Why would I put .30 over pistons in my 304 when 360s are cheaper

I broke down the 304 today, and I started to make the (LONG!) parts list. 4Wheel Drive lists .30 over 304 pistons at $39.95ea, yet the 360 standard pistons are $31.95ea. As I did the math, and please check my work...standard bore 304 is 3.75" + .30" = 4.05" and with the 360 pistons being 4.08", why not just jump to the 360s? Am I missing something?

 

That's 300 over, not 30.

 

OK, I'm a dumb @$$ !!!! Even though the jump is bigger, if the only diff. between the 304 and the 360 is the bore and cyl head dome, Why not make the jump? Or am I again missing something?

 

What is the stock bore of a 304?

What is the stock bore of a 360?

What is the stock stroke of a 304?

What is the stock stroke of a 360?

If the only differance is the bore and both engines have identical strokes with identical piston pins and pin location and the top of the pistons don't have any bumps that will interfer with your heads or valves.

It could work.

lets see:

AMC 360 V8. Bore x Stroke, 4.08" x 3.44".

AMC 304 V8. Bore x Stroke, 3.75" x 3.44"

Ok the diff is just .330" between them this would mean you would have to bore the engine out 330 thousands to fit the larger pistons. That is 11 times as much as a .030 over bore. I seriously doubt the cylinder walls were designed for that much material removal.

Even a small block chevy can only be cut .125" and then only certin blocks can handle that.

I would have to say NO WAY your idea could work. You would be removing more the 5/16th inch of material almost 3/8" How far apart are your bores is there a water jacket between them? could you cut 3/16" into the center without hitting the water jacket doubtful.

 

Let me correct both of you, thats .030" over and not .300" over, Big difference!!!!!!!!!! If you buy a master rebuilt kit, from someone like Autozone, Advance or someone else those pistons will be cut in half on price.

Autozones master rebuild kit for a 74 304 is $592, the part # is AM304RV01, this includes pistons, rings, cam, lifters, all bearings, timing set, gaskets, freeze plugs and oil pump kit. I used one of there kits to rebuild my 225 v6!!

 

Novak Conversions leads me think that the block is the same up to the 401, but maybe I have miss read it. Look foor the part about "Mid Block"
http://www.novak-adapt.com/knowledge/amc_v8.htm

 

Only the exterior dimensions are the same the wall thickness of the bores will be altered to account for the final bore size. The small block Chevy, Ford and Chrysler is the same also but there are bore limitations based on the casting of the cylinder wall thickness, and this is directly related to what the engine displacemnt was suppose to be. Now mixing and matching cranks, and rods to gain displacement is usually ok if there is not a deck height difference. Most engines cannot be bored more than .060 over without serious cooling problems!!

 

OK....I buy that.

Anyone need a good anchor?

 

Thinking back to our AMX & Javelin days, the 390 & 401 were considered the Big Blocks.

gj

 

The 290, 304, 343, 360, 390 and 401 all have the same external block dimensions. Not sure about the 390, but the 401 was its successor. The 401 has a different block alloy (high nickel content) and uses a forged steel crank and rods. The smaller engines use cast iron components, which is pretty standard for the industry now. The 401 block also uses different bearing widths, though I don't know the details. Just means that you can't put a 401 crank in a 304/360 block and vice versa.

The 401 is pushing the limit for bore size in that block . I expect AMC had to use the high-nickel block because of the cylinder wall thickness. 30-over is about all you can safely overbore all 401 blocks; some can be bored to 60-over, some not, depending on the accuracy of the core alignment at casting time.

BTW it's not really correct to say that the wall thickness of the blocks is changed to get different displacements. As I understand it, the blocks are cast to use a minimum amount of material and require a minimum amount of machining. AMC could have cast the 360 and 304 blocks with the same core (the sand that's removed to make the coolant passages), but that would have required excess machining for the 360 block, and made the 304 block heavier than it needs to be. Instead, the casting is changed to provide the same wall thickness for each engine after machining. Thus you cannot overbore a 304 block to 360 - you'll hit the water passages before you remove 300 thou material.