351 Block??

[slow90lx]

Looking for a new block but whats the difference between the 302 mains, 351c mains and 351w mains?

[black50]

you have a pm

[greenbullitt]

diameter

[1fast4]

diameter

That's what she said!

[slow90lx]

That's what she said!

Nice!!!

[greenbullitt]

to elaborate, you change the diameter of the mains to help with bearing speed

[VETTKLR]

to elaborate, you change the diameter of the mains to help with bearing speed

how does changing the main bearing diameter increase or decrease speed? Seems like a crank spinning at 800rpm's is gonna spin at 800rpm's, regardless of the main bearing diameter?


I thought it was a surface area thing? less surface area = less drag/friction

[Kart21]

how does changing the main bearing diameter increase or decrease speed? Seems like a crank spinning at 800rpm's is gonna spin at 800rpm's, regardless of the main bearing diameter?


I thought it was a surface area thing? less surface area = less drag/friction

Surface feet per minute
Larger diameter w/same RPM more or higher surface feet per minute

[VETTKLR]

OK, cool. Thanks

[Txstang1]

how does changing the main bearing diameter increase or decrease speed? Seems like a crank spinning at 800rpm's is gonna spin at 800rpm's, regardless of the main bearing diameter?


I thought it was a surface area thing? less surface area = less drag/friction

Surface feet per minute
Larger diameter w/same RPM more or higher surface feet per minute

Yup.

think different gear ratio, kinda sorta the same thing.

[slow90lx]

Any reason to pick one over the other?

[turbostang]

Any reason to pick one over the other?

Bearing speed

LOL - At a given engine speed, the engine with the smaller bearings would tend to have less wear and tear.

For example, a 3.000" main bearing travels 9.42477796076938, but a motor with a 2.250 main journal only travels 7.0685834705770345" per revolution. (imagine putting a line on the main journal, turn the engine over till you see that line again - it has traveled the distance listed above by the time you've turned the engine 360*)

The reason for the Cleveland main size, it's in between the 302 and 351W I believe, but can't remember the size exactly. There's a point of diminishing return in which a smaller main journal is a detriment to longevity and durability.

[VETTKLR]

Cleveland mains are 2.75" and the 351W's are 3.00". I've got a Cleveland main crank in my SVO A-351 Windsor main'd block with spacers

[Lason]

There's a point of diminishing return in which a smaller main journal is a detriment to longevity and durability.

Like expecting a pencil to support a crank spinning at full speed.

The way I think of it is this. Larger bearings use more metal and are more durable in the long run because of the surface area. Great in a minivan that you want to go 200,000 miles and only spins to 3500 at most, most of its life.

Smaller bearing use less metal but offer slower bearing speed so at higher RPM's the bearing surface area is taking less abuse. less surface area though so long term wear and tear will hurt it though.