Can you run a 6.700” rod on an SGI 4.500” crankshaft?
 

Hey guys just needed to know if anyone is running a 6.7 rod on an Star Galaxy 4.5 stroke crankshaft? I’d like a little more Compression distance on my 490 build but I need to know if I have room for the shorter rod without having to cut down the counter weights?
I just haven’t used the sgi crank before Thank you

If I recall I have a 6.7" rod with my 4.5" stroke crank!


GTO George

Yes, for sure

Thanks, I just wasn’t sure on the SGI crankshaft if they were any different

Thank you Paul

I have a Moldex cranks with Aluminum rods But shouldn't be a difference, the block maybe.


GTO George

More about the counter weights than the block in this case

That’s my concern! Thanks

FYI you can get SGI forged crankshafts for 621$ Shipped through their eBay store, best deal I could find

What's different about their counter weights? I have a Scat Forged 4.5" crank with 6.7" rods

That’s what I’m trying to figure out SGI has a note under the Crankshaft saying you got to use a 6.8 inch rod and I don’t like using the 6.8” Rod with the 4 1/2 inch stroke crank because I think the Pistons too short so I want to use the shorter rod and so I figured I’d ask people here if they have any experience with this Crankshaft, I’ve ran shorter rods on the Scott cranks no problem and I believe that’ll be the same here it’s just good to ask before I order parts

As far as pistons, is there a very big difference between the piston design for 6.7 vs 6.8 rod?

0.100" does not seem like much, but is it the difference between needing oil ring support or not? Or is there more to it?

My machine shop was trying to talk me into going 4.5 stroke instead of the 4" I have waiting in the box, and while the extra cubes would be nice I just wasn't sure about it with a stock block build.

I am thinking SGI says 6.8 rod just because the crank is 2.2" rod journal, but 6.7 should work also....

Yeah there is a difference between a 1.165 compression distance and a 1.275-1.3 CD As far as oil consumption, piston scuffing etc, I’m trying to run a little longer skirt to hopefully have a little less piston rock and wear.
this is a street deal, unfortunately even at 1.3cd it will still have oil ring support rails but still I believe it’s better to get the pin out of the oil ring as much as possible, jmo

Even my 4.35 stroke 6.7 rod Ross pistons use an oil ring support. No big deal to me, I wanted to keep more of the piston in the bore at the bottom.

Really? I run a 6.7 rod in my 4.375 stroke motor with no oil ring support needed. Did the match on the combo before ordering the custom pistons from Diamond. The pin is close to the ring land, but no support needed. Maybe I have a hair more deck height than you.

I got them thru Butler and thats how they came. I didnt ask before I ordered the rotating assembly so thats on me.

I've built 2 motors with 4.5" stroke. Both with 6.7 rods. JE Pistons did not need a ring support. Diamond pistons did.

depends on what its used for and where you want the ring pack --

Im building my 496 with a 6.7 rod & 4.5 stroke crank.

SPEED SAFE, AIR RAM

So after getting the Crankshaft today and doing some rudimentary measuring I think that there’s going to be plenty of room to run a 6.7 rod
piston should clear the counterweights no problem on this SGI crank
There seems to be some confusion I’m only talking about the SGI crankshaft in this thread I was not talking about Scat, Bryant, muldex, or any of the other companies those are ones I’m familiar with this one I was not also hence why I asked but now that I have the Crankshaft I have the answer yes you can definitely run a 6.7 inch rod and probably a 6.635-6.66” if needed

I think your blocks deck height can make a diff.Im putting a 4.125 stroke engine together and we found the deck height is 10.1275.I had bought 6.8 rods when I started the project.That gave us I believe a 1.2 Comp height.No one felt great about that so we are exchanging for 6.7 rods getting us to 1.3.FWIW.Tom

Pontiac is 10.24” stock, with a 4.125 stroke you would have Lots of compression distance with a 6.8 rod, unless you are building some type of short deck deal

our block is 10.1275!

What kind of block? I’ve ran them deck’d at 10.175 before but that’s only Because the block had the O-ring grooves machined off.
That’s a very strange deck height you have there

No kidding!4 bolt 455 block.Cant go to the market and get another one.We are living with it.Building it for a friend,he supplied the block and heads.Tom