What size is ment by "small journal"? What is "large journal". Is Lt1 2.25"? -Tim

 

clik on my signature links at bottom. Some sizes there. It means the size of the journal on the crank where the rod bearing spins on it. Only 400ci cranks have big journals after 1969. Some custom aftermarket cranks may have different journals too, but stock LT1 350 rod journals are all the same.

 

There are 3 Journal Sizes in SBC/LT1 motors.....

"Small Journal" 2.30" Main Journals, 2.00" Rod Journal, 2.125 +/- .00025 Rod Bearing Bore

This is the size of the orginal SBC design and lasted until 1968 where they switched over to the "Large Journal" sizes, also was the start of a 350 cube motor too. A 1962-1967 327 Block is a good item for drag racing classes because of the small main journals.

"Large Journal" 2.45" Main Journals, 2.100" Rod Journal, 2.225 +/- .00025 Rod Bearing Bore

This is the 350 size and the standard that we think of when we talk about LT1's. It was the standard sizes for all 350 cube and small SBC V8's made after 1967.

"400 Journal" 2.65" Main Journals and the same 2.100" Rod Journals.

This was only used in 1970-1980 400 SBC blocks. The Main size was increased so there was enough main journal/rod journal overlap when you are looking down the front of the crank.

Today GM makes Bowtie Blocks in all of these main sizes (finally) but you have to really want a small journal main to run them since the blocks are only really for drag racing, road racing and NASCAR and are not cheap.

The reason for wanting small journal sizes is reduced bearing speed, which is lower friction and frees up more HP. It will also reduce the overlap from main to rod journals weakening the crank except if you shorten the stroke. That's common for high RPM motors.

Bret

 

http://web.camaross.com/forums/showt...=large+journal

Search feature is not used nearly enuf on this forum.

 

Just incase you didn't get what he was saying.

The journal on the crank is 2.100. When companies list rods, they list the crank size NOT the rod size. So the journal of the rods you want for the LT1 are made for a crank that measures 2.100 and the journal of the rods themselves WITHOUT the bearings installed will measure 2.225. The bearings take up the rest of the space MINUS the oil clearance.

I think 2.25 will be a little too large and may be hard to find bearings for it. BUT I'm not sure about that. I am sure about the 2.225 measurement though, as Bret expained previously.

Dave

 

Yeah I just put the 2.250" in there for the rod journal bore because some places (al la Crower) list the rods like that. It would be a bitch to get "Large Journal" bearings in a 2.125" Rod Bearing Journal.

Bret