Polaris Engines Defined

[tr waters]

Can someone enlighten me, it simple terms, what the difference is between "small block" and "big block" Polaris engines. Is it the actual case width, i.e., bore spacing?  Thanks.

[Vintagesleds.com]

[AHood]

Yes it's bore spacing, stud pattern ect. In simplest example a Polaris TX 340 is small block. A TX 440 is big block. Which pretty much carries back to the older engines. Starfire ect. A 650 triple Starfire is big block. A 440 triple Starfire is small block as are the 295 and 340 Starfire.  The bigger twins I'm not sure about. 530 twin ect.   A carryover is the 650 Indy triple is a small block pattern where as the earlier 650 free airs were big block.

[73 RATX]

I never really heard of anyone referring to Polaris engines as small or big block.  On the old ones the only real difference between engine families is the stroke. 55.6mm or 60mm.  530 and 795 are 60mm stroke but have a larger base pattern.  I think the only exception for 795 was the 73 kit cylinders which I believe had the 650 base pattern.

[Mario]

Small block is short stroke, 250, 295, 340 twin, and 439, 399, 500 triple. Big block is the longer stroke (340, Electra only) 398, 440, 488, and 530 twin, and 650, 795 triples.

It gets blurred up in the 80s a bit when the shrunk a big block long stroke crank to fit in a centurion small block case for the 600-650 triple. They just moved the pins closer to the edge of the crank wheels to simplify explanation

[73 RATX]

Mario, glad to see you back.  Long time no post.

[Mario]

Mario, glad to see you back.  Long time no post.

Not really back. Just felt obligated to give correct info.

Unfortunately, this site has run it's coarse for a lot of us. Too much drama I guess. Miss the old days like a lot of others do

[opsled]

Mario, glad to see you back.  Long time no post.

Not really back. Just felt obligated to give correct info.

Unfortunately, this site has run it's coarse for a lot of us. Too much drama I guess. Miss the old days like a lot of others do

Mario, glad to see you back.  Long time no post.

Not really back. Just felt obligated to give correct info.

Unfortunately, this site has run it's coarse for a lot of us. Too much drama I guess. Miss the old days like a lot of others do

 You ain't alone.

[AllenJ]

Mario, glad to see you back.  Long time no post.

Not really back. Just felt obligated to give correct info.

Unfortunately, this site has run it's coarse for a lot of us. Too much drama I guess. Miss the old days like a lot of others do

Mario, glad to see you back.  Long time no post.

Not really back. Just felt obligated to give correct info.

Unfortunately, this site has run it's coarse for a lot of us. Too much drama I guess. Miss the old days like a lot of others do

 You ain't alone.

Truer words were never spoken ! A small group has taken any fun that there was to be had.

[pj81ac]

So where are you guys going to talk vintage sleds if not on this site?  FB really sucks for technical discussion...

[motorman45]

I dont see anywhere else on the web that has this much knowledge saved and a still functioning and posting vintage sled base. no matter what some do here it wont sway me from the hobby or posting here. only been on here for 5-6 years so im not sure who the usurpers are frankly. met some really helpful, friendly and knowledgeable guys here