blocks will safely take the bore? Or if someone could point me in the right direction, that would be great! Thanks!

 

[replicaracer43]

almost any block can handle a .040 bore. You could sonic check to be sure, but its no big deal in my opinion

 

[fratzog lover]

My 360 is .040 over, just under 9.5, xe 268 cam, 2.02 j heads, performer RPM and a thunder 650. Doesnt even have headers. Its a nice daily driver even with me swapping 3.23's for 3.73's. Other than a 2500 converter and tf-2 kit the 904 is stock. If you can find a '71 block like mine buy it.

http://www.forabodiesonly.com/mopar/showthread.php?t=280115&highlight=360+0.060+overbore

http://www.forabodiesonly.com/mopar/showthread.php?t=154487&highlight=360+0.060+overbore

 

[7e5hangten360]

the use of 340 pistons in a 360 requires a lot of machining, so i would advise you not to do so. however, there are 360 pistons that will give you 10:1 compression which are great for street use and mild racing. i used speed-pro h116 pistons in mine . they work good for stock-stroke 360s and dont need balancing the motor. some use keith black pistons too. both are relatively low-cost.

 

[txstang84]

Welcome to FABO!! Post a thread in the welcome wagon and tell us about yourself and your projects too; now onto your question:

Unless it suffered severe core shift, I don't know of an LA that can't take .040" overbore, but, you need to use 360 pistons--not 340. The compression height between the two is significantly different due to the stroke. If you're just looking to make a street engine, the hypereutectics from speedpro/sealed power as 7e5 mentioned would be a good set to use. But, I will depart with him on one aspect, the aftermarket pistons are likely lighter by enough of a margin that rebalancing should be done--at least have it checked. Off balance engines can wear bearings unevenly and cause premature damage.

EDIT: Also keep in mind if you're swapping from a 318 to a 360 there are a couple differences...balancers, flexplates/converters, engine mounts...

 

[rumblefish360]

When you rebuild the 360, ether balance it internally and use the B&M flexplate to mate to a neutral balance converter or build the 360 with a internal balance.
All this the machinist can handle.

The drivers motor mount is different in width only and a simple nut &/or washer can take up the space difference.

Always balance a new assembly to be sure unless the new pistons are the same weight EXACTLY! And that's not ga-ren-tee! LOL! Be safe than sorry.

 

[fishy68]

340 pistons cannot be directly used in a 360 because the piston pin height is different due to them being made for a different stroke. If you try use 340 pistons with a 360 crank and they'll stick out of the block a whole bunch. Another thing that comes to mind is the old 340 pistons were pretty heavy so using today's pistons designed for a 360 I think you'll find their a bunch lighter and that adds up to a quicker revving engine with more longevity. IMO your always better off not over-boring an engine any farther than needed. Cylinder wall rigidity is far more important that the few cubic inches you'd gain from an extra .010 or .020" over bore

Welcome to the board!

 

[winstoninwisc]

yah the Kb 107s with a singe valve relief or the speed pro are cheaper and just cut it .030 unles you need to go more then youmight as well pick up a stroker kit for 1200= 1300 and it really doesnt cost much more than your looking to spend already , i havent heard ofmany hyperutectic piston problems and havent had any with mine thow its lust over broke in Ill sell you mine with the RHS x heads and m1 intake 7 k for the long block
fly down and take a ride , your wallet will pop rite out of your pocket.

 

[70aarcuda]

use either the kb107 or the seal power 116cp ....bore the block to the minimal amount...

you would need to use the low compression 72-73 340 piston..still need to cut the top of the piston...and cut the bottom of the piston to clear the crank....beside they weight too much as said...

 

[PlumCrazy26]

Dang, you all seem to know what you're talking about. The insight is much appreciated! As luck would have it in my search for heads I came across a 72 duster with a 360 in it. No way would I put that on a dirt track but I'm thinking she will make a nice little street rod! That being the case I don't think it's worth my trouble to go all out for the few extra cubes. Regardless, thanks to everyone for their swift and knowledgeable input!

 

[moper]

Cylinder wall rigidity is far more important that the few cubic inches you'd gain from an extra .010 or .020" over bore

Welcome to the board!

x2. You don't need that "340" bore. Find a good running 360 core and have better pistons put in it at std bore or .030 over, internally balance it, and be done with it.

 

[krazykuda]

x2. You don't need that "340" bore. Find a good running 360 core and have better pistons put in it at std bore or .030 over, internally balance it, and be done with it.

there are many different piston choices for the 4.00" and 4.04" bores... It shouldn't be hard to find one that works...

 

[PlumCrazy26]

Thanks!

 

[PlumCrazy26]

I'm sure this has been addressed on this site before but what would it take to internally balance a 360? Is it just a caseof taking the block and bottom end to a machine shop?

 

[70aarcuda]

I'm sure this has been addressed on this site before but what would it take to internally balance a 360? Is it just a caseof taking the block and bottom end to a machine shop?

mallory metal and your credit card....

need to take crank...rods..pistons...one set of rings...one rod bear....and if you want a neutral balance damper...and flexplate/flywheel that are also for a neutral balance engine..

just had one internally balanced earlier this year...

 

[moper]

Normally one wouldn't include the dampener or flywheel for internal balancing. If this is a special engine (racing, super high rpm, etc) you certainly can and it may result in a smoother feeling engine, but by including them on the calculations and spinning you are adding external elements because you are offsetting any weight issues those parts with the crank. Persoanlly I never include those items.