Technical 327 : Large vs Small Journal

Aside from the obvious......
What is the difference between the large and small journal engines?
Is one better than the other? (performance, parts, size .....)

 

.....got busy had to answer the call BRB
friction ,
reciprocating weight ,
lot of variances to rpms and intended use
dang phone brb

 

Calling Squirrel........ He knows these things.

 

From what little I have heard the small journal is supposedly the strongest & the heaviest,but I am no expert - The guys I thank are as knowledgeable as any is Squirrel & Beano. HRP

 

HRP is correct on the stronger crank , small journal also decreases the surface speed of the bearing and it a has a reduced negative torque that the large bearing does.
might be worth 3-5 hp, but you will never see that on a dyno.

If i was in the room with Jim and beano out of the 3 of us BOTH of them would still BE smarter than me.

 

It's been a long time, but I recall that the early small journal 327s had a forged crankshaft, while the large journal cranks were cast.

Overall crank strength may be similar though, given that larger journals generally mean more pin overlap.

 

I'm not so sure about that...

 

I seem to recall certain M/P guys sought the small journal cranks for twisting those screamers into the twilight zone (& beyond).

 

What do you plan to do with this 327, if I might ask...Makes all the difference in the world. LOL

 

You know a lot more than your letting on~
Am I right in thinking that tall the small journal 283 & 327's cranks were forged steel cranks? HRP

 

No

 

There are large journal forged cranks (GM ), but Eagle is much more plentiful. It's tough to find as good small journal rods as large journal for the money. In the '60's I knew a couple of guys that had water leaks at +.060". AS stated above I think the main thing is bearing speed.

 

What do you want to do with it ? If you wanna say I have a 327 it don't matter. If you wanna swing it high in rpm's a small journal then.

 

How much hores power are you wanting? It really don't make much difference.

 

Most 283 and small journal 327 cranks were forged; the later 283's got cast cranks however. The large journal 327 used both cast and forged cranks; I have both in the garage. Holler if you need one. Guys used to use the large journal, forged, 327 crank, but have the rod journals turned to small journal size, thereby slinging lighter connecting rods, less rod bearing surface/speed, and a stronger bottom end was the purpose. But, in a street car, it makes NO difference at all. I am Butch/56sedandelivery.

 

Bearing surface speed is lower on the small journal making less friction for higher rpm's.
That helps the 327 wind up to the sky if you can get the air to them!
Higher rpm's translates to more HP per cu. in.
Plus the 327 has an ideal rod to stroke ratio (1.75) for lower piston side thrust, meaning less friction. That's why everybody likes them.

That ought to stir the pot.

 

283 cranks fit into small journal crank 327.

 

hmm, I have a nos gm 302 nitrated crank for sale if interested

 

Most of the small journal cranks did not have a drilled snout for a bolt to hold the harmonic balancer on. And a 283 crank will fit in a small journal block. the large journal block is practically the as a 350 block. Boring a small journal block past .030 is kinda iffy. I have several of both kinds of 327,s in my hoard. they aint for sale.

 

I have an NOS oem nitrided small journal crank in my Nova 327 plus .040 as well as NOS rods.
No they are not for sale.

 

One day I would like to get one and rebuild it.....Stick into a hot rod that I do not currently possess.
Daily driver mostly, not to mention the drag strip is only 6 miles away.
I have a heavy foot and like to play.
I've always known about the two models, just not the differences.
I wasn't sure if it was anything like the 351c/351w scenario.

 

In that case, just build a more modern 383 and tell everyone it's a large journal 327.

 

ah yep.... 383

 

Raced both in Modified production . Put studs in the mains ,ran aluminum rods turned them both over 8 grand. GM cranks turned polished and balanced.

 

I always preferred the small journal. I have been told they all have steel cranks. Less bearing speed. Guy who used to build our roundy round dirt car engines only built small journal for that reason. The only negative, small as it might be, is that you can used a 4 bolt main cap block to build a large journal but that just a lot of smoke and mirrors people have been sold IMO. Never seen a well built small journal for a street car have lower end issues.

 

You won't see a difference in performance between a big or small journal 327. The big journals came out in 1968 because Chevy had transitioned to big journal when the 350 came out. Most small journal 327 cranks were steel, some were cast. I have found the opposite to be true with the big journal stuff. Big journal 327 cranks are hard to find, especially steel, because by mid 1969, the 327 production was stopped, and it's applications were split between the 307 on the economy end and the 350 on the mid and high performance end. The 327 is one of my favorite small blocks because it does everything right. It's got decent torque, great midrange, and will rev to the moon. And on the big block side, the 427 is the same kind of animal, only meaner. It was like the stars were in perfect alignment when the 327 and the 427 were conceived. GREAT ENGINES.

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Butch/56sedandelivery is correct about turning the rod journals down on the forged large journal 327 cranks! Some would machine them off-center---"ECCENTRIC "--to increase the "THROW"--and-"STROKE ".Re-balancing was the KEY!




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Put a 327 crank in 400 block get the short stroke and 350 inches

 

Put a 283 crank into a 327 and you've got a 301 (basically, a 302 Z28 motor). Small journal is apparently easier to get the good stuff. The ratio between bore and stroke of this hybrid is considered perfectly square (old fart language) for torque vs RPMs, bleh bleh. Small has more balls.
This is great thread, love this board for details.

 

bore (4.00)x bore (4.00) x .7854 x cylinders (8) x crank stroke 3.00 =
you do the math

the old 283 turned into a ---___________<---