SweetS10v8

Ok, I have heard that 400s dont oil as well with the 2.65 main journal size, and that 350s do a better job with the2.45 main journal size. Anyone have any articles to back that up, I read something somewhere along time ago.

Also, they make 400 rotating assemblies with 350 mains. I can see how you take a crank from 2.65-2.45(typical 383), but how do they make 400 block take 350 mains? Or is it just using a spacer like in destroking to a 377?? What would the benifits be? Is it worth looking into?

AJ_92RS

HUH?

You want to put 350 main caps on a 400 block? Is that what you're saying?

Or are you talking about using a 350 crank stroke in a 400 block?

You need bearing spacers for a stock crank (or stock crank size), or you can get a new, unfinished crank and have it machined to 2.65"

AAMOF, I'm sure they sell them over the counter, but they're probably hard to find because they're not real popular.

SweetS10v8

thats what im trying to figure out, see the pic?? 377-434 w/ 350 mains?? how and why??

ede

they're both just pieces of iron with no oiling, wouldn't make any differance. even the differant main bore in the block wouldn't make a differance since the oiling system is the same

SweetS10v8

So would they make them thinking that smaller journal sizing would reduce friction? Im just trying to understand the idea behind it....

MrDude_1

they oil just fine.... theres nothign wrong with the oiling system on either of them...... IMO its one of the reasons the SBC lasted so long without a major redesign.

AJ_92RS

Well that's easy. It's because of the circumference.

A 2.65" journal is 5.52" in circumference

A 2.45" journal is 4.71" in circumference

Spin an engine to 6000 RPM and the 2.65" journal is traveling 33,120" per minute, or 552" per second.

Do the same with the 2.45" journal and it’s only 28,260" per minute, or 471" per second.

Which one is going to heat up less? Which one will take longer to break down the oil?

SweetS10v8

I can do the math, well after some refreshing, lol

I just wondered if thats the ONLY reason?

ME Leigh

There is less friction with smaller bearings due to the smaller contact area. So yes smaller bearings are better thats why serious racers use honda size bearings. I think they are something like 1.7".

littlebagz

True about smaller bearings travelling less distance, but dont forget that the smaller the journal the less strength it has, also if the journal / bearing is smaller ther is also less contact area to bear both the forces of compression and power , and they wear out quicker.

Racers may use 1.7 inch bearings, but dont forget that they probably rebuild engines every week.....

a73camaro

Circumference of a circle is 2*pi*r or D*pi, where pi equals 3.14159....

So 2.65" diameter times 3.14159 equals 8.32"

and 2.45" diameter times 3.14159 equals 7.70"

RB83L69

There's no advantage to using smaller main journals. The bigger they are, the more area there is for the oil film, which makes it more capable of withstanding large loads without squeezing out. That's why larger engines that produce more power, such as big blocks, have larger bearing journals, not smaller.

The reason people run smaller rod journals in conjunction with better quality rods than stock such as old stock small-journal ones is weight. The frictional loss is about the same. However the oil film is more stressed, and bearings don't last as long under racing conditions. But when you do a complete tear-down and rebuild after every race as a matter of routine maintenance, and that rebuild includes all brand-new moving parts such as crank and rods, that doesn't matter so much.

I've never "heard" anything about 400s not oiling well, not even from professional circle-track racers that bore and stroke them to much greater size. I've "heard" about small blocks generally not oiling very well, and that's true, as far as it goes, as the stock oil system in these motors is well known to be one of their weak points in racing applications; but that has nothing to do with mains diameter. It has alot more to do with the convoluted oil passage arrangement in the block.

I've also never seen an actual "400" rotating assembly, which is to say an assembly with 3.75" stroke and 4.125" bore, with 350 main bearing size. I can't imagine what block you'd put that in. Not to say that it doesn't exist; just that I've never come across one.

85TransAm406

iTrader: (1)

They use honda journals on the rod bearings and rods, as RB said for weight reduction.

I wouldn't ever TRY to run smaller bearings, personally, but i'm not a mechanical engineer (yet, at least). As a machinist, though, i've rebuild a lot of Cat 6 cyl diesels, and they run about a 4" main bearing, so i don't think they'd use this size if they could use a smaller bearing, if it caused oiling problems.

I'd just use a nice high volume pump if i was worried about it. I'm not big on high pressure pumps, though.

AJ_92RS

You're right. I was calculating area of a circle.

But circumference is still the reason they do it.

MrDude_1

you could do it with a motown block.

get a block with 350 mains bored to 4.125 and get one of the common "383" stroker cranks ment for the 350...(or go the older route of turning down a 400 crank)



athough i dont see any reason why you would want to do that... just a idea that came to mind.