differences between the 318 and the 340?

[Sport340]

well iw as just looking through some engine specifications... and.. i was wondering what the differences were between the 318 and the 340.

i mean the 318 and the 340 both have a 3.313" stroke
the 340 has a 4.040" bore
the 318 has a 3.910" bore

now im thinking... what else would be different if i got the 318 bored 0.01625" (0.20") over? put some high compression pistons (10.3:1)... well maybe lower so i can use 87 octane gas.... in it and get some X heads?

what would be the difference? crank different? connecting rods? just wondering because i want to build an engine but i want to build something with the potential that the 340 has. thanks...


has any seen/attempted this? what was the outcome? is there any reason why it wouldnt be a 340? thanks...

[MoPaul]

I have heard that the block must be sleeved for that much of an increase in bore. This was an unreliable source, however.
Just judging from the ridiculously low price of my 340 crank, I would say they are the same.
Try to get the bigger rods, pre-'72.
Sorry, not much help here...

[Locomotion]

The main reason you can't bore a 318 to 340 specs is that the cylinder walls are too thin to support it.

Even if you go with bigger 340 heads, cam, intake, etc, you will always be 22 cubic inches short and more cubic inches are needed to take full advantage of the aforementioned parts on the street.

You can hop-up a 318 to perform well upgrading parts and using 360 heads with 1.88" valves, or get even more with building a 360.

Cranks are balanced differently due to the different rod and piston weights.

[pishta]

about 100 HP and about 1000 bucks....

[Lasalles]

Hey Sport340 the cranks are the same,rods the same.U know u could always use the 360 crank with the 318 engine but u need to get the main journal turned down to 318 size and also the rear seal.Now if u use the 360 crank with 30thou over pistons u get a 350cubic inch 318.Not to bad at all.Ofcourse u would have to use 360 heads aswell.
I was going to do this but ive since got a 360 block,but i do have an article on everything that needs to be done which i can send u.
Get met at Steven@oz2000.com

[rumblefish360]

If you wanted to do a stoker 318, MoPar has the 360's 3.58 stroke crank to fit the smaller 318/340 mains. Now, where to get pistons that dont cost a $$$$$$$$
I've done 318's in the past. Its not easy being down 22 cubes or even 32 on the chevys. They can run well though.

[Billydelrio]

The difference between the 340 and the 318 is this: I have many 318 blocks, but no 340 blocks!!

I talked to C&A Monday about making my 318 pistons. The pistons will cost $73 each to make and another $15 each to fit the pins. This is a light weight racing piston for a 3.31 stroke, 3.97 bore, and 6.123 rod. The dome volume will allow a 12.00:1 ratio with 56cc chambers.

I got the impression that it had been a while since they had made a 318 racing piston.

Billy

[Dustbuster]

ok main differences between the 318 and 340...

BUTT STOMP!

ok lets think about this...the 318 was a grandma engine once the 340 hit the scene, 318 has way to small intake and exhaust, doesn't have factory ported heads, has a small wussy cam, has a cast crank, not a forged as all pre 73 340 blocks did/do....umm it was 22 cubes smaller, used small compression, never had performance exhaust built for it by factory...

and it could never make a 71 duster 1/4 mile in 14 seconds!

318 is a commuting engine...thats all there is to it, unless you are toying with the engine, trying to blow one up for kicks, or slapping on power adders (can you say NITRO?) its just a good get you to and from work engine

i love the 318, you can kick the $hit out of it for 100,000 miles and still get another 100,000 out of it, a 318 can be tuned to 20MPG, 340's...bit harder but can be done

i'd suggest getting a 360 block and build up from there, great engine, has a huge stroke which gives you unbelieveable bottom end torque